Timing belt snapped and distributor housing questions
05-29-2004, 02:03 PM
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Timing belt snapped and distributor housing questions
well guys last night my timing belt snapped as i was turning into my road. I downshifted to second and revved to about 2k when i heard this pop, and it pushed the clutch back in and my engine stalled. i was like wtf?
So i try to start the engine, but to no avail it didnt start. So i drift to my driveway and pop my hood. I couldnt see what was wrong so i went into my house grabbed a flash light and my dad to help me.
Well we got out there, and i looked into the distributor when my dad cranked over the engine, no spark. Well we took of the distributor cap and cranked her over again, the rotor didnt even move. Then i thought, ha im f'ed, my timing belt is done. We noticed that there are black depoists and shaving all throughout the distributor cap. We look at the distributor housing and see that the rotor button was digging into the dist. housing. wtf? i had that problem on my other engine and never thought of it as serious, so since my other engein didnt come with a dist. i used the one from the old enine which is on here now. not to mention the dist has over 270k on it.and with a closer look at the distributor rotor button, and we can move the rotor button to the left and the right without moving the rotor. Well thats not good, i look at the button screw and it is almost all the way out WTF again.
Well i go into the garage, get a 10mm socket/wrench and start to remove the valve cover. Sure enough there is my timing belt popped up and snapped in half.
Now my questions are what is causing this:
and just a photo of the work in progress
also whenever i turn the engine over, i dont hear anything bad like bent valves and such, so lets hope for the best.
So i try to start the engine, but to no avail it didnt start. So i drift to my driveway and pop my hood. I couldnt see what was wrong so i went into my house grabbed a flash light and my dad to help me.
Well we got out there, and i looked into the distributor when my dad cranked over the engine, no spark. Well we took of the distributor cap and cranked her over again, the rotor didnt even move. Then i thought, ha im f'ed, my timing belt is done. We noticed that there are black depoists and shaving all throughout the distributor cap. We look at the distributor housing and see that the rotor button was digging into the dist. housing. wtf? i had that problem on my other engine and never thought of it as serious, so since my other engein didnt come with a dist. i used the one from the old enine which is on here now. not to mention the dist has over 270k on it.and with a closer look at the distributor rotor button, and we can move the rotor button to the left and the right without moving the rotor. Well thats not good, i look at the button screw and it is almost all the way out WTF again.
Well i go into the garage, get a 10mm socket/wrench and start to remove the valve cover. Sure enough there is my timing belt popped up and snapped in half.
Now my questions are what is causing this:
and just a photo of the work in progress
also whenever i turn the engine over, i dont hear anything bad like bent valves and such, so lets hope for the best.
05-29-2004, 10:05 PM
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Re: Timing belt snapped and distributor housing questions (Honda2nr4life)
either the dust cover was not on correctly, or the rotor is the wrong size. it should not be chewed up like that.
06-19-2004, 01:45 PM
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Re: Timing belt snapped and distributor housing questions (King_j)
This is interesting to me.
Have you thought of why, if the timing belt broke, the distributor is damaged?
Have you looked at the distributor shaft itself? Look for differences in machining between the top of the shaft and the bottom.
Have you thought of why, if the timing belt broke, the distributor is damaged?
Have you looked at the distributor shaft itself? Look for differences in machining between the top of the shaft and the bottom.
06-22-2004, 10:06 AM
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Re: Timing belt snapped and distributor housing questions (2fcknfst)
And this is what happenend to me...
I find this very interesting.
1.0 INTRODUCTION
This report deals with the failure of a distributor assembly on a 1997 Honda Acura Integra Type R which occurred in July 2001.
The distributor on a spark ignition internal combustion engine is the device which permits the spark plugs to fire at a pre-determined sequence and time. The rotation of the distributor is synchronized to the rotation of the engine crank shaft, the motion of the pistons in the cylinders and the movement of the intake and exhaust valves. The latter permitting the inner fuel air mixture and the removal of combustion products. There are a variety of methods by which synchronization is achieved and in this particular engine synchronization is maintained between the crank shaft rotation, the motion of the intake valves and the rotation of the distributor by means of linking the distributor shaft to the end of the intake valve camshaft and driving this camshaft in synchronicity with the engine crank shaft by means of a reinforced tooth belt. In this way as the pistons reciprocate and the crank shaft rotates the crank shaft a toothed pulley at the end of the crank shaft drives a toothed belt which causes the intake camshaft and hence the distributor to rotate at half engine speed. In this way the timing of the four cycle engine is maintained. This ensures that the spark plugs ignite the fuel air mixture at or about top dead centre, the relevant intake and exhaust valves open and close without contacting the face of the reciprocating piston. Failure to maintain synchronization between the spark plugs and the rotating or reciprocating parts of the engine can result in consequences which range from rough running and poor fuel efficiency to catastrophic engine failure to the type of catastrophic engine failure that occurred in this instance.
The distributor and its timing relative to the rotation of the engine is a critical element in the efficient safe running of the engine.
This particular engine is described as having overhead camshaft. These require two sets of cams, one driving the intake cams and the other the exhaust cams. These rotation of these cams are controlled by an approximately 1200mm long tooth belt which is reinforced with high strength fibres to prevent stretching and to maintain its integrity. Any stretching or loss of teeth on this belt introduces the risk of a loss of synchronization between the camshafts, the distributor and the engine rotation.
Note to carry out this investigation both the distributor assembly which had undergone failure and an undamaged distributor assembly of identical part number were examined. Measurements were made using micrometers or dial gauges which had been maintained and externally calibrated. Details of the investigation.
2.0 EXAMINATION OF COMPONENTS
Two sets of Honda Acura Integra Type R distributor assemblies were delivered to our offices, these are described at Part #30102P72-006 Cap Assembly, #30103P73-003 Rotor Head Assembly, two lower distributor assemblies Part #D3179 were also supplied, finally a timing belt Part #14400P72-014 was provided. This was the belt which had been involved in the failure. The distributor assemblies are shown in Figures 1 and 2, Figure 1 shows the lower surface of the distributor assembly and the shaft assembly which connects to the end of the intake cam and rotates at the same speed as the intake cam. Figure 2 shows the upper surface of the distributor assembly with the four connections for the spark leads. Figure 4 shows the distributor with the cover assembly removed and the rotor and internal dust cap are visible. Mode of operation of the distributor is that as the shaft shown in Figure 2 rotates at half engine speed the rotor cap shown in Figure 4 rotates at the same speed and distributes the electrical signal to the ?? spark plug leads shown in Figure 3. Figure shows the dust cap moved and the rotor assembly mounted on top of the distributor drive shaft can be clearly seen. Figure 6 is a close up of this and shows the rotor head mounted on top of the distributor shaft which carries a ferrite cap which is part of the ignition system. The rotor is locked to the distributor shaft by means of a flat machined on the shaft which engages a flat informed in the injection moulded rotor assembly. The flat can be clearly seen in Figure 21 left hand side which is a photograph of the undamaged rotor assembly. The relative dimensions of an undamaged shaft and rotor are given below:
• Shaft outside diameter - .4905"
• Internal diameter of injection moulded rotor assembly -
• Internal diameter of the hole in the new rotor assembly - .4905491 - this is described as ___ tolerance in the ?? category of the Association of Automotive Engineers.
The protrusion of the shaft in a new distributor assembly can be clearly seen in Figures 8, 9, and 10 which show both the indexing flat on the shaft and the position of a tapped through hole into which a retaining screw is fitted to prevent the rotor from becoming detached from the driven shaft. The measurements show that with the new rotor fitted on a new shaft the angular play in the shaft between the rotor shaft and the rotor assembly is less than 2° without the retaining screw being fitted and when the retaining screw is fitted the rotation becomes negligible. Figure 7 shows the damaged component, the rotor cap, the rotor assembly is seen to suffer significant damage both to the electrical contact and to the upper and lower surfaces. Figures 18, 19, 20 and 21 show additional views of the damage.
Significant differences behaviour are noted when either the old or new rotor head assembly are mounted on the old and new alternator shafts. In the case of the new shaft there is less than 2° of angular rotation occurs when the rotors are fitted to the shaft. In the case of the old rotor assembly which we understand to have been fitted by Burrard Acura in January 2000 relative angular movement of approximately 20° occurs between the rotor head and the shaft. Since the internal dimensions of the old and new rotor assemblies are essentially identical the reason for this ten times greater angular motion must lie in the portion of the shaft which makes contact with the inside of the rotor. An examination of the old and new distributor assemblies makes it obvious why this angular play occurs, the distributor assembly fitted by Acura in January 2000 has the section making contact with the internal hole on the rotor assembly reduced in diameter by approximately .009". This was mentioned above the contact area of the new shaft has a diameter of .4905" whereas the old shaft has a diameter of .4805.481". Hence the portion of the shaft in contact with the rotor assembly is .009" undersized relative to the new shaft. This difference in diameter accounts for the much greater play between the rotor head and the distributor shaft. Using the terminology of the American Society of Automotive Engineers the fit between the old shaft and the rotor head would be described as sloppy.
In summary the tolerances between the “the shaft of the old distributor fitted by Acura in January 2000 as a new part and the shaft on a new distributor differ by .009"”, this permits a rotor head to have an angular play of approximately 20°. It should be noted that this angular play will be reduced by the insertion of the locking screw but if the locking screw for any reason disengages a gross rotational play will develop between the rotor heads and the distributor drive shaft.
3.0 CAUSATION
Based upon our examination of both the old and new parts and knowing the mode of operation and the intention of the designers we are able to develop a sequence of events which were the causation of the engine failure. In essence the events are as follows:
• In January 2000 the car was taken to Acura for service related to other problems.
• Acura fitted the “old distributor assembly” which had a reduced drive shaft diameter which did not match the internal dimensions of the rotor assembly.
• The installation of this distributor assembly would permit angular rotations between the rotor and the drive shaft. This random angular rotation would have resulted in the timing errors that the owner referred to in his letter to Acura, dated February 2nd when the owner complained about errors in timing after the vehicle had come
With the benefit of hindsight it is of course easy to see why these timing problems arose. Because of the sloppy fit between the inside of the rotor assembly and the undersize portion of the distributor there was angular movement between the rotor head and the shaft. Since the shaft is timed relative to the camshaft and engines by means of the toothed timing belt any relative angular motion of the rotor assembly would result in timing errors on the car. These would manifest themselves as rough idle, difficulty starting, etc. The problem was not identified by Acura and it is doubtful whether the owner had any reasons to suspect that he had been supplied with an incorrectly dimensioned distributor assembly. The owner continued to drive the car with intermittent timing problems until July 2001 when a catastrophic failure developed. In our professional opinion the following sequences of events occurred immediately before the catastrophic failure:
• The retaining screw passing through the rotor assembly and into the tapped threaded hole in the top of the distributor drive shaft worked loose. This was almost certainly because of the intermittent loading and motion between the distributor drive shaft and the rotor head.
• As the screw loosened it initially came into contact with the inner surface of the dust cap which lies below the rotor assembly. Figure 14 shows scoring of the dust cap assembly which is shown in its mounted position in Figure 4.
• The scoring by the head of the loosening screw continued until it cut completely through the portion of the dust cap surrounding the lower end of the rotor.
• At this point the screw was able to separate completely from the rotor drive shaft assembly and indeed the screw was found loose in the distributor assembly when it was disassembled. Figure 15 shows the portion of the dust cap which was cut away by the screw head as it loosened in the course of time.
• Once the screw was separated from the rotor drive shaft assembly the rotor was able to move up the shaft towards the top of the distributor assembly. As it did so it impacted the electrical contacts in the distributor cap.
• Initially the rotor assembly continued to rotate in synchronicity with the drive shaft and it produced wearing damage on the inside of the distributor cap, see Figures 22 and 23.
• Finally however it seized and at this instance since it was still in contact with the rotating distributor shaft and held in contact with the shaft by means of the flat on the shaft and the flat on the inside surface of the rotor assembly it seized.
• In doing so it underwent substantial mechanical damage, see Figures 18, 19, 20 and 21. This jamming between the rotor assembly and the inside of the distributor cap momentarily caused the distributor shaft to stop rotating and in its turn this stopped the intake camshaft since the distributor shaft is locked to the end of the camshaft by the dog assembly shown in Figure 2.
• As soon as the distributor drive shaft locked and caused the intake cam to stop rotating the timing belt which drives the intake camshaft by means of a toothed pulley was faced with the problem of being driven by the pulley on the engine crank shaft but was faced with a seized pulley in the camshaft.
• Since the engine forced the belt to continue to move the teeth on the belt were stripped off as it ran pass the seized intake camshaft pulley. Figure 24 shows a portion of the belt with the normal tooth configuration and on the right hand side a portion of the belt which has had its tooth pattern stripped off by the locked camshaft pulley. Figure 25 also shows the before and after profiles of the timing belt.
• The damage to the timing belt is analysed below and gives an indication of the duration of the time that the intake camshaft was seized. With the timing belt teeth being stripped from the elastomeric timing belt the timing of the engine was destroyed, i.e. the synchronization between crankshaft, cams, valves and pistons.
• The crankshaft continued to be driven by the pistons which oscillated in the cylinders however the intake valves were now mistimed because of the stoppage of the camshaft caused by the rotor jamming in the distributor housing and the exhaust camshaft was faced with a portion of belt approximately 640 mm long which could no longer drive the camshaft of the exhaust valves.
• The motion of the intake and exhaust valves was now no longer synchronized with the motion of the pistons. There was contact between the pistons and the mistimed valves resulting in severe damage to the valves, valve guides and assorted other components in the upper part of the engine.
• This damage necessitated a complete rebuild of the engine.
• The duration of the instance can be determined by an examination of the belt. The owner reported that the engine speed was approximately 3000 RPM when the failure occurred. At 3000 RPM the engine is turning over at 50 revolutions/second - 1 revolution will take .02 seconds.
• At 3000 RPM given that the circumference of the timing belt drive pulley is approximately 250 mm the crankshaft will have undergone 2.6 revolutions, i.e. length of damage portion of belt - 641 mm, circumference of timing belt crankshaft drive pulley - 250 mm, dividing 640 into 2, 250 to 641 is 2.6, so the crankshaft will have undergone 2.6 revolutions in order to cause 640 mm of strippage on the belt.
• At 3000 RPM 50 revolutions/second the duration of the seizure will be 2.6 revolutions ÷ 50 revolutions = .052 seconds. On this basis we can say with considerable accuracy the distributor shaft jammed the camshaft for a period of approximately .052 seconds.
• On a 4-cycle engine 1 cycle requires 2 revolutions of the crankshaft, i.e. the piston reciprocates twice and the intake and exhaust valves complete a full cycle once every 2 crankshaft revolutions. On this basis 1 cycle at 3000 RPM requires .04 seconds thus .052 ÷ .04 indicates that the camshaft was seized for approximately 1¼ engine cycles. In the course of this time the pistons and valves would have had ample time to impact and cause catastrophic damage.
• Since the engine would not have stopped immediately subsequent damage would have occurred in the time taken for the engine to come to rest.
4.0 CONCLUSIONS
We are of the opinion that the undersized portion on the distributor drive shaft which was installed as a new component by Acura in January 2000 permitted relative angular motion between the rotor head and the drive shaft assembly. Over a period of time this relative angular motion permitted the retaining screw to come free and this in turn allowed the rotor head to slide into interference contact with the inside of the distributor cap. This in its turn briefly prevented the distributor shaft rotating, this in its turn caused the intake camshaft to seize which caused the stripping of the timing belt and the resultant effect was interference between the valves and the pistons resulting in catastrophic engine damage. Simplistically the root cause of the failure was a shaft which had been machined by the manufacturers at .009" undersized.
In the course of our investigations we have found that there have been at least two failures of this type reported with identical cars both in the United States. One occurred in New Jersey in April 1999 and the second identical failure occurred in Michigan in April 2001. We are disturbed from a professional perspective that the engineers within Honda US did not see fit to release information about these failures and the potential for this type of damage to owners of these vehicles. It is of course possible that only a limited number of undersized distributor shafts were produced however at the very least since this could have resulted in life threatening occurrences whilst the vehicle was in motion we believe that it would have behooved the manufacturer to at least inspect all vehicles of this type. The inspections could have been extremely brief since it is very obvious from a visual inspection of the upper portion of the distributor shaft whether or not the distributor in question was fitted with the undersized shaft.
I find this very interesting.
1.0 INTRODUCTION
This report deals with the failure of a distributor assembly on a 1997 Honda Acura Integra Type R which occurred in July 2001.
The distributor on a spark ignition internal combustion engine is the device which permits the spark plugs to fire at a pre-determined sequence and time. The rotation of the distributor is synchronized to the rotation of the engine crank shaft, the motion of the pistons in the cylinders and the movement of the intake and exhaust valves. The latter permitting the inner fuel air mixture and the removal of combustion products. There are a variety of methods by which synchronization is achieved and in this particular engine synchronization is maintained between the crank shaft rotation, the motion of the intake valves and the rotation of the distributor by means of linking the distributor shaft to the end of the intake valve camshaft and driving this camshaft in synchronicity with the engine crank shaft by means of a reinforced tooth belt. In this way as the pistons reciprocate and the crank shaft rotates the crank shaft a toothed pulley at the end of the crank shaft drives a toothed belt which causes the intake camshaft and hence the distributor to rotate at half engine speed. In this way the timing of the four cycle engine is maintained. This ensures that the spark plugs ignite the fuel air mixture at or about top dead centre, the relevant intake and exhaust valves open and close without contacting the face of the reciprocating piston. Failure to maintain synchronization between the spark plugs and the rotating or reciprocating parts of the engine can result in consequences which range from rough running and poor fuel efficiency to catastrophic engine failure to the type of catastrophic engine failure that occurred in this instance.
The distributor and its timing relative to the rotation of the engine is a critical element in the efficient safe running of the engine.
This particular engine is described as having overhead camshaft. These require two sets of cams, one driving the intake cams and the other the exhaust cams. These rotation of these cams are controlled by an approximately 1200mm long tooth belt which is reinforced with high strength fibres to prevent stretching and to maintain its integrity. Any stretching or loss of teeth on this belt introduces the risk of a loss of synchronization between the camshafts, the distributor and the engine rotation.
Note to carry out this investigation both the distributor assembly which had undergone failure and an undamaged distributor assembly of identical part number were examined. Measurements were made using micrometers or dial gauges which had been maintained and externally calibrated. Details of the investigation.
2.0 EXAMINATION OF COMPONENTS
Two sets of Honda Acura Integra Type R distributor assemblies were delivered to our offices, these are described at Part #30102P72-006 Cap Assembly, #30103P73-003 Rotor Head Assembly, two lower distributor assemblies Part #D3179 were also supplied, finally a timing belt Part #14400P72-014 was provided. This was the belt which had been involved in the failure. The distributor assemblies are shown in Figures 1 and 2, Figure 1 shows the lower surface of the distributor assembly and the shaft assembly which connects to the end of the intake cam and rotates at the same speed as the intake cam. Figure 2 shows the upper surface of the distributor assembly with the four connections for the spark leads. Figure 4 shows the distributor with the cover assembly removed and the rotor and internal dust cap are visible. Mode of operation of the distributor is that as the shaft shown in Figure 2 rotates at half engine speed the rotor cap shown in Figure 4 rotates at the same speed and distributes the electrical signal to the ?? spark plug leads shown in Figure 3. Figure shows the dust cap moved and the rotor assembly mounted on top of the distributor drive shaft can be clearly seen. Figure 6 is a close up of this and shows the rotor head mounted on top of the distributor shaft which carries a ferrite cap which is part of the ignition system. The rotor is locked to the distributor shaft by means of a flat machined on the shaft which engages a flat informed in the injection moulded rotor assembly. The flat can be clearly seen in Figure 21 left hand side which is a photograph of the undamaged rotor assembly. The relative dimensions of an undamaged shaft and rotor are given below:
• Shaft outside diameter - .4905"
• Internal diameter of injection moulded rotor assembly -
• Internal diameter of the hole in the new rotor assembly - .4905491 - this is described as ___ tolerance in the ?? category of the Association of Automotive Engineers.
The protrusion of the shaft in a new distributor assembly can be clearly seen in Figures 8, 9, and 10 which show both the indexing flat on the shaft and the position of a tapped through hole into which a retaining screw is fitted to prevent the rotor from becoming detached from the driven shaft. The measurements show that with the new rotor fitted on a new shaft the angular play in the shaft between the rotor shaft and the rotor assembly is less than 2° without the retaining screw being fitted and when the retaining screw is fitted the rotation becomes negligible. Figure 7 shows the damaged component, the rotor cap, the rotor assembly is seen to suffer significant damage both to the electrical contact and to the upper and lower surfaces. Figures 18, 19, 20 and 21 show additional views of the damage.
Significant differences behaviour are noted when either the old or new rotor head assembly are mounted on the old and new alternator shafts. In the case of the new shaft there is less than 2° of angular rotation occurs when the rotors are fitted to the shaft. In the case of the old rotor assembly which we understand to have been fitted by Burrard Acura in January 2000 relative angular movement of approximately 20° occurs between the rotor head and the shaft. Since the internal dimensions of the old and new rotor assemblies are essentially identical the reason for this ten times greater angular motion must lie in the portion of the shaft which makes contact with the inside of the rotor. An examination of the old and new distributor assemblies makes it obvious why this angular play occurs, the distributor assembly fitted by Acura in January 2000 has the section making contact with the internal hole on the rotor assembly reduced in diameter by approximately .009". This was mentioned above the contact area of the new shaft has a diameter of .4905" whereas the old shaft has a diameter of .4805.481". Hence the portion of the shaft in contact with the rotor assembly is .009" undersized relative to the new shaft. This difference in diameter accounts for the much greater play between the rotor head and the distributor shaft. Using the terminology of the American Society of Automotive Engineers the fit between the old shaft and the rotor head would be described as sloppy.
In summary the tolerances between the “the shaft of the old distributor fitted by Acura in January 2000 as a new part and the shaft on a new distributor differ by .009"”, this permits a rotor head to have an angular play of approximately 20°. It should be noted that this angular play will be reduced by the insertion of the locking screw but if the locking screw for any reason disengages a gross rotational play will develop between the rotor heads and the distributor drive shaft.
3.0 CAUSATION
Based upon our examination of both the old and new parts and knowing the mode of operation and the intention of the designers we are able to develop a sequence of events which were the causation of the engine failure. In essence the events are as follows:
• In January 2000 the car was taken to Acura for service related to other problems.
• Acura fitted the “old distributor assembly” which had a reduced drive shaft diameter which did not match the internal dimensions of the rotor assembly.
• The installation of this distributor assembly would permit angular rotations between the rotor and the drive shaft. This random angular rotation would have resulted in the timing errors that the owner referred to in his letter to Acura, dated February 2nd when the owner complained about errors in timing after the vehicle had come
With the benefit of hindsight it is of course easy to see why these timing problems arose. Because of the sloppy fit between the inside of the rotor assembly and the undersize portion of the distributor there was angular movement between the rotor head and the shaft. Since the shaft is timed relative to the camshaft and engines by means of the toothed timing belt any relative angular motion of the rotor assembly would result in timing errors on the car. These would manifest themselves as rough idle, difficulty starting, etc. The problem was not identified by Acura and it is doubtful whether the owner had any reasons to suspect that he had been supplied with an incorrectly dimensioned distributor assembly. The owner continued to drive the car with intermittent timing problems until July 2001 when a catastrophic failure developed. In our professional opinion the following sequences of events occurred immediately before the catastrophic failure:
• The retaining screw passing through the rotor assembly and into the tapped threaded hole in the top of the distributor drive shaft worked loose. This was almost certainly because of the intermittent loading and motion between the distributor drive shaft and the rotor head.
• As the screw loosened it initially came into contact with the inner surface of the dust cap which lies below the rotor assembly. Figure 14 shows scoring of the dust cap assembly which is shown in its mounted position in Figure 4.
• The scoring by the head of the loosening screw continued until it cut completely through the portion of the dust cap surrounding the lower end of the rotor.
• At this point the screw was able to separate completely from the rotor drive shaft assembly and indeed the screw was found loose in the distributor assembly when it was disassembled. Figure 15 shows the portion of the dust cap which was cut away by the screw head as it loosened in the course of time.
• Once the screw was separated from the rotor drive shaft assembly the rotor was able to move up the shaft towards the top of the distributor assembly. As it did so it impacted the electrical contacts in the distributor cap.
• Initially the rotor assembly continued to rotate in synchronicity with the drive shaft and it produced wearing damage on the inside of the distributor cap, see Figures 22 and 23.
• Finally however it seized and at this instance since it was still in contact with the rotating distributor shaft and held in contact with the shaft by means of the flat on the shaft and the flat on the inside surface of the rotor assembly it seized.
• In doing so it underwent substantial mechanical damage, see Figures 18, 19, 20 and 21. This jamming between the rotor assembly and the inside of the distributor cap momentarily caused the distributor shaft to stop rotating and in its turn this stopped the intake camshaft since the distributor shaft is locked to the end of the camshaft by the dog assembly shown in Figure 2.
• As soon as the distributor drive shaft locked and caused the intake cam to stop rotating the timing belt which drives the intake camshaft by means of a toothed pulley was faced with the problem of being driven by the pulley on the engine crank shaft but was faced with a seized pulley in the camshaft.
• Since the engine forced the belt to continue to move the teeth on the belt were stripped off as it ran pass the seized intake camshaft pulley. Figure 24 shows a portion of the belt with the normal tooth configuration and on the right hand side a portion of the belt which has had its tooth pattern stripped off by the locked camshaft pulley. Figure 25 also shows the before and after profiles of the timing belt.
• The damage to the timing belt is analysed below and gives an indication of the duration of the time that the intake camshaft was seized. With the timing belt teeth being stripped from the elastomeric timing belt the timing of the engine was destroyed, i.e. the synchronization between crankshaft, cams, valves and pistons.
• The crankshaft continued to be driven by the pistons which oscillated in the cylinders however the intake valves were now mistimed because of the stoppage of the camshaft caused by the rotor jamming in the distributor housing and the exhaust camshaft was faced with a portion of belt approximately 640 mm long which could no longer drive the camshaft of the exhaust valves.
• The motion of the intake and exhaust valves was now no longer synchronized with the motion of the pistons. There was contact between the pistons and the mistimed valves resulting in severe damage to the valves, valve guides and assorted other components in the upper part of the engine.
• This damage necessitated a complete rebuild of the engine.
• The duration of the instance can be determined by an examination of the belt. The owner reported that the engine speed was approximately 3000 RPM when the failure occurred. At 3000 RPM the engine is turning over at 50 revolutions/second - 1 revolution will take .02 seconds.
• At 3000 RPM given that the circumference of the timing belt drive pulley is approximately 250 mm the crankshaft will have undergone 2.6 revolutions, i.e. length of damage portion of belt - 641 mm, circumference of timing belt crankshaft drive pulley - 250 mm, dividing 640 into 2, 250 to 641 is 2.6, so the crankshaft will have undergone 2.6 revolutions in order to cause 640 mm of strippage on the belt.
• At 3000 RPM 50 revolutions/second the duration of the seizure will be 2.6 revolutions ÷ 50 revolutions = .052 seconds. On this basis we can say with considerable accuracy the distributor shaft jammed the camshaft for a period of approximately .052 seconds.
• On a 4-cycle engine 1 cycle requires 2 revolutions of the crankshaft, i.e. the piston reciprocates twice and the intake and exhaust valves complete a full cycle once every 2 crankshaft revolutions. On this basis 1 cycle at 3000 RPM requires .04 seconds thus .052 ÷ .04 indicates that the camshaft was seized for approximately 1¼ engine cycles. In the course of this time the pistons and valves would have had ample time to impact and cause catastrophic damage.
• Since the engine would not have stopped immediately subsequent damage would have occurred in the time taken for the engine to come to rest.
4.0 CONCLUSIONS
We are of the opinion that the undersized portion on the distributor drive shaft which was installed as a new component by Acura in January 2000 permitted relative angular motion between the rotor head and the drive shaft assembly. Over a period of time this relative angular motion permitted the retaining screw to come free and this in turn allowed the rotor head to slide into interference contact with the inside of the distributor cap. This in its turn briefly prevented the distributor shaft rotating, this in its turn caused the intake camshaft to seize which caused the stripping of the timing belt and the resultant effect was interference between the valves and the pistons resulting in catastrophic engine damage. Simplistically the root cause of the failure was a shaft which had been machined by the manufacturers at .009" undersized.
In the course of our investigations we have found that there have been at least two failures of this type reported with identical cars both in the United States. One occurred in New Jersey in April 1999 and the second identical failure occurred in Michigan in April 2001. We are disturbed from a professional perspective that the engineers within Honda US did not see fit to release information about these failures and the potential for this type of damage to owners of these vehicles. It is of course possible that only a limited number of undersized distributor shafts were produced however at the very least since this could have resulted in life threatening occurrences whilst the vehicle was in motion we believe that it would have behooved the manufacturer to at least inspect all vehicles of this type. The inspections could have been extremely brief since it is very obvious from a visual inspection of the upper portion of the distributor shaft whether or not the distributor in question was fitted with the undersized shaft.
06-22-2004, 12:06 PM
#7
Re: Timing belt snapped and distributor housing questions (LSTEG96)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by LSTEG96 »</TD></TR><TR><TD CLASS="quote">thats a long ******* post...and a good ******* post.</TD></TR></TABLE>
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06-23-2004, 08:45 AM
#9
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hooly **** the end of the article sounds EXCATLY what happened to me several months ago...my car was okay, but man thats eeire
https://honda-tech.com/zerothread?id=798708
https://honda-tech.com/zerothread?id=798708
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