Hello H-T,
I did a swap on my 99 hatch a while back and have noticed an occasional grind from 1st to 2nd or from 2nd to 3rd under full throttle acceleration. I'm wondering if there's a way to adjust the linkage? At first I thought the grind was me missing the gear but even paying close attention to my hand and foot coordination it still happens. Could the frame or subframe be slightly bent. I only have the crappy Haynes manual and I know I need to invest in the Helms one to get a better idea of diagnosing the problem. Here's a list of what's in the car that might help with anyone willing to help. Urethane linkage bushings, an ACT clutch (stage 1) the motor mounts are kinda old but I have new Hasports waiting to go in. The throwout bearing does squeak a bit but was replaced when the clutch was installed. BTW all this stuff is on a B18. Any help would be really appreciated.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ein020 &raquo;</TD></TR><TR><TD CLASS="quote">Hello H-T,
I did a swap on my 99 hatch a while back and have noticed an occasional grind from 1st to 2nd or from 2nd to 3rd under full throttle acceleration. I'm wondering if there's a way to adjust the linkage? At first I thought the grind was me missing the gear but even paying close attention to my hand and foot coordination it still happens. </TD></TR></TABLE>

I doubt it could be a gear linkage problem or engine mounts etc. Could be simply worn synchro rings (like that would be good news!), or perhaps you're just rushing the shift too quickly to allow the synchro rings to properly synchronise the gear speeds. Maybe a combination of the two?

Do your rpm start dropping immediately as soon as you are off the throttle pedal and depress the clutch? Or do the rpm 'hang' there for a moment or so before starting to drop? Do the rpm drop quickly or slowly?

 

The rpms drop pretty quickly, that is to say I don't notice them hanging up, and the trans only has 20K on it. I got a factory rebuilt one which is partially why it makes no sense to me. I don't see a way to adjust the linkage either. You just hook it up and that's it. A friend of mine had an 99SI and had to have the trans rebuilt after a less reputable shop installed a short shifter in it. The dealer said since the short shifter was the wrong one the trans was damaged and needed to be rebuilt (shift fork I believe due to the bolt in the bottom not having shims to takeup some slack) I have an ITR shifter in place with the linkage being from the same car. Just some more pieces to a messy puzzle.

 

Work Bump

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by johnlear &raquo;</TD></TR><TR><TD CLASS="quote">

Could be simply worn synchro rings (like that would be good news!), or perhaps you're just rushing the shift too quickly to allow the synchro rings to properly synchronise the gear speeds.


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I'm thinking the same thing. I had my 2-3 gear set replaced(while under warranty thank god) because I missed going into 3rd while driving in snow and it made a zzzZZZP sound right beffore it would engage, and the guys at the Honda dealer said it looked like I was power shifting it. Either the rebuild is ****, or your 1-2, 2-3 synchros are toast.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ein020 &raquo;</TD></TR><TR><TD CLASS="quote">The rpms drop pretty quickly, that is to say I don't notice them hanging up, and the trans only has 20K on it. I got a factory rebuilt one which is partially why it makes no sense to me. I don't see a way to adjust the linkage either. You just hook it up and that's it. A friend of mine had an 99SI and had to have the trans rebuilt after a less reputable shop installed a short shifter in it. The dealer said since the short shifter was the wrong one the trans was damaged and needed to be rebuilt (shift fork I believe due to the bolt in the bottom not having shims to takeup some slack) I have an ITR shifter in place with the linkage being from the same car. Just some more pieces to a messy puzzle.</TD></TR></TABLE>

I don't know exactly what sort of shift linkage your car has, but on my CB7 it's a cable type. With this linkage you can adjust it on the cables at the lever end, but all this does is change the position of the gear lever, it can have no affect on the box internals. With this type of shifter fitting a 'short shifter' can't cause any problems with the box itself.

I'd be surpised if an 'incorrectly' adjusted rod shifter could cause internal box damage, but I could be wrong. It's conceivable that with either type of shifter that forcing the shift could cause the internal selector forks to be bent, but I reckon you'd have to be really abusing it...

I was asking about the rate of rpm 'drop' because on at least some Hondas the IACV tends to cause the rpm to remain high (or even to jump slightly) after getting off the throttle pedal and onto the clutch pedal (and then for the rpm to drop only fairly slowly, slowing the speed with which upshits can be made smoothly). This has nothing to do with poor shifting technique (as some seem to think), but is a problem with the IACV (unfortunately the IACV seems designed to do this). It is something that can be improved if not totally eliminated with a fairly minor modification the the IACV, which results in faster and smoother shifts.

 

I'll try anything. Do you know what's entailed in this IACV fix or is this just something I can easily find on a search?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by johnlear &raquo;</TD></TR><TR><TD CLASS="quote">

....slowing the speed with which upshits....
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As opposed to downshits? Sorry, typo's can be funny as hell. I think the rpm "hanging" that johnlear is describing has something to do with emissions. I know the older Neons and the new Si seem to have an rpm "hang-up" when you would free- rev the engine. Now that's not to say your IAC isn't a piece o' ****, but it's something to ponder.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by King V &raquo;</TD></TR><TR><TD CLASS="quote">
As opposed to downshits? Sorry, typo's can be funny as hell. </TD></TR></TABLE>

I noticed my typo just after I posted, but it seemed too much trouble to edit it, besides I thought it might mildly amuse somebody!

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by King V &raquo;</TD></TR><TR><TD CLASS="quote">I think the rpm "hanging" that johnlear is describing has something to do with emissions. I know the older Neons and the new Si seem to have an rpm "hang-up" when you would free- rev the engine. Now that's not to say your IAC isn't a piece o' ****, but it's something to ponder. </TD></TR></TABLE>

I used to think it must be an emissions related thing, but I'm not so sure now.

With carburettor engines it used to be fairly common practice to provide some sort of air bleed mechanism that effectively disallowed the throttle to be fully closed on the overrun or when changing gears (which creates a brief overun like condition, i.e. very high manifold vacuum at higher rpm), the purpose of which was to reduce oxides of nitrogen that are produced in higher quantities under these conditions (more air lessening oxides of nitrogen when some fuel is being burned, I think).

This might take the form of a spring loaded valve in the butterfly plate that opened when manifold vacuum was high (as you would get on the overun at higher than idle rpm with a closed butterfly), or some more sophisticated mechanism that does more or less the same thing.

But, carburettors always flow some fuel if any air flow (even slight) exists past the idle jet, even on the overun some fuel is being burned and therefore oxides of nitrogen are being produced. On EFI engines the injectors are typically shut off in overun conditions (until engine appraohes idle speed), so no fuel is being burned and thus no oxides of notrogen are likely (?) to be produced.

I tend to think the overun 'air bleed' on EFI engines (at least on some Hondas via the IACV) is used as a means to 'smooth out' the transition from fuel being injected to fuel not being injected and vice versa.

If you competely disable the IACV by unplugging the electrical connector (which shuts the IACV air metering valve) the on / off throttle behaviour becomes quite harsh, and when feathering the throttle the engine can cut in and out harshly causing a bad vibration through the drivetrain. I think this is more likely the real reason why the IACV is set up to prevent air flow being cut off instantly when the butterfly valve is shut off, but I could be wrong and it may also be an emissions thing.

 

This may have absolutely nothing to do with your problem, which I suspect is more likely to be due to the synchro rings or posssibly the clutch isn't fully disengaging, in which case you might have hydraulic issues in the clutch.

Have you tried re-bleeding the clutch? I had troubles with mine after I thought it was fully bled, but it still wasn't quite right so after a while I had another go and got more air out. Clutch has been great since then.

At any rate, the mod to the IACV is to reduce the degree to which the rpm tend to momentarily 'hang' at the same rpm which they were at when the throttle was closed and the clutch depresed (or even to slightly jump higher), before lazily dropping lower. If your rpm don't do this then I doubt modding the IACV will help your crunching problem. Even so here's the why and how of what to do:

If you remove the IACV (typically two bolts, the coolant lines, and the electrical connector, not hard or long to do), you'll see two ports (holes) in the plenum chamber body that correspond to two ports in the IACV. One hole on the IACV has a mesh screen on it, and the other doesn't.

The IACV draws air from a long narrow port that starts just in front of the butterfly valve in the throttle body, and then exits at the port hole in the plenum that corresponds to the port in the IACV that has the screen. The IACV then meters air according to instructions from the ECU, this air then passing into the plenum through the port with no screen.

With some IACVs (that I've seen photos of) one of the ports in the IACV is a lot smaller than the other, but on others (e.g. that fitted to the f22A9 engine in my CB7) both ports are the same size. In this case the IACV has the capacity to flow a fairly substantial quantity of air, certainly much more than required merely to adjust idle speed when auxilliary loads are placed on the engine.

We can 'cripple' the IACV to reduce how much air can actually flow into it by making a restrictor plate from thin metal (shim or drink can aluminium or similar will do fine). Bur first we have to discover what size restrictor hole to make in the restrictor plate. This is done by making a temporary cardboard gasket from good quality gasket paper (thickish, i.e. light cardboard).

One hole in the restrictor plate 'gasket' should be fairly large, nearly as large as the port diameter, the other hole must be a lot smaller, and placed in front of the IACV screen (this is the restrictor hole that controls the max quantity of air that will pass through the IACV). I'd start by making this smaller hole about 5mm in diameter (a 'starwheel' type leather punch is useful for making the hole), then re-installing the IACV with the restrictor 'gasket' between the IACV and the plenum.

Start the engine up and run to temp, then switch on the air-con to see if the idle rpm drop excessively, then try the lights as well. If the rpm drop too much then the restrictor hole is at least a bit too small, so take the gasket out and try a slightly larger hole (only a small increase in diameter makes a fairly big difference to how much air can pass, so only make it slightly bigger). Try again.

If you now have a well behaved idle with auxilliary loads on, take the car for a test drive to see how much difference to rpm 'dropping' you've made. If you still have too much idle 'hanging' during shifts then try a smaller hole, but this will affect idle speed compensation to some degree.

When driving you should notice the engine rpm drop more quickly during upshifts (not 'upshits', that what you get if it doesn't work!). This ought to allow smoother and possibly faster upshifts, but you might also find the engine easier to 'rev match' when downshifting (I did), because the engines response to 'blipping' the throttle may become more predictable.

You shouldn't find that the engine becomes harsh in on / off throttle conditions, nor when feathering the throttle between no acceleration and slight accleration (or just trying to hold a steady speed at very light throttle opening), but if you do then you might have to slightly increase the size of the restrictor hole.

Now we've found the correct sized restrictor hole, but the cardboard gasket won't last more than a few weeks (months if you're lucky), the air passing through it will eventually start shredding it and then you're back where you were before. You now have to make the actual restrictor plate from metal shim with a restrictor hole the same size as the restrictor hole in the temporary cardboard restrictor gasket. The new restrictor will need to be fitted using a smear of non hardening gasket sealant, and using a light smear on the stock '8' shaped rubber IACV gasket will also be a good idea (it's a good idea to do this with the temporary gasket as well, just to avoid any leaks that might confuse things).

On my car I have the restrictor hole size such that turning on the air-con causes a slight idle rpm drop, but not enough to cause vibration. The smaller the restrictor hole the more effective the mod will be at allowing the rpm to drop faster during shifts, but the more it affects idle speed compensation, you have to find the balance that suits you. This may sound like a lot of work, but it's not so bad since the IACV is (at least on the CB7) easy to access and quite quick to take off and refit.

Note that this IACV mod is my own coprighted idea, so send all cheques / cases of beer to:
John Learmonth, Australia...!

 

It's pretty sweet to read stuff like that at 8 am with a hot coffee. Gets the gray matter going. So here's my first installment on that case.

 

Now THAT"S a reply and a half. I'll definitely try that and let you know how I make out. It might be a bit cause the weather has been pretty bad here recently and I'm slammed at work. Keep an eye out for this post. I'll break it out of storage if I have to. On the clutch thought I was thinking about the same thing, ie: bleeding the brakes, but the pedal feels good. I had to do it three times after I installed the clutch to get it right. The clutch has been in for just over a year and the problem has been around for the last six months. It hasn't been a problem because I rarely drive the snot out of it. I was thinking of getting the OMNI quick shift to eliminate the chances of it being operator error. But I was thinking that your IACV makes more sense, and is cheaper, because the new clutch might weigh enough to throw off the valve in its stock form (stock clutch size, weight / to the stock valve size opening). If you increase the weight of the clutch assembly you need to decrease the amount of air the valve passes through it. I'm not too sure how much an ACT clutch and pressure plate increase the weight of the assembly but I imagine the assy. plus 8600RPM's makes the difference much more than one would think. Do you think I'm correct in this assumption?

Btw I'll offer this for beer. Have a case on me!

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ein020 &raquo;</TD></TR><TR><TD CLASS="quote"> I'm not too sure how much an ACT clutch and pressure plate increase the weight of the assembly but I imagine the assy. plus 8600RPM's makes the difference much more than one would think.
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AS far as I know ACT uses Integra style PP's on their kits(at least thats what the dude at ACT told me). I have an Xtreme PP and Street/Strip disc in my 99 Si, and it really didn't seem to have much of an effect on RPM ramp up/spin down. Now the engagement, thats a whole different story.....

 

At least I'm not the only one who's not a fan of the engagement and mine is only a stage one.

 

It would only be a problem if the clutch isn't fully disengaging due to air in the hydraulics. This would cause clutch 'drag' that tends to keep the cluster gear at a higher rpm because it's still being kept there by slower dropping engine rpm, which might cause a 'crunch' when selecting the next higher gear due to the cluster gear rotating too quickly relative to the gear you're trying to select on the main shaft.

Unless the clutch were 'dragging' quite badly I doubt this would be likely to be an issue if the synchro rings are in good condition, i.e. good synchros should be able to synchronise the gear speeds adequately, at the possible expense of slowing the actual shift a little.

What's a "quick shift"? Not a 'short shifter'?

Only if the IACV is actually causing a significant 'hanging' of engine rpm at shift, or for the rpm to drop lazily rather than promptly. Even so, if the synchros are in good condition they ought to be able to prevent gear crunches, unless perhaps you're slamming it through the gate very quickly.

If the engine rpm drop faster, you will be able to release the clutch slightly sooner after making the actual upshift without the too high engine rpm causing that little 'shove' in the back as the clutch pedal is released, but it may not make the actual shift faster as this is more to do with the cluster gear itself losing rpm in neutral with the clutch disengaged, i.e. this is a function of the synchros synchronising the gear speeds, and if the synchros are worn it may still crunch on fast shifts.

To quickly get some idea of just how much the IACV might be affecting rpm drop during shifts, disconnect the IACV electrical connector and take it for a drive. This will cause two things other than (probably) allowing rpm to frop faster, you'll get a CEL, and the on / of throttle behaviour will become harsh causing intermittant vibrations through the drivetrain when geting on and off or not really on the throttle pedal (the idle may also drop, and drop further if you use air-con, lights etc).

When you reconnect the IACV you'll need to stop and restart the motor, or else the CEL won't go away, and the IACV will compensate for load at idle but won't prevent on / off throttle harshness.

If you do the restrictor plate mod, the rpm won't drop as quickly as they will with the IACV electrically disconected (which closes it off completely, unless it's leaking air through the valve), but at least the idle will compensate for auxilliary load.

Any difference in mass between one clutch and another is I think not likely to be great enough to cause any issues, and is not going to be equivalent to the difference between a heavy and light flywheel (though a heavier clutch will have some affect similar to increasing flywheel weight, just likely to be very little IMO).

If you were to fit a light flywheel, then this would allow faster rpm drop at upshift despite what the IACV was doing (though the IACV will still slow rpm drop if it is having this affect, just that the affect will be less obvious). A heavier clutch will have the opposite affect, further slowing rpm drop but IMO only very slightly.

If the rpm are momentarily 'hanging' at shift, then the lighter flywheel probably won't affect this. This is because we're talking about a static rpm with no rise or fall, meaning we must have a momentarily constant power input to maintain that rpm for however long that power input exists with no change. In this case with no rpm change the inertia or mass of the flywheel etc has no affect. But, a lighter flywheel will still allow very slightly faster rpm drop once the rpm actually starts dropping. With 'hanging' rpm the heavier clutch would also have no affect on how long the rpm 'hangs', but will slow the rate of rpm drop once it does start dropping.

If the rpm are actually rising slightly at upshift (when you get fully off the throttle and depress the clutch), then a lighter flywheel may make this 'jump' in rpm a bit worse. A heavier clutch would make it slightly less.