i know what the factory clearances are. most people do. however, some of you engine seasoned, salty engine builders use looser clearances. will you list clearances you have used that are more prone to making power, but are safe to be actually driven with, not just 6-8 passes

1. piston to wall
2. rod bearings
3. main bearings

 

1)Piston to wall clearance is dictated by your piston manufacturer. Expansion rates would be different from manufacturer to manufacturer. However, if you buy pistons that have super high tolerances during manufacturing, you don't have to worry much about machining. For example, I bought a set of CP pistons that had exactly .003 piston to wall clearance between the piston skirt and my super low milage B20 block. Don't forget that you will need to still measure the clearances even if the pistons spec out. Example: I measured my OEM pistons and my CP pistons and got a difference of .001, which specs out. OEM clearance is .002 and CPs call for .003 which is perfect, but that doesn't mean that the cylinder bores are perfectly straight or worn down.

2,3)I think slightly looser main clearances will give you a little more oil pressure on the rod bearings and I remember reading that .002 is gonna be alright as well on the rod bearings. My motor spec'd out at .0015 on all rod/main bearings and it's fine so far.


What about ring gaps/clocking? All this stuff has been covered before though, so a simple search will bring up a lot of good reading. I spent days, maybe even weeks reading old threads on clearances and such before I started building my motor. There's a lot of GOOD information on this site

 

i used all OEM stuff so i stuck with OEM specs.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Toadfart &raquo;</TD></TR><TR><TD CLASS="quote">1)Piston to wall clearance is dictated by your piston manufacturer. Expansion rates would be different from manufacturer to manufacturer. However, if you buy pistons that have super high tolerances during manufacturing, you don't have to worry much about machining. For example, I bought a set of CP pistons that had exactly .003 piston to wall clearance between the piston skirt and my super low milage B20 block. Don't forget that you will need to still measure the clearances even if the pistons spec out. Example: I measured my OEM pistons and my CP pistons and got a difference of .001, which specs out. OEM clearance is .002 and CPs call for .003 which is perfect, but that doesn't mean that the cylinder bores are perfectly straight or worn down.

2,3)I think slightly looser main clearances will give you a little more oil pressure on the rod bearings and I remember reading that .002 is gonna be alright as well on the rod bearings. My motor spec'd out at .0015 on all rod/main bearings and it's fine so far.


What about ring gaps/clocking? All this stuff has been covered before though, so a simple search will bring up a lot of good reading. I spent days, maybe even weeks reading old threads on clearances and such before I started building my motor. There's a lot of GOOD information on this site </TD></TR></TABLE>

very good. pistons are RS machine so im going to stick to the tighter side of oem on this.

ring clocking and gapping is all taken care of.

 

so youre saying go maybe one step looser on the mains and stay oem on the rods or maybe one step tighter on the rods?

 

Purely performance youd wanna run looser on the rods as well.

 

I like middle of the road on mains, and loose on the rods. To each their own.

 

this is what i want to hear. everyones opinion based on facts, that way i can form my own.

 

I know I'm not a pro but I used .0015" bearing clearance after seeing people like IB and Combustion run them. I've understood that tighter clearances are good for reliability and looser is good for reving. The reasoning I found for .0015" is that it's a good compromise between the two...kind of like reliable rev'ing I guess.

 

if you build it loose only you will know about it
if you build it tight, everyone is going to find out

 

So you're saying that looser is better for performance?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 91SiZ6 &raquo;</TD></TR><TR><TD CLASS="quote">So you're saying that looser is better for performance?</TD></TR></TABLE>

yes, but i want to know how loose before you loose reliability

 

If your building an all out race motor, extra loose wont hurt you.

If your building a high perf street motor, it could. What takes most of the beating, the rod bearings or the main bearings

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Combustion Contraption &raquo;</TD></TR><TR><TD CLASS="quote">If your building an all out race motor, extra loose wont hurt you.

If your building a high perf street motor, it could. What takes most of the beating, the rod bearings or the main bearings</TD></TR></TABLE>

rods i would say, mr. riddler. man who answer questions with more questions.

besides, anyone whos pulled a motor apart knows the copper shows more in the rod bearings due to them absorbing the combustion event, plus the rocking motion where as the crank just spins in circles. at least thats what i have seen, so unless my motors have been wacky...

 

wow, that looks like a coke can pull tab laying inside an intake port in your avatar. its ok if you hate me.

 

Well then, if you run your rods on the loose side, that extra clearance will allow you a 'cushion' so to speak and you could minimize the need to run an excessive main bearing clearance which will maximize longevity. IF thats what your going for. For all out performance, run loose. Just dont get carried away and run SBC clearances on your B-series.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by xDEFTONESx &raquo;</TD></TR><TR><TD CLASS="quote"> its ok if you hate me. </TD></TR></TABLE>

good.

 

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

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Combustion Contraption &raquo;</TD></TR><TR><TD CLASS="quote">Well then, if you run your rods on the loose side, that extra clearance will allow you a 'cushion' so to speak and you could minimize the need to run an excessive main bearing clearance which will maximize longevity. IF thats what your going for. For all out performance, run loose. Just dont get carried away and run SBC clearances on your B-series.</TD></TR></TABLE>

Good info. Thank you, sir.

 

I don't think there is any "power" in increased clearances.It's like JDogg is referring to.Engines rarely fail from too much clearance but many fail from too little. Increased piston to wall can cause the piston to rock in the bore and effect ring seal.Cast pistons will break the skirts off with to much clearance.Increased rod clearance helps the bearing run cooler from the increased flow but you may get more surface wear at start-up.Almost all "normal" bearing wear is from start-up.Bearing surface fracturing is from combustion stresses.Main bearing clearances increase as soon as the block heats up.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Toadfart &raquo;</TD></TR><TR><TD CLASS="quote">2,3)I think slightly looser main clearances will give you a little more oil pressure on the rod bearings and I remember reading that .002 is gonna be alright as well on the rod bearings. My motor spec'd out at .0015 on all rod/main bearings and it's fine so far. </TD></TR></TABLE>

is this also true on balance shaft engines such as the f & h series?
would looser mains cause more wear and tear?
also what are your views on coated rod bearings?
will they help reduce chances of spinning bearings on long stroke engines?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by xDEFTONESx &raquo;</TD></TR><TR><TD CLASS="quote">wow, that looks like a coke can pull tab laying inside an intake port in your avatar. its ok if you hate me. </TD></TR></TABLE>
i think its behind a itb throttle plate

 

I'd run loose on both main/rod bearings for an all out motor, although i'd have the oil holes chamferred and shaped tear drops to improve oil flow which trade off some oil pressure.....a little less oil pressure yield a little more power anyway....as far as piston to wall, I found 3 1/2 thounsand for all motor engines is great, and 4 - 4.5 thousands on the turbo engines depends on boost/gas/etc...

 

i really need a good crank shop!
with a high flow oil pump i could offset that lower oil pressure

 

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

is this also true on balance shaft engines such as the f & h series?
would looser mains cause more wear and tear?
also what are your views on coated rod bearings?
will they help reduce chances of spinning bearings on long stroke engines?</TD></TR></TABLE>
but will running looser clearances compermise longevity 40,000+ miles?