Don Terrill’s Speed-Talk

What is the minimum rod side clearance on sbc

now my rod side cleance is

on 1-2 rod .022
3-4 rod .007
5-6 rod .011
and7-8 rod .007

I think it's really to tightened!

cmre07 wrote:What is the minimum rod side clearance on sbc

now my rod side cleance is

on 1-2 rod .022
3-4 rod .007
5-6 rod .011
and7-8 rod .007

I think it's really to tightened!

If your using a big radius crank make sure your using chamfered or narrow bearings.

Hi,

seems odd that you have 0.022" clearance between 1 and 2 and significantly less on the others.
I'm with the bearings too... sounds like you have a radius fouling problem.
Also check that the conrod small ends are not fouling on the piston pin bosses when moving the rods sideways.

+3 for check the bearings. There will either be a chamfer on the bearing or if narrowed bearings they will be marked upper and lower.

Take a couple of rod caps and a feeler gauge and recheck without the bearings. Use the same pair of caps for each journal and that'll tell you if the variation is with the rods or the rod journals.

If everything's fine without the bearings, you need chamfered bearings, or you can use the rod bearings for a 1980 Chevy 229 V6, CB1227 (?) which are narrower. The correct way is to use chamfered bearings, but I've encountered a number of kit strokers that use the V6 bearings, which apparently hold up well enough.

If your measurements with the feeler gauge aren't repeatable, put some bearings in, color everything with Magic Marker, and rub them against the (dry) journal to see where they're hitting. I had a Stroker From Hell some years ago where the rod side clearance was driving me nuts; it turned out the place that had offset-ground the crank hadn't properly dressed the wheel on the crank grinder, and the sides of the journals were tapered quite a bit. As in, .010 clearance at the top, but tight enough to bind the inner edge of the rod down below.

I've seen imported cranks where *all* the rod journals were too narrow, but at least they were all the same...

You side clearances don't seem right however, if the crank has been ground or the rods are used then something like this can happen when everything is put together correctly.
To answer your question - rule of thumb is 4 X the rod bearing clearance is the minimum side clearance.

rmcomprandy wrote:You side clearances don't seem right however, if the crank has been ground or the rods are used then something like this can happen when everything is put together correctly.
To answer your question - rule of thumb is 4 X the rod bearing clearance is the minimum side clearance.

"4 x the rod bearing clearance is
the min. side clearance."
Now you are really starting to scare me.

I don't understand your answer ... On a two rod per journal V type engine, that IS the MINIMUM side clearance required.
I have digested two SAE reports on this subject and there are probably several which I don't know about which address the subject of the affects of oil flow through the connecting rod bearing / crank journal interface.

IF you have another answer, please tell us as I'm always interrested in actual test results.

rmcomprandy wrote:I don't understand your answer ... On a two rod per journal V type engine, that IS the MINIMUM side clearance required.
I have digested two SAE reports on this subject and there are probably several which I don't know about which address the subject of the affects of oil flow through the connecting rod bearing / crank journal interface.

IF you have another answer, please tell us as I'm always interrested in actual test results.

Are we talking about a drag engine that
spends 10 seconds at 8,000 rpms or a circle track engine that will
spend hours at 8,000 rpms??
Yes,there is a difference.

NO ... you are NOT correct ... there is NO difference in MINIMUM side clearance no matter the intended use of the engine.
Presuming you are using a STEEL connecting rod, 4 times of whatever the actual bearing clearance dimention, is what is NEEDED to have correct oil flow. It's a multiplication factor; the running bearing clearance determines the MINIMUM side clearance.

OPTIMUM and MINIMUM are completely different circumstances.

new engine builder wrote:

rmcomprandy wrote:I don't understand your answer ... On a two rod per journal V type engine, that IS the MINIMUM side clearance required.
I have digested two SAE reports on this subject and there are probably several which I don't know about which address the subject of the affects of oil flow through the connecting rod bearing / crank journal interface.

IF you have another answer, please tell us as I'm always interrested in actual test results.

Are we talking about a drag engine that
spends 10 seconds at 8,000 rpms or a circle track engine that will
spend hours at 8,000 rpms??
Yes,there is a difference.

This type of post is pretty useless. If you have a technical point to make, then please do explain what you mean. rmcomrandy specifically stated his formula for side clearance. If you feel he is incorrect, you need to explain why and offer the correct method.
Cryptic posts like yours do nothing to enhance anyone's knowledge and seem solely designed to put down another poster and make yourself seem more knowledgeable. Really no different than saying "that's for me to know and you to find out!"

So new engine builder, what is the correct way to determine proper side clearance?

bobqzzi wrote:

new engine builder wrote:

rmcomprandy wrote:I don't understand your answer ... On a two rod per journal V type engine, that IS the MINIMUM side clearance required.
I have digested two SAE reports on this subject and there are probably several which I don't know about which address the subject of the affects of oil flow through the connecting rod bearing / crank journal interface.

IF you have another answer, please tell us as I'm always interrested in actual test results.

Are we talking about a drag engine that
spends 10 seconds at 8,000 rpms or a circle track engine that will
spend hours at 8,000 rpms??
Yes,there is a difference.

This type of post is pretty useless. If you have a technical point to make, then please do explain what you mean. rmcomrandy specifically stated his formula for side clearance. If you feel he is incorrect, you need to explain why and offer the correct method.
Cryptic posts like yours do nothing to enhance anyone's knowledge and seem solely designed to put down another poster and make yourself seem more knowledgeable. Really no different than saying "that's for me to know and you to find out!"

So new engine builder, what is the correct way to determine proper side clearance?

WOW!!,Bob I can see I've got you a little excited and
very DRAMATIC.
"Cryptic posts"??
That was a bit of a stretch and not my intent.
I think you may have read way to much into my post.
I can only tell you what has worked for us and other's USMTS engines that I've built.
Oil is Brad Penn 20w-50.
Our rotating assembly is a Callies crank with 350 mains and 1.88 Honda
rod journal size.
The rods are an Oliver Ultra light.
rod clearance is at .0025
We use to set rod side to side at .012 to .015 and we starting seeing "blueing" after about 10 nights.
Since we expanded side to side to .020 we don't see "blueing" at even 20 nights.
All I'm saying is multiply 4 x the bearing clearance did not and will not work for ANY of our applications.
Our R & D tells us that it's better to be a few thosandths "loose" than a few
thousandths to "tight" on rod side to side.

rmcomprandy wrote:I have digested two SAE reports on this subject

Could you post the paper numbers when you get a chance? I can get SAE papers through Inter-Library Loan.

I have no idea what the paper numbers are. The first one was over 25 years ago. They all have to do with "oil flow through plain friction bearings" or something of that sort so, you should be able to just look it up.

I think rmcompbrandy is correct in his formula , BUT it is a formula that is designed for stock type applications, I prefer more side clearance for performance engines.