[NeighborsComplaint]

Let's say I have my crank machined to next standard undersize d I have but find I have excessive side clearance between the rod big ends.

I understand this causes low oil pressure. How does one fix this condition?

Swap rods (Weight matched when balanced) around for best clearance?
Buy new rods and hope it's not the crank?
Send the crank out to be welded up and new chamfers cut?

At the low cost of today's crank and rods kits, I am guessing the answer is to just buy all new.

Just curious. Always been a gray area to me in terms of a fix.

[steve25]

It makes for a lot more oil being held up in windage aroundtge Crank and Rods , not so much a oil pressure drop.
It effects the oil volume moved thru the motor, wasted volume !
If it's a steel Crank you can have it welded up , but I would not trust any mom and pop shop that can weld and grind to do this type of work!

I new Crank with the proper Rod jurnal widths to work with your current Rods would be the way I would lean!

[74Grandville]

What do you consider excessive? What is the spec you're seeing?


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[Tom Vaught]

Originally Posted by 74Grandville

What do you consider excessive? What is the spec you're seeing?

Very good question before you "think any harder" on this deal.

Tom V.

[steve25]

Well I concider .020" plenty for a pair of steel Rods!

I have never liked the amount of excess side clearance that gets ended up with when Rods that are long version of BB Chevy are used!

[tiacguy]

Well like most Iv'e been building and running Pontiac's for 40 years now. At least the last 20 using the narrower BBC rods which always yields bigger rod side clearance in the range of .026-.028 I've believe the wider clearance also helps to keep the journal and bearing cooler by allowing more oil to pass through???

My early bearing issues with the Pontiac's went away when I got away from the traditional Pontiac dimension parts. BBC rods = smaller bearing wider side clearances??? Just my opinion. Scott

[steve25]

Two notches machined in cheek side of the rod will accomplish thing with less Rod shuffling side clearance.

[NeighborsComplaint]

.020-.025"

[Bruce Meyer]

Originally Posted by NeighborsComplaint

.020-.025"

Your OK. I ran that much on a bracket motor that went 1000+ passes and around 30 K street miles. Its not a problem.

[PAUL K]

Factory specification for the SD-455 is .023 plus or minus .004
63 SD spec is considerably wider.

[East]

I have 455 SD rods in my 428 and I have more than that with more than 112,000 miles of driving.

[steve25]

Let me clarify what I mean, am not talking about long term street motor longevity, I am commenting on high rpm oil control at revs above 5K.

[Tom Vaught]

Originally Posted by Bruce Meyer

Your OK. I ran that much on a bracket motor that went 1000+ passes and around 30 K street miles. Its not a problem.

X2, right in the range where it should be.
As was said, some of the rods at .028"-.032" were based on old racing specs.

The rods are never exactly open fully (in the middle between the two rods) like they are when you are doing a very simple rod side clearance test. The clearance number will always be smaller in actual operation. There has to be enough clearance to send some oil to the crank filets and some oil between the rods. That is the way oil cools the parts.

I have done bearing tests on a connecting rod rig (operating at different engine speeds) and a slight reduction on oil clearance causes the oil temp at the surface of the bearings to skyrocket. You can cheat on a bit loose, you will hurt parts on a "touch to tight" clearance, ask Marty Palbykin about that deal on a engine he built one time.

ps Thanks OP for a number on the clearance.

Tom V.

[shedgpeth4]

if OP had excessive side clearance, how would that be corrected to be in spec?

["QUICK-SILVER"]

Originally Posted by steve25

Let me clarify what I mean, am not talking about long term street motor longevity, I am commenting on high rpm oil control at revs above 5K.

Given same bearing clearance and oil pressure.....how much more oil comes out when rod side clearance goes from .020" to say .030"?

I don't how it could make a difference
Clay

[NeighborsComplaint]

Aha.

Rods are 455SD. That explains why some are outside of spec (for cast iron rods).

All's well then.

[HWYSTR455]

I went through a similar event and had many of the same questions, when I was building a blower engine. Butler did all the machine work, and the side clearances as I recall were like 28-30.

After talking to a number of reputable engine builders, what I found all were in consensus with is that it doesn't impact oil psi or volume. The bearing clearance is what dictates that.

Now there were some that argued if it actually added to the cooling effect of the big ends. I wasn't too concerned with that, so moved on.

One interesting fact that all did agree on is that if you are running floating pins, they do get better oiling. Now that I found interesting, and is certainly a benefit.

So that brought the question up to what is too much? Never got a straight answer on that, answers were all over the board, some said over 35, some as high as 65, and since it was well out of the range I was in, I dropped that too and moved on.

Fixing it, yes, you can swap the rods around to get a more consistent clearance across the big ends, but, it the crank throws/cheeks are in 'spec', then the real answer would be to go to different rods.

If the crank throws/cheeks are what's causing the 'unacceptable' clearances, then obviously, it's time for a new crank.

I've only had 2 engines that had rod failures, one was a standard rod, one was an early SD rod. These days, with so many rod options, I just can't see a reason to run anything but new rods. Period.

.

[Tom Vaught]

Originally Posted by "QUICK-SILVER"

Given same bearing clearance and oil pressure.....how much more oil comes out when rod side clearance goes from .020" to say .030"?

I don't how it could make a difference
Clay

Formula for circumference of a circle (as the oil "leaks" around the entire rod journal past the bearing): C=2 x Pi x R

So say we use "easy math" on a big block chevy rod journal (2.20")
(Pontiac Rod journal is .050" bigger and will leak more.)

Radius = 1/2 of the rod diameter so 2.20" divided by 2 = 1.10" (easy math)
Pi = 3.1416
The Number 2 is obvious.

Everyone knows that the circumference of a 4" pipe is 12.566 inches.
Plug it into the formula and you will see the formula gives the correct answer.

So now we do the single BB Chevy rod journal 2.20" in diameter

1/2 of 2.2" = 1.1" or the RADIUS
We already know Pi is 3.1416
2 is a simple number to multiply the numbers above.

So 1.1 x 3.1416 x 2 = 6.91152 TIMES .020" clearance = .1382304" (a .020" wide oil leak around the rod journal).

1.1 x 3.1416 x 2 = 6.91152 TIMES .030" clearance = .2073456" (a .030" wide oil leak around the rod journal).

.1382304" times 150% = .2073456" so the .030" wide Rod clearance leaks 50% more oil vs the .020" rod side clearance. Bet a bit more than you thought, huh, Clay as far as cooling of the bearing goes. Been doing this stuff for years. Simple math does not lie.

That would be the difference in a simple experiment but as I said the rods move and constantly change the value when in motion BUT
it does answer your basic question.

Tom V.

["QUICK-SILVER"]

Originally Posted by HWYSTR455

After talking to a number of reputable engine builders, what I found all were in consensus with is that it doesn't impact oil psi or volume. The bearing clearance is what dictates that.


So that brought the question up to what is too much? Never got a straight answer on that, answers were all over the board, some said over 35, some as high as 65, and since it was well out of the range I was in, I dropped that too and moved on.

Back during the "gas crisis" lots of V8's got converted to V4's. Single rod per throw with a plug in the unused oil journal.
Talk about some serious side clearance.
Don't recall working on any of them after 75 or so. Don't know what happened to them.

Clay

[Tom Vaught]

Originally Posted by "QUICK-SILVER"

Back during the "gas crisis" lots of V8's got converted to V4's. Single rod per throw with a plug in the unused oil journal.
Talk about some serious side clearance.
Don't recall working on any of them after 75 or so. Don't know what happened to them.

Clay

You actually saw some of these engines?

At the minimum the crank would be totally out of balance with a rod completely missing.

I saw engines built up in that same time frame with One Normal Rod and Bearing per journal and a second rod bearing with the shank cut off an inch or so above the bearing, and a .010" oversize bearing used on that rod on the empty cylinder. The cut down rod was clamped in place so it could not move (no oil feed required) and the "working" rod would still have a .020 or .030" side clearance.

So did YOU actually see these engine when they were built or just hear a story somewhere? Sounds like you built them.

Tom V.