Are new bearings supposed to be thicker than your old ones?

[bpu699]

I continue on my path of discovery...

Got my case and rod bearings. The latter are the more expensive automobile associates one, the former are the glyco...

The glyco ones look fine, and seem consistent. I measured at the midline, and they are all within 1/2 a thousand of each other. So far so good.

Then I measured my existing original bearings that have been in for 60k miles but look new...

My older bearings are the same thickness, or even .0005 thicker than the new ones. That's only 1/2 a thousand thicker, but multiply by two, and that a thousand difference...

My rod bearings do show wear. So I was sure that the AA ones would be thicker. Nope. Same, or .0005 thinner.

Is it unreasonable to expect new bearings to be thicker than old ones??? Or, is a digital caliper not accurate enough to pick this up? I did get both a 1 inch and 2 inch calibrated stock to measure against, and it's spot on... I know the readings may be off .001 or so, as the instrument has limitations. Both comparatively, the new bearings definitely aren't thicker...

My oil pressure is about 4 bar or a tad higher at anything over 3000 rpm. Was thinking new bearings would boost it even higher...now, not so sure...

Are manufacturers just making everything at the low end of spec?!

[KTL]

Bo,

Need to measure the bearings with a micrometer using a dowel or drill bit to get a good measurement. Measuring them with calipers doesn't work well.

Glyco vs clevite rod bearings - with data

[Catorce]

The real question is: Are your brand new Clevite bearings within spec? If so, slam them in, and don't worry about how thick the old ones were.

The only exception to this is if you mistakenly ordered or received oversize bearings.

[bpu699]

Originally Posted by KTL

Bo,

Need to measure the bearings with a micrometer using a dowel or drill bit to get a good measurement. Measuring them with calipers doesn't work well.

Glyco vs clevite rod bearings - with data

Saw that thread...

May do that this weekend...

The caliper reading were repeatable and precise... I was just looking for a relative difference...thought the new bearings would be thicker, and assumed the old bearings get thinner with age....

Did do plastigauge using the old bearings on the rods. Put a light film of oil on the bearing, and a tiny dab of assembly lube on the crank to hold the plastigauge. Put silicone spray on the bearing. Tightened to 30 lbs or so...

Plastigauge reads about .002 clearance.

Plastigauge is interesting stuff. First time I used it... Pretty difficult not to move the rod while tightening. No matter what you do, it moves a bit.

The plastigauge was attached to the crank pretty good. I thought it would easily come off... Not so. Had to use my fingernail or a degreaser...

I would think that after the rod gets resized, and the new bearing goes in, should be even tighter...

[bpu699]

Originally Posted by Catorce

The real question is: Are your brand new Clevite bearings within spec? If so, slam them in, and don't worry about how thick the old ones were.

The only exception to this is if you mistakenly ordered or received oversize bearings.

Can't be oversize, they are thinner .

Saw that Clevites makes Chevy bearing that are either standard, or +.001 and -.001. So, you never have to turn a worn crank... Just upsize your bearings for a couple bucks...

I love Porsches. But working on a Chevy v8 would be infinitely cheaper and easier...and cheaper...much.

[manbridge 74]

Well if you are truly getting those measurements consider having old bearings coated with some uber high tech process. Vintage cars for which there are no longer any bearings available have been having good success with this.

[bpu699]

I'm going to remeasure over the next couple days. Will use a micrometer...

I may go the recoating route. Ollies mentioned in another thread you can add .0003 to .0006 to each shell, decreasing clearance a full .001.

I am kind of frustrated though. You really shouldn't have to be doing all this just to rebuild a motor. I fully expected the new bearings to be thicker than the old ones by at least .0005... Not thinner...

Will try to post some data tomorrow...

[smokintr6]

The thickness of the bearings is only somewhat relevant.. you want them to be consistent thickness. Personally, the only thing I would be concerned about is the running clearance between the rod journal and the bearing ID. You would check this using a bore gauge and a micrometer, then compare to the factory service manual.

[bpu699]

Originally Posted by smokintr6

The thickness of the bearings is only somewhat relevant.. you want them to be consistent thickness. Personally, the only thing I would be concerned about is the running clearance between the rod journal and the bearing ID. You would check this using a bore gauge and a micrometer, then compare to the factory service manual.

But if the bearing is thinner, all things being equal, clearance will be greater... Right?

[smokintr6]

Originally Posted by bpu699

But if the bearing is thinner, all things being equal, clearance will be greater... Right?

Correct, but if the original clearance was on the tight side you might actually be better off with a little more clearance. You don't know what you have until you measure. I wouldn't hesitate to reject bearings that don't give the right clearance, but you don't have that information. You may even be completely right, however it's important to remember that a really tight engine isn't necessarily a good engine, this is especially true the harder you run it.

[bpu699]

Ok, I am totally bummed here...

Went and remeasured the new Clevites con rod bearings, with a micrometer, and they are in fact .0005 smaller in most measurements than my old 60k mile bearings... That's .001 larger clearance...

Double checked with plastigauge, got the exact same results...

My rod clearance with the old worn bearings is .002. With the new bearings its .003.

What the heck?!?! Measurements are below, subtract .139 for the dowel rod used due to curvature...

Clevites were .1975 in the middle, .196-.197 close to the ends

Old were .1975-.198 in the middle. Most were .198. same on the ends...

Basically, old ones are .0005 thicker... Old ones have wear at the end where they meet.

Will call automobile associates Monday, see if they have any info...

My options...

1) return these to pelican parts... Use my old ones
2) do number 1, but also have the old bearings coated by hm Elliot coating, which should add .0003
3) take the new Clevites bearings, which weren't cheap, and coat them. But even with a coating they may be thinner than the old ones. Also the Clevites already look coated? Can they be coated further???
4) spring for the Porsche measured ones...$$$$$ and hope they are thicker than the old ones...


Thoughts??? Risks???

Had my nonporsche family mechanic double check. He too was surprised the new bearings weren't thicker...

The new glyco main bearings are the same story. Most measuring ever so slightly less than old. Will plastigauge both old and new case bearings tomorrow... If the old one are in spec, will probably just reuse them....

[911pcars]

Not sure those coatings are the equivalent of bearing material (they're not). They're applied to reduce/prevent scuffing during cold starts, momentary oil starvation, etc.

If they're Clevite 77 bearings, realize the bearing material they use is harder than factory-type bearings. That increases the load capacity, but also harder on the crank journals. They up to snuff?

Do some research, then go from there. E.g.
https://www.corvetteforum.com/forums/c4-tech-performance/1133367-clevite-77-rod-brgs-h-or-p-series.html


Sherwood

[manbridge 74]

I would agree that coatings don't make up for wear. I didn't see where your old bearings were worn out by spec. Consider bearings from Porsche or Supertec.

[bpu699]

Originally Posted by manbridge 74

I would agree that coatings don't make up for wear. I didn't see where your old bearings were worn out by spec. Consider bearings from Porsche or Supertec.

The old bearings especially the crank ones aren't worn out. Look like new. Since I had the motor apart was going to put in new ones. But the new ones are thinner than the old.

[bpu699]

Ok, talked to AA who make the clevite bearings. And, I wasn't imaging things...

They INTENTIONALLY make them .0005 under as they are intended as a race bearings, and they want additional clearance, shooting for .003 clearance on the rods...

They have had no issues. I brought up the concern about a possible decrease in oil pressure, and they felt that was unlikely, as the oil pump is well up to the job...

Gotta say, they were very nice and knowledgeable.

I still worry, that adding another .001 clearance on the rod bearings AND crank bearings, can't do great things to oil pressure...

Thoughts???

[Catorce]

Originally Posted by bpu699

Ok, talked to AA who make the clevite bearings. And, I wasn't imaging things...

They INTENTIONALLY make them .0005 under as they are intended as a race bearings, and they want additional clearance, shooting for .003 clearance on the rods...

They have had no issues. I brought up the concern about a possible decrease in oil pressure, and they felt that was unlikely, as the oil pump is well up to the job...

Gotta say, they were very nice and knowledgeable.

I still worry, that adding another .001 clearance on the rod bearings AND crank bearings, can't do great things to oil pressure...

Thoughts???

When I built my 930 turbo motor, Walt Watson from competition engineering (very knowledgeable) had the crank journals ground down to the minimum spec for exactly that same reason. He wanted more clearance for oil, not less.


I think you're good.

[bpu699]

Originally Posted by Catorce

When I built my 930 turbo motor, Walt Watson from competition engineering (very knowledgeable) had the crank journals ground down to the minimum spec for exactly that same reason. He wanted more clearance for oil, not less.


I think you're good.

Ok, then here is my question...

I have 4 bar oil pressure at anything over 3000rpm. Its the same whether 3000, 4000, 5000, or 6000 rpm.

Per porsche manual, its plenty as they only spec it at 3000 rpm.

But I keep hearing about folks getting 5 bar, or 75 psi... Or 10 psi per 1000. So, at 6700+ should have 70 psi? Yet, see many threads on here with others peaking at 4 bar.

My car NEVER goes to 75 psi.Checked the relief springs, changed springs, plungers, shimmed it, etc. No difference. Old bearing clearances in spec. I figured the bearings were worn, but they look fine (rod bearings with slight wear).

How are people getting 5 bar??? What the max pressure generated by a 930 oil pump at 6700 rpm???

My oil pressure is good, but I would love for it to be even higher. My thought was that putting in new bearings would accomplish that. Now, I worry new bearings will have the opposite effect...

Oil pump seems fine. Will look inside when I get a change. Everything in the motor looks great...

[Neil Harvey]

Bpu699,

First off, you are Ok and if I can give some advice and how we would approach this.
Oil pressure. Less is better than more, if everything that needs lubrication is living. It takes work to pump oil and this work could be going to the crankshaft output.

Measuring your clearances with plastic gauge it must be accepted that there is higher probability of error than with an accurate bore gauge. I would risk it to say that your clearances could be between 0.0025” and 0.003”.

What is often overlooked is the Rod BE bore size. Have you measured this. If this is on the high end of the spec or above, this can change the bearing inside diameter.

What is equally important is the finish on the crank journals. This finish is critical for oil flow and forming the wedge. Any microscopic high spots will affect the oil flow, so having tighter clearances will hurt you here if not finished properly. The finer the surface finish the tighter you can run the clearances. This also allows a lower oil viscosity to be used. In some race engines, the wider clearances are often used to get a thicker oil film and help build a bigger wedge. There is nothing wrong with this but be sure to choose the correct weight of oil. The heavier the oil weight, the more friction you will add and will build more oil temps as well. These may be minor but these are the draw backs. Today, we want to run the clearances as tight as possible, the lightest weight oil and make the engine do less work to pump oil and rotate the crankshaft.

If you go with the clearances at 0.003”, choose a heavier weight oil.

As for why the engine will not make 5b pressure, first you need to ensure that the measuring device used to measure the pressure is correct. The weight of the oil and the temp both affect the pressure. Then you need to look at all of the places where the oil is distributed. You may have a piston oiling valve leaking around its outside, the camshaft journal clearance to the cam housing may be bigger than spec, or the pump gears may have more clearance than normal. Check that the 3 seals at the pump have enough crush to seal. We have seen engine cases where the main webs were so misaligned and beat up that there was no seal between the 2 halves and the oil sent to the piston valves leaked between the case halves. An update you can do is to O ring the through bolt holes.

If you have checked the relief valves and springs and shimmed them to no avail, then check for leaks, (added clearances) and check the pump body.

Good luck and hope this helps.