Shimming main and rod bearings?? Am i crazy?

[twentyover]

Building a quasi hot-rod European Ford motor, a Cologne V6. Known in the US by displacemenst of 2.6, 2.8, 2.9, 4.0, and 4.0 SOHC.

I'm going to use a word not often heard in Pro-Touring- Budget. I'm using Clevite Michigan 77 bearings, and am finding clearance with standard mains is just a skosh on the high side- it's coming on about .003, 5 tenths over specification limit. Looked for .001 oversize mains to close it down to .002, but they appear to be unavailable.

I'd rather not cut the crank. I seem to remember hearing somewhere that people have shimmed the back side of a bearing shell to get correct clearance.

So am i nuts? (although that doesn't really have any relevance to the question presented.) Anybody done this, or have any recommendation how to close the clearance down a little, or should i just blow off the deal since I'm only out 5 tenths. All input appreciated, and will be considered, even if in the end i ignore it.


greg fast

[Vegas69]

I'd run it .0005 off before I'd backwoods it. It will cost you oil pressure but you can likely make it up with a thicker viscosity. If you plan to beat the snot out of it, it may not be the end of the world to build it a hair loose.


Brought back a funny memory. I once knew a guy that built a small block chevy and needed to tighten things up a bit. He used a hammer and a hard surface to "adjust" the bearing shells. Needless to say, it ran for a while. A short while. :lol:

[Che70velle]

Journal to bearing clearance is 0.001-0.0026 service limit 0.006
Mian bearing to crankshaft is desired:0.0008-0.0015 allowed 0.0005-0.0019

So, are you consistent with your numbers across the board, on all journals? You using plastiguage, or real tools?
Are you gonna run boost?

Biggest problems we have in America with the 4.0 sohc, is the rear timing chain giving up. That's the weak link on this engine platform. Make sure you purchase Melling timing components.

[twentyover]

Clearance is about the same on all of the mains. Used plastigage. The engine is the 2.9L variant. No boost.

[358Mustang]

.0005" isnt much, I don't use plastigauge much so I cant speak for its accuracy. .003" isnt too bad though, I would run it. That is pretty much what my motors are anyways. .0025"-.003" is about right for a race motor. What is the journal diameter?

[twentyover]

Nominal? 2.25 main, 2.125 rod

[Che70velle]

If your putting this thing together to go 200k miles, and last 20 years, then I'd consider turning the crank, and going with oversized bearings.
If your just throwing together a motor to rip around in on occasion, and don't mind a slight loss in oil pressure, run it. It will be fine.
Me personally, I'd consult a competent engine builders advice before I'd listen to someone out there in cyberspace. But then again, if it's on the internet, it must be true...

[twentyover]

Che70velle- Point taken. Unlikely I can assess the talent of those giving advice on this, or any other forum.

I think you are correct though- where in the grand scheme of this vehicle project does this engine lie. Since I consider it a placeholder until i get the next iteration gets funded, it doesn't need to last for more than 30-40K.

Also, the deal with bearing clearance is, if there's too much it won't hold hot idle oil pressure, so I can pull the engine out and return it to the engine builder (me) and make him pay for the fix

[214Chevy]

I'm glad to just be a fly on the wall in this convo. This site is amazing and I'm glad to be a member. Although, I have the slightest knowledge of what all this means...you guys who've helped the OP rock. I mean, I understand all of it, as far as, turning the crank, rod journals measurements, bearing size, etc...I know what all that means, but moreover, I am ignorant to the fact of what y'all are saying.

[twentyover]

Just to see if my understanding is correct- on a motor destined for high rpm application and or a service life of a quarter million miles (to the Moon), First guarantee the mains were in line via line bore or hone. Assuming the crank needed to be turned, insert a set of .010 (or the next oversize) bearings, and measure ID of the bearing installed in the saddles. Subtract the clearance from that (say 2.2377 bearing ID, .0019 clearance), that main should be turned to 2.2358. repeat for all mains, then do the same for all rods, same deal. Resize, install oversize bearing, measure bearing ID and subtract the clearance from measured bearing ID to get journal OD.

I'm ignoring the fact that the mains bearing bores do need to be bored/honed to the correct diameter

If I had the correct (decent) instruments (ID bore micrometer, 2-3” outside micrometer- I’m not opposed to getting quality instruments and doing this myself), the correct feel (I believe you can change the measured dimension by how you turn the spindle on the micrometer, finger grip force and torque you apply- something I would like to learn), and equally important- a crank grinder who believes the number I give him and actually grinds the journal to specified diameter rather than ‘grind ‘er .010 under’. Unfortunately, I don’t have that guy in the town I live in. He may be here- I just don’t know who he is.

Thanks all for the input. I think, in this case, I’ll live with the additional clearance (I won’t know if it’s excessive until I run the engine.)

[Che70velle]

Well...that's a funny subject to talk about among engine builders. Longevity, versus high rpm/power. You can't have both. It's a one or the other deal.
A race engine, for instance, will have an oil pump that will make up for any loss of oil pressure caused by setting up bearings a "little looser". Adding more bearing clearance does free up power, and helps keep oil temps down. Now if I'm selling engines that are supposed to go a couple hundred thousand miles, and I give a crap about my reputation as an engine builder, then I'm gonna set up my bearings to the tight side of spec, because bearings wear over time. If you add boost into the equation, or a high compression naturally aspirated engine, it changes things as well. These type of engines are hard on rod bearings, which is why you often see aluminum rods used in extreme applications. The aluminum rods take a lot of shock from the rod bearings, and crank as well.

[David Pozzi]

I'd carefully sand the main cap on a flat surface. I don't think it would take much to remove .005" & increase bearing crush. I'd look into the bore specs & see if you can safely reduce the bore a tiny bit.

[TheJDMan]

I would consult a competent engine builder first but to tighten the clearance by .0005 should not take much work. Like David said, carefully sanding the mating surface of the main caps should allow more crush to the inserts. The alternative is leave it as is and run a heavy diesel engine oil like 15w40

[twentyover]

Thanks all for the input