Main bearing clearance...

[Cheeseburger]

Building 2 motors at the present time, engine one is stock street motor with .0019-.0025.
Engine 2 is a race motor .0025-.003.
Bored just thought i would post the numbers and see what some of the pros have to say!

 

[Lee Thompson]

Too tight-- open them up some.

 

[Russ Merritt]

I don't have a problem with those...........0015-.002 on a street engine is just about perfect.

Everyone of my race engines that I ever ran were .002. Not one problem using stock oil pumps...............

 

[Cheeseburger]

Originally posted by Lee Thompson
Too tight-- open them up some.

Lets see, what do you run your motors at lee?
0.004-0.005?

 

[Blown&Injected]

The engineers that designed the engine say .0004 to .0018.

I am about to bring my engine back to the machine shop because I am at .0033. Even with a plus one on the bearings I will be too big.

 

[Cheeseburger]

.0004 is real tight.
I am happy with the numbers, if anything the race motor is a little loose but not much.......still within my specs!
Could have got it tighter but did not want to cut a std/std crank.
Also my crank shop said its a bad idea to use (patch job) +1 bearings.....said they saw alot of failures with them.

 

[Russ Merritt]

Use +1s on the caps and std on the block................Saw that a few times on tear downs and no problems...............

 

[Dusty Bradford]

When I tore down my original motor it had +001 main bearings from the factory.

 

[S2V6RACER]

Originally posted by Cheeseburger
.0004 is real tight.
Could have got it tighter but did not want to cut a std/std crank.
Also my crank shop said its a bad idea to use (patch job) +1 bearings.....said they saw alot of failures with them.

Who is your engine builder??


We have all discussed coating the bearings and some high HP applications, this is a very proven method of tightening up the clearances without getting into other ways it can be done.

 

[Nick Micale]

Originally posted by Blown&Injected
The engineers that designed the engine say .0004 to .0018.
................................

Those clearances should just about guarantee a spun bearing on a performance motor.

When this engine was designed back in the '60's, it was Buick's answer to the economy car market. Am sure they never figured it would be a high performance motor.

This is verified by later engineers in the Buick Motorsports program that listed main clearance up to .0032" and rods as much as .0039".

One of Buick racers I work with [8 sec. car.] who has wasted MANY rod bearings over the years, now builds his motor to almost .003". Of course oil supply and flow is crutical in keeping this motor alive.

There was a recent thread about the horrible repeatability of stock rods when re-sizing. So if you start in between the "factory" specs say .0008, and the rod tightens .0010 [which we have seen], you lose a bearing.

In recent years of tearing down Buick turbo motors, our build, others build and stock, we have never seen a bearing trashed because of too tight clearance. Oil starvation and detonation are the biggest causes.

So to give an opinion on the original question, would agree that the different clearances are appropiate for each application.

 

[Blown&Injected]

I agree that .0004" sounds extremely tight, but I do not have experience with comparing the differences between tight and loose builds. I say sounds tight because it sounds near the type of clearance spec for a press fit part like a BHJ to crank spec

 

[Blown&Injected]

Nick, you got the simulpost in while I was writing the above.

You start off by saying factory specs will guarantee a spun bearing then end the post with we have never seen a bearing trashed because of too tight clearance. You also said recently, so maybe you have at some time found that condition?

About now seems to be the time to say - Not attempting to start a flame fest. I believe this type of thread is all about learning and sharing mistakes.

I also am sure a definition of performance build is in order. There seem to be many people claiming solid 10's with stock, never touched, bottom ends and maybe even oil pumps.

For the larger clearances, is it more a factor of more RPM's, or more force on the power stroke? Im sure it has some to do with lots of variables and there probably is not a point where one can say:
The engine will push a 3500# GN to 10.50, we expect about 600 hp, therefore you need the .0032" engine. And you, the 11.000 guy, you just need stock about .001 on the mains.

Probably makes more sense that there is a rolling progressive change in specs for the rods and mains as the engine builds more power.

So where does the street fun type car that goes to the track twice per year and runs low 11's fit into this equation anyway?

funny you say this:
>>One of Buick racers I work with [8 sec. car.] who has wasted MANY rod bearings over the years, now builds his motor to almost .003". Of course oil supply and flow is crutical in keeping this motor alive.<<

The machine shop that did the work on my engine also does "lots, or tons" of engines for a well known single turbo V6 guy that is now in the 7's. Maybe they though I wanted an engine like that!?!?

I know that type of engine gets a check every XX number of runs and probably goes back with new rings and bearings, but for the street engines - damn, I don't want to do a rebuild even every five years.

 

[Ormand]

The engineers who designed the engines knew what they were doing. And so did the ones who put together the Buick race engines. You can much looser clearances when you are only going to go 500 miles, and when you have spent a few thou in improving the lube system. Get yourself a dry sump, an external belt driven oil pump, and go for loose! On the other hand, in the Buick "Power Source" there is blue print data on several race engines. The turbo Indy engine making 800 hp, more or less, used 0.0025 on the mains, and 0.0024 for the rods. (Carlillo steel rods, by the way) A Stage II unblown drag engine, with aluminum rods, had 0.0026 to 0.0032 for mains, and 0.0036 for the rods, for a roughly 450 hp engine. Like Nick says, too loose is relative, and whatever clearance you got, oil supply is CRITICAL!

 

[Cheeseburger]

Originally posted by Ted A.
Who is your engine builder??


We have all discussed coating the bearings and some high HP applications, this is a very proven method of tightening up the clearances without getting into other ways it can be done.

I am the builder.

I have seen a coated cam and it was too tight in the cam bearing journals, do these coatings eventually ware out and send coating particles throughout your motor?
What is the purpose of coating bearings other then to tighten clearences?
I checked my clearences with platigauge by the way, some say it is not accurate.

 

[Blown&Injected]

Originally posted by Cheeseburger
I am the builder.

I have seen a coated cam and it was too tight in the cam bearing journals, do these coatings eventually ware out and send coating particles throughout your motor?
What is the purpose of coating bearings other then to tighten clearences?
I checked my clearences with platigauge by the way, some say it is not accurate.

I too am interested in learning about these bearing coatings. Might help me close things up a bit.

BTW, when I used Plastigauge I was told it is not that great so I got a dial bore gauge and a set of micrometers. Confirmed what the Plastigauge said. Those tools are better, but the Plastigauge seems to work good enough for a simple clearance check down to maybe +/- 5/10,000ths

 

[Russ Merritt]

Bearing coatings are not for tightening clearances, they are for frictional perposes. Typically the coating is .0002 - .0004 thick. I have used coated bearings in a couple engines including my own street car. I didn't change the clearance for the coating and haven't had a problem.........Haven't had a problem racing with .002 main and rod clearance and stock oil pumps too.................No oil cooler, 5/30 Amsoil, front cover mods and a booster plate............No big filters or external turbo filter/savers.

I used Swain Tech Coatings and haven't had my engine apart for inspection to see if it's wearing off. Ain't fixin what ain't broke!!

 

[TurboBuickSix]

Originally posted by Ormand
The engineers who designed the engines knew what they were doing. And so did the ones who put together the Buick race engines. You can much looser clearances when you are only going to go 500 miles, and when you have spent a few thou in improving the lube system. Get yourself a dry sump, an external belt driven oil pump, and go for loose! On the other hand, in the Buick "Power Source" there is blue print data on several race engines. The turbo Indy engine making 800 hp, more or less, used 0.0025 on the mains, and 0.0024 for the rods. (Carlillo steel rods, by the way) A Stage II unblown drag engine, with aluminum rods, had 0.0026 to 0.0032 for mains, and 0.0036 for the rods, for a roughly 450 hp engine. Like Nick says, too loose is relative, and whatever clearance you got, oil supply is CRITICAL!

You forgot to include the Kenne-Bell bracket car data which best represents what most are doing.

 

[Bad as L]

I've been told that a good rule of thumb is .0011 per inch of bearing journal diameter, (performance steel rod app).

 

[TurboBuickSix]

EDIT: I meant to say Ken Duttweiler and was talking about the stock blocked drag car in the front of the book just to clarify.I wanted to fix that before I got flamed.