Guy's
What are you engine builders running for Rod Bearing clearances? I have slightly conflicting info. My 04 GM Service Manual specs are: Production: 0.0009 - 0.0025, In Service 0.0009 - 0.003. I also have HP Books Chevys LS1/LS6 Performance and on page 47 it states 0.0028 - 0.003 with 0.0028 being right on the money. So which is it???? Help before I have my machine shop size to .0019 - .0021 That is what they normally run.

Monty

 

I wouldn't go any tighter then they want to run.

 

I was thinking .002 seemed on the tight side. After reading my book (HP Books Chevys LS1/LS6) and talking to a buddy it seemed to .0025 would be better.

Monty

 

Looks whos name is in the credits in the book

Do you know how to set thrust? Wouldn't want to see you lose a bearing..Are you using dial gauges?

Dave DiLuca

 

With lose clearances you will have low oil pressure.
GM has been running tighter clearances and thinner oils.
I would check with some LS engine builders.
I think that .0015 to .0021 is in the ball park.

 

Too tight and I recommennd 20/50oil for motors, especially during the heat of the summer. I've built some that tight and they had problems.

 

.0028 pretty much across the board here in my 427 built by SLED. So far so good, and great oil pressure at idle (~50psi) with the oil pumped shimmed to full pressure and only running 10w40.

Best Regards,
Adrian

 

You might be the person I talked to on the phone. The GM spec is correct and we're at around .002".

 

Well Guy's,
The clearances worked out to be .0022-.0023 with a set of 1 under bearings. I think i'll leave them there. Thanks for responding so quickly.

This subject seem as it might cause a nice long discussion. I did get a different answer from almost everyone I talked to.

Jason, I was the one you talked to this morning. Again thanks for the help and the 427 block I got from you is awesome. My machine shop said those bores were perfect!

 

Did you expect anything less than perfect?
Thanks for the support!

 

I agree on the rods there. .0020"-.0025" is fine on a 2.100" rod journal and thinner oil like a 30-40. I use the rule of .00095-.00110 x journal size to get me my ball park on most situations using steel and cast iron, that can loosen up depending on the parts and application.

Bret

 

You are one of a few people who recommend such a thick oil in the LSx series of motors.

Is this only applicible to your aftermarket built motors with the looser bearing clearences?
Or would this apply to stock motors and motors put together at .002 as opposed to your recommended .0028?

 

I just like it for the added insurance in those hot summer months.

 

Yeah, there are two sides to this camp. The thick oils or something along the lines of a 5W-30 or 10W-30. I setup my oil pumps and clearances for the 5W-30 and the oil pressure is dead nuts where I want it if customers use that, gets a little too high if they go any thicker, especially on start ups. A 0W-30 actually works better most times for me.

Bret

 

To set the record straight, I am not using thicker oils to bandaid oil pressure, rather just added insurance. Lots of my builds use 5-30 all the way to 20-50. After 575 builds later I know where the clearances should be! Keep discussing. Thanks

 

If you want some more (similar) discussion, you can look at a thread that I started in January of this year https://ls1tech.com/forums/showthrea...hlight=optimal.

Steve

 

Hey guys. I am the application engineer for GM bearings at Federal Mogul. I have done rod bore distortion studies on the LS2 rods and the resulting clearances are between 0.001" (0.025mm) and 0.0025" (0.065mm) based the 8-sigma tolerance range. That is a healthy range for running 5W30 oil. I know some of you like to run thicker oil so opening up the clearance with the thicker oil is o.k. I also work with allot of race teams that like to run high clearances. The high clearance helps cool the engine because the oil flow is much higher and that helps transfer heat away from the engine quicker. However, the oil film thickness drops (along with friction and pressure) so it is typical to go with a thicker oil to get some pressure and film back for safety. But I'm not sure if you lose the cooling benefits by going back to the thicker film which is why the clearances are opened in the first place.

 

Interesting info... anything else you want to add?

Bret

 

I guess I could comment on the material since that's usually a hot topic. We have found that our A-590 aluminum material used in the OE rod is a very good all-around type material that can handle up to about 500-550 horsepower or more. Typically the aluminum works better with a nodular iron crank because the silicon in the bearings conditions the nodules on the journal surface. Once you step up to the steel crank it's best to go with our overplated copper lead race bearings. The steel tends to be "sticky" compared to the iron, so the overplated bearing is a better match. I wouldn't necessarily recommend the race bearings for an iron crank though because the iron is a little rougher than the steel and this could wear the overplate at a higher rate. It seams like the crank and bearings both have the same power limitations in most applications. A rule of thumb is to keep the iron crank / aluminum bearings for most bolt on mods (500-550 hp max), but if you are building a more race oriented engine or want more insurance then go with the steel crank / copper lead bearings.

 

Interesting....

In our motors the LS1 stock crank is a killer crank that has seen 8000rpm and 1000hp and can take 700hp easily. With better crank prep in terms of polishing or other surface treatment preps would the aluminum bearings work better still at high HP?

Bret