Crank main clearances for serious street/track motor?

[Turbo'dBuick]

Ok... I have found many people with many diferent clearances...I have heard
.0018-.002 & .0022-.0025.....Looking for someone to help me figure it out........I have a new CAT stroker crank, std King bearings & a fresh line bore....the info for making the clearance choice.... The motor will be a street(but will have a lot of time on the track)...I plan on running 25 lbs boost with Alky on a 3 billet main cap, girdled block. I have a large oil cooler & a deep sump oil pan. Hoping for around 650+rwhp. I plan on making the motor last 2 seasons ..roughly 2 years be for the next freshing..... Please help! I have a crank polisher I can work on as long as I need to make the clearances right.

 

[Lee Thompson]

Imo

.0015 Max.

 

[cchilly]

Wow, you guys run a tight clearance. I'm not fimilar with Buick stuff, but all V8 stuff I have built is closer to a 0.003" clearance. The motors range from pump gas street motors to pro mod motors. Why so tight for GN motors?

How are you measuring your clearances, I hope with a mic and dial bore indicator.

Chris

 

[V6gofast]

Bearing clearances

It will depend on what type of oil pump you are also going to use,std or
high volume. Most dual purpose engines that leave here are set up at .002
.0022 with high volume cover . Also important to note is how round and
straight the bearing journals are on the crank, .0002-.0003 either way will
effect the final clearances.

 

[TurboDave]

Wow, you guys run a tight clearance. I'm not fimilar with Buick stuff, but all V8 stuff I have built is closer to a 0.003" clearance. The motors range from pump gas street motors to pro mod motors. Why so tight for GN motors?

How are you measuring your clearances, I hope with a mic and dial bore indicator.

Chris

That's why everybody on this board so stringently preaches to never take these blocks for machining to a standard chevy shop, because the clearances will be set to chevy standards. Not good!
Unless such shop has experience with the Buick V6's.

 

[cchilly]

TurboDave

I see. Why such a difference though. I worked on more than just chevy's and they are all more than 0.0015. Just curious.

I'm assuming this is like this from the factory. So shouldn't any shop that knows the standard journal size and cut 0.010 off or whatever off the crank. You get matching bearings and then the clearance should be back or close to stock.

Thanks
Chris

 

[machinegun]

Here are my personal experiences.

I use a tight clearance. 0015 - 0018

I have a good shop that does excellent work. We strive for 00175.

Mic and bore gauge s the only way I measure it.

I personally never use a high volume pump. I have seen excessive wear on the cam bearings although not positively sure that the high volume is the culprit it does seem to be a good possibility. I usualy blue print, polish and build my fron cover and use a stock oil pump and so far never any oiling issues. The clearances on these engines are very important to the oil pressure being suppplied.

My second opinion is that the tighter clearances seem to stand up better in a forced induction application. I have talked to LS1 LS2 builders and read articles that when building primarily turbo engines they actaully tighten up the clearances to help support the bearings under high loads.

again only my opinion.

 

[TurboDave]

TurboDave

I see. Why such a difference though. I worked on more than just chevy's and they are all more than 0.0015. Just curious.

I'm assuming this is like this from the factory. So shouldn't any shop that knows the standard journal size and cut 0.010 off or whatever off the crank. You get matching bearings and then the clearance should be back or close to stock.

Thanks
Chris

one and a half thou is a little on the tight side. More common is 2 to 2.2 thou, 3 is too loose.
Your last paragraph makes too much common sense, unfortunately most non buick shops don't go that far in depth and just cut everything to the wrong clearances.

 

[Turbo'dBuick]

Well, I will be running a high volume pump & cover for sure...I am using a dialbore gauge for all my measuring... Thanks for all the help..again alot of diferent clearances! LOL... anyone else have any suggestions?

 

[SouthernCal GN]

Yup. Send your engine to Dan Strezo or Bill Anderson and have it built the right way......:biggrin:

Too many opinions will lead you down the road of rebuild squared. Build it per the clearances Dave laid out, and you should be fine...

Remember, these things, for being 20 years old, were screwed together pretty well from the factory.....

 

[noahzark]

so .0015 to .0018 for high volume pump cover etc.???

and .0020 to .0022 for stock standard cover?...is that about it?...thanks noah.