Clearance on mains

TurboDave

RIP DAVE
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May 24, 2001
What's the best clearance to run on the mains??? IOW, what are you guys running?
This will not be a competition build. I'm re-assembling the numbers matching block using all the original hardware. Just new bearings on the mains and rods. But will get a new cam/lifters.

I am to the point of assembling the bottom end.
The factory manual seems to recommend .0003 to .0018 clearance on the mains. Do any of you run looser?

I've measured mine both ways. Plasti-gage, and the mic and bore gauge method.
Mic and bore gauge method seems to yield the following:
.0019
.0019
.0023
.0024
Front to back

While the plasti-gage seems to yield VERY close to the same results, somewhere very near .002 (as close as the eye ball can see plastic spread).

Would a set of -.001 mains fix me up better?
 
What's the best clearance to run on the mains................The factory manual seems to recommend .0003 to .0018 clearance on the mains. Do any of you run looser?

Mic and bore gauge method seems to yield the following:
.0019
.0019
.0023
.0024
Front to back......

Dave, not to be a bore, but I have mentioned in the past that the factory specs cover V-6's back to the 2 barrel carb days. :confused:

On many turbo engines, which are performance builds from the factory, bearing specs are never at the low end, and we usually aim for 0.018"-0.020" on rods and mains. Race builds can get more, especially since we mod the oil pump and cover.

In your case, the front 2 mains would be fine, maybe split a set of bearings to bring the rear 2 mains closer to the specs of the front ones.

Having sent out many turbo V-6 engines, we never have seen a failure from a "looser" bearing specs we have used. :biggrin:
 
dave, not to be a bore, but i have mentioned in the past that the factory specs cover v-6's back to the 2 barrel carb days. :confused:

On many turbo engines, which are performance builds from the factory, bearing specs are never at the low end, and we usually aim for 0.018"-0.020" on rods and mains. Race builds can get more, especially since we mod the oil pump and cover.

In your case, the front 2 mains would be fine, maybe split a set of bearings to bring the rear 2 mains closer to the specs of the front ones.

Having sent out many turbo v-6 engines, we never have seen a failure from a "looser" bearing specs we have used. :biggrin:

+1
 
Thanks guys!! And Nick, no need to worry about being a bore, I value your expertise.

Basically I'm hearing it's a good idea to order another set of mains that are -.001, and do some mixing and matching.

As I recall, my rods are at around .0018-.0020 so I don't think I'll mess with them.
 
OK!!! Got another set of -.001 bearings, and followed the experts advice and did some mixing and matching.

Used full .001 set on two of the mains and half a .001 set on the other two(block side).

Used two different measuring methods. Double and triple checked the zero setting on my dial bore gauge, and measured them up. Clearance on all four mains ended up being .0016-.0017(depending on how I bent one of my eyebrows ;) )

Then I plasti gaged the whole setup, and according to the MK1 eye ball method they all looked like .0015 plus a teency bit.

Sooooooo, I'm happy and the crank is in and fastened down.


P.S. The one thing I did notice throughout all these measurements was that (since I've installed main studs) the measurements were/are far more consistent!!!

P.P.S. Thanks Nick and bison.
 
P.S. The one thing I did notice throughout all these measurements was that (since I've installed main studs) the measurements were/are far more consistent!!!

Dumb question :eek: since you installed main studs... you did line hone the registers correct. :confused:

:wink:
 
Dumb question :eek: since you installed main studs... you did line hone the registers correct. :confused:

:wink:

Yes. Machinist said they were very nearly perfect as is and just gave them a quick "touch up".
 
OK!!! Got another set of -.001 bearings, and followed the experts advice and did some mixing and matching.

Used full .001 set on two of the mains and half a .001 set on the other two(block side).

Used two different measuring methods. Double and triple checked the zero setting on my dial bore gauge, and measured them up. Clearance on all four mains ended up being .0016-.0017(depending on how I bent one of my eyebrows ;) )

Then I plasti gaged the whole setup, and according to the MK1 eye ball method they all looked like .0015 plus a teency bit.

Sooooooo, I'm happy and the crank is in and fastened down.


P.S. The one thing I did notice throughout all these measurements was that (since I've installed main studs) the measurements were/are far more consistent!!!

P.P.S. Thanks Nick and bison.

Do you feel that those clearences are a little tight? I've shot for .0020 on my motors but had one that used a pollished crank and i couldnt get the clearences to sit anywhere out of the range of .0016-.0019. Most sat at about .0017.
 
Do you feel that those clearences are a little tight? I've shot for .0020 on my motors but had one that used a pollished crank and i couldnt get the clearences to sit anywhere out of the range of .0016-.0019. Most sat at about .0017.


I don't really think so. If this engine were going to see a moderate amount of racing then maybe so.

I also just got the rods/pistons mounted in and their clearances are also in the .0016-.0018 range.
 
Then I plasti gaged the whole setup, and according to the MK1 eye ball method they all looked like .0015 plus a teency bit.

You better keep that oil clean. Any amount of dirt that gets into the oil, kiss the bearing good bye. Although the clearances would work but your playing with fire. I've many motors trashed that had tight clearances.

Oh another thing, you're driving on the highway and a Mustang pulls along side you.......remember you can't nail it to race him because your clearances are too tight.

Tight clearances = heat.

Choice is yours.

Billy T.
gnxtc2@aol.com
 
I'll see about opening them up another half a thou.


You better keep that oil clean. Any amount of dirt that gets into the oil, kiss the bearing good bye. Although the clearances would work but your playing with fire. I've many motors trashed that had tight clearances.

Oh another thing, you're driving on the highway and a Mustang pulls along side you.......remember you can't nail it to race him because your clearances are too tight.

Tight clearances = heat.

Choice is yours.

Billy T.
gnxtc2@aol.com
 
everyone has their opinion

And what works for them are great. Personally, I like mine tight. My current engine has .001--.0012 on rods and mains. Having said that it is going on 3 years @ those specs. Probably somewhat looser now.
 
Not only that but Lee's (Lot)) car runs in the 9's and Iv'e rode in it and heard the engine and it runs and sounds very nice and SMOOOOOTH !! for a Stage engine.
 
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