I was just curious how the professional builders set their bearing clearances for the main bearings. I have talked to one builder locally and he stated that sometimes he goes thru 6 sets of bearings sometimes to get them all with the correct clearances.

I read on here about using a .001 under set of bearings and just use one half which would effectively reduce clearances by .0005, wouldn't it?

Reason I'm asking is I went thru 2 sets of Main bearings for my current motor. The first set was a set of Federal Mogul Competition bearings, which had the following installed clearances as measured by dial bore gauge:

#1 .0035
#2 .0040
#3 .0055
#4 .0065
#5 .0015

I promptly returned them and was told to go with Clevite 77's. I got their set and got all between .0030 and .0033 as measured by a dial bore gauge. Spec was .0027 to .0030. They were a little loose so I used a little thicker oil 10W-40. I also used a new stock GM pump and the high pressure spring, and the pressure is only 30 psi when hot. I tried a Melling +25% volume pump as well and didn't get much more pressure. Rod bearings were all inspec and right at .0021.

What could Have I done to tighten up clearances a little more short of buying another set of bearings? This was on a .0020 undersized crank that I used in the last motor that bit the dust. Do they make .0019 bearings?

On a side note I reused the stock lifters that I had that had some metal in them. They were dissassembled and cleaned of course, but I did end up replacing one of them with a spare I had, as when I was priming the oil system, one lifter was spewing oil from it. When the motor was started it had a funny miss for 10 miles and it went away. I'm wondering if I may have some more lifters that aren't right. Anyone recommend Comp R lifters?

Thanks

Bill

 

Yep just did this acctually... one set of .001, one set of STD and one set of X for the mains and a .001 and STD for the rods... if you want to get the clearances dead nuts then this is the only way to fly.

Gotta check it, sometimes you have to play around with them and sometimes the set doesn't exactly move everything .0005

Yeah that's ugly.... .0020-.0025 is what I shoot for on 1-4 and .0025-.0030 for the rear on a NA motor. I'm a fan of Clevite 77 H series bearings. If you are going with a turbo application I shoot for .0027 on the 1-4 and .0030-.0035 on the rear.

Did you set your mics on each journal then set the bore guage with that to get just the clearance rather than do math to get the clearance?

30psi when it's hot is not a bad thing.... have you tried a 20W-50 and 10W-40 mix (say half of each) and see what that does to your oil pressure?

That .0021 sounds good to me for the rods for a NA motor, I'd like to have a little more clearance there say .0025 for a boosted motor.

Nope your SOL there...

OI would but the dam things keep breaking retainer clips so, unless you have a fix for that I wouldn't run them.

Bret

 

just on a side not, why do you shoot for a larger clearence one the rear main compared to 1-4?



-john

 

Bret,

Yes each main was mic'ed individually and then used to zero out the Dial bore gauge. Clearances were mearured on the 12 o'clock position, and then eccentricity verified.

Thanks for the tip on the rod clearances. I actually just measured clearances for a friend putting together his motor (boosted) and they were in spec for the LT1 (.0013-.0035) closer to the lower side. I think I'll have him pick up another set and see if we can get them a little looser. We are dealing with a .010 under crank all around.

Do you recommend sticking with the OEM hydraulic lifters then. I may pick up a new set then. My cam is relatively mild (224/220 .544/.544 114 LSA) and doesn't require anything extreme.

I did try 10W40 oil, and the pressure did come up a bit. I threw in 20W50 yesterday and I'm putting in my oil cooler as well. I'm thinking the 2 turbos heat up the oil quite a bit. We will see what happens.

Thanks

Bill

 

I'm curious, did you measure the main bore housing before you fit your bearings? How close were you to spec there.

Also I typically use 2-3 sets of bearings or more to get where I am happy with my clearances. With a crank that is ground .002 under I would have started with -.001 bearings for starters.

 

I measure the main bores without bearings as well just to see what I'll be chasing and even this last one which was within .0002 I still had to use 3 sets to get the clearance where I wanted it.... So many factors come into play here that it's silly.

Bill, You should be ok with stock lifters on your setup, mostly it depends if the lifters can take the spring you are throwing at them.

Bret

 

No, unfortunately I did not measure the main bores without bearings. I Just had it line bored for the new 4 bolt mains, so it "should" have been in spec. Never thought of it...

When you guys are buying multiple sets of bearings, are you out the cost of several sets, or are you returning unused ones for credit. I believe once you break the wrap on the Clevites, you own them

 

Yeah it's not cheap to do it the right way.

I've never seen a line bore do it very accurately, that's why I make sure to line hone the bores to final size.

Bret

 

Whoops, I reread my previous post and I stated the crank was .0020 undersized, should have read .020 under. So do they make a thousanth variance bearing for the guys who have ground cranks? Got the oil cooler on and 20W-50 and get like 20 psi idle and about 35 still at speed. The turbo's don't seem to like that thick oil, and it smokes when at WOT now. Guess it isn't draining fast enough.

I'm considering giving up on this engine building crap and having a professional do it. I am a DIY'er but it sure gets expensive when it isn't right. I may try once more though.

I have a friend that had built over 10 motors, some in drag cars, and the latest for his airplane and he never checks anything. He did my first rebuild and nothing ever went wrong with that, lower end wise. I try and do things right and I get screwed I know it's a learning experience, and I appreciate the tips guys, just venting some frustration.