HELP SBC crank Bearings!!

Is having an extra 0.001" of clearance on crank journals (mains and rods) TOO excessive????

 

What does your plastiguage read?

 

What is the clearance? Are you planning on racing this motor?

 

.003", is thise too much?

 

don't plan on racing, but need an engine that's gonna last...

 

Yes, it's too much.

 

Everything you measured was at the same temperature?

 

yes it was

 

You can get 0.001" undersized bearings if you need them. Make sure your measurements are accurate.

 

imo
.003 is a little loose for a street motor for long life, but how are you checking? dial bore gauge or plasti gage? borrow a dial bore it will give you precise measurements ck it from 2 oclock to 7 and again from 11 to 5
x measurement. you may be surprised

 

i guess I have to go talk to that god danm machinist tomorrow, He was slacking I thing when he ordered the bearings!!!!!!!!!

 

ya I mesured with plastigauge.

 

.003 sounds good to me. I would not put it together with less than .003 clearance.

 

Three thou is huge on a sbc.

 

Yes 3 is too much,,,like the guy said,,get 1 under bearings.
Small Chevy has been known to lose a rod with too much clearance.
Double check the plastigage,,,it could give you a false reading.

Tommy

 

Ok I'll throw some chips on the table here 0.003 aint too much clearance for a small block chev !! As long as the clearance never got any looser than that in the entire life of the engine. But when the engine gets some time on it the clearance will creep it's way up to 0.004--0.0045 and then things get ****py. So my motto would be to start with 0.0018 to a snug 0.002. I always ask my customers why they would start out on a fresh rebuild with the clearance of a wore out engine >>>>.

 

I think that .003 on the mains is the upper end of being okay but .003 on the rods is excessive. On the small Chevys I build, I shoot for .0025 on the mains and .002 on the rods.

 

yup, careful with plasticgage.. if used on rods, ..when they are torqued on the journal for "squishing" the plastigage, they will twist,and cause false readings.. (we use a bore gauge accurate to +/- .0001" )
usually on a 350" chevy, .0025" on mains, .002" on rods, for street applications.. general rule of thumb is .001" clearance for every 1" diameter of crank pin.. sometimes you have to "mix" bearings to get the correct clearance. ie; std lowers/-.001" uppers, or -.010" uppers/-.011" lowers.. etc.. don't get too crazy if it's just a street engine though.. also very IMPORTANT.. when checking rear main bearing clearance on a chevy, be sure to install the oil pump,and torque the bolt/stud to #55,as it will have a dramatic effect on the bearing clearance.. hope this helps..
tricky
good luck,and may the bearing gods be with you...

 

I just got off the phone with the machinist, he said allowable clearance is anywhere between 0.001"-0.0036", and if I run a high volume oil pump, I should have no problems.

 

Refer back to post #17 >>>>.

 

Thanks engine pro, deep down I know ur right and I know the right thing to do, but I am so frustrated at that machine shop, because they wont come good for new bearings...not even half!, All because it's"within tolerance" and now its gonna set me back ANOTHER 150$!
But I'm jus venting!

 

That machinist is blowing smoke, might be crack. One to three and a half? Good Lord! I feel your pain brother.

 

.003 is fine, run a 40 or 50 weight oil

 

Engine pro is right. Why start out with an engine with wore out clearances! JMO here but, I always strived for one and a half thousandths to two tops ,on the rods. You should not need heavy oil to have good oil press!! SBC's do not like excessive rod clearance. Stop and do the bottom end right. You will be glad you did. Hopefully the rods have been re-sized also and new bolts. Lippy

 

Oh hell yes with the heavy oil !! I have bad news for you as heavy oil still won't carry good oil # when the oil is hot !! Ask me how I know this ??? >>>>.

 

Why even bother otherwise, put the .001 under bearings in and don't worry about it.

 

thanks for all your help guys, I ordered 0.001" undersized bearings today.

 

How do you know?

 

#### Oh **** where did I put that note ??? Ahh yes here it is ""Note to self as the stupid myth of the 50 weight oil bull-**** has failed again"" For future reference quit trying to doctor a screw up and fix the engine correctly the first time !! Dated Summer of 1975 !!! >>>>.