Bakerlite
Well-Known Member
- Joined
- Nov 12, 2007
- Messages
- 6,431
- Reaction score
- 3,311
Well in that case. give it a whirl !!!
What Oil Clearance on Mains?
- Thread starter eekvonzipper
- Start date
-
MopaR&D
Nerd Member
I... don't think that's correct? From what I remember, spec for mains is at least .0015. I think you'd spin a bearing with only 5 ten-thousandths of clearance on these older engines.
Blaine
416 H
So, this how to fix your clearance. Looks like if you use the next size (as explained in the text) bearing (important - installed all in the same position) that you will get the 2-2 1/2 clearance that you want.
Blaine
416 H
I think the clearance is perhaps only slightly tight. The clearance allows for proper oil flow. And certainly the modern oils of today are better, and flow better than the oils from the era of these engines, which can allow for smaller clearances.
Dale Davies
Well-Known Member
The first question that requires an answer is, are the journals std or ground undersize.
If std and the clearance is a bit on the large side, 0.001 and in some cases 0.002 undersize are available. If being real picky for a high performance build, 0.001 undersize can be used in the block or the caps. Just use them in one location or the other. Same applies to the con rod bearings but you could slightly alter deck height by moving the 0.001 under shell from the rod to the cap or the other way.
Now if the clearance is tight as shown and bearing selection is not an option, the machine shop can use the polish operation to take 0.0005" off to bring it up to a more reasonable 0.002". For street driving that is livable. Just as long as the crank spins freely after the main bolts are properly torqued.
Swinger 340
Well-Known Member
Depends on what you are doing with the motor. Green for a motor to last high mileage, but not for all out racing (this is what I use). The others depend on your application. Rule of thumb, the more clearance you have the easier the crank moves, but you need to change the bearings more often.
When you frig with the clearance and make it bigger, you'll wish you hadn't when you end up with a main bearing rattle on startup.I caint believe this thread is still goin. I'd have that engine built and idlin in the driveway by now.
Rapid Robert
Well-Known Member
I thought you used plastigauge dry, am I wrong on that?
cudamark
Well-Known Member
I always used a drop of oil on mine.
dibbons
Well-Known Member
On Page 25 under chapter heading "Specifications" in the official Plymouth 1965 Service Technical Manual is listed this for all small/big block Mopar V-8 powerplants main bearings: "Diametral Clearance Desired .0005" - .0015" and Diametral Clearance Allowed .0025". Exception is the 426 Hemi where clearance desired is listed at .002" - 003" and clearance allowed before reconditioning .0045".
I used plastigage when building my bracket racer 273 back in the 1970's. I had a friend "polish" the crank (at a community college machine shop class) to increase clearance to the "high side" of recommended main bearing clearances of .003". My friend said it wouldn't be easy to polish the journals that much, but it worked out in the end. As mentioned in previous posts above, probably not the recommended way to do things, but I was fortunate enough to run the quarter mile a couple of hundred times without a problem.
And as mentioned already, for a street application, .0015" main bearing clearances should be fine.
I used plastigage when building my bracket racer 273 back in the 1970's. I had a friend "polish" the crank (at a community college machine shop class) to increase clearance to the "high side" of recommended main bearing clearances of .003". My friend said it wouldn't be easy to polish the journals that much, but it worked out in the end. As mentioned in previous posts above, probably not the recommended way to do things, but I was fortunate enough to run the quarter mile a couple of hundred times without a problem.
And as mentioned already, for a street application, .0015" main bearing clearances should be fine.
-
