moparspares
Well-Known Member
Has anyone run tighter clearances on their Rod Bearings. Of course I would like it a touch bigger but thats what I got on a couple of the rods. The others are .002
.0015 on Rods Too Tight 408?
- Thread starter moparspares
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I hope that you are off a decimal...
Those clearances are waaaay too big....
Those clearances are waaaay too big....
moparspares
Well-Known Member
Oops .0015 and .002. Not enough zeros
Rapid Robert
Well-Known Member
Was that miked or with plastigauge. If "measured" I'd think that is too tight. If plastigauged I would mike them. The rods are the end of the line in the circuit/hardest to oil because of the convoluted passageways to them and the centrifugal force & the bearings are loaded the most. Can you source a bearing set with a bit more clearance built in?
moper
Well-Known Member
If the journals have no taper then .0015 is the tighter end of the scale. I aim for .002-.0025 but you can go tighter if the machining is perfect.
The 68 Plymouth service manual lists conn rod bearing clearance at .0005" - .002" for 340 with maximum of .003"
You should be ok.
moparspares
Well-Known Member
This is with plastiguage and it is honestly a flyshit bigger than .0015. I thought I would run a thinner Full syn oil and that would help. This already has the X bearings for extra clearance. Krazycuda you are right on the standard specs. My "How to modify your Mopar Magnum V8" and "How to build big inch Mopar Smallblock" books states rod bearing tolerance as between .0005 -.0022. The lower number being very tight and puts my .0015 just about in the middle.
My brother ran close to .003 on his 451 and he now has low oil pressure on idle. He said if he did it again he would run tighter tolerances. I am leaning towards leaving it as is.
My brother ran close to .003 on his 451 and he now has low oil pressure on idle. He said if he did it again he would run tighter tolerances. I am leaning towards leaving it as is.
Mrmopartech
Well-Known Member
Tried to send message to you,clear your message box,mrmopartech
if you want the motor to live,have the crank ground down so you have .0025-.0030,and it will live for ever,mrmopartech
if you want the motor to live,have the crank ground down so you have .0025-.0030,and it will live for ever,mrmopartech
I would let it go as is.
If you want to feel better, put a high volume oil pump on it (you will have to bang out your oil pan a smigeon). Or even a high volume oil pump with the high pressure spring. I run the high volume Mellings pump with the MP high pressure spring.
Many people will argue volume vs pressure....
I like the high volume with the high pressure spring. I've had many years of success with them that way, why change now...
fishy68
Tyr Fryr's Inc.
.0005-.0015 is fine for a factory built stock engine that's built for longevity but for something that's built to make big power .0015 is the very bottom of the scale of what I like to see. Have you tried swapping around bearing shells to see if you might be able to split the difference? There shouldn't be much difference between them but even if you can get another .0001-.0003 out of it it'd help
moparspares
Well-Known Member
nm9stheham
Well-Known Member
It's on the tight side, but if you break-in it in easy and then go to full synthetic, it'll be fine. I would also check the side clearance as part of making this judgement; a really loose side clearance will lower the pressure in that bearing, and make the tighter clerance more critical, and if that were the case, I would make more of an effort to clearance it more.
Also, it would not take much to polish down a couple of journals a few .0001 more.
Also, it would not take much to polish down a couple of journals a few .0001 more.
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