1 connecting Rod bearing tight... Help

[elks]

I am working on a motor. The Book calls for .001 to .0025 clearance. It is an inline 6. Connecting rods 1-4 and 6 all check good with plasti gauge at .0015. Number 5 was right at the tight .001 maybe a little tighter. When #5 is torqued down it makes the assembly almost impossible to turn, it is very scary tight. I have checked the cap and the rod direction etc. It appears to be assembled correct. What are my options?

It is not a race motor etc. But it needs to be right. Can I take a little bearing material off with scotch bright pad or something? Can I take the rod and bearing to the machine shop and have anything done? Or do I need to pull the crank out and have the journal polished?

The crank was machined and polished. When I checked the crank with a mic. it seemed good. Should I try a different bearing? The torque spec on the caps is 30 to 35. At 33 it is tight at 28 it is at .0015

[rcazwillis]

Sounds like the rod needs to be sized. A machine shop can do this for you. It may be out of round. Need to mic the inside dimensions 90 degrees apart to see if it is round. If not, resizing the end will fix it.

I would not modify the bearings. You could swap a bearing from one of the rods that is working as expected to see if the bearing is an issue.

[davepl]

If it mics out good then it must be an assembly issue. I'd pull that apart, clean the hell out of all surfaces with a LINT FREE cloth and lacquer thinner.

Even a speck of lint can be a problem when you're talking about clearances like that. You can swap bearings like willis mentions too in order to try to narrow things down.

I prefer the rod-bolt stretch method for one good reason: when you know the initial length and you see it "overstretch", then you know the bolt is toast. With the torque wrench method you don't really have a way to know (maybe super-experienced guys can tell from feel, I don't know).

However, I don't like your clearance specs. I'd never go under 0.002 and the specs I can find are 0.0020 - 0.0025. You might starve splash-lubricated parts like the cam with clearances so tight.

The numbers you're quoting, 0.0010 - 0.0025, sound a lot more like rod bearing side clearance. Is it possible you looked at the wrong line/column in your specs?

FWIW when I had one that was too loose I swapped in a one-thousandth smaller bearing shell but only half. I didn't know you could do that but many builders confirmed you could (obviously not with a big difference between the two bearings and the bearings must be otherwise identical). It allows you to change in smaller increments than the next size bearing.

[hamjet]

If you truely have .001 clearance it should not be too tight that it would prevent you from turning the engine over. a 250 ci engine calls for .0007 - .0027.. As stated, either the conn. rod is egg shaped or its the crank. Do try swapping around rods as stated to see if its the rod or crank. You say the crank was machined, what was it turned down to.. Good catch by the way...

[leadfoot067]

its not terribly uncommon to get a wrong bearing in a set....my vote is the bearing...