Alright so I'm freshening up a 7mgte I picked up, found arp's and oem head gasket already done so I left that alone. Pulled all my bearing caps and plastigaged the clearances, rods and mains are all mostly around .002" ranging from .0018" - .0023" (hard to tell exactly with plastigage). Journals are all in good shape. I'd like to replace the all the bearings before installing the engine in my truck, as they look worn, some worse than others. My question is should I just replace the select fit bearings number for number, or should I go up a number or two on all bearings to tighten up the clearances a little bit? The rods are 2s, 3s, and a 5. The mains are all 2's except for one 3.
Rod and Main bearing question
- Thread starter zackdocks
- Start date
Also here's some pics of the rod bearings, 1 and 3 are the worst and look like this:
The babbit layer is pretty spotty and rough looking, and these bearings are loose in the caps. Like they are almost squished into a tighter "C" shape. Any ideas what would cause this? Previous owner says head gasket was redone as preventative maintenance, not as a result of BHG. There was no signs of coolant in oil either.
with the rest looking like this, and fit nice and snug into the caps:
Mains all looked like the above 3 pics, they look ok to me. The #4 main bearing looks like it had something run through the bearing, as there is 2 light grooves in the bearing material, but the crank journal was not affected whatsoever. Pricing out the select fit bearings, they are ridiculous. $40-45 apiece for mains and $28 each for the rods, thats almost $400 and that's online from japan. It seems it would be cheaper to get the crank machined to fit standard bearings jesus christ.
The babbit layer is pretty spotty and rough looking, and these bearings are loose in the caps. Like they are almost squished into a tighter "C" shape. Any ideas what would cause this? Previous owner says head gasket was redone as preventative maintenance, not as a result of BHG. There was no signs of coolant in oil either.
with the rest looking like this, and fit nice and snug into the caps:
Mains all looked like the above 3 pics, they look ok to me. The #4 main bearing looks like it had something run through the bearing, as there is 2 light grooves in the bearing material, but the crank journal was not affected whatsoever. Pricing out the select fit bearings, they are ridiculous. $40-45 apiece for mains and $28 each for the rods, thats almost $400 and that's online from japan. It seems it would be cheaper to get the crank machined to fit standard bearings jesus christ.
It would be much better to just machine the crank and get over sized bearings.
At that point might as well throw new rings in and maching for a metal head gasket.
At that point might as well throw new rings in and maching for a metal head gasket.
Measure the crank journal and the bearing bore/rod big ends, then you can use the chart to figure out what bearing you need to get the clearance you desire. You are just guessing if you are using plastigauge and worn out bearings to figure which new size you need.
You actually could do what you want with select fit bearings. Like you said each size is a very small difference. I would start with the sizes the factory started with. I prefer math over plasigauge. Either get and inside micrometer or snap gauges to use with the micrometer to measure crankshaft. Unlike some on here I prefer my bearing clearance to be on the tight end of spec. This is the way they come from the factory. The is MY OPINION. If you are going big power IE 700 whp or I don't see a " flex or distortion issue" Or "off road dirty dusty issue" These would be two reasons I would set an 7M on the loose side. Again "MY OPINION". Good luck
Found the oem bearings overseas for $180 canadian, shipped. I will be running this engine in an offroad truck so I will aim for .002", checked with mic's and telescopic gauges. The worn out bearings are probably a few tenths bigger than the new ones, they won't be any smaller I'll tell you that much! And since none of my tolerances were over the max spec, I feel comfortable replacing them number for number. I'll doublecheck everything once I've installed them of course, but I'm expecting either slightly tighter clearances, or at the very least the same clearance. Impossible to be any looser.
That first bearing looks like classic oil starvation. The crank was touching the bearing. Vancouver is pretty cold in the winter?
hvyman;2026582 said:
If hes going o machine the crank then the bearings need to be undersized. Undersized bearing means the internal diameter is smaller. Oversized is the block side has been machined or line bored. Common mistake though.