I think i broke rear main bearing

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Don’t run it the way you “fixed” it. That is going to vibrate out and it will probably suck air in and you will lose oil pressure. The no screwing around right way is a new cap and line hone. Which requires engine removal. Are there fixes that could work? Yes. On an inexpensive motor, I kinda liked the drill the hole a 1/2 deeper, thread it and I would epoxy a stud in it. If I fixed it that way a clock would be ticking in my head.
 
Option 3... yeah find the right size. This is for the main webb in a 6.5l GMC diesel. Upside down "Christmas tree", the more you torque it the tighter the crack closes up.

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Welding the cap would actually be the way to fix a hard to find part. But if you don't have a welder and those caps are everywhere. I would send some young guys to a motor pile and grab a couple rear mains for $10 . Bring them home and torque them up with your bearing and plastic gauge. Most of them are real close from what I have seen. Luck may be on your side.
 
Really the only proper way would be to find another block. You could look for a rear main cap from a scrap block. That requires engine removal and complete disassembly to enable align honing the mains for proper alignment of the new main cap.
Taking the cap to a machine or welding shop to be spray welded while bolted to another block is an option.
A welding shop could weld it clamping the broken piece into place and grinding the crack to use a nickel rod or braze it. Then install a helicoil or Keensert. Not much metal to support the Keensert, so I would helicoil it. Being the oil pump mount bolt holes they do not require tightening the crap out of them. I would be inclined to braze it with the helicoil. Just grind the crack down to the threads before welding. Cast iron rod is another possibility but involves preheating and tapping with a chipping hammer while allowing to cool slowly to stress relieve. A good welder should know the proper procedure. My concern with cast iron rod is warping, requiring the align hone.
 
It looked like the cracked area was raised up a bit so if it is, you had better at least grind that area down flush so there won't be a gap between your oil pump and the main cap. Check it with a straight edge and flashlight. Probably should use some red Loctite threadlocker on the bolt too.
 
Since that is just the bolt that holds the oil pump on the main cap I'd maybe CLEAN the crack real well, JB Weld the crack, then drill it oversize and a bit deeper and tap for a ThreadCert. There is not a lot of side loading on those bolts so I'd lock a stud into the ThreadCert.
 
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4eighteener said:
I was wondering if the oil pump needed clearance between the main cap bolt?
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Definately not. The pump body must be flat and tight on the main cap to hold it in place. Remember the output that then goes to the oil filter passes through there. If it is not tight it will leak like a rabid babboon with diharea.
 
Dale Davies said:
Definately not. The pump body must be flat and tight on the main cap to hold it in place. Remember the output that then goes to the oil filter passes through there. If it is not tight it will leak like a rabid babboon with diharea.
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Sorry DD, I was referring to the top of the pump hitting the main being bolt when it was being installed, not if there should be any clearance with the pump and the pump location.
Although you bring up a good point. Who uses a gasket there and who doesn't?
 
On the gasket thing I've done them both ways. As thin as the gasket that sometimes comes with a new pump is, I can't see it helping much vs a perfectly machined flat surface as are both the pump and the cap it bolts to.
In the case of the problem posted in the thread any heat applied (welding, brazing etc) would make me wanting to take that cap to a machine shop and have a few thou shaved off the pump mount surface to guarantee flatness
 
Don’t a lot of aluminum engine parts like blocks and heads have thread inserts out of the factory?

Putting a helicoil in a cracked hole isn’t a good idea, but if it was welded up, what’s the big deal? I have seen 2 inch diameter helicoils.
 
I haven't been following, cuz my mind was set about 4 posts in.

I hope somewhere it was mentioned the owner should be told, and the decision should be his . jmo.
 
I have always bored my SB rear main hole out to 1/2 inch and then taper it some and do the same to the NEW oil pump. I do use the paper gasket but spray CooperKote sealant on both sides.

I then use a flat plate with emory cloth and WD40 to lightly dress the oil pump and caps mating surface. I do lazy 8's making sure I keep them square.

Most pumps will clear a factory main cap bolt, even the HV ones. But they will hit most cap studs like ARP's
 
Dave_J said:
I have always bored my SB rear main hole out to 1/2 inch and then taper it some and do the same to the NEW oil pump. I do use the paper gasket but spray CooperKote sealant on both sides.

I then use a flat plate with emory cloth and WD40 to lightly dress the oil pump and caps mating surface. I do lazy 8's making sure I keep them square.

Most pumps will clear a factory main cap bolt, even the HV ones. But they will hit most cap studs like ARP's
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I went back and looked at the op's initial picture and you are correct, it is the factory bolt with plenty of clearance.
I am currently assembling a 340 and used arp bolts with their washers which stick .020 above the pump mount.
I will definitely check clearance with the pump when I get it.
Not the best straight edge, but it works

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One thing to remember is that once you tighten a bolt into a helicoil the helicoil expands. If that cap was helicoiled I can see how it would crack seeing that there is not enough material to support that expansion.
 
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