Engine Rebuild Questions

So I picked up a 96 Cherokee with what I believe is a cracked head. I've got the engine disassembled as well as a remanned head and gasket set. Once I got the engine apart it was apparent that there was a lot of carbon build-up on the piston heads as well as in the intake and exhaust manifolds. I'm guessing this build-up was a result of coolant/oil getting into the intake/exhaust ports.

Because the engine has 236k miles I'm starting to thing that I will need to replace the piston rings as well... I already cleaned up the piston surfaces and got all of the deposits off but I'm worried that the remanned head will cause excessive blow-by.

If I'm going to replace the rings I'm assuming that I need to replace the connecting rod bearings. I really would like to avoid replacing the main bearings however and don't feel that it's too necessary considering the Jeep was well taken care of until the overheating incident that resulted in a cracked head. The oil that was drained was still very clean and I don't believe that any significant amount of coolant entered the oil system. When the vehicle runs (before the tear down) the oil pressure was still above 60 psi. How critical is it that I replace the piston rings? If I do the rings I will replace the rod bearings, but how critical is it that I mess with any of the other crank bearings? I would preferably like to get away without pulling the crank.

Thanks.

Anyone?

I think I'm going to place the head gasket and new head on and tighten with old head bolts, then check compression by rotating crank with breaker bar.... If all of the compression checks out then I'll just remove the old bolts and place the new ones in and tighten to spec. If not then its off to replacing the cylinder rings.

I think if it were me and the cyl head was off, I would buy, beg, borrow a dial bore gauge and check the cylinders for taper. The inexpensive but less accurate way is to see if there is a ridge at the top of each bore. The process of boring an engine is 2 fold, making sure the cylinders are round and cleaning up scratches grooves in the cylinder walls. Strong oil pressure really has nothing to do with ring seal, however over time, eg. 236000+ miles the actual cylinder bores can become eggshaped and not perfectly round, causing poor ring seal as well as blow by. Installing a new cylinder head will only improve compression if there was a valve sealing issue. A new valve job wont show a loss of compression unless done improperly. The most common issue with an old head and oil consumption is due to worn valve guides or bad valve stem seals. This is a complicated and drawn out process and can become very expensive. You can install the head and it may run just fine, then again the increased sealing of the valves may cause an increase in cylinder pressure creating more oil consumption threw the rings. I have never had much luck in just putting a patch on an engine. Just my .02, good luck with your project

Sorry forgot about this one, try and use a cylinder leak down gauge rather than a compression gauge, more accurate in determining which cylinder and how bad it is.

Bottom line is that to do it right you should bore the block and replace with new pistons, rings, rod bearings, main bearings at the least.

Unfortunately I'm on a college budget so new pistons and a rebore probably aren't in the mix...

I have a clearwater remanned head and I think what I'm going to do is hope that the rings are fine and install the head gasket and head then check the compression. Hopefully everything will be just fine... If not I'll pull them off and do piston rings. Obviously if I have the new head and gasket on and there is low compression then it is very likely that the rings are bad.

The car is a one owner and the guy never dogged it and took very good care of it so I'm not expecting the bearings or bottom end to be bad. If I had the money I would certainly pull the motor and stroke it, but I don't.

If I replace the piston rings I'll replace the rod bearings but I don't really want to replace any of the other bearings.

Wanting and needing are rarely the same.
Signed old_man

old_man said:

Wanting and needing are rarely the same.
Signed old_man

Click to expand...

Well, I am going to place the new head and gasket then check my compression. If they're all within spec and there are no signs of scoring on the walls then I think I'll just leave the rings and bearings be. If any compression is low or in the bottom end of spec then I'm going to pull the motor and rebuild the bottom end.

If I'm already in there I'm contemplating finding some 258 rods and a crank to get some more displacement... This would be a budget stroker and all I'm looking for is a little more power. I'm guessing that I'll need to get bigger injectors, what else would be absolutely necessary for that swap? Computer? Cams? Pistons? From what I've read in a few articles just the crank and rods will do it, but wanted some more info from some people that may have done a budget stroker.


Thanks.