crank shaft fun

[JeepJunkie]

Well after a while a screwing around i finally got around to putting the new flywheel on the back of the crank and guess what! the bolt holes dont line up, so i go back to the jeep junk yard where i got it and talk to them about it and they think its strange, even stanger is that the ID number matches. I guess whoever rebuilt this engine was doing something crazy. Anyway, they just said i should prob just put a crankshaft that came of an original XJ back in. So i got the crank for 75 bucks, now heres my question. what should i do to get the thing ready, should i have it checked out... or what:confused:

[Dukes69]

you should get the crank checked for cracks (magnafluxed). Also, have the main and rod journals turned just to clean then up some. Dont forget to put oversized bearings in there to compensate for the undersized main and rod journals.

[JeepJunkie]

well another problem arose...the crank shaft pulley for all the belts would not move, first i pulled the outside piece off, then i broke another piece, so i ended up using a hack saw and cutting the freaken thing off the crank. so i dropped the knew crank in to check it out and it seems to fit fine. the only difference is on the crank i took out there was some sort of number that said W3 and on the new one it said W5 should this worry me that they may be different sizes?

[JeepJunkie]

hey...if im turning the crankshaft and i hear air hissing out of what seems to be the sides of a piston thats bad right...real bad?

[Dukes69]

Originally posted by JeepJunkie
well another problem arose...the crank shaft pulley for all the belts would not move, first i pulled the outside piece off, then i broke another piece, so i ended up using a hack saw and cutting the freaken thing off the crank. so i dropped the knew crank in to check it out and it seems to fit fine. the only difference is on the crank i took out there was some sort of number that said W3 and on the new one it said W5 should this worry me that they may be different sizes?

The engine shop can tell you if its the same size of not. I doubt its different.

[Dukes69]

Originally posted by JeepJunkie
hey...if im turning the crankshaft and i hear air hissing out of what seems to be the sides of a piston thats bad right...real bad?

I'm not quite understanding you, but I think the hissing noise is the sound that engines make when turned over by hand. Intake - Piston goes down and sucks air in, Compression - piston goes up to compress the air/fuel, ignition - piston goes down, exhaust - piston goes up to expell the gasses. The air you are probably hearing is normal, unless you have a hole in the block . . . but I think you'd probably see it :yawn:

[JeepJunkie]

well when i push the piston down by hand air seems to hiss out the sides like there is a bad seal, i wouldnt worry but its only happening on one piston....so i guess it could be normal.

[Dukes69]

Originally posted by JeepJunkie
well when i push the piston down by hand air seems to hiss out the sides like there is a bad seal, i wouldnt worry but its only happening on one piston....so i guess it could be normal.

With the heads off? I've built a couple engine and I dont really remember air hissing past the pistons. In fact, there shouldnt be. Sounds like a set of bad rings to me, if I'm understanding you correctly.

[goodtimes]

If you are pushing the piston up from the bottom, with the head on, and valve train set up, one of your valves could be slightly open (depending on camshaft position), the air could be pushing past that. If the valves are closed, the air could be coming back past the piston rings--this does not mean they are bad. Piston rings do not make a perfect seal, ever. They can't.

Based on the fact that you hear air escaping somewhere, I am led to believe that the rings are at least usable. I say that because if you hear the air, then it is moving from a high pressure area to a low pressure area, through a restriction of some sort. I am guessing that the restriction here is the gap in the rings. The cylinder walls are also probably dry, so there could be some leakage there as well (that goes away for the most part when the walls get oil on them). When the engine is running, a certain amount of combustion air leaks past the rings and into the crank case, and that is handled by the PCV valve.

Or, I could be wrong, and you could have a major problem. I don't have enough info to be sure, but I'd bet that you are OK.

[JeepJunkie]

alright thanks guys! i will say that when this thing ran it seemed the engine was fine, after all it was recently rebuilt. thanks again!