#4 Cylinder Dead - Rebuild or buy a used block?

[KenC]

So my #4 cylinder is dead... 50psi or so upon compression test. The car was idling for ~2.5 hours, started to run a little rough, I thought it might have been carbon build up on the plugs so I revved the engine up. It idled fine again for 5-10 min and then got pretty rough again. I pulled the plugs and #4 was full of gas (3-4 table spoons... like swimming in fuel).

I'm deciding whether or not to rebuild the bottom end, or just purchase another used block. Getting another used block would probably be the cheapest and easiest route, I would guess.

I've completely torn apart an M42 before aside from the bottom end. I'm familiar with the parts and such, but not super familiar with the process by which to rebuild it. Cylinders 1,2, and 3 are great, so I'd probably just replace the rings on #4, and rehone it if it looks scarred.

Any advice? What does it all entail? New crank bearings?

M44 crank time?

[xwill112x]

good excuse to do a phsyco m42 build :)

[3bvert]

did you mean 3-4 tbls of oil
sure that is low compression, but fuel in there makes me think something else is up. like not spaarking and burning off the fuel or something. Ive got one low cyl in my m42, #3.but not s low as yours, , but when I had the head off, the cyl was not scored, just full of antifreeze ( self steam cleaned cylinder). I did not go into it, im still low, but running fine, little lumpy idle

you can go cheap and just throw in rings, if the cylinder is not scored too bad, and rod bearings and not dig any deeper right now.
rod bearings would be optional, but they are not too expensive and might get you a few more years out of the lower end depending on your use/abuse

when I priced mine last winter it was , rod bearing are in the $30 for all 4 cyl, mains run about 100, rings, are about 50. then of course a full engine set, head bolts

we all know it can be a can of worms when you open things up, rods, mains, chain, rails, oil pump, rod bushings, oversize pistons, machine work...the beat goes on

one local shop I talked too said the m42s would wear the bores out of round, I find tht hard to believe

if you can find a good lower block, Id still go into rings rods etc, and then spend the weekend swithing it out top get you threw for a while while you do a decent real rebuild of your block . thtas what Ill do this spring, I have a spare block to throw into mine. opver time build a real good m42 and swtch them out again, and be good for another 200k

remind me, what is the advantage of a m44 crank ?

good luck

[xwill112x]

did you mean 3-4 tbls of oil
sure that is low compression, but fuel in there makes me think something else is up. like not spaarking and burning off the fuel or something

if there isn't enough compression, then it wont ignite. it will just continue to foul the plugs.

[KenC]

if there isn't enough compression, then it wont ignite. it will just continue to foul the plugs.

Exactly.

[KenC]

good excuse to do a phsyco m42 build :)

The only thing I'd consider is maybe getting an M44 block. Will it mate right up?

I already have an m20 flywheel, Mark D chip, COP, etc.

[3bvert]

how true, but Ive seen cylinders fire with less compression, my #3 is running only 60 pounds, and fires just fine, ive had another worn engines with even less
idles a little rough

[blueapplesoda]

if you are sure its the rings, you could just re-hone the cylinder and toss a set of new rings on. I've done this inside of a car before, imho it is easier to just pull the motor. If you can get your hands on another block for cheap, why not? drop it in and run it, then rebuilt/scrap/sell the other block.

[KenC]

I haven't pulled the head to inspect the cylinder wall yet.

Is there a guide online, or does the Bentley include, how to replace the rings (gap spacing, etc)? I've torn my m42 apart before, but haven't really dug too deep into the bottom end.

[decay]

The only thing I'd consider is maybe getting an M44 block. Will it mate right up?

I already have an m20 flywheel, Mark D chip, COP, etc.

http://www.m42club.com/forums/showthread.php?t=3717