Rebuild Questions

[PaulS]

First some pictures:






Questions (from one who has never torn down or rebuilt an engine before):

1.� Is it normal to have such uneven wear on the pistons?� #3 is the bad one, while all the others look like #4 (the other one pictured).

2. Is that amount of carbon build up on the top of the piston normal?� (The head looks the same, and all four cylinders are similar.)

3.� Is this normal wear for a rod bearing?� It looks worse than it feels--by finger touch, it's actually fairly smooth.� � Need replacing?� If so, how does one determine what undersize to buy?

4. The crankshaft bearing surfaces all look nice to the eye, and feel smooth.� The picture shows scoring, but it's so fine, I can't feel it with my fingertip.� Normal?

5. The main bearings feel smoother than the rod bearings, but you can still see very fine scoring.� Need replacing?� Again, how to determine undersizing?

It is my intention (after getting the valves out, which is my next task), to take the block to a machine shop for hot tanking, magnafluxing and honing.� (I don't think it need boring, but I'll let them tell me if I'm wrong on that.)� I'll probably get them to do the valve seats, too.� I'll get them to check the head and crankshaft as well.

Background:� This is a 1944 engine (if I believe a stamp I saw on one of the seal surfaces--I think the oil pan).� From the casting number (638632) and location of the serial number (with a CJ2A prefix) and Googling I've done before, I believe it is a block that was made for a military Jeep, but not used and bought back by WO after the war.� It was rebuilt around 25 years ago, and probably doesn't have more than a few thousand miles on it since then.� It was pretty messy (from leaks) on the outside, but the inside is very clean (other than the carbon build up in the combustion chambers).� I initially opened up, planning on replacing all the seals, but I decided I should get the cylinders honed after I felt them.�

Thanks,

-Paul

[1955CJ-5]

I would not order parts until after the machine shop has done whatever needs to be done. They can measure the crank journals after they have been ground and then you will know which bearing inserts to buy.

The same goes for the pistons and rings. With pistons that have that scoring there must be some scoring on the cylinder walls.

If you look closely at the tops of the pistons they may be marked std. or .010 etc..that will tell you if it's already been rebuilt with oversize pistons.

[athawk11]

Hi Paul,

The carbon build up on the piston top looks like what I've seen on both engines I've opened up.  In my view...common and not a big concern.  Clean it all up and you'll be good.

I Agree with 1955CJ.  Have the machine work done, then purchase the correct bearings based on the amount of material they needed to remove.

The scoring on the pistons is a little disturbing.  Are they as rough as they look?  What is the condition of the cylinder walls? If they are as rough as the pistons appear to be, they will need more than just a honing.

The bearings need to be replaced.  If you see a new bearing up close, you'll see what I mean.

I don't want to bumb you out, but if I opened up an engine and it looked like this, I would be pretty disappointed.  It sounds like you're up for the challenge though.  Keep us in the loop on your process. 

Tim

[PaulS]

The cylinder walls really don't feel bad at all.  Not perfectly smooth, but pretty good.  But I don't have a feel for what the limits of honing are, so the shop can decide that.

Other than the spots on the pistons that are scored, they look brand new.  And on three of the pistons, the scoring is limited to a pair of narrow bands on opposite sides.  Any idea what could cause this (since you suggest it's not normal)?  I want to know what to be extra careful of when I put it all back together!

This engine was remarkably clean on the inside.  No sludge anywhere.

-Paul

[oldtime]

That piston is ruined.
That looks like a lot of carbon build up for such a fairly recent rebuild.
The crank bearings need replacing.
Hopefully the crankshaft will only require a polish.
A good crankshaft grinder will need to measure the crankshaft.

Forget the magna flux.
Just clean and look it over yourself with magnifying glass especially between the #2 and #3 exhaust valves.
Cylinder bores should be re-measured by the shop.

[1955CJ-5]

Here are a couple of pictures of my engine while it was at the shop...you can see how smooth the bores are and they are not yet finished...

And you can see the crank being ground...

And my old pistons...nasty for sure, but they have no scoring on the sides as your one piston does.

I think those wear marks around the skirt (the end away from the rings) shows that the piston was traveling a little sideways on the power and compression strokes...when it was under load...you may find that your bore is egg-shaped...but the shop will be able to advise you which course to take...

[oldtime]

Hard to say what caused the excessive piston scoring.
Could have been a metal flake caught up in the ring groove or possibly the bores are way out of specification / out of round.
Be sure to thoroughly clean out the oil gallery.

If the block is rebuild-able you'll need to buy a matched set of  new or even good used /  pistons.
New rings and a cylinder hone job at minimum.
Re-polish the crankshaft at a minimum with all new bearings.

[athawk11]

Here is a piston I removed from a working engine.  Notice the carbon build up, but also how smooth the piston skirt is...



This is why I was  disturbed by the amount of scoring on your pistons.

I wonder if the person that rebuilt it didn't do a thorough cleaning prior to assembly.

Tim

[oldtanker]

The scoring as others have said can have a number of causes. One that wasn't mentioned is overheating. That can be cause by low fluid levels, bad water pump, bat thermostat, plugged radiator (either plugged so that the antifreeze doesn't flow or the fins plugged and no airflow) or junk in the water jacket now letting the antifreeze evenly cool each cylinder.

Looking at your pictures I'd guess dirt is the problem looking at the scoring plus the bearings given the short run time sense the last rebuild.



Rick