No compression......

[gmcjr]

This sucks....While we was traveling in the FCT, I noticed my little desert tan willys wasn't running as good as the rest of the crowd. Returning home, did some checking, had slightly low compression on a couple of cylinders due to leaky valves, so I replaced the valve guides (for some reason didn't get replaced when I had the block machined 8 years ago) and hand lapped the valves.... It Brought the ole girl back to life...........until Thursday........then this happened........

Broken rings on the number four cylinder.
Cylinder walls are not scored, does anybody have any ideas what might have caused it?� (I posted on the IFFC site too)

[F Bill]

Did only the top ring break? Was there a ring ridge remaining from the last rebuild?

Where did the new ring set come from and how did you install them on the pistons, and how did you compress them to install the pistons in the cylinders?

My guesses.....upper ring could have broken hitting ring ridge.  Installation techniques may have prestressed the parts causing them to break in service...Or you were running a lot of advance or very lean,and had some serious engine damaging pinging going on. Poor quality parts failed in service. (Scary)....

Might want to see if any of the engine rebuilders check in on this. I know we have a couple of guys who do this sort of work for a living.

[duffer]

It could have been the ridge but I don't know any mechanics that would rebuild an engine without at least removing the ridge.  And by the looks of the other pistons, I think we can eliminate too lean and it would take a LOT of advance at the compression we are talking to get pre-ignition.

I'm going to guess it was the ring set and that would make me highly suspicious of the remaining three cylinders.  Probably no way in hadies you know whose rings were used?

[Carls_jeep]

I will assume the ring ridge was removed. If the cylinders were not bored there is taper in them larger at top than at bottom. It's also hard to blend the removed ridge to the taper of the cylinder and if over cut will allow ignition compression to bypass the top ring. There is also the fact that the rings will rotate in the bore as the engine runs and be squeezed and released as they move up and down causing stress on the metal . The top ring in a worn cylinder is constantly under movement and rotation and as it opens up at the top of the bore is subject to pressure and heat that may exceed it's ability to respond. Depending on the quality of the rings they may not be able to stand the conditions of a worn bore.

All the above is dependent on the fact the cylinders were not bored. If the engine was bored then I would suspect the rings are defective and all of them should be replaced with quality rings.�

[gmcjr]

Both compression rings are broken, I had the block sleeved BACK to a standard bore when I rebuilt it eight years ago.(was already bored .060 over and had a bad wrist pin knock) There was no ridge when I installed the rings (perfect circle part number 5007 STD according to my notes) using sears ring pliers and a band style ring compressor to install them. Gaps where within spec. Timing is good, the jeep doesn't run lean, but most of the carbon you see in the picture is from a small amount of transmission fluid. (I figured it was a ten million to one shot that the rings where stuck from carbon, I lost that bet haha)

[Carls_jeep]

Gary, from what you posted I suggest you replace all the rings and if the rod bearings show no wear use them over. Number 3 and 4 cylinders get a little hotter than the front two. Also #1&2 and #3&4 are Siamesed, meaning there is no gap between those cylinders. There is a gap at the front, between #2&3 and at the rear of the block. That makes the heat greater between #1&2 and #3&4.

Has your engine been overheated during the past 8 years? 

[F Bill]

Time to replace all the rings for sure.. Deglaze the cylinders if they aren't still cross hatched. Given everything you posted I'd be complaining to the manufacturer.


Where in  N TX are ya? We are running windmill stuff out of Dumas to Adrian these days. It has been feeling a lot like Fargo instead of TX though.

[gmcjr]

Carl, the hottest I can remember the engine running is 210, I hope to have my bottom mount radiator repaired and installed soon. It has a shroud. I'm less than impressed with the crown radiator that is in it now. Thanks for the advice, I'm going to replace all the rings, bearings look good, they only have about 10,000 miles on them. I'll probaly plastiguage them just to be sure.

Bill, I live 40 miles noth of the dallas metro-mess.
I have had real good luck with perfect circle rings in the past, i reckon I'll shoot a email to them.

Not much to see out in the pan handle is there.....spent alot of time there when I was younger. Still liked it though....


Might give sealed power rings a try.
If I remember, the old ones where plain cast rings, do yall see any reason to use different?

[Carls_jeep]

I see no reason to use anything different.

[gmcjr]

Small update, finally had a break to work on the willys again, after removing the rest of the pistons, number 1 and 2 also has broken rings� � .




Still don't really know why.....



Finally got it warm in my little garage, us Texans ain't built for this cold stuff...

[Gunslinger]

I have to admit to being a bit baffled by this one, those pistons look like they are in really good shape.  All of the broken rings I've encountered have had carbon encrusted pistons and a lot of wear on the side walls.  I agree with the team in replacing all the rings, but maybe taking some measurements of the bore would be in order as well.  Just another 2 cents.

[Carls_jeep]

My guess is a bad set of rings. I agree to check the bore clearance. Use a long .003" feeler gauge and a moderate drag on it as you pull it between the piston and bore. The manual says it should be a 5 lb pull but that is too hard of a pull for me to agree with.