Blown engine at 3000 miles-WTF?

After 3000 miles on a new long block I have a blown engine. Here's what's been done to it, I'm trying to figure out why it blew, or find out if the machine shop is just hosing me:

89 Jeep Cherokee that's totally been rebuilt. Includes the following:
New Long Block from Machine shop
All new cooling system
All new sensors (except Hall in distributor)
Reconditioned Auto Tranny
New Fuel Injectors
Lots of other new stuff
Cleaned up wiring

The engine blew on a 500 mile trip when I was climbing a steep grade at approx. 65 MPH. At the top of the hill, as I coasted down the backside, I could hear rattling in the engine and pulled off immediately. Oil was pouring out of the airbox. This was after a break-in period of about 1000 miles of mild driving.

Machine Shop that did the work tore it down and says its a collapsed piston. I went and looked and sure enough, there's scuffing on the cylinder walls and some of the rings are looking funky. Bearings don't look too hot either with scuffing on them.

Machine shop says it was caused by detonation. Suggested computer or fuel injectors (even though they are new).

Neither of those sound plausable, since the engine was running good prior to that incident (you think you'd hear pinging or something).

Only other thing I can think of is that I'm running 32" tires with stock gears and the engine/tranny was hunting pretty hard for gears during the 65 MPH hill climb.

Engine has NEVER overheated since it was installed.

So, what could cause this to happen?

Detonation will kill an engine as you described, but you should be able to hear it. It will put up a large clatter. Pull the spark plugs and post up some pictures. Detonation will normally show up on the plugs.

Scuffing on the sides of the pistons is not a symptom of detonation unless the pressure snaps the rings.

At first look, it sounds like the shop may just be trying to get out of warrantying their work.

If the plugs are intact, and the electrodes are not eroded and do not show running hot, since you say you didn't hear any ping or clatter, I say they should warranty it.

old_man said:

Detonation will kill an engine as you described, but you should be able to hear it. It will put up a large clatter. Pull the spark plugs and post up some pictures. Detonation will normally show up on the plugs.

Scuffing on the sides of the pistons is not a symptom of detonation unless the pressure snaps the rings.

At first look, it sounds like the shop may just be trying to get out of warrantying their work.

If the plugs are intact, and the electrodes are not eroded and do not show running hot, since you say you didn't hear any ping or clatter, I say they should warranty it.

Click to expand...

X2^

it sounds as though the oil control rings never seated causing high heat in the cyls and one of the rings "stuck" long enough to fracture a piston. Poor cyl preparation is my guess.

--Shorty

Although I don't know how well it works the Renix system does have a knock sensor. It would take pretty heavy detonation to do that in such a short amount of time. Sounds like poor assembly/tolerances caused this problem.

If a lifelong friend of the family didn't own a machine shop I wouldn't know what to do for machine work. Seems most all the shops around here have some kind of bad rep.

Thanks for your insight. There was no deteririation of the plug electrodes. Yes, the oil rings did collapse. Brand new knock sensor, and agree, knocking that would be that extreme would be heard.

I can't see how, even at full throttle I could have toasted the engine in 15-20 minutes.

By the way, the oil in the airbox problem was coming on 1000 miles before the engine went. It was literally coming out of the bottom of the airbox and dripping all over the steering box. Once the engine finally blew (meaning I could hear rattling) oil into the airbox shot up tremendously. The result being lots of black crap on the electrodes, valves and pistons.

No doubt the oil control ring went. Didn't break, but was rounded off.

Any suggestions on how to "prove" it was the shop's mistake?

By the way, friend's engine blew as well from the same "reputable" shop. In his case, the engine did overheat on 1st test run (which is why I was so thorough on mine) and broke a piston skirt. If, as is postulated, the engine was assembled too tight, I could see that as being a cause for both engines to fail at roughly the same time.

Needless to say, this is getting depressing.

Detonation usually causes the top ring to break, not the oil ring.

So are you saying all the plugs are blackened? If that is so, then you were not running lean. If you were lean enough to cause detonation, the plugs would have burned off any crap on them. You might only have a redish type crust on them from the burnt oil and deposits. If you were running lean enough to cause this problem, you should see a rounding on the spark plug electrode edges caused by melting.

The ultimate way to tell if you had detonation is to pull the crank and main bearings, then reassemble the main caps and mike the inside to see if the main caps are stretched. Detonation serious enough to cause a hole in a piston will normally stretch the main caps so that the hole is out of round. The bearings will also show a lot of wear on the bearing cap side.

Knock Sensor!! Would have found the Detonation. I would Say you are getting bent over. Sounds Like a bad piston!! The crank should show if there was a detonation problem. If you heard nothing them you just had a bad piston. If they keep bucking you just have a laywer give them a call on it. ( Hope you have some Laywer friends)!!!! They are great when a good call is needed

this is an excellent thread guys! I'm real sorry to hear about your troubles man, but your experience is teaching me a bunch! My 89 was having a horrible time keeping oil in it, and I was getting oil in my air box. I've since torn mine down and as I look at the cylinders I can tell where the bad rings are, and where the blow by was occouring! It makes sense, you are in the right and the machine shop has got to fix this stuff! Good luck with it! Post again when you have an update!

That sucks! Are you sure you want them to try again?

OK,
Thanks for all the advise.

To clarify a few thing:
1. There was no hole in the piston. Only some scuffing on the cylinder and also on the crank bearings.

2. Plugs have nice sharp edges. They are black from the fw moments that the engine ran after it blew the rings.

Pulled the plugs out of the trash, heres what they look like:


as you can see, the electrode edges are sharp and no sign of any oxidation.

Prior to the engine going, the plugs were that nice toasty tan on all 6 cylinder -- just like they should be.

I'm thinking the shop and I need to have a talk.....

I'm getting ready to go talk to the shop.

Any feedback now that we have spark plug photos?

One more time... really need some answers...

The one item that the shop will still contend is detonation is the scuffing (evidenced by grey marks) on the mail crankshaft bearings.

Is this only caused by detonation, or could there be another cause?

Issue is two-fold: If the shop made a mistake, it needs to be corrected at their expense; If I have a problem that I caused, I obviously don't want to go through this again.

Do you still have any of the oil from the engine? Have it analytically tested. That will tell you a lot. Can you post up pix of the bearings? Was it all of the cylinders that had scuffing? If not, which ones?

The scuffing could be caused by bearings that were set up too tight, loss of oil, or detonation. If it was detonation, the scuffing should be fairly pronounced and the main caps stretched out. Plastigage all the bearings and see what their clearances are.

Sounds like the machine shop screwed up on the hoaning of the cylinder and created an air pocket that was trapping the air fuel mixture which can also cause detonation.

i suggest that you go over there and destroy them ::

old_man said:

Do you still have any of the oil from the engine? Have it analytically tested. That will tell you a lot. Can you post up pix of the bearings? Was it all of the cylinders that had scuffing? If not, which ones?

The scuffing could be caused by bearings that were set up too tight, loss of oil, or detonation. If it was detonation, the scuffing should be fairly pronounced and the main caps stretched out. Plastigage all the bearings and see what their clearances are.

Click to expand...

Well, scuffing I guess is pretty ponounced. You can see grey streaks about 1/16-1/8" wide on the bearings. Nothing you can feel, just see.

Hmmm... probably still have some of the oil, but it was outside in the open and prolly has rain water in it by now. Lots of sludge in it and it was really dark, for such new oil (~700 miles on it)

Sounds very familiar to me. I built a mild 401 for my CJ5 and after 1000 miles it starts rattling like crazy. I pulled the oil pan and found one of my new piston skirts broken off. the cylinder was very scored and the Rod bearing was hammered. I pulled the motor, tore it down and took it back to the machine shop. I said find out what's wrong with this. He refused to take responsibility for his work so, I took the block and pistons to 4 seperate machine shops. I asked them to tell me what was wrong without telling them who did the work or what had happened. All 4 shops told me that the block had been bored but, not line bored. I other words all the holes were punched but not in a straight line. this allows for slightly egg shaped holes and added stress on the rotating assembly. Cost me another rebuild but, I now have a machine shop that I trust for all my work. Expensive lesson but, at least the original guy finally went out of business. Have the cylinder alignment checked if it was bored. And good luck.
Dave

OK, went back to the shop, here's what he said:

"The scoring and scuffing on the crank bearing are clear indication of detonation"

He suspects, since it was mostly cylinder 5 and 2, that these injectors may not be working right. Could be, and I intend to have them tested.

Does this make sense?

If the injectors were running lean enough to cause detonation, the plugs should show a lean burn. They don't.

Call the Lawyer!!! Did the labor or the block or anything come with a warrenty? If it did take that to an attorney and have him mull over it for a minute or 2. 100 bucks at the law office beats 1000 for something that was the other guys fault. Dam this gets me angry and its not even my XJ

OK, so anyone have a reason why the Crank bearing would be shot? He's claiming that's a sure sign of detonation. True?

What else could cause scuffing on the crank bearings?