rebuilt head... now rod bearing and oil ring shot... why?

[armada]

I bought an 89 sprint 3cyl with 100,000 miles on it thinking that all it needed was a valve job. The car had a bad middle exhaust valve and shook at idle but had lots of power and was fine at speed. It was driven this way for at least 600 kms maybe more.

The mechanic and I changed the head. It ran smooth and quiet at first but had a significant loss of power. I drove it for an hour until the oil light came on and it had a huge loss of power (this came and went). Also the crankshaft seal started pouring out oil. It lost a quart. I brought it to the mechanic and we replaced the seal and changed the timing so that it ran rough but had lots of power. Compression was 149 146 150. I drove it for a half hour and brought it back. It turned out that the machine shop had given us a bad head and they agreed and replaced it ... the valves didn't close properly.

The shop and mechanic replaced the head... when I showed up to check out the car the compression turned out to be 170lbs with the third head but it smoked lots (blue), the middle sparkplug was oil soaked and there was significant rod bearing noise. Even more power though, and 170lbs of compression.

The mechanic did drain the coolant (I saw him) from the engine before removing the head.


I think, (though iI have v. little mechanical experience) that the new problems were caused by either one of two things... either...

1/ The rod bearing and oil ring couldn't stand up to the 170lbs of compression and instantly gave out... Extra wear could have been caused by having driven the car with a bad middle exhaust valve for so long.

or...

2/ The hour of so of driving while having the timing out (there were a few small backfires) caused damage to the rod bearing and oil ring. The mechanic says that timing between 5-8 degrees is normal... (the book says 6).

We haven't taken the bottem end of the car apart yet.

The Mechanic has done 200 Sprints (that's all he does) and can't figure out the problem as he hasn't experienced it before.

My question is what happened, and who should foot the bill. I would also be interested in polling readers to see who agrees with what diagnosis.

Thanks for your help,

Armada

[Moppie]

An engine with lots of miles on it will waer itself into a complete system.
bascily the wear on all the parts even outs any weakness from wear in other parts, in your case it sounds like the worn head lowered the compresion just enough that the worn bearings were able to stand up.
Everything was in balance, and although not running properly, the engine was able to still run.

As you suggested, but replacing the head you upped the compresion, this of course puts more strain on the bearings etc etc etc.


It sounds to me like your mechanic has done nothing wrong, and you simply have a very old worn engine.
Since you've already done the head there is nothing left to do but rebuild the bottom end as well.
At least with only 3cly it shouldn't be to expensive.

[armada]

Thanks for your reply. I understand what you are saying about the increased compression on the bottom end. I wonder if it is common that the bottom end problems would happen so quickly. The mechanic has done this literally 200 times to the same car and never had such a result so quickly. He has had people come back a month later, though. Have you heard of such a quick failure of this kind? Because it happened so quickly I wonder about the timing...

I like the mechanic and he seems good and I am leaning towards thinking the same way that you are.

Thanks again

armada