M50 Worse than just a HG

[93 525 Paul]

Sooo, car was fine with 178k miles. Was driving it last fall up a long freeway climb, steady power, consistent RPMs, all was well. Felt engine kind of go off song. It started to lose RPMs, temp normal, power dropped off, saw smoke in the rear view, let off worked over from #1 lane to shoulder. Temp had begun climbing quickly. By the time I pulled over the engine wouldn't idle. Died.
Got it to the shop next day, they said HG, coolant in the #4 cylinder, $3k to repair. I said no thanks. Threw it on the side of the house and forgot it for awhile.
In the last month or so got motivated to replace it, seemed like a big, but not overwhelming task. I used to race karts, did my own engine work on those, and have built a handful of engines, set up differentials and even a couple of transmissions.
Via a poorly titled thread, I've used your help to yank the head, pull the cams, remove the valves, clean up the head, prep for reassembly and reinstallation.
I found the gasket remarkably intact, had expected a "blown" hg to be self evident. It was not. Expected the head to have problems, none. It's flat to within .002" in every direction, no cracks, valves and seats look good.
Today I went to clean up the block deck and my heart dropped. Partly because of the gravity of the situation and partly because I'm disappointed I didn't see the damage earlier.
Aaaaagh!!!
The cylinder walls of #3, #4 and #5 where the 3 cylinders adjoin look scorched from overheating and lightly scored. There appears to be some aluminum transfer from the pistons, but only at the very top of the cylinder above the ring level.
When racing a kart and letting the motor get too hot, many a karter "stuck" a piston. In those cases the piston would stick in the bore and the aluminum transfer would be in the middle of the stroke. We'd use acid to remove the aluminum, hone the bore, drop in a new piston and ring and be on our way.
This seems more mild than that and concentrated to the tops of the adjoining cylinders.
Any guesses on what transpired? How did just those areas get so hot?
What would you do in this situation?
Replacement engine time?
Hone and rings?
Other?

[bubba966]

If you could find a well cared for M50 I'd say throw a used engine in there if you plan to keep the car for a while.

Did you look at the oil pump? Not sure just a water cooling problem would do that. Seems like a lack of oil flow might've heated things up 'till they started binding causing problems which then caused coolant to enter your #4 cylinder. I'd be tempted to pull the crank & rod bearings and see it those got roasted while you've got it all apart.

But I think you need to figure out what you want to do with the car and how long do you want to keep it?

If you just want it to run for a bit then a hone & rings could get you by just fine. If you wanted to have it around for a few years a used engine might be worth looking into. If you wanted to keep it longer than a few years I might find a decent used engine and pull it apart and use the best parts from it & your blown engine to make one rather nice one.

Would also be a good time to change things up if that's your desire. Maybe add a third pedal. How 'bout an S50?

Point being this seems like a decision needs to be made based on your long term goals. And I wouldn't want to run that engine long term without knowing a little better what all got roasted and how bad was it cooked. I'd also want to give the pistons a good look at before I ran that engine.

Actually, the more I think about that the more inclined I am to say grab a used engine and at the very least give it a new HG before you slap it in...

[whiskychaser]

This guide gives pics of lots of piston problems and causes:
http://www.mlcmotorfactors.co.uk/Tro...s/PistonTT.pdf
I think I'd be taking the crank and pistons out to see the total extent of the damage. I'd be concerned about using the same pistons because they seem to have gone oval, have been in contact with the bores but mainly because getting that hot may have damaged them and they may break apart if reused. Depending on the shape of the car and how much money I had to throw at it would decide the way forward. But if I decided to put a new motor in, I'd want to be damn certain the cause of the problem wasnt still in the car - like a partially blocked radiator or cat?

[Ross]

"long freeway climb"
I'd be thinking detonation. Pull the pistons and have a good look at the top ring lands.
Quick bottle brush hone job and rings(pistons?) would be my solution. And maybe knock sensors.

[93 525 Paul]

I think you need to figure out what you want to do with the car and how long you want to keep it.

Great question. At this moment I simply don't know. I had intended to get it going and drive it daily while I get my POS Lincoln LS V8 squared away to get rid of without taking a bath on it. (Needs an H-pipe and a tranny rebuild.)

Now that it's more involved, I will probably go ahead and pull the motor and pull it down all the way and go from there. The S50 is an intriguing idea, particularly the manual (however it seems more than a bit complicated.)

Based on Bubba's response and the piston pdf, I believe the damage to be oil related. The car used to leak inconsistently. Sometimes not so much, other times it would leak like a sieve and I feel like and idiot because I can't say for a fact what the oil level was that day. Until now I didn't suspect oil but since we went out of town for a couple days it is possible that enough leaked in those days to create a problem at the back of the motor.

[BMW4LIFE]

Great question. At this moment I simply don't know. I had intended to get it going and drive it daily while I get my POS Lincoln LS V8 squared away to get rid of without taking a bath on it. (Needs an H-pipe and a tranny rebuild.)

Now that it's more involved, I will probably go ahead and pull the motor and pull it down all the way and go from there. The S50 is an intriguing idea, particularly the manual (however it seems more than a bit complicated.)

Based on Bubba's response and the piston pdf, I believe the damage to be oil related. The car used to leak inconsistently. Sometimes not so much, other times it would leak like a sieve and I feel like and idiot because I can't say for a fact what the oil level was that day. Until now I didn't suspect oil but since we went out of town for a couple days it is possible that enough leaked in those days to create a problem at the back of the motor.

stupid question but wouldnt the low oil warning come on?

[whiskychaser]

stupid question but wouldnt the low oil warning come on?

I never had this warning. But like the low coolant warning, I wouldnt expect it to come on with the engine running. The low oil pressure light might come on but probably after the damage has been done.
I'm not about to add insult to injury by asking the OP how much oil it has in it

[Mordan]

like a partially blocked radiator or cat?

off subject but are the consequences of a partially blocked cat?

[whiskychaser]

off subject but are the consequences of a partially blocked cat?

Engine gets hot as it has to work harder and cant get rid of the exhaust gases properly

[Tiger]

Mmm.. a mechanic who lied to you about HG problem and coolant in cylinder... wanted you to cough up $3000... even if he fixed it, you will still have problem with the car and he would just say he did the job to the 'best of his ability' and you will still be out of $3000. NEVER EVER GO BACK TO HIM!

I would find a donor E34 engine and put it in... the question is how cheap can you get the engine compared to buying a whole nother car and part out yours...