Bent Valves/Head Gasket?

[Webb Sledge]

Ok, so here's the story. It's not about a Triumph, but I figure engines are similar enough and you guess could still probably take a good guess at the problem, especially the guys who have worked as mechanics at one point or another:

I've been looking around for an E36 ('94-99) BMW M3, and I found one, but it has one problem. I called the guy and he said he was in Maryland visiting family and he turned to go up a hill and hit the gas to accelerate and lost all power. The car was towed to a local BMW dealership, and they replaced most of the ignition components to no avail before running a compression test to find that cylinders 5 and 6 could hold almost no compression at all, and 4 fluctuated between 80 and 100. Since they didn't pull the head, their best guess was the it was either bent valves or a blown head gasket. They also replaced the camshaft sensor, and the problem remained.

I'm not an expert, but I just don't see how the car could bend valves like this. Again, I'm not sure, but I don't think the M50 engine (what the M3 uses) is an "interference" engine. The reason I ask is because this would make a great deal for me if I could buy this car and have something simple like a head gasket replaced, but it would require me spending almost $2500 more if it was indeed bent valves.

The current owner also mentioned how the dealership told him it would cost him $6000 to replace everything with labor, and then made him an offer on the car for $10,000, basically trying to get him to sell the car. I can't verify this, but in my experience with car dealerships this doesn't sound to far fetched. The owner also said he bought it last year for $21,000 and needs four wheel drive right now and he just got married so he can't afford to fix it.

Any ideas as to what the problem could be? BMW charges an arm and a leg just to pull the head and check it out, so I'd really like to have a good idea as to the problem before I get into this one.

 

[vettedog72]

Webb:
BMW charges an arm and a leg for everthing they do, but I never had them replace anything that was not broken nor have I had any experiences where their diagnostics were not correct. If the electronics were replaced, they were likely bad; if they replaced the crank sensor it was likely bad. Sounds like the whole engine needs replacement and I bet you can not get BMW to put one in for $6K. The question that comes to my mind is "what happened" to the engine? BMW to my experience did not use trial by error for repairs. The blown gasket, electronics, bent valves all seem unrelated as far as a domino effect would go. Possibly a sever over heat could warp the head, blow the gasket and the head could warp enough to bend the valves...naaaaw. I don’t know where the sensor is on the M3 but I threw a fan belt and knocked the sensor out on a 535i (Can't believe it happened but the water pump froze and I broke the belt; why it was in such a vurnerable place is beyond me). My 535 and 533 both had chain drives for the oil pump and a separate chain for the cam. They were not likely to break but the models with belts may be another situation and I would not be surprised that the valves would contact the pistons. Rebuilding an “M” BMW engine is very expensive for the parts. There are not many choices and not many aftermarket sources. Obviously the M’s run well but they come at a very high price. A PAECO TR6 engine will be cheap compared to a BMW M rebuild.

 

[Webb Sledge]

I can't see how the engine would need replacing like that though. Even if had had the crap run out of it, it's only got 78,000 miles on a '99 model M3, which is low for even that model year. I just don't see how the whole engine could be bad. Also, I need to call the guy back. I can't remember if he said he had the car taken to Turner Motorsport or the a BMW dealer. He mentioned that it had been to both places but I can't remember where the "diagnostics" were done.

 

[Dave Russell]

Hi Webb,
This would be an excellent opportunity to do a cylinder leak down test. It would tell you almost exactly where the problem/problems were. I can't imagine a good dealer or shop not doing this.
D

 

[Webb Sledge]

How does a cylinder leakdown test differ from a compression test. If that would tell me what the problem is, I'll be on it in a heartbeat!

 

[vettedog72]

I recall one of the elements of the major tune up was a compression check (I don't think they did a leak down). Valve adj was an element too and bent valves would be id there. Some of the engine may still be ok, possibley the short block less the pistons where the valves contacted; the head would be a serious investment.

 

[Banjo]

A compression test measures the engines ability to build cydinder perssure, or compression by using the cranking of the engine to give a readout on a guage
A leakdown test uses compressed shop air to tell you what percentage of air pumped into the cylinder is leaking out, and by listening for hissing, also where it's going.
The first will indicate a weak cylinder, the second will give an indication of why that cylinder is weak.

 

[Webb Sledge]

Ok, here is my current scenario. I was mistaken, the car is actually in Maine, not Maryland, and the owner is in Virginia. The owner says the car is currently in storage up there until it sells. Since it's not running, it can't be driven to a shop to have a leakdown test done. I would not buy the car without having this done, but if I tell the owner to have it towed down to VA he will be fully expecting me to buy it. Would it be unreasonable to ask a shop to go to where the car is stored and perform this?

 

[tr8Fan]

Sounds similar to what I went through with my TR8. I completely rebuilt the engine (worked heads, pistons, cam, etc..) on my Triumph and reinstalled it back into the car. It was run several times and had less than 3 miles on the dang thing. I was on my way to get the top installed, turned right out of my neighborhood and started to accelerate. The engine just quit. Not knowing what the problem was, I towed it back to my house. I then pulled the distributor and could see that the timing chain snapped. This brand new chain (I can tell you who not to buy from) broke for no reason. Both heads had to come off due to bent valves. Needless to say, only a few cylinders had compression. Its since been put back together and runs great.
If you're concidering purchasing the BMW, make sure that you know whats wrong with it. It looks like you may be spending large $$ on this car.

 

[Webb Sledge]

I'll have to ask him, but I really don't think the timing chain snappen. From the sound of it, the car ran, but extremely roughly. I'm definitly going to figure out what's up with this car before purchasing.

Any suggestions on getting a dealer to go check this car out?

 

[Dave Russell]

[ QUOTE ]
Would it be unreasonable to ask a shop to go to where the car is stored and perform this?

[/ QUOTE ]
Go here to see how to build a simple cylinder leak down tester.
https://www.britishcarforum.com/ubbthreads/memberfiles/139216-LeakdownTester.jpg

It requires a small compressor of a few cfm capacity & capable of maintaining 80 psi. Don't know if you can find a shop with a portable compressor, but I would think so. You could even do it yourself if there is power available at the car location or you have a gas powered compressor.

Do this test on all cylinders, with the cylinders on TDC firing stroke. If the piston is exactly on TDC the crankshaft will not try to rotate.

The test shows how much cylinder leakage there is & you can tell where the leakage is by listening/observing at various locations with a small piece of rubber tubing. Eg. -

Sound at the air intake = leaking intake valve
Sound at the exhaust = leaking exhaust valve
Sound at adjacent cylinders = leaking head gasket
Bubbles at radiator cap = leaking head gasket
Sound at the oil filler = leaking rings

Give it a try, once you use this method you will find it much more useful than a simple compression test. It is the only acceptable way to test piston aircraft engines.
D

 

[Webb Sledge]

Cool stuff Dave, thanks. Hopefully the nearby shop has one of these and will be willing to check it out for me.

 

[piman]

Hello webb,

my thinking is that it comes down to cost, what price will the owner accept?, can you get a replacement head from a salvege dealer, and at what cost? If the two above plus some contingency comes to 75% of current second hand price of a good car then it's worth a gamble. If you start getting people to look at the car, you are spending money upfront with no guarantee that the diagnosis is correct and could just be dead money.

Alec

 

[Webb Sledge]

Yeah, after thinking about it, I think I'm gonna walk away from this one. It's not worth the hassle, and it would be just to much work and $$$. Thanks for the advice.