My first experience with an m42 motor - dumb chain!

[bimmerlover]

When I bought my new cabrio.. I had been told that a timing chain guide rail was broken and needed to be replaced. I took the covers off and checked it out.. could see where it had broken but the chain looked ok and seemed good and snug. I ordered all of the parts (all new rails, chain, and gaskets).

I drove the car a bit. On my way to my parents last weekend to do all the work.. it died. I made it almost there.. and it left me on the side of the road.

So we got her home..


And today when we tore into the engine.. here's what we found:


Pretty ain't it? I did a real number on the pistons.. the cylinder walls look kinda rough too.




I think the broken rail above (top/middle) must have caused there to be enough slack for the chain to slip.. and at 65mph, it caused real havoc. If you have any other theories, let me know. I'm dreadfully frustrated with my stupidity already, so I don't need anybody to beat me over the head for this. All other comments/questions are welcome.

[AndrewBird]

M50 or atleast an M20 time, I say.

[AdironRider]

Go to m42club.com and read Febi Guibos thread on his Metric Mechanic engine. If that doesnt show you the pure power potential of an m42 I dont know what will. I say keep the m42, I really love this motor. Ive had 2 m20's before this, and while they did make more power, the m42 is just fun. Pretty hard to quantify but Id keep it.

[FredK]

Keeping the M42 will likely be the most economical and sensible route. You can get a used M42 with low miles fairly inexpensively, and you already have the wiring, DME, and accessories, so you can usually pick up a fairly stripped engine super cheap at a salvage yard.

An M50 swap is rather expensive and more time consuming than swapping longblocks. I guess it all depends on how soon you need the car to run!

Good luck with whatever route you choose. The M42 is a great engine.

[02stu]

M42s are great motors, unless your trying to modify them. Febi Guibos motor is strong but 210 hp at what cost? He had to put in a new crank, new pistons, new cams, new fuel delevery. That had to cost more then a s50 swap. All in all though I would stick with the m42. My 318is had the same thing happen to it. I decided to go with an m50 which I am still trying to get running and have spent twice what I was anticipating.

[golde30]

how many miles did the engine have on it?
the 318is i bought had a worse motor than that, totally grenaded. did u have any symptoms before the guide rail went out?

[bimmerlover]

how many miles did the engine have on it?
the 318is i bought had a worse motor than that, totally grenaded. did u have any symptoms before the guide rail went out?

The engine had 115k miles on it. The guide rail went out before I purchased the car. I bought it with full service records showing the last time they had it in they found plastic and metal in the oil pan that had clogged the pump pick up and it was from that one guide rail falling apart.

So what I'm trying to say is.. I don't have any experience with the car to know about symptoms before the rail went out; the service records do not seem to indicate anything relevant either.

[bimmerlover]

I finally finished tearing apart the engine to see exactly the cause for the slipped chain... the pics pretty much explain it all.






This last picture simply shows what was left of my guide rails.. compared to what they should have looked like (the new ones I had in the car with me when this all happened.)

Anybody ever seen this happen before?