Revisit to M42 with no compression 2, 3, 4 cylinders

[roadbiker_2]

Folks it's been a long crummy winter and I am ready to tackle the E30 that died late last year. It was thought that the pistons had been damaged on the car as there appeared to be deep gouges on the pistons. I started looking for some stock pistons in the hopes of pulling the engine and doing a rebuild with stick pistons, a hone out, new rings, bearings, timing chain and tensioner, water pump and rebuilt head. Well low and behold I find out the stock pistons have heavy valve reliefs in them and that may have been what we saw through the boriscope.

Anyway, my question now is could we have lost tension on the chain, bent the valves, lost compression and still be good on the bottom end? I was not running the car hard at all when this all happened.

  - I have had others state they had a had that could be purchased, please chime in.

[DesktopDave]

The stock BMW cam chain tensioner has been redesigned at least once - the cam chain can stretch past the tensioner's adjustment limit and skip timing. The early M42 also had problems with the idler gear on the cam chain...the roller bearings can die. We've had a few even break the mount inside the front case. BMW replaced it with a slider block.

You might note "pointy" cam drive sprockets if your chain is loose. The motor can run for years like that but the cam gears should have flat-topped teeth.

As a last-ditch effort, I'd try re-timing the motor then run a leak-down test again.

[roadbiker_2]

Dave, so would you suggest throwing a new timing set on this along with gears and give it a shot?

[DesktopDave]

I wouldn't advise a new timing set until you've eliminated bent valves as a cause. You ran a compression test, right? A leakdown test could also give good results in this case. One unconventional way to eliminate timing as a potential problem is to remove the cams & trays beforehand.

I'd also price out complete used motors...a new timing chain set could be as expensive as a running E36 engine. The '94-'95 vintage of the M42 was the best. It had all the durability upgrades from the factory and drops in once you've fitted the E30 manifolds, accessories, oil pan, etc..

[roadbiker_2]

Dave, thanks! You answered my next question which was how interchangeable the motors are. I have found a few newer motors, but was not sure how fit on manifolds and other items would be.

[DesktopDave]

No problem, keep us posted!

The later M42 is your best bet. Newer M44 motors can also work, but require more parts...like the complete wiring harness, DME, etc. I don't think anyone has tried the newest generations of BMW four-cyl.

[roadbiker_2]

Dave, I have a mechanic that will loan me a leak down tester. It may be a few weeks, but I will report back in a few weeks.