M20 Diaries: known weak points, a first hand experience

[Jon325i]

So I finally took some time to investigate what happened to the M20 which I pulled from my car a while back. My initial thought was a spun rod bearing because of the loud knocking sound that occurred when I ran it for the final time. However, removing just a couple of parts revealed what really happened. It started with removing plug #4....



Once that was revealed, I took a 23mm ratchet and rotated the motor.....and it could only do 1 revolution. Peeking inside the plug hole I could see a piece of the exhaust valve embedded in the piston going up and down as I rotated the crank. It quickly became apparent that this wasn't a rod bearing issue as I first suspected (sorry - no photo).

Next I pulled the valve cover and spotted a broken intake rocker arm for cylinder #2. The second and third picture detail this discovery.





More searching continued while the valve cover was off. This next photo shows fragments of the t-belt clumped (note the varying gaps in the grooves of the pulley). Sorry for the bad quality.....low light.



Removing parts off the engine, I make the next discovery. A portion of the t-belt cover broke away but was still in place. A slight touch with the finger and it dropped to the floor. What it revealed confirmed the disaster that took place. Needless to say, when this belt let go, it did so in grand fashion.








The troubling part of all this was that the t-belt and tensioner had about 58K miles on it. I believe, based on my experience, these parts should be changed at more frequent intervals (instead of 60K per factory, maybe 45-50K) especially if you do plenty of spirited driving, auto-x or HPDEs now and then.

The moral of my story - this post just re-affirms what many know. The t-belt and the valvetrain are weak links with these engines. Stay on top of maintenance and whenever overhauling/rebuilding, incorporate parts which are better than OEM spec.

Jon

[paperplane94]

Another testament to change the timing belts more often.

[jlevie]

50k or 5 years for a timing belt would be the absolute upper limit in my opinion.

The timing belt isn't a weak point, it is simply something that requires scheduled maintenance. And there are others. 100k or 10 years for the entire cooling system, ignition wires/distributor cap/rotor, and 100k for the O2 sensor. The cam seal and all belts should be replaced when the timing belt and tensioner are changed. OE shocks are good for no more than 60k, Bilsteins for perhaps as much as 80k. Suspension bushings, no more than 100k. Koni SA shocks with standard or mild sport springs are good for a lot longer is initially adjusted for no more than 1 turn from full soft (which matches the spring rates).

Entire cooling system means the radiator, expansion tank, cap, hoses, thermostat, water pump, and fan clutch.

Any vehicle isn't something that you drive until breaks. Every vehicle has replacement schedules for various parts. Neglect or defer that scheduled maintenance and you are risking failure.

[FredK]

Dang Jon, sorry to see the carnage! I hope you can get the car back on the road!

Immobile E30s are frustrating, but once it drives again, you'll remember exactly why you own one all over again.

[Jon325i]

All valid feedback guys. I'm no stranger to E30s.....I've had 3 over the course of 10 years but this is my first major engine failure. I have another identical motor being readied for install. The wasted engine died at 209,xxx miles, the replacement has about 100K less miles on it so plenty of life if maintained properly. The replacement engine is getting all new belts, h2o pump, injectors, hoses, clutch & pressure plate, etc.

I'm hoping to get the E30 back in the road soon....its been immobile for a while and it is starting to bug me

Jon

[paperplane94]

50k or 5 years for a timing belt would be the absolute upper limit in my opinion.

The timing belt isn't a weak point, it is simply something that requires scheduled maintenance. And there are others. 100k or 10 years for the entire cooling system, ignition wires/distributor cap/rotor, and 100k for the O2 sensor. The cam seal and all belts should be replaced when the timing belt and tensioner are changed. OE shocks are good for no more than 60k, Bilsteins for perhaps as much as 80k. Suspension bushings, no more than 100k. Koni SA shocks with standard or mild sport springs are good for a lot longer is initially adjusted for no more than 1 turn from full soft (which matches the spring rates).

Entire cooling system means the radiator, expansion tank, cap, hoses, thermostat, water pump, and fan clutch.

Any vehicle isn't something that you drive until breaks. Every vehicle has replacement schedules for various parts. Neglect or defer that scheduled maintenance and you are risking failure.

words to live by.

[delatlanta1281]

I just did a similar job Jon. Not too bad if you can just source a lightly used head and send it out to be checked for @ 30 bucks. Took me @ 4 hours to replace. Honestly, the exhaust manifolds were the toughest part. You got this.