I decided to work on a perfectly good M20 engine with about 500 miles since rebuild. Being my first rebuild it had some noise. I decided to check the lash in the cams and pinion and rechecked valve clearances. I also did an oil change.

I took off and less than a mile down the road it lost power. I checked a couple of things and got it to start again. a mile or so later and I was loosing power but made it back to my shop. I took the timing side cover off and discovered That I forgot to tighten the timing pinion nut...(crap)!

Obviously the pinion had moved enough to disengage the oil pump! I pulled the sump plate while it was still hot and the oil was scorched! No metal bits though...

So I checked the splines on the pump spindle and pinion and can't see any broken teeth.

Now I get a couple of miles down the road and its over heating and losing power. It appears to be returning oil but wonder if I messed the oilpump up in some way?

Any Thoughts?

Adam

email (option): xeon25@hotmail.com

The engine is overheating really quickly if it is within mile or so! Are you sure the cam pinions were replaced correctly (see page 17 of the manual) and that there is a sufficient gap on the decompressor (i.e. the exhaust valve is not being left open slightly.

If it was the mag pinion nut that came loose, then the bike would have spluttered to a stop.

I would check the valve timing as suggested...I would also check the ignition timing and whether you have a 'slack' advance or 'tight advance' magneto adv/rtd points assembly casting fitted...

Running with the ignition timing retarded is one of the common causes of engine overheating...

See the 'technical section' of this site for a full explanation of setting ignition timing, the reasons for advance and retard etc. etc....It's all covered there..
Be ABSOLUTELY sure the setting is correct before moving on to other possible causes...

Also check that the fuel/air mixture is correct...Weakness of the mixture will also cause overheating...

Check...Correct tappet clearances..
The valve lifter is set correctly..
The head gasket is sealing correctly..
The carb mounting flange is flat and the gaskets are sealing..(and a tufnol heat insulation spacer of at least 1/4" thick is fitted)
There is an annealed copper washer under the timing bolt in the head..
All carb specs./settings are correct and it is internally clean..
The fuel supply is not restricted..
The exhaust valve and its seat are in good condition and not leaking..

...Ian

email (option): ian@wright52.plus.com

I am more pissed than any thing!

I caused it to over heat!

It was running great!


I will run through the check list.

Thanks,
Adam

email (option): xeon25@hotmail.com

I pulled the head. I have valve clearness set to .008 But I have noticed that the exhaust valve doesn't seat on the admission stroke till the piston is half way down. That doesn't seem right. That would cause a lean condition? I'm guessing the exhaust cam is uneven as the valve seats fine on compression.

Adam

While I had the head off I cleaned the carbon and lapped the valves. I opened the clearance a bit on the exhaust. The exhaust is now on its seat during the intake stroke. Looks like I need new cam gears if I want to tighten up the clearances or can the profiles be machined to match again?

So my problem was two fold. I forgot to tighten the pinion nut which caused oil to stop flowing and by tightening up the exhaust clearance I caused over heating. So the motor got it top and bottom. It took a licking but its still ticking. Learning is expensive!

I took it for a Ride and seems to be back to its old self.

Adam

email (option): xeon25@hotmail.com