Quote:
Originally Posted by blakjak3000
So..... after redoing everything a 4th time I took the head off. Testing the valve tension (by blowing in the exhaust port, and then the carb inlet port) it was apparent that air could flow freely with the valves 'shut'.
In my over zealous and excited state when i sat on the finished thing, i gave her some wellie, when i should have run her in for a few hours first 
It appears the valves have bent from impact with the piston, and logically would make sense seeing as they have bent upwards (to wards the head).
Quick final question....
whats more likely....bent valves OR poor quality/milling of the head?
JB |
Poor quality/ milling of the head would result in the head not seating properly, blowing gasket and leaking. If you had the stock head milled over 35 thousands then you possibly have valve clearance issues, 25 t0 30 on some. the numbers depend on the particular manufacture , some have more clearance than others.
you didn't state if you were using an aftermarket piston or cam so if they were stock, my guess is the cam chain tensioner you mentioned didn't reset properly, the cam skipped a few teeth and bam!!!! I'm afraid your back at base one. Replace the piston, head Assembly and cam tensioner or your going to keep on having trouble. You can pretty much count on everything from the connecting rod on up is trashed.The piston hit the valves with enough force to bend them so the impact transfered to the connecting pin at the crank connecting rod. that piston will wobble around in the cylinder eventually beat itself and the cylinder walls apart. Hone the cylinder for fresh rings. The cam itself is probably o-k.
When resetting the cam, DON'T use the timing marks on the flywheel, they are seldom accurate. With the head off, rotate the piston to top dead center and put your own marks on the fly wheel. rotate 180 and mark again. Use the mark closest to the factory mark. Use a dial indicator if possible or some sort of measuring device.
if your worried about valve /piston clearance, it can be checked by forming a pancake out of silly putty or clay on the top of the piston, assemble, rotate by hand a few cycles Remove the head, the valves will leave indentions in the putty that can be checked by removing pancake, slicing a cross section and measuring.