Quote:
Originally Posted by attnondeck  the fly wheel end of that shaft is really messed up! what happened to this engine mr ski? |
First of all this motor has sat in it's busted state for 17 years. I'm sure a lot of the rust was a result of being left to the elements.
There was severe detonation. That is without question. There are a few things I found and from the history I know of this boat, I can start to paint a picture. The timing was advanced so someone got into the front cover area. There was no hose clamp on the pulse line coming off the crank case so it was probably sucking air. The fitting is on the rear and it had a rear piston seizure. Plenty of carbon on the pistons so in general, the carb setting looked OK.
So this is what I think....
The new Laserjet was prepped by the mechanic by advancing the timing. This hull is not at all very freindly to work in...not like a very open
JS hull. So removing the front cover is a little challenging as one bolt would interfere with the battery mounting area of the hull. This bolt was actually left off upon reassembly and the hole filled with silicon...he probably should have found a little shorter bolt and sealed it up the right way.
Also, you can't really get your head down in there to see the stator alignment with the flywheel still on. So I suspect the flywheel was removed to set the timing. I found copious amounts of grease on the crank nose and adjoining hub of the flywheel. This tells me the mechanic thought it a good idea to grease the flywheel upon installation, presumably to prevent it from welding together as these tend to do. I have never used grease here. Only a slight dab on the keyway to keep the key from locking in place. I actually use loctite green sleeve locker on the crank nose and glue the sucker in place.
It looks like the grease allowed the flywheel to walk around and it eventually sheared the key. 1/2 of the key is still in the crank nose, the rest of it ground into pieces and stuck to the grease that was there.
What happens on these motors is that heavy flywheel on the front keeps it's momentum when the front piston pushes down on the power stroke. At the same time, the rear piston is trying to compress gasses into the combustion chamber. You have two forces operating in opposite directions axially on the crank. The crank twists a little in the middle between the 2 cylinders. The spark timing is always triggered off the front of the crank where the flywheel is. With the flywheel then leading the rear cylinder a little more than the front due to the crank twist, the rear cylinder gets it's spark a little more advanced. So set your timing at say 26 degrees advance, this works for the front cylinder but the rear is actually more like 29-30 degrees advance.
This stator looked to be about 28 degrees by eyeball and my experience...add 3 for crank twist and the rear is at 31 degrees. Then rotate the flywheel say 10 degrees due to shearing the key and you're at 38 and 41 degrees advanced.
Add in the 185 compression, pump gas, probably rear cylinder air leak at the pulse line and huge spark advance and walla, detonation.
Apparently this boat was run on tour all of 1992 (or was it 1993) and at the finals it seized up in the middle of a moto...bummer.
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