Honda BF8 knocking

"I have a 2005 w/ approx. 30 h

"I have a 2005 w/ approx. 30 hours of use. Has a knock at anything above idle. Motor shakes and hesitates or dies after about 2 minutes of running. Bought the motor for practically nothing off of Craigslist knowing there was something wrong w/ it any ideas as to where to look? Compression feels great when pull started, plugs are clean, removed pull start cover and same noise continues, noticed scrathes on the magnets on the underside of the flywheel not sure what made them. Are the sensors on this motor for knock? I have an older 86' honda 7.5 that has performed flawlessly so I know how this motor should run. Thanks, Thad"

"These are pretty simple, stra

"These are pretty simple, straightforward two cylinder engines and no, there is no knock sensor.

I have found a few that came frome the factory that had a timing gear problem. The nut that secures the timing belt drive gear on the crank gets completely loosened from either not being properly torqued or the thread locker that they used is defective I'm not sure which.

At any rate, the timing belt drive gear starts to float on the crankshaft and starts to eat out the keyway in the gear and starts destroying the index key. This, of course. can lead to a change in valve timing. A sure sign of this while the engine is idleing is a faint "ding-ka-ching" ringing noise from under the flywheel made by the large timing belt guide washer bounceing up and down between the timing gear and the crankshaft seal boss and generally jiggleing around in there.

I would investigate for that defect immediately. I have repaired the engines by simply replacing the gear, key, washer and nut as Honda makes a really hard crankshaft and the keyway and threads for the nut were virtually undamaged.

Other than altered timing, you are probably shooting in the dark since the engine was purchased used. It might be hard to tell, without disassembly, if there is bearing damage from inferior or contaminated oil or if the engine was run too much up against the rev limiter and incurred some lean burn abuse. Other stupid human pet tricks are the use of ether to start engines and overdosing of fuel additives.

I would pull the flywheel and see what made those scratches and see if that timing gear is secure. You can't really tell much about compression without actually using a gauge, so I wouldn't trust the "pull on her" technique. Check the valve lash adjustment while you're in there.
Good luck."