I picked up a pair of GX340s for $50 and spent yesterday stripping one for parts and fixing the other. They're both from generators, so I'll have to modify the crank or make an adapter and mill off the "bellhousing" for use on something else.
First impressions:
I like how much bigger and chunkier everything is. The intake port is light years ahead of what the GX200s have. The single-bolt valve cover and rubber gasket is also nice. 340s have a 6mm smaller bore than the 390 and I'm not sure if they used the same block casting, but the 340 sleeve is really thick.
Carnage:
One had so much compression that it was hard to pull through. I tried starting it anyway and it would backfire through the carb. Figured the flywheel had slipped, but it hadn't. Maybe the valve clearance was loose enough to keep the compression release from working. Yeah, that was the problem, but a little more involved than simply adjusting the rockers:
Exhaust rocker:
I almost didn't change the intake rocker because it looked normal from above. It wasn't centered on the valve, though, so it came off for investigation. Out came a bent pushrod and this:
What I think happened is the exhaust rocker folded and prevented the cylinder pressure from being released. Then the intake valve tried to open against that pressure and more bad things happened. Hopefully the bottom end didn't get hurt. It's back together with good parts from the spare engine and runs well, at least.
First impressions:
I like how much bigger and chunkier everything is. The intake port is light years ahead of what the GX200s have. The single-bolt valve cover and rubber gasket is also nice. 340s have a 6mm smaller bore than the 390 and I'm not sure if they used the same block casting, but the 340 sleeve is really thick.
Carnage:
One had so much compression that it was hard to pull through. I tried starting it anyway and it would backfire through the carb. Figured the flywheel had slipped, but it hadn't. Maybe the valve clearance was loose enough to keep the compression release from working. Yeah, that was the problem, but a little more involved than simply adjusting the rockers:
Exhaust rocker:
I almost didn't change the intake rocker because it looked normal from above. It wasn't centered on the valve, though, so it came off for investigation. Out came a bent pushrod and this:
What I think happened is the exhaust rocker folded and prevented the cylinder pressure from being released. Then the intake valve tried to open against that pressure and more bad things happened. Hopefully the bottom end didn't get hurt. It's back together with good parts from the spare engine and runs well, at least.
ut: I'm going to make an adapter for a 34mm Lectron and see how it likes a carb that big.
