TOPIC:

wiredgeorge wrote:

I have bent several crank shafts and the reason was missing a shift and running the engine way past redline.

OK Now we're answering questions I haven't even asked yet. My bike is the first manual-transmission carburated vehicle I've owned, and I am starting to learn that I have been spoiled by computerized rev-limiters. There isn't a rev-limiter to babysit me here, is there...
I'm such a klutz with the clutch that I'm starting to worry a bent crank is in my future. I'll just have to be more careful.

The valves that lapped never sealed fully or did they? my guess is that the valves are bent and the crank is bent as a result of the valves hitting the piston. Bent valves wont lap.

Is welding a crankshaft something any competent welder could do or should it be left to the experts? My $0.02 worth would be that the piston hitting the valves would not be sufficient to diturb the indexing of the crank? Bend the valves, definately but maybe not cause the crank problem?

Barney, I don't think it would be the valves bending the crank bwhahaha The other way around might be possible but I have never bent a valve when the crank bent.

If Jay is telling tales about the GS1100, he might mention their steller clutch baskets as well. I took material off my boot when I blew one of those up!

As far as rev limiters, you CAN buy a Dyna2000 and probably Dyna sells rev limiters. www.z1enterprises.com is now a Dyna volume dealer and their prices reflect the volume dealer price breaks. APE may also sell them. I can't imagine twisting a crank unless you are shifting at redline and miss a shift... You get those gears undercut and it CAN happen!

They lapped in eventually, but it took for-ev-er on #1, and I got a little bit of a grove on the valve face. Is this an indication that they're bent? They seem to be sealing fine. I tested the seal with some penetrating oil and none of it made its way through the valve. Maybe I need new valves and the seats ground?

So if my #1 piston actually crashed into the valves, wouldn't it knock it 'back' on the crankshaft so that #1 would hit TDC after indicated on the timing? Would there be some evidence of the crash / impact on the top of the piston?

you would have took the top out of the piston and destroyed that valve in order to twist that crank.lay the head on the front or back fill the ports full of solvent and blow air around the valve face and seat with valvesprings installed.if you see any bubbles in port you have problems,thats how i check them anyway. goodluck,happy wrenching!

What actually twist these press together four cylinder cranks is that the clutch gear is on one end. From hard takeoffs, the clutch basket is putting resistance on one end of the crank. Because it is connected to the rear tire via the transmission / chain, it doesn't want to turn up as fast as the rest of the crank does. The other end of the crank is trying to go, and the clutch end is resisting. I guess you can figure it out from there.

The bikes with the biggest problem twisting are ones with a slick and wheelie bar.

Jay

have the valve seats cut lighly then to test your lap, insert a valve in its seat, twist it half way around while pushing on it. Then fill the chambers with water and wrap a rag around an air nossle with 90lbs or more pressure. Push down on the valve with your thumb, insert the air nossle into the port, shoot the trigger and if you have no bubbles your ggood. Cutting the seats will allow a valve to lap in in a short time, and no bubbles.