Our GS's: Interference engines or not?

[roeme]

Question just came up in my head when adjusting the valve tolerances.

[hampshirehog]

Yes they are.

[Steve]

Not just a simple "yes", but a hearty VERY MUCH SO.

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[roeme]

Hmm, isn't the zip tie method to change valve shims a bit dangerous then?

Not just a simple "yes", but a hearty VERY MUCH SO.

...that sounds like you had the misfortune of experiencing a piston/valve crash? Care to tell the story?

[Burque73]

It would be easy to hear any contact if it occurred when turning the crank by hand. Doesn't happen with a thin zip tie. Maybe because the top of the piston has just enough of an indentation where it comes closest to the valve.

If the timing chain snapped and the valve was completely open while at the top of the stroke I'm sure bad things would happen.

[Steve]

Hmm, isn't the zip tie method to change valve shims a bit dangerous then?

No, not dangerous at all. The zip tie does not hold the valve open far enough to be a problem.
Perfect for removing a shim, but not far enough to hit a piston.

...that sounds like you had the misfortune of experiencing a piston/valve crash? Care to tell the story?

Not me, and why not?

I was helping one of the local GSers get his 650 up and going. About a week or two after getting it going, he called me to say that he needed some help, and he was out on a ride, but not far from home. On a hunch, I took my trailer. A quick inspection showed that it would crank, but not fire. However, the cranking did not sound quite right. After getting the bike on the trailer, we took it to my garage and did some inspection. Found some extremely LARGE valve clearances, so we pulled the head. Found three bent valves, found some replacements and installed them.

I asked him how this had happened. He admitted to some "exuberant acceleration" as sort of a victory ride after getting it running, a week earlier. At first, he only admitted to getting it close to redline, but later admitted that he hit a false neutral and probably zinged it to 11 or 12k.

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[hannibal]

If the timing chain snapped and the valve was completely open while at the top of the stroke I'm sure bad things would happen.

I'll go ahead and comment here. I had a cam sprocket bolt back out at low rpm while approaching a red light. The cam stopped and bottom end didn't. Obviously broke a timing chain. A piston hit a valve and the valve lost. After tons of reading, advice, and a new valve and chain, she's back!

Yes it's an interference engine lol.