1980 gs850gl compression test

[ceh3523]

I have a dumb question when doing a compression test on 1980 gs850 do you need to ground spark plug wires ?

[mnferwerda]

Nope, but I would keep them tucked away from anything flammable...

[Nessism]

It's generally advised to ground them. The ignitors typically tolerate an ungrounded plug but it won't hurt to hedge your bet.

Before doing a compression test is critical to adjust the valves and put some miles on the bike. Bikes that have sat in long term storage may have sticky rings that loosen up quickly once the bike enters service. And since the valves tighten with mileage, and so many people don't adjust them, it's critical to make sure that is done before hand. Also, the engine needs to be hot and the throttle held open during compression testing.

[Steve]

It's generally advised to ground them. The ignitors typically tolerate an ungrounded plug but it won't hurt to hedge your bet.

You have experience with that, Ed? The "ignitor" is just a box of transistors that interrupt current flow through the coils. Whether the coil output is grounded shouldn't affect the load through the ignitor.

Maybe there is something about it that I don't know.

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[Nessism]

You have experience with that, Ed? The "ignitor" is just a box of transistors that interrupt current flow through the coils. Whether the coil output is grounded shouldn't affect the load through the ignitor.

Maybe there is something about it that I don't know.

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Steve, If you are 100% sure that the plugs don't need to be grounded I defer to your knowledge. I was a little unsure so I take and recommend the conservative approach.

[Brendan W]

This question is interesting. I take the view that if high voltage finds route 1 is not available it will look for an alternate and that could be undesirable.
I have heard advice about modern cars that this could damage the ecu.
On balance I would disconnect the coils if only to prevent zapping myself.

[Steve]

Steve, If you are 100% sure that the plugs don't need to be grounded I defer to your knowledge. I was a little unsure so I take and recommend the conservative approach.

Not sure if I could assign a percentage of confidence here, have just never worried about it. Actually, never even thought about it.

It certainly would not hurt anything to ground them, but now I wonder if something nasty might happen if you don't.

Hey, Posplayr, you have any input on this?

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