Quick question (compression test)

[nickr234]

For a 1978 gs 750 is a compression of 130-120-120-120 good?

[SqDancerLynn1]

That's fine. Depending on mileage it increase slightly after some use

[Flyboy]

Yep, sounds fine to me.

[Nessism]

It's good for a cold engine, but only fair if the engine was hot (of course, the throttle needs to be held wide open during the test).

[nickr234]

would replacing the piston ring help, or not?

[Nessism]

would replacing the piston ring help, or not?

Maybe, if they are worn. When were the valves adjusted last?

[Hoosier Daddy]

Ring replacement is a LOT of work to try and increase those numbers. I'd check the valve adjustment and ride it. Like SqDancerLynn1 said, depending on if she has sat for a while, those baseline numbers may increase after a 100 miles or so.

[tkent02]

These are not high compression engines, those numbers are fine. Adjust the valve clearances and ride the snot out of it.

[nickr234]

thank you all

Alrighty. The valves were adjusted a little bit ago. i just replaced the head on it, so everything may have settled after some riding and gotten out of spec. i will check it out.

I have had the bike for a little more than 1 3/4 years. But before that this bike was sitting in my dad's garage for about 15 years or so and i had to break the pistons free by putting marvel mystery oil in the plug holes. Then I let it sit for a week and the pistons moved nicely afterward. So i will probably be replacing the rings in a year or two because they probably didn't like sitting for 15 years.

Thanks everyone for your answers,

Nicholas.

[tkent02]

So i will probably be replacing the rings in a year or two because they probably didn't like sitting for 15 years.

.

What it needs is to be ridden hard, they like it rough. Test the compression again after several thousand miles, it will still be in spec.
The rings will be fine.