Cylinder bore service limits

[Redman]

I can pretty much agree with the assessment that at 84K miles, (and last 30 thousand of those miles with oil that turns black in 1 or 2 hundred miles) that rings and cylinders will be worn. But I dont have much of any experience with such, and am trying get a better understanding of what ever I can.

And I recall some folks saying that if cylinder is worn that can feel a hump in cylinder at the top of the rings travel.
At first I thought I could not feel anything, but after trying again and again, I think I can feel a little little bit of something.

Let me describe more what I have observed, and maybe some of you more experienced folks can provide some words of wisdom.

I know pic cant really show what need to see, but.....


Other thing, with piston at very top, I can try to push it back-forth or side-to-side and dont really feel or see any movement, but if do look real close can see oil maybe push out a very little on one side and down on other side.

Bore service limit in FSM is 72.08mm 2.8378"'.
And I see the engine spec is bore of 72.0mm 2.835"
Gee, surprisingly small difference.

I finally recieved the expanding bore gauge I ordered 3-4 weeks ago (to go with the micrometer I have, both cheapies.)
SO thought I would give it a try. But, I dont really think I can measure that accurately, to detect such a small difference.

But golly, I get a measurement right at 72.0 mm


But now that I think of it, that was down in deep (so piston top could help me get it straight across).
I should try more tommorow up nearer top of the stroke. WOuld that be different? Maybe hotter there?

[Redman]

The FSM does show to check at bottom, mid and near top. And front to back and side to side.

[Grimly]

You need to make measurements at twelve points across to get the picture of the bore - it might be barrel-shaped.
However, there's a very good chance it won't be and you'll get away with a hone and new rings, assuming the pistons are still within spec, that is.

[Nessism]

A bore gauge is needed to measure the cylinders properly. Those telescoping gauges are extremely tricky to use and not particularly accurate. Also, you need a micrometer that reads down to .0001" to measure them if you insist on using them, not calipers.

[Baatfam]

Might be worth having a shop check the cylinders, and if OK, hone them for you...They would clean the thing, too.

[Nessism]

Tom had a super low mileage big bore 1000 pistons/cylinder that would work great in your GK. You might want touch base with either him or our friend that snatched up the parts he dumped to see if you can get your hands on it.

https://www.thegsresources.com/_forum/showthread.php?258361-Mostly-free-motorcycle-parts-in-Littleton-Co

[Burque73]

Tom had a super low mileage big bore 1000 pistons/cylinder that would work great in your GK. You might want touch base with either him or our friend that snatched up the parts he dumped to see if you can get your hands on it.

https://www.thegsresources.com/_foru...n-Littleton-Co

There were quite a few parts he held on to, those included.

He did send a head from a GK that has Dave's name on it, should it be needed. 👍

[Nessism]

Make Tom an offer he can't refuse. He's not the greedy sort and may well bite!