Ring Advice

[Nobby 'C ']

I have to remove the barrels to fix a small leak in the base gasket. Is it worth replacing the piston rings as a matter of course? The speedo shows 28,000 miles but as I am not the original owner I cannot guarentee the acuracy of this. Thanks in advance.

[Big T]

Do a compression test first. If the compression numbers are good, no new rings needed.

If compression numbers are low, test for rings vs. Valves as the source of leaking by adding in a few cc's of oil to the cylinder and retesting. If the reading goes up, rings are the problem, so replace. If the reading stays the same, time for a valve job.

You might want to consider the camchain guides as well when you have it apart.

[Nobby 'C ']

Thanks for the advice, I had overlooked a compression test. I do like the idea about changing the camchain guides.

[bwringer]

I'm rebuilding a GS850 engine with very few miles, and the rear cam chain guide was cracking and falling apart just from age even though it had no visible wear at all. So it's definitely worth checking as long as you're going to have it apart.

[49er]

I'm rebuilding a GS850 engine with very few miles, and the rear cam chain guide was cracking and falling apart just from age even though it had no visible wear at all. So it's definitely worth checking as long as you're going to have it apart.

I agree. I recently rebuilt my 850 with 76ks on the clock. There were deep wear grooves on the contact face and the rubber/plastic molding was breaking up. I strongly suggest you replace yours while you have the top end apart.
Some will even suggest a light honing of the bores before re-fitting the barrells to ensure a good reseal of the rings. It's not ideal to disturb the piston rings and expect them to reseal again.
Also worth replacing are the gasket and seals on the automatic cam chain tensioner. This is a major source of oil leaks on these ageing motors.

[Road_Clam]

I have to remove the barrels to fix a small leak in the base gasket. Is it worth replacing the piston rings as a matter of course? The speedo shows 28,000 miles but as I am not the original owner I cannot guarentee the acuracy of this. Thanks in advance.

A compression test is the most accurate way to tell the condition of your top end. I replaced my head gasket (another leaker), with 17K on my odo. My compression was about 145 right across the board. I saw no reason to replace the rings. My piston skirts looked perfect, as did my cylinder. The one thing you will want to check is the valve guides. If you have excessive play, you may want to consider a valve job.

[Nessism]

Some will even suggest a light honing of the bores before re-fitting the barrells to ensure a good reseal of the rings. It's not ideal to disturb the piston rings and expect them to reseal again.

I'm not an expert but it seems to me that honing the cylinder IS far more disturbing to the seal than just taking the cylinder off.

My understanding is to compression test to check seal. If okay, slam it back together with new gaskets and valve stem seals. If compression is low double check after adding oil to the cylinders - if compression increases you need new rings. If rings are needed it's best to measure the cylinders before assuming it's green light to just hone. If the cylinders check out go ahead and hone. One additional note though, some folks around here have reported the lack of availability of rings on some models. You might want to check in advance to see what the story is on your particular model before you get too far down the road this way.

Good luck.

[Nobby 'C ']

Run a compression test....less thah 30 psi. Added oil..120 psi. Looks like new rings and maybe a rebore. Might be cheaper looking for a used set of barrels and pistons. With my luck, maybe I am not really meant to ride

[mark]

Run a compression test....less thah 30 psi. Added oil..120 psi. Looks like new rings and maybe a rebore. Might be cheaper looking for a used set of barrels and pistons. With my luck, maybe I am not really meant to ride

Make sure your throttle is wide open when you do the compression test......

[Nobby 'C ']

OK, I'll confess...... I did the whole compression test wrong. I will try again at the weekend.