Changing piston rings w/o honing

[Eli_Slaminko]

Here's another question while I have the top end off my '73 CB350 twin:  Would it be better to just put it back together with the same piston rings, as the bike's compression was just fine, or would it be better to put new rings in, even though I won't be honing the cylinders?  I'm on a tight budget for this bike, or else I'd do it right.  The bores are in good shape and the compression's good.  Thanks

[Searchguru]

Hi,
My last re-build (removing a gearbox shaft) went without incident and I re-used the old rings as the engine was fine beforehand.
The bike suffers from the symptoms of low compression now, in that it doesn't start that easily and uses a bit more oil than before. It was apparent from shortly after the re-build. That was 10.000 miles ago so it was not the end of the world.
New rings was something I thought about but didn't bother with, but I wish I had. Performance is pretty much as it should be but there is always a niggling doubt that it could have been perfect.
For the sake of a little money and time your engine would probably be happier with new rings.
Tony.

[sono]

After over 30 years, piston rings need a break... even cleaned to new, spring effect is weaken , oil rings are notoriously the first to fail and careful measurements are needed to make sure you are still within standard specs for just ring replacement (new cylinder pin clips are mandatory no matter what)

Rebore is not needed if within specs, just some light depolishing of the surface will allow new rings to properly seat on the softer cylinder metal (with standard break-in procedure and quick oil changes)

If beyond specs, you will need to rebore your cylinder at the next oversize piston and rings you can find. As mentionned by another forum member  http://www.davidsilverspares.co.uk/ is your best place to find such critical part.

No matter what you do with cylinders and pistons, if valves in your head are not cleaned, reseated and valves oil seals replaced, your compression may not be restored and your time and money on new parts will be wasted (burning a valve is quite likely if not cleaned and adjusted).

Good luck

[sono]

If you are doing the work by yourself your rebuild cost will be reduced by 50% (the good news). Refurbishing the engine head is the expensive part, because it requires an experienced and well equipped machine shop.

Any mistake refurbishing the engine head will ruin it beyond repair. Any failure of the valves (likely if not refurbished in 30 years) may ruin the whole engine. (the bad news).

Being on a tight budget is precisely why I don't gamble or ride on worn out tires or cheat on my wife. I cannot afford to loose it all !    CB350 was my dreambike when I was riding a CB175 twin in the 70's. It is my 1980 CM400 grandfather. I wish you good luck in keeping your beloved bike alive and well !