Author Topic: Bad rings  (Read 1988 times)

Dirty Steve

  • Newbie
  • *
  • Posts: 12
    • View Profile
Bad rings
« on: May 13, 2015, 12:54:34 PM »
How likely is it for a bike to have bad rings after sitting for 25-30 years, even if it's only got 13,000 miles on it? It's a 1975 CB750 K5 that smokes a little and gas gets into the crankcase. Compression is around 135 psi for all cylinders. It's supposed to be 170 psi.

mechanista

  • Sr. Member
  • ****
  • Posts: 433
  • The OTHER Rick
    • View Profile
Re: Bad rings
« Reply #1 on: May 13, 2015, 07:32:51 PM »
I would fix the carbs and fuel valve, change the oil, and ride it. The compression will probably come back up a little. Books spec compression at sealevel. It will be a little lower up here any way.
Who are the grateful dead? And why do they keep following me?

Chris

  • Sr. Member
  • ****
  • Posts: 386
    • View Profile
Re: Bad rings
« Reply #2 on: May 13, 2015, 07:35:26 PM »
My guess would be that they are just stuck from sitting that long. If you can get the bike running mix some SEAFOAM  additive in
the oil as it says on the can and let it idle for 10min or so until it is hot. Don't ride it or rev it up. Drain oil and refill with clean pil
and ride it. Chances are it'll only get better with time. Check your carb float levels.  But the fact that all cylinders read the same is good.
I revived several engines this way. Put some SEAFOAM in the gas too for a while, it works wonders.

Dirty Steve

  • Newbie
  • *
  • Posts: 12
    • View Profile
Re: Bad rings
« Reply #3 on: May 13, 2015, 09:49:56 PM »
Well...135 is an average. The lowest is 132 and the highest is 140.
Much appreciated, though. I didn't realize it could get better with time.
Thanks for the tips.

buggiebuggie

  • Sr. Member
  • ****
  • Posts: 356
    • View Profile
Re: Bad rings
« Reply #4 on: May 14, 2015, 08:17:42 AM »
What Chris said... 2x

Chris

  • Sr. Member
  • ****
  • Posts: 386
    • View Profile
Re: Bad rings
« Reply #5 on: May 15, 2015, 06:57:32 AM »
Here's another interesting little ditty. One of my XT's only had 50 psi compression. I made a connector where I could hook my air hose to the spark plug hole to pressurize the engine. On top dead center air was blowing out the exhaust valve but not the intake or crankcase vent, indicating
the weak spot. Took the exhaust of and sprayed some PB-Blaster into the exhaust port and onto the valve stem and let sit over night.
Cranked the engine over with the air hooked up and a whole bunch of black soot came out. A new compression test now showed 100 psi,
which should be enough to get it running. SEAFOAM will probably complete my engine overhaul  ;D once it runs.

buggiebuggie

  • Sr. Member
  • ****
  • Posts: 356
    • View Profile
Re: Bad rings
« Reply #6 on: May 15, 2015, 04:26:23 PM »
Good deal...