Low compression

[ronstern]

I just gave my bike a compression test and found low: 40 -60 lbs. Gonna have to get a manual now. I don't have many specialty tools but the usual set of sockets and wrenches. What tools would I typically need to start an engine teardown?

 

[bbillington]

Was it running before? what conditions did you do the compression test? A little history of the bike and what led you to this would be helpful.

 

[ronstern]

I'm the original owner of a 1977 - The bike ran last about 16 years ago and then sat in my garage till my kids grew up. The last time it ran I think rust got caught in the carbs so it was running really rough. I just garaged it and it sat until I tore it apart several weeks ago. It's out of the frame and looks good cleaned and all, but the compression tells me it needs work. I sprayed some WD-40 inside the valves and you can see it bubbling on compression stroke. I put some 10-40 in the plug holes but compression remained the same, about 40-60 lbs. I just got my carb and petcock re-build kits from Mikes so I'll be doing that this weekend.

 

[5twins]

Be careful with the carb rebuild kits. The jet sizes included are all wrong. Usually, you won't get a good reading doing a compression test on a cold engine so things may not be as bad as you think.

You can get it mostly apart with the tools you have but will need a few "special" tools for valve work (spring compressor, lapping stick & compound). And it does sound like your valves need to come apart and be lapped.

 

[retiredgentleman]

I just gave my bike a compression test and found low: 40 -60 lbs. Gonna have to get a manual now. I don't have many specialty tools but the usual set of sockets and wrenches. What tools would I typically need to start an engine teardown?

Torque wrench............5 to 80 ft-lbs works well. Valve spring compressor. Manual impact tool. Manual valve grinding tool i.e. 2 wooden sticks with suction cups, plus fine and course grinding compound. 1 used popsicle stick, also known as a ring compressor.

Dial indicator would be useful, so that you can measure wear of the valve guides. A clutch holding tool if you plan to dis-assemble the clutch while the engine is on the bench. A micrometer is handy to measure clutch plate thickness.

The 1977 carb re-build kit from Mikesxs comes with the wrong stock jets (unless they have corrected that). Refer to the nice carb specs diagram that 5twins has put together for the correct jets etc.

 

[ronstern]

Thanks, looks like I have a fall/winter project ahead of me.