Engine pressure at 90psi + no change after oil test...rebuil

WillP · Full Member Joined: Dec 22, 2008 Posts: 46

I just tested the compression on my 71xs650. About 90 on the left and a bit below on the right: I squirked a bit of oil in the cylinder and no change in the reading. I did have the vacuum slide and throttle open.

Thoughts?

jayel

did you set the cam chain tension and valves first?

WillP · Full Member Joined: Dec 22, 2008 Posts: 46

No. I thought testing the engine was a test of the valves. What is the process you suggest? Thank you: I sincerely appreciate your advice.

jayel

putting in oil will temporary raise the compression of weak rings, won't do a thing for a valve(s) holding open

WillP · Full Member Joined: Dec 22, 2008 Posts: 46

Yes of course. Cheers.

royfisk

will do a leak down test. This is a test that can be simply done by breaking a old sparkplugs porcelin off and tapping the center of the plugs base to 1/4" pipe. Then install a air chuck that fit you compressor into the plug base. now install the unit into the cylinder to be tested. Bring the bike up to top dead center on the compression stroke, and lock it there, compress the cylinder with compressed air. Now you should be able to tell where the air is escapeing, either from the valves or from the rings. Rings will sound air from the crankcase, valves from the head. To further your test pull both exhaust and carbs and spray soapy water into the ports and watch for bubbles, this will tell you which valves are leaking by. MYOU HAVE ADJUSTED YOUR VALVES LONG BEFORE NOW RIGHT? Useually if you have a leaking valve its in the exhaust port for they generally burn up first.

WillP · Full Member Joined: Dec 22, 2008 Posts: 46

Royfisk - Thank you for your advice. I apologise but the air chuck? What is that? I have not adjusted the valves [you mean checking the valves' seating and adjusting the cam chain right?] yet but will do so.

yamaman

Air chuck - what connects the air line to the valve. Gently with the air or it can push the piston down, needs to stay near the top!

If camchain/valves are not adjusted correct, valves can be held open showing leakage. Make sure they're right before you worry about any compression testing. Do that, then re check compression. If still low, do leak down test as advised!

Camchain has to be tensioned correctly, then valve clearance checked & adjusted to spec. Check the vault or plenty of threads around on valve adjustment! Here's one:

650rider.com/index.php...6297#66297

WillP · Full Member Joined: Dec 22, 2008 Posts: 46

Cheers Yamaman. I really appreciate it. Thanks as well for the link. I will print and use it.

One little question: what minimum psi output does one need for an air compressor for using it on a bike? Might look around for a used one for house chores and might s well have one sturdy enough to use on the bike.

yamaman

Mines just a $100 GMC jobbie, cheap & nasty, but good enough for most things if your patient! Any compressor basicly will go to 100 psi, it's the ability to maintain that pressure that costs, and that depends on your ability to pay..........

schtipp

i'm stumped?

650skull · Support Staff Joined: Jul 19, 2007 Posts: 1186

What have you done to get to the point of being stumped?............... Do you know/understand what you are trying to do?..........What have you read that you are having trouble relating to?

I ask these things, (not to be smart), because if you are reading stuff then by asking questions it will sink in. Just takes time and you will get help if you are trying to help yourself by reading as well.

What Happened to 650rider.com?

Yamaha xs650