81' xs650, no compression, any ideas?

[Hombre Verde]

I just purchased an 81' 650 that ran a few years ago according to the previous owner that has been sitting. I have been going through the motor to see if it does work. I am now at the point of compression testing and I am not getting a reading at all. There seems to be a lot of air coming out of the crank vent on the compression stroke, is that normal? Also the valves look to be working but I am getting air pushed back out the intakes.
Just looking for any suggestions before I take it completely apart. This is my first XS so don't have any experience with them.
Thanks for the help.

 

[BigJimmyW13]

I just purchased an 81' 650 that ran a few years ago according to the previous owner that has been sitting.

Famous last words.....

On another note welcome to the site!

 

[inxs]

- welcome...sounds like youve got valve and ring seal problems on at least one cylinder...could be on top of whatever problem caused it to be stored in the first place...take your time and meet your engine from the inside out

 

[gggGary]

Before I got drastic and started pulling it apart I would check valve clearances and see if the cam and crank are "in time" with each other. I have bought more than one non runner that just needed valves set to become a "runner"

 

[fancyketchup]

Broken cam chain?

 

[Hombre Verde]

The cam chain is not broken as the cam turns when the engine is turned over. The intake valves where way out of alignment, re-lashed the valves. Same issue. The cam seems to be timed to the the crank, at TDC the valves are closed.
Maybe the valves are not closing all the way?
Going to start the tear down tomorrow. Thanks for the help.

 

[hooktool]

Do you feel compression? Or just not read it on your gauge? If it's the latter, open the throttle when you crank it over-it has to have something to compress.

John

 

[gentlemanjim]

Sounds like holed (from pre-ignition melting a hole) pistons because you are getting air flow out the breather . Even bad rings would have some compression. An open valve being adjusted too tight would get air flow out the exhaust or intake depending on which valves are hung pen.

 

[Hombre Verde]

The only place I feel air coming out is the intake and crank vent. Cant get a reading with at all with the gauge. The carbs are off, it should have plenty of air to suck. It sucks in pretty well but it also blows back out the intake.

 

[xsjohn]

Maybe someone has mentioned putting your finger over the spark plug hole to see if it compresses.........xsjohn

 

[txpowdercoater]

"ran when parked"
check compression first thing and go from there.

 

[Tech7]

You shouldn't be getting any pressure on the intake side. Check for plugged exhaust.(if it's been sitting, maybe something moved in?) See it on cars with plugged cats. Either that or you valve timing is waay off. Think basics. Suck ,squeeze, bang, blow. The 4 stroke internal combustion engine.

 

[XSLeo]

On the intake valve that is blowing back, remove the valve adjuster cover. Watch the valve action as you turn the engine over. The valve could be sticking.
If sticking shoot some penetrating oil around the stem.
Sounds like you may have to pull the engine and tear off the head. Could have holed pistons.
A broken piston may have bent the valves.
Not a total loss. All the necessary parts are available.

 

[Hombre Verde]

Update: Pulled it apart. The intake valves are hanging up, not closing all the way, looks like just from build up. The valves are not bent. No holes in the pistons, although the rings are shot in the left cylinder. Everything else looks good for being 29 years old. SO nothing major just a little extra work.
Thanks for the help.

 

[inxs]

- check this thread out for rings