GS850 No Compression

[wdavie]

I'll try to get a picture of it this week, bike is at my lock up garage so only go down when I'm doing work on it. I'm thinking of swapping the cams over anyway set the timing again and see if that fixes problem. If not at least it rules out that theory

[Nessism]

I'll try to get a picture of it this week, bike is at my lock up garage so only go down when I'm doing work on it. I'm thinking of swapping the cams over anyway set the timing again and see if that fixes problem. If not at least it rules out that theory

Basscliff has the factory service manual you can download for free. The manual will show that the valve lift is the same for the different years, the cam timing changed in 1980 but it's no big deal and won't cause the problem as noted unless maybe you changed the cam sprockets (and even if you did I'm not sure that would cause a loss of compression).

Did you check the valve clearances?

[SqDancerLynn1]

Did you open the throttle when you checked it ?? Other wise to have No compression it would almost have to be cams out of time or valve adjustment

[lti_57]

I read the replies but I might have missed this suggestion
pull the plugs remove cam cover on the right side put a 19mm socket on the crank end.
rotate motor using the ratchet and put your thumb or finger over the plug hole and watch the cam lobes you should during one rotation of course feel some compression or air trying to escape the cylinder also at some point during the rotation both valves should be closed or in other words both lobes should be on a flat spot.
The other thing you can do is rotate the motor to the "T" mark and on the left side plug removed piston should be at the top of its stroke and both cam lobes should be flat against the shim buckets if not rotate one more time till you see the "T" and recheck

[wdavie]

OK Guys pulled the rocker cover off agian today. Set the timing correctly, no difference. Checked all the valve clearances and on number 1,2, and 4 cylinders had massive clearance on the exhaust cams acceptable clearance on number 3 exhaust cam. Inlet cams were ok. I had some compression on number 3 cylinder but nothing on the others. Could the fact that the gaps were big cause no compression? I thought it would have to be the other way round and too small a clearance to cause problems? I'm more confused than normal now any help greatly appreciated

[Nessism]

Massive clearance means the valves are sticking open. Maybe bent valves.

Honestly, before installing a head and going though all the work that entails, I strongly recommend pulling the valves out and performing a complete inspection and seal change. A little work on the front end helps save massive work on the back side like is occurring now.

[Steve]

Depending on your definition of "massive", yes, it can affect the compression.

"Massive" clearances indicate that the valve is being opened late, not being pushed open as far, then closing too soon.

Tight valves can open the valves too soon, open them too far, then clost them too late (if at all), again reducing compression numbers.

Your best bet is to set the valves properly, then check again. You need to minimize/eliminate as many variables as possible.

.

[Nessism]

Depending on your definition of "massive", yes, it can affect the compression.

"Massive" clearances indicate that the valve is being opened late, not being pushed open as far, then closing too soon.

Tight valves can open the valves too soon, open them too far, then clost them too late (if at all), again reducing compression numbers.

Your best bet is to set the valves properly, then check again. You need to minimize/eliminate as many variables as possible.

.

It goes without saying that the valves need to be properly set, but massive clearance occurs when the valves are not closing fully (often because of bent valves), so changing shims won't get it. If for some reason the valves are not bent, and there is still a lot of valve clearance, the compression would be fine which is not the case here.

Something is drastically wrong with this engine so I'd pull the head now and remove the valves and check it properly. Done this work before installing the head would have saved all this trouble (unless the valves were bent at a later time).

[wdavie]

Thanks guys, Ed, the head I used was running fine in another engine before I swapped it over so I assumed that it was alright. I only swapped it over as the gearbox was knackered on the donor engine. I doubt if the valves have been bent in the short time it came from one engine to another. I agree though about using bits without inspecting them first but in this instance I used a part from a well running engine. Will reshim the head and test it again. The clearance on one of the shims was 0.20 Thanks for advice. Wayne

[hampshirehog]

The clearance on one of the shims was 0.20 Thanks for advice. Wayne

Wayne, that clearance would suggest a bent valve or sticking bucket.

[wdavie]

Have had a eureka moment. When I first put the head on I set timing up wrong, obviously have bent valves when trying to start it with incorrect timing. Glad I now have an idea what I have done wrong and should be able to sort it out now. Thanks to all for the advice. Numpty of the week award goes to me I believe.