No compression

[Lively]

No compression (0 psi) from the rear cylinder, front has 185 psi. Never had a case of 0 psi, any idea what im dealing with? Could it be as "simple" as a head gasket? or am i looking at a potential hole in my piston lol.

 

[CopperSpyder]

Hello Lively, when posting a question always state what bike you are working on like 2010 RS SM5 with 990 engine. I think that is what you said you had in the welcome area. Sounds like you have a real problem. If you are doing the test right I would say you will need to tear the engine down to find the problem, even a head gasket you would see the top end. But hopefully some others will chime in and give you more direction then I can on the next step you should take. Good Luck with your project I hope it works out better then it sounds.

 

[Freddy]

What was the lead-up to the need to check compression?

 

[Navydad]

Never had a head gasket give me a "0". I have had a stuck valve valve give me a "0". Have you changed spark plugs lately? I ask because I have had a small piece of carbon from the combustion chamber get on a valve seat and cause the valve to remain open which caused a "0" compression test. This happened right after a spark plug change that apparently dislodged the bit of carbon.

 

[larryd]

Turn that rear cylinder so both the valves are closed with spark plug removed, Compression stroke...Put compressed air in that cylinder...Listen to where the air leaks out...If it leaks out the intake manifold, probably a intake valve problem...If the air leaks out the exhaust, probably exhaust valve problem...If air leaks out in the crankcase, probably a piston problem...If air bubbles in the coolant tank could be a head gasket problem...If all was well when you last used the bike and this happened suddenly, I would suspect a valve or valve seat problem or head gasket...If this gradually happened I would suspect a piston problem...A simple air test on that cylinder will locate the loss of compression quickly...

 

[Lively]

Hey everyone thanks for the replys!
@copperspyder Im sorry, i think i said it in my head then and thought i typed it haha.

Its a 2010 Spyder RS SM5, @Freddy i purchased the bike cheap knowing there was an issue, dealer told the owner (WITHOUT LOOKING INTO IT) it was head gaskets and they wanted 4K.

Well i got the rear valve cover off and it seems to be a stuck valve, one doesnt move but maybe 1/10 of an inch, but the other valve thats visible moves as it should.

@larryd How did you get your valve unstuck? Did you have to remove the head?

 

[Freddy]

Does the stuck valve appear to be stuck open/down? ie is there lots of valve clearance? If so, the head must come off to investigate, but it won't be pretty.

 

[Lively]

@freddy, its stuck in the down position, however it comes up very slightly, point im making is there some movement but not enough to do anything. From the manual i believe its the intake. Why wont it be pretty

P.S. i realized i can see all 4 valves from certain angles, and all the others move as they should.

 

[Freddy]

because the valve will be bent and have hit the piston - perhaps due to a dropped valve seat.

 

[Haikanko]

I would remove the head as if the valve stuck open it could have damaged the head and the valve will need replacing also! If you look at video the valves and pistons take up the same space but at different times. https://www.youtube.com/watch?v=JjOk3lXBjQw

 

[PMK]

Not sure what level of mechanical ability and tools you have.

If it were me, before removing the head or accomplishing any disassembly, I would use a video scope and examine the top of the piston inspecting for contact between the piston and valve. This would be seen as obvious damage to the dome of the piston. Access would be through the spark plug hole.

While inspecting, you could also verify the valve seat remains in the head and there is not hole in the piston.

If there is no mechanical contact indicated between the piston and the valve, try to free the valve with the use of penetrating oil. It could be possible the valve is simply stuck in the guide from buildup on the valve stem.

Sadly though, Since it appears you bought the machine not running, I suspect the previous owner somehow over rev’d the engine and floated the valve causing the issue. Hopefully not, and maybe the bike sat with that valve open and has corrosion on the valve stem that will not be an issue.

You might start researching the Aprillia websites also. Possibly those folks will know if valve contact is possible

 

[PMK]

Wanted to add, it could also be if the intake valve, something was drawn into to engine past the throttle body a d became lodge so tnat the valve is held open. Is so, hopefully no bent valve.

 

[stmike 1800]

At this point you have no choice but to remove the head .

 

[larryd]

Lively, You have some VERY knowledgeable and helpful members answering your posts after me...Just follow their advise...

The exhaust valves are the ones closest to where the exhaust pipes hook on the cylinder heads...

 

[JoshHefnerX]

Almost any modern engine is what's called an 'interference' engine whereby the piston and valves occupy the same space, hopefully not at the same time. So if the valve/piston timing is off by more than a couple of degrees it's very likely that they would collide. The result is the valve stem is bent. The bend causes it to lock up. The result is a bad valve, possibly head damage, in the guide and maybe seat area and usually some degree of piston damage.

As you've turned the engine over to get your compression readings the damage has already resulted. You are pretty much guaranteed at this point to need to remove the head and do a thorough inspection.

Please post pics when you do.

 

[Lively]

Managed to get the head off without removing the engine like it says to do in the Manual. Here are some pictures.



Is the piston savable? i see damage but can it be saved? it needs new rings thats for sure, gonna have to figure out how to install the rings, and seat the piston the the head. Never had to do that on a car when changing out head gaskets.

BTW I didnt notice the timing chain tensioner (small bolt like object) and i believe it FELL INTO THE ENGINE. gonna go buy a high powered bendable telescope magnet to make sure its out.

 

[Lively]

DONT CALL ME AN IDIOT! But i just realized i removed the cylinder too haha, let me go separate the two and see if i can see damages. On the bright side the rings didnt look good and now the will get replaced.

 

[Navydad]

Piston may be, probably is compromised. You are this far in so replace it. Check all the valves as well. This may seem like it's getting expensive, but cheaper to check all and replace now than to have to tear it down again.

 

[Freddy]

Good work Larry. Did you find the cause of the stuck valve? Bit hard to pin-point the cause from pix. A couple of the cam/valve buckets look to marked/damaged by the lobe so replace them. How do those lobes look? The piston can probably be used again but it needs a close inspection in the 'hit' area to ensue the ring grove is not deformed or cracked.

Reassembling the piston to the rod first is the usual process then sliding the barrel of it is the normal procedure. The taper at the bottom of the barrel allows the rings to compress but extreme care must be used to ensure that the oil rings (if they are 3 piece) do not get dislodged while doing so. An alternative procedure (which I adopt when possible) is to fit the piston to the barrel while both are in hand so you can see and feel that the oil rings are compressed and one has not folded over, then with the piston pin bore exposed at the bottom of the barrel fit the assembly to the rod with the pin, fit the 2nd pin clip and push the barrel into position. As for the cam tensioner, I gather you didn't remove it beforehand. Good luck with the job. :2thumbs:

 

[Freddy]

Is the scarred valve bucket the one with the bent valve? Curious. Valve clearance check & adjust is done with shims, just so you know - if you haven't encountered such previously.