Worried [about compression reading]

[Axel]

Machine: 2012 Super Tenere, about 35 k miles, I'm the second owner.
While changing air filter, I decided to have a look at the spark plugs, and with the plugs being removed, 'decided to check compression. Expecting to get readings up to 100 or more psi, I was disappointed in getting 64 on left and 74 on right. Isn't that too low? Shouldn't I be expecting higher pressure?
IF those triple-checked readings are abnormally low, what's the cause: rings? valves seats? (I haven't done the oil-in-the-cylinder test yet. BUT this is where I need thoughts...would valve gap (we used to call them tappets) affect compression? I'm thinking that worn lobes, arms, or shims on an overhead cam would allow valves to close tighter...or am I missing something?
It would be great to get thoughts from more Tenere-experienced folks than I am.
Thanks

 

[Jlq1969]

At starting speed it should give you around 100 psi….(at starting speed it suggests: engine Hot, decompressor activated, ignition key on, throttles butterfly completely closed when the engine is hot).. with 35k miles you should have already adjusted the valves at least once
If you leave only one spark plug, and test the compression by accelerating the engine, it will indicate much more than 100... (the decompressor is deactivated at higher rpm and when you open the butterflies, much more air enters to be compressed)

 

[Cycledude]

Is your gauge reliable ?

 

[thughes317]

The S10 has an automatic compression release, so those numbers are normal.....find something else to lay awake at night worrying about.

Were the valves checked at 26K? If not, make plans to get them checked soon. (That's just normal maintenance.)

 

[EricV]

Gen I Super Tens are known to sometimes build up carbon on the valves and seat too. @thughes317 had the answer, but it won't hurt to run some Yamaha Ring Free thru the bike for a few fuel tanks either. I used that on my '12 after the tech mentioned I had some build up when I got the 52k valve check/adj. It works to clean things up. Piston tops and valve train all looked much better later after running that as indicated on the label for a month.

 

[Tenforeplay]

For a compression test the throttle blades need to be open. Leak down test is my preferred method.

 

[Jlq1969]

The S10 has an automatic compression release, so those numbers are normal.....find something else to lay awake at night worrying about

Those numbers are not normal…normal would be around 100psi (with the decompressor running at cranking speed with the electric motor)…and 100psi is not normal for an engine with an 11,2:1 compression ratio (with that ratio should give a compression above 120psi as a minimum), so the 100 psi in the ss manual must be with the decompressors running.
At least from what we have seen in a video from a user who took the trouble to corroborate it, the butterflies do not respond to the hand accelerator "until the engine starts"

 

[Jlq1969]

Gen I Super Tens are known to sometimes build up carbon on the valves and seat too. @thughes317 had the answer, but it won't hurt to run some Yamaha Ring Free thru the bike for a few fuel tanks either. I used that on my '12 after the tech mentioned I had some build up when I got the 52k valve check/adj. It works to clean things up. Piston tops and valve train all looked much better later after running that as indicated on the label for a month.

You are right about the carbonization. But the Ss manual refers to carbonization as an “increase” in compression, rather than blaming carbonization for a loss of compression….although we know that it usually causes decompression as you say

 

[Checkswrecks]

Thread moved to appropriate power & exhaust sub-forum.

 

[Axel]

At starting speed it should give you around 100 psi….(at starting speed it suggests: engine Hot, decompressor activated, ignition key on, throttles butterfly completely closed when the engine is hot).. with 35k miles you should have already adjusted the valves at least once
If you leave only one spark plug, and test the compression by accelerating the engine, it will indicate much more than 100... (the decompressor is deactivated at higher rpm and when you open the butterflies, much more air enters to be compressed)

That's exactly the kind of information that I hoped to get. I learned a lot, there. Thanks, jlq!

 

[Axel]

Is your gauge reliable ?

Yes...double checked that. Good question. Thanks.

 

[Axel]

Those numbers are not normal…normal would be around 100psi (with the decompressor running at cranking speed with the electric motor)…and 100psi is not normal for an engine with an 11,2:1 compression ratio (with that ratio should give a compression above 120psi as a minimum), so the 100 psi in the ss manual must be with the decompressors running.
At least from what we have seen in a video from a user who took the trouble to corroborate it, the butterflies do not respond to the hand accelerator "until the engine starts"

Those numbers are not normal…normal would be around 100psi (with the decompressor running at cranking speed with the electric motor)…and 100psi is not normal for an engine with an 11,2:1 compression ratio (with that ratio should give a compression above 120psi as a minimum), so the 100 psi in the ss manual must be with the decompressors running.
At least from what we have seen in a video from a user who took the trouble to corroborate it, the butterflies do not respond to the hand accelerator "until the engine starts"

Thanks for the great help. I came to the right place for counseling.

 

[Jlq1969]

Thanks for the great help. I came to the right place for counseling.

If it doesn't consume oil, if you don't have oil-wet spark plugs or an exhaust with oil moisture, don't worry about the compression measurement. But with 35k miles without adjusting the valves (unless the previous owner did it), you surely have some exhaust valve near the lower range...that would be the urgent thing now. And if the mechanic is not your friend, don't mention the compression thing...

 

[Axel]

The S10 has an automatic compression release, so those numbers are normal.....find something else to lay awake at night worrying about.

Were the valves checked at 26K? If not, make plans to get them checked soon. (That's just normal maintenance.)

Didn't know about the auto decompressor....duh. (My '80 xs650 never gave it a thought). 'Appreciate the info.
'On my way to doing my first valve check.
Big thanks, there.

 

[Axel]

Perfect!

 

[Axel]

For a compression test the throttle blades need to be open. Leak down test is my preferred method.

Points taken!

 

[Sierra1]

I wonder if Steve, eemsreno, worries about his compression. His bike only has 300K miles though.