Triumph Rat Motorcycle Forums banner

1 - 7 of 7 Posts

·
Registered
Joined
·
57 Posts
Discussion Starter #1
Anyone know what values you have got or should be getting from a compression test on a 1996 speed triple?
Mine are 135 , 130ish , and 140 from left to right. Hows that sound.
 

·
Premium Member
Joined
·
16,670 Posts
I don't know a whole lot about compression tests, but I do know that the cylinders being close to one another is more important than absolute numbers so you're good there at least. Perhaps after I finish my very late dinner I'll wander over to the bookshelf and see if the FSM has anything to say about it...

Cheers,
-Kit
 

·
Premium Member
Joined
·
16,670 Posts
No pressure specified in the service manual.

Cheers,
-Kit
 

·
Registered
Joined
·
232 Posts
Anyone know what values you have got or should be getting from a compression test on a 1996 speed triple?
Mine are 135 , 130ish , and 140 from left to right. Hows that sound.
Important to do the test on both a cold and hot engine, but those figures look OK. As Kit said its more about them being similar. If there is a problem one of them is usually way out e.g. 135, 95, 140, so the bad news is easy to spot
 

·
Premium Member
Joined
·
134 Posts
If I read this right compression ratio for your bike is the same as mine @ 10.6 to 1
and 1 being atmopheric pressure then you should get around...

10.6 X 14.7=155.82psi or Kpa being 101.4 X 10.6= 1074.84Kpa

It's not exact but it should give you a ball park figure.
Squirt a little oil into each cylinder and make sure throttle is fully open.
Do another test.
 

·
Premium Member
Joined
·
6,462 Posts
If I read this right compression ratio for your bike is the same as mine @ 10.6 to 1
and 1 being atmopheric pressure then you should get around...

10.6 X 14.7=155.82psi or Kpa being 101.4 X 10.6= 1074.84Kpa

It's not exact but it should give you a ball park figure.
Squirt a little oil into each cylinder and make sure throttle is fully open.
Do another test.
I'm no expert on this, but there's a flaw in calculating real or effective compression in this way that I've read about.

The 10.6:1 & all published comp ratios AFAIK are stated based simply on cyl volume at BDC & volume at TDC. So far so good, but in most engines the inlet valve is still open at BDC - on these T3s with 'green' cams, it doesn't close until 50 deg after BDC.

Of course at normal engine running speeds a number of other factors are in play to determine actual cylinder filling with mixture.

But at the low cranking speeds of a compression test, I believe that there will be significant leakage back out the inlet valve as the piston initially rises from BDC to TDC with the inlet valve open. Hence the compression measured in this way will always be lower than the published figure.

With my limited knowledge on this, to me, what others have said about the numbers being very close across all cylinders (& not too low) suggesting all is well seems the right interpretation.

I guess this suggests the OP's oil burn/blue smoke issue (from another thread) has to be the valve stem seals - maybe from being a bit dry &/or hot from a low oil situation?
 
1 - 7 of 7 Posts
Top