Compression Test Mis-Information

[v4andy]

My Yamaha manual lists compression test results in the "Periodic Maint." section should be "Standard 142- Minimum 128- Maximum 171" But in the back of the manual it lists compression pressure as 206. But my clymers says medium is about 200. My bike is a 2001. Also what are the valve lash values on the sticker under the air box cover? They list numbers much higher than the valve clearance in the manual.

 

[sdt354]

I'm at 180 all around on my 89, on the last check. I think 150 and above is ok. I think Dave Specialops was getting quite a bit higher than 200 psi,but may have some internal mods. Equall is important. Compression readings can be artificially inflated from carbon build up too.
The valve clearance sticker? If 89 had one, it's long gone. I use the specs from the Yamaha service manual. I think they're written on the wall in my shed.
Steve-o

 

[Rusty McNeil]

When stock my 99 was around 175-180

Equal is what your looking for as previously stated.

How you do the test matters if you care about the actual number. Numbers of compression cycles etc. I've never been real clear on what's proper if your going after the number in the book.

 

[Rusty McNeil]

Google compression test and add a "Car Craft" tag and you should get a good write up.

Same goes for leak down testing.

 

[Rusty McNeil]

And after reading up a bit the proper method for compression test is; if I comprehend what I read,

Engine warmed up

As many strokes as it takes to get the max number, usually between 5-8

Same number of strokes for every cylinder after doing the first one.

Don't cheat the test with oil on the cylinder, that's to be done afterwards to determine whether its a ring problem or a valve problem.

 

[maleko89]

Make sure throttle is wide open.

 

[06VMAXIMUS]

Make sure throttle is wide open.

+1, and you should ground out the spark plugs too.

 

[johnpclynch]

The valve in my POS compression tester gives me a false reading. with the air valve in the tester will hold at about 80-100 psi after 6 strokes, when I take it out the meter will flick up to 120-130psi and back again on each stroke

 

[v4andy]

i am fairly experienced with compression tests having done hundreds over the years. i was inquiring about the different values in different publications. mine are between 172 and 180 but if all 4 were low i would start to question the way the motor was treated before me.