......compression test

[Brook]

........ I just bought a compression gauge, the directions are for a V8, .... what is the right procedure??
.. Should the other three plugs be in or out??
.. By not having the spark plug wires connected, is that good enough??
.. do I need to do anything with the throttle??
.. I know all four cylinders, should be close to each other, What should a good # be??
.. 1219cc, wiseco pistons, five angle valve job, 10.000s shaved off the head.

                            Thanks, Jeff

[Harvy]

Jeff....... all plugs out.......throttle wide open.
Sorry mate......... someone else will have to tell you what the pressure should be (but they should all be within a bulls roar of each other).

Harvy

[VMS]

I believe factory cranking compression was around 170-172. What your numbers are will depend on many other factors;cam timing/degreeing, valve lash, warm or cold, stock  or mod cams, age of rebuild, etc.
Scientific wild ass guess, you would be in the mid to high 180's with some miles on it, but there are too many variables. I've had a stock 1188 rebuild in the 190's.
Just like Harvy said...something about roaring bulls  

[andyb]

.. I know all four cylinders, should be close to each other, What should a good # be??
.. 1219cc, wiseco pistons, five angle valve job, 10.000s shaved off the head.

Kinda depends on where the cams are, more than anything else....

[VMS]

Valve adjustment can have a big effect on cranking compression. I had one that was 180-180-181-180 and was able to get it down to 166-168-167-169 just by adjusting the valves (did not have slotted cam gears in it) and it still ran strong

[SlowOldGuy]

Valve adjustment can have a big effect on cranking compression. I had one that was 180-180-181-180 and was able to get it down to 166-168-167-169 just by adjusting the valves (did not have slotted cam gears in it) and it still ran strong

I thought if you pumped over 160 they would DQ you?  Has that rule changed?

DavidR.

[VMS]

The rule dropped cranking compression from 180 down to 165, luckily I didnt have to worry about that back then, only top 5 in the A main were pumped at random, and I didn't have that problem of running in the front!
Of course everything is legal now 

[Mike 86 in San Dimas]

Recently had a local shop with good rep (works on many of the local sport bikes) do a compression check and valve adjustment for me. If you recall I just got my bike back on the road after a nine year nap. It runs well.  If I let sit for over a week or sobut will smoke some at start up. All things considered  I considered this "normal". Anyway he reported that valves were with in spec and did not need adjustments. The compression was between 125 and 135 PSI at 50 degree F ambient temp. He did not recommend any work at this time. My bike is stock. 51K miles. I was ready to go ahead with some work, valve seals or rings. Do those numbers seem Ok to you guys? 

Mike

[VMS]

I assume he did a leak down test also? Personally, in a road bike application I wouldnt worry about it. Warmed up you're probably in the 150's. You can always spend money, but do you need to?
I'd say "no"

[Mike 86 in San Dimas]

Cool. I felt good about the mechanics opinion, and better he was not trying to do build up a tab of work not really required. So I had him replace the clutch. Great improvement there.
Thanks for the reply,
Mike