Wired compression test

[uri gal]

Wired compression test

Hello all, I a few days ago I got my new vmax from USA

This is a 1985 vmax with 18,800 miles

I perform a compassion test and got reading that I do not understand:

The two rear cylinder (number 1 and 3) had both a 196 psi
while the front cylinders (2 and 4 ) got both 176 psi

In the Haines book:
standard – 142 psi
max 171 psi
min 128 psi
and max difference between cylinders 14psi

before 100 miles the bike got a full service that include valve clearance (in the USA)
the bike equipped </SPAN>with drilled cobra exhaust
and that’s it.

how the two reading is more than the max PSI that should have?
How I have a big difference between front and rear cylinders?
How the reading is so symmetric, I could have four diffents reading, but not, I got this 196,196,176,176
:worthy::worthy::worthy::worthy::ummm:

Any ideas ?

Thanks

Uri

 

[Fire-medic]

Did you do it? Did you have the throttle held wide open when you cranked it? Generally speaking the values should be within 5%-10% of each other. I would try doing it again and see if you repeat the values. usually valve clearances are set in the middle of the values range, too-loose is better than too-tight, but following the procedure listed in the factory service manual or aftermarket service manual should work. If the heads have been milled then the timing marks are not the same values as stock for setting the valves.

 

[uri gal]

yes I did the test myself
and yes I did throttle wide open when I cranked it - cold engine

so what is the meaning of all that ?

 

[thor_eyerdhal]

Do it warm...

 

[Fire-medic]

Checking the valve clearances shouldn't cost you anything but time, unless the gaskets rip because they're old, but if they're fresh, you should be able to re-use them. Then re-test for the compression check and compare the results to your first attempt.