How to check compression

A

Aka Kane

X-H2
I have the compression gauge and the right attachments. My question is about where to put the cables when I put the gauge in one cylinder and turn the motor over. If I remember correctly I am supposed to only remove one cable from the plug and put it on a headbolt. Leave the other one attached to the spark plug and turn it over. Then repeat for the other one. There is a cover and I do not see how to attach the cable to a head bolt. Could someone tell me the easiest way to do this. I dont want to short something out and cause myself another problem
 
A

Aka Kane

X-H2
Also I have not started, or turned the motor over in awhile, its been sitting for winter, so should I do anything to it?
 
Sanford

Sanford

ECF
Location
Freeride capital of the world
1) Run motor until cylinder is barely warm then shut off. Clear motor if filled with fogging oil because it will give you a false (higher) reading.

2) Pull plugs/wires and insert plugs into the loose plug wires and let plugs touch an exposed metal part on motor (both plugs).

3) Turn gas to OFF

4) Screw gauge adapter into cylinder

5) Hold throttle @ WOT

6) Hit start button and don't let off until gauge doesn't move any higher.

7) Release pressure valve and repeat #6 a couple times, average that value.

8) Repeat process from #4 for next cylinder.

FWIW: I never had a problem by not grounding the plug wires. I sometimes hold the STOP button while cranking and this kills spark but not starter.
 
Last edited:
D

Don 79 TA

Still Fat....
Location
Madision/Huntsville AL
a Q:
do you remove both plugs so one cyl is open while gauge is in the other?

i've dont it both it ways, plugged and open
and i didn't see a difference
i've done this on numerous motors too

all i know is the Snap-On gauge is probably the best one to use.
i'll never trust a craftsman or sun-pro again (on anything past 170psi)
 
Boris

Boris

The Good Old Days
Location
The surf-less coast
Sanford said:
1) Run motor until cylinder is barely warm then shut off. Clear motor if filled with fogging oil because it will give you a false (higher) reading.

2) Pull plugs/wires and insert plugs into the loose plug wires and let plugs touch an exposed metal part on motor (both plugs).

3) Turn gas to OFF

4) Screw gauge adapter into cylinder

5) Hold throttle @ WOT

6) Hit start button and don't let off until gauge doesn't move any higher.

7) Release pressure valve and repeat #6 a couple times, average that value.

8) Repeat process from #4 for next cylinder.

FWIW: I never had a problem by not grounding the plug wires. I sometimes hold the STOP button while cranking and this kills spark but not starter.
Click to expand...

9) Make sure you have a fully charged battery.:biggthumpup:
 
Sanford

Sanford

ECF
Location
Freeride capital of the world
Don 79 TA said:
a Q:
do you remove both plugs so one cyl is open while gauge is in the other?

all i know is the Snap-On gauge is probably the best one to use.
i'll never trust a craftsman or sun-pro again (on anything past 170psi)
Click to expand...

Having the other plug in the non-tested cylinder doesn't technically cause a faulty reading. However, having the non tested cylinder plug removed helps with cranking speed and doesn't tax the battery/starter as much.

On your comment on Snap-On being the best gauge, I say that is complete hype. I've tested my motor with 5 different gauges that ranged anywhere from 175psi to 215psi. A cheap Sears gauge showed 195psi while the Snap-On read 215psi. In order to eliminate erroneous readings from all these gauges I bought a "lab" quality 4.5" gauge rated at 1% full-sweep (most are rated at 5% half-sweep). The lab gauge read 185psi! Obviously a faulty gauge is just that, but don't believe the hype.

Also, what Boris said is very true. If you don't have a fully charged battery, the motor can't spin fast enough to give good results. Especially the Yamaha since the cranking speed of the starter is very low to begin with (because of bendix).
 
A

Aka Kane

X-H2
Well guys, I am getting really pissed off here. I went to test it yesterday and now the thing will not turn offer. I think its the starter because it trys to spin, and I can hear it, but it goes for just one second. I am going to remove the plugs, and see if less compression makes it spin more, and see if I can feel air coming from the plug holes.
 
DaUpJetSkier

DaUpJetSkier

I like square
Location
Marquette, MI
youll know if the motor is turning over, you should hear it. Check the battery, and pull the flywheel cover to see if the bendix engages onto the flywheel.
 
A

Aka Kane

X-H2
Yay I need a new starter,

If the bendix was not engaging then the motor would not spin right? I can look in the holes and see the piston moving up and down, and get a gush of air. When I took the plugs out and hit the starter they actually make a full rotation and stop. When the plus are in they bairly move. I have to guess that this is because of a weak starter. My battery is fully charged, but maybe it could be just totally bad right? Would it be ok for me to take a batter out of our ATV and test the FX1 with it?
 
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