compression check procedure

[tschamp20]

can someone please post the proper procedure for doing a compression check.thank you

 

[OBJ]

Re: compression check procedure

Moving to Outboard Discussion Forum.

 

[phatmanmike]

Re: compression check procedure

wow, obj......now they got ya working?!@?!?!?!?

anyways, remove all sparkplugs and ground the plug wires to the block somewhere. insert comp guage in plug hole, turn motor over either by hand or by starter if equiped. make sure to do all holes the same amount of time. usually only 1 second or so is needed. maybe 2

 

[canadian_fisher]

Re: compression check procedure

As an add-on to Phatmanmike.....

If you have a Kill-switch, use it to protect your "expensive" ignition system.
This is effectively the same as "grounding" the igntion. Also, you don't want any spark where there's open-air fuel.

Kill switch is usually right beside the Ignition switch.

Good Luck......... CF

 

[Bob_VT]

Re: compression check procedure

You should be holding the throttle plate wide open for a true reading.

 

[canadian_fisher]

Re: compression check procedure

Bob_VT.

I have alwasy done Compress test w/o the WOT setting. Can you explain how it might affect readings versus leaving throttle closed (neutral) ?

Curious..... CF

 

[Silvertip]

Re: compression check procedure

WOT is necessary for four strokes. It is not necessary on two strokes. There will be little if any difference in readings at cranking speeds..

 

[jtexas]

Re: compression check procedure

With engine at operating temp, or does that matter?

 

[Silvertip]

Re: compression check procedure

Do both. The closer the hot/cold readings the better. Low cold readings and higher hot readings would indicate coking has occurred and a thorough decarbon job is in order. Do a search on decarb - its been discussed here numerous times.

 

[SeaKaye12]

Re: compression check procedure

Can someone discuss the grounding thing further? I've never grounded the wires...I just move them out of the way on my Merc 850 (no distributor)

Which engines are sensitive to needing grounding? What happens if you don't?

Now that I think about it though...I've always tripped the starter solenoid at the engine to get cranking...so I suppose the ignition was not activated anyway.

More info would be appreciated.

Thanks, Chuck

 

[jtexas]

Re: compression check procedure

seakaye, the "ignition" referred to here is the system that generates the voltage required to fire the spark plug and ignite the charge inside the cylinder. Ignition coils generate very high voltage, and with no path for current to flow, you can get a high voltage spike that causes all kinds of damage.

On OMC motors, the kill switch grounds the ignition wire, so pulling the emergency lanyard does the trick...not sure about Mercs.

 

[tschamp20]

Re: compression check procedure

what about controls w/o kill switch?i hope i did this right but i disconnected the #1 black/yellow wire from the power pack which comes from the ignition switch.if not what would be my proper proceedure?thanks

 

[jtexas]

Re: compression check procedure

Connect the black/yellow wire from the pp to ground.

 

[VADER8674]

Re: compression check procedure

good to know