compression check

[Thumpbass]

could some one post a step by step method of doing a compression check on a '79 100hp Johnson. Looks easy enough but I guess there's always a way to "fry" something when you're a "newbie" like me....I'm just good enough with tools to break stuff. :}

Thanks!

 

[MASTER Brian]

Re: compression check

I think there are instructions on the FAQ's pages somewhere, but if not...

Pull all plugs, put back into boots and ground them to block. (or use a spark tester instead) Insert the compression guage into one plug hole, open the throttle up, turn key and let the engine turn over several turns. Note reading on gauge and repeat for all cylinders.

My understanding is grounding of plugs is essential to ensure you don't fry a coil or other electrical component. If you can lay the plugs on the block, so they won't move, that's fine. Otherwise they need to be held there, wich would require a seperate set of hands or you can make/buy a spark tester. O'reiley's sells individual ones for about $5 appiece. You put the plug boot over the end on the tester, then clamp it to the block.

You might also unhook the lanyard, which may kill the spark, if your boat is equiped. You want to ensure the plugs aren't over the plug holes, so the boat won't try to start.

 

[Walker]

Re: compression check

If your control box hsa a safety lanyard all you have to do is pull the lanyard to kill the spark. If it doesn't have one then just jump the starter at the solenoid. Those 2 ways eliminate the problem of having to graound the plugs.

 

[Silvertip]

Re: compression check

If you use a compression tester with a threaded adapter, make sure you use the short one. If you use a long adapter the piston may hit it and as you might guess, that's not a good thing.

 

[rickdb1boat]

Re: compression check

No need to crank the adapter all the way in tight. It will read just fine if you thread it in the length of the spark plug threads or less....

 

[Thumpbass]

Re: compression check

would disconecting the stator/charge coil plugs from the power packs do the same thing as far as protecting the power packs from getting fried?

 

[wilde1j]

Re: compression check

Just pull the safety stop lanyard ... no spark and nothing to hurt and nothing else to disconnect.

 

[Thumpbass]

Re: compression check

the reason I asked about the charge coils being disconnected from the power packs is because my manual says to disconect them when checking compression...was just curious as to if it was the same reason you might pull the lanyard (kill spark).

the manual doesn't give instructions as to how to check the compression with a guage (unless I have just completely over looked it)...it basically says to crank it with the rope to feel if the compression (or lack there of) is suspect.

I'm no electrician or marine mechanic but from what I gather from reading the manual, the charge coil sends current to a capacitor in the power pack and the charge stored in the capacitor is realesed to the ignition coil...so my assesment is that no charge in the capcitor equals no spark but like I said...I know just enough to start tearing stuff up:%

thanks for all the help guys!

 

[F_R]

Re: compression check

Sounds like your manual has a slight credibility problem. I'd burn it.

 

[i386]

Re: compression check

If you use a compression tester with a threaded adapter, make sure you use the short one. If you use a long adapter the piston may hit it and as you might guess, that's not a good thing.

Words to live by.

 

[KYHunter2]

Re: compression check

I dont know , how much you'll learn from feeling the compression, when pulling rope.

A compression guage , will stay at the highest point, during series of pulls.

Then reset for each cylinder.

KYHunter