1968 40hp Erude - compression test.

[jai070404]

My motor was purchased having sat idle for at least 9 years so I am not ready yet to attempt firing. I would like to know if I can do a compression check without forward controls. Can it be done with the bottom unit removed? There seems no point in continuing down the current path if I am going to find serious commpression / piston/ring problems further down the track. Thanks.

 

[DJ]

Re: 1968 40hp Erude - compression test.

Yes you can.<br /><br />Just make sure the ignition is disabled. Open the throttle to wide open and have at it.<br /><br />I believe I would squirt some WD-40 down the plug holes before I did it though.

 

[jai070404]

Re: 1968 40hp Erude - compression test.

Sorry, I need more information. Do I make the starter "live" in order to turn the flywheel for an accurate compression test?

 

[G DANE]

Re: 1968 40hp Erude - compression test.

Yes, just make a jumper between the battery terminal and start terminal on the starter solenoid. Since this has a point and condenser ignition, you dont have to worry much about that, just leave both plugs out. Let it cranck for at least 4-5 turns on each, with a good squirt of WD-40 in each hole as John suggested.

 

[jai070404]

Re: 1968 40hp Erude - compression test.

I have hooked up the negative lead to earth on the motor, I then hooked up the positive lead to the right hand terminal of the starter solenoid (the one with a lead going to the starter). The starter spins fast but the top does not pop up and engage the fly wheel. If I hook up the positive lead to the left side of the solenoid nothing happens. What am I doing wrong? Thanks.

 

[jai070404]

Re: 1968 40hp Erude - compression test.

I have tried this again. Starter motor spins no problem but still no engagement with the fly wheel.

 

[hkellogg]

Re: 1968 40hp Erude - compression test.

seems the starter is not fully engaging, are you holding the connection long enough for it to engage ?

 

[rickdb1boat]

Re: 1968 40hp Erude - compression test.

Shoot some WD-40 on the starter gear and make sure the battery is fully charged... Make sure you are jumping to the large bolt on the starter

 

[blgrams]

Re: 1968 40hp Erude - compression test.

lube the shaftinside the gear that is supposed to move upwards to engage the fly wheel. work it up and down untill it slides freely it must be twisted when moving it and it only twists one way up and the opposite way on the way down, if it already slides freely the torsion spring inside the gear is probably bad.

 

[blgrams]

Re: 1968 40hp Erude - compression test.

one more thing I forgot DON'T get too AGGRESSIVE with the WD40 or what ever oil you use. if you get oil on the windings of the starter motor it will eventually fry.

 

[jai070404]

Re: 1968 40hp Erude - compression test.

Thanks guys you are the best. The WD40 loosened it up and she spun for the first time in at least 9 years. The compression results were : top cylinder -115, bottom cylinder 117.5. Are these figures OK? I'm hoping I don't have to remove the head. Thanks.

 

[G DANE]

Re: 1968 40hp Erude - compression test.

You dont have to remove head, that compression is VERY VERY fine, must have low hours or been rebuilt.

 

[hkellogg]

Re: 1968 40hp Erude - compression test.

those compression readings are good, here is a rule of thumb when doing compression tests minimum amount of pressure should be 100# and each cylinder should be within 15# of each of each other just for your future reference but it sounds like you are now ready to start that engine up

 

[jai070404]

Re: 1968 40hp Erude - compression test.

Well first I will have to finish adding the new impeller and water pump housing. Then redrill a couple of new threads in the lower unit before I reattach it. Of course I have a number of wires that need replacement and I now have the flywheel off to update the coils and points while my carby is being rebuilt. I don't like the look of the old fuel line and I'm thinking about removing the engine so I can respray the exterior shell. But at least I now know I am not wasting my time, effort, and money.