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40EL75 delemma

oldrem

New member
Before I spend too much on parts, I was hoping to get a compression reading on the cylinders. I replaced a bad neutral safety switch, but found the solenoid to also fail testing. I first tried to compression test by using a rope to manually crank the engine, but this old fart can't pull fast enough to get a reading over 60 psi.

I tried running jumper cables directly from the battery to the starter, but can't even get it spinning as fast as I did with the rope.

The battery is a 6 month old 625 crank amp marine battery with full charge.

Next, I yanked the starter and ran it on the bench. It runs full bore like it should, though I know it's not load testing.

I'm figuring my next step is taking the battery to get a load test. If that passes, where go I go from here? I was hoping to not invest in a starter unless I know compression is good. Catch 22?
 
Have you checked ALL your battery cable connections for being clean and tight ??

I was using a direct connection from the battery to the starter using some old jumper cables. I did wire brush and file the cable clamps, but will admit those cables are about 40 years old. Probably time to pick up some new cables and try again?
 
Pull the gearbox and see if it spins any easier. You can run it for short spurts just don’t let it get hot. 70psi on both cyls pulling by hand is a good sign tho. You almost certain need a new impeller anyways?
 
OK, here's where I'm at.

1) had battery tested at O'Reilly and told it was good
2) picked up new set of solid copper 4ga cables
3) thoroughly cleaned all contacts and applied light coat of Noalox
4) applied light coat of white lithium grease to the gears
5) reinstalled starter motor
6) applied power and it spins beautifully
7) ran compression tests

I'm not looking for great speed from this motor. Can I get by with compression readings of 88 and 89? (at least both were consistent), assuming my cheap compression tester is accurate.

I tested the coils and both tested bad. Lord knows how much more I'll be finding as I go, but want a decent running motor when I'm done.
 
Test your lawn mower for compression it could be the gauge or possibly a head gasket leaking between cylinders. Disconnect the yellow blac stripe wire from the power pack and see if you get spark? It should jump a open air gap of at least 7/16 inch with a spark gap tester.
 
I assumed it has the CD type ignition it looks like it has breaker points. If so you need to isolate the two black kill wires and then check for spark?
 
Haven't even tried for spark yet, little time to work on it. I did borrow a much better known good compression tester, which showed compression at 110 and 111, so I'm feeling much better there. I took the cheap one from HF back.

I bench tested the coils. One dead and one marginal, so have two news ones coming. Before I even try, I'm replacing the coils and points as well. I picked up new head and cover gaskets, so will also be pulling the head to clean the carbon from the cylinders as well as resurfacing the head and inspect cylinders, water channels etc.

Looking like a long cold winter here, so no reason to rush anything.
 
You have a simple / rugged / reliable / easy to fix motor.------I see expensive gear / lower unit failures on newer 40 hp motors that simply do not happen on a 1975 model.
 
What are your thoughts on the newer impeller full kit vs replacing just the old impeller with a NOS. I don't mind spending a little extra if it's going to make for a better motor.
 
Any pump kit with a stainless liner is an improvement over the original.----In freshwater you will only need to install a new impeller every 2 years !
 
Thank you. Made my decision easy, plus I like the fact that they're still showing as a current item on OMC's site so parts should be available longer.
 
While I have the carb off to rebuild it, do you guys recommend pulling the intake manifold assembly apart before reinstalling it? Do they usually need service? (more gaskets to buy)
 
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