Cranking outboard on the stand

[fmjnax]

I’m getting ready to start another old bass boat restoration. Picked it for $100 out of some country folks land where it had sat for 4 years. Before I get overly invested, I need to make sure the engine is good. It is a 1987 Johnson 90 (VRO bypassed). It was clearly winterized before it was parked so I have high hopes that it is still good. The lower unit was still full. No metal shavings or water in it. Shifts and turns freely. Needs a new water pump for sure. Carbs have been taken down, cleaned, and rebuilt. Needs new fuel lines, of course. Pulled the plugs and they looked ok. Cylinders and piston looked ok from what i could see through the plug holes. Water passages seem to be unobstructed. Flywheel turns freely. So next step is to check compression, which is where my question comes in.

The previous owner couldn’t locate the key. I have already taken the outboard off of the boat. I need to crank the engine but I’m not sure how to do it. I’ve read to jump the solenoid but I have also read to pull rectifier wires and power pack wires. What are the proper steps to crank without the controls?

 

[Joe Reeves]

A small jumper from the battery cable terminal of the starter solenoid to the small 3/8" nut terminal of the solenoid (NOT the ground 3/8" nut terminal!) will engage the electric starter.

The ignition is self powered, meaning that the ignition will fire when the main electrical harness is disconnected at the large RED plug, so have "ALL" of the spark plugs removed... Best to ground the spark plug wires so that a spark does not ignite whatever fuel might shoot out of the cylinders.

The spark igniting fuel shooting out of the cylinders?... Been there, Done that, Very exciting!

 

[F_R]

Been there, done that too. Dang lucky I wasn't standing in the way or I'd have gone up in a ball of fire.

 

[Joe Reeves]

Been there, done that too. Dang lucky I wasn't standing in the way or I'd have gone up in a ball of fire.

Damn!... Where's that guitar when I need it?

 

[fmjnax]

LOL! Thanks Joe and F_R. Luckily I'm no stranger to pulling compression (just never had to do it via jumper). I made sure there was no fuel left in the engine (and when the PO winterized it, they disconnected all fuel lines). Of course, all plugs were removed and the disconnected wires/boots were shielded. Carbs are still sitting on the workbench.

Jumping the solenoid/starter was a piece of cake. Engine cranked with authority! Readings were 78-75-76-78, so well within 10% of each other. I'm not used to seeing psi's that low, though, so I put some 2-cycle oil in each of the cylinders and rotated the flywheel to coat. Second readings were 80-78-78-90, so a bit higher and slightly out of tolerance. I'm going to let the oil soak for a while and take some more readings later.

Overall, I think the engine is good. I know having tight tolerances between all cylinders is more important than a higher number, but what SHOULD I be seeing on this engine? I might need to fog it or get some ring free and see if compression comes up some more. Thoughts/suggestions?

 

[racerone]

Those numbers are not encouraging.----Test with another gauge.

 

[Joe Reeves]

PSI readings are too low.... faulty gauge??..... Slow cranking engine??

 

[fmjnax]

I only have the one gauge, but it should be fine. It's only been used a half-dozen times and stored in its hard case in the shop. Of course, that doesn't mean it's not faulty or out of calibration. Next time I have to run to town, I'll see if I can borrow one from the auto parts store for comparison.

Thinking maybe it was a slow crank, I took the battery (it's a generic marine/RV dual purpose - 550CCA) to the charger. It was about 12.36V, so needed a charge. Charged it back up to 12.6+V. Meanwhile, I pulled the starter off and disassembled it for inspection. Didn't look bad at all. Brushes had plenty of life left in them. Cleaned up the commutator, armature, magnets/case, brushes, and connections. Applied some light oil to the bendex drive. Reinstalled the starter and took out the fully charged battery. Compression on all 4 cylinders is now right at 95psi (+/- 1 due to analog gauge reading). I ran two checks just to make sure; one by jumping the solenoid and one by applying the battery directly to the starter. Same results both ways.

I already know you guys are going to say that's still too low so I decided to go ahead and pull the heads (I needed to get a better look at the water passages anyway). Even after using PB Blaster and Liquid Wrench, I sheared off about half of the cover bolt heads. Seeing all the white corrosion had me bracing for the worse when I pulled the heads. I was pleasantly surprised to see good cylinders and pistons. Not a single gouge in any of the 4 cylinder walls. Nice a smooth. No pitting or rusting. Pistons are not malformed. No sign of broken rings. No binding. Absolutely nothing that would look to me like a blown (or about to be blown) engine. Nothing sticks out to me to scrap the motor or tear it down for a full rebuild. So maybe my compression gauge just reads low.

Once I figure out what to do about the broken head bolts (I may decide to just buy new heads/covers) and get that taken care of, I'll see if I can borrow another gauge and see if my reading are any different.