Johnson 1956 15hp Flywheel Jammed! After turning fine with good compression!

[bonito1]

In my ongoing rehab project on my 1956 15hp I have run into a big snag. Engine was turning over fine with good compression and some spark. I moved on to reattach the hood cowl, etc., then tried pulling the recoil starter again and it was JAMMED! Would not budge one iota. I removed the recoil starter and tried turning flywheel again-jammed. Prop turns but not the flywheel.

Someone suggested it is the nuetral lockout/linkage problem but I can not see where or how a nuetral lockout is or works. Any ideas?

Thanks, Bill

 

[Joe Reeves]

Re: Johnson 1956 15hp Flywheel Jammed! After turning fine with good compression!

With the manual starter removed, there is nothing to prevent the flywheel from turning.

Are you saying that the engine turned over good during a compression and spark check and then within minutes locked up solid? What else might you have done between the comp/spark test and installing the hood?

You're missing mentioning a operation there.... installing the spark plugs. Did you by any chance install the wrong plugs and they're hitting a piston?

If you don't find the cause of the problem, remove the lower unit to determine if the lockup problem is with the powerhead or the lower unit.

 

[bonito1]

Re: Johnson 1956 15hp Flywheel Jammed! After turning fine with good compression!

It is pretty much like you say. It was within 1/2 hour of a positive compression test, and mediocre spark test. Both of which required turning the engine over several times with no troubles. I did reinstall plugs and they were new (but they were also alternately in during the compression test), I replaced the hood cowl (in the process knocking the gear shift lever in and out of gear), and I removed and reinstalled the lower unit drain/fill plugs to check for old lube/signs of trouble. Finally, I lubed up the throttle assembly and worked it back and forth several times.

If I can not find the problem. Can anyone point me to good information on removing/reinstalling the lower unit as suggested?

Thanks, Bill

 

[ONERCBOATER]

Re: Johnson 1956 15hp Flywheel Jammed! After turning fine with good compression!

I would suggest removing both spark plugs and seeing if that changes anything... I know it sounds dumb, but easy check.
then I would say remove lower unit and see if that "fixes" things...

Sean

 

[bonito1]

Re: Johnson 1956 15hp Flywheel Jammed! After turning fine with good compression!

UNBELEIVABLE! You guys were right. Spark plug was too long. I asked for two plugs to replace Champion J8 and I was handed two. Didn't even look closely to insure both were right-one was not! I must have swapped that one plug back and forth while doing the compression test- Boy oh Boy! Thank you for the simple fix suggestion!

I just ordered new ignition wires, points, coils and condensers, water pump impeller and carb kit. I hope to get her in the water as soon as those are in. Before that, I am sure I'll be back here for more help...

Thanks again, Bill

 

[Chinewalker]

Re: Johnson 1956 15hp Flywheel Jammed! After turning fine with good compression!

Install a set of Champ J6Cs...

 

[ONERCBOATER]

Re: Johnson 1956 15hp Flywheel Jammed! After turning fine with good compression!

Glad it was an easy fix.... sounded right to me as well, Chinewalker is very exp.... his suggestion for the plug will likely please you as well.

Sean

 

[Joe Reeves]

Re: Johnson 1956 15hp Flywheel Jammed! After turning fine with good compression!

J8 plugs? Do not use those plugs unless you would like to melt a piston or two. Use either Champion J4C or J6C plugs, gapped at .030 .

 

[1946Zephyr]

Re: Johnson 1956 15hp Flywheel Jammed! After turning fine with good compression!

Yep, certain brands of spark plugs will do that, eventhough they made a crossreferenced size to match the Champion J6C. The NJK comparrison was notorious for getting slammed shut by the pistons, but after some years they decided to correct that and shortened the shank. I try to only stick with Champions in OMC outboards, because that is what the factory designed them with. I recemend the J6C for that motor. J4C as far as I'm concerned is good for nothing, but a fishing weight. I have found that a lot of motors under perform with those.

Oh yea, one more thing. Make darned sure that the plugs you take out, have everything there. You don't want any small chunks of your bad plugs bouncing around in your combustion chamber. That would shorten the life of your gem, rather quickly.

 

[bonito1]

Re: Johnson 1956 15hp Flywheel Jammed! After turning fine with good compression!

Great suggestions everyone...

I am a bit uneasy note regarding the comment on the J8's. Between that and another post thread I saw on my same motor I'm wondering if it would be worth it to tear this beaut down further than I had. Just in order to really check on things. I don't want to get her all fired up just to have a melt down in a month!

Heading to the garage to lube up lower unit, prop, etc. See you all soon!

 

[Joe Reeves]

Re: Johnson 1956 15hp Flywheel Jammed! After turning fine with good compression!

You can either purchase a inspection light.... small light on the end of a flexiible wand that you can insert into the plug hole with the piston in the down position, OR remove the cylinder head. I wouldn't go beyond either test mode unless you find a piston that's started to melt down.... and I think that highly unlikely.

 

[Chinewalker]

Re: Johnson 1956 15hp Flywheel Jammed! After turning fine with good compression!

I agree with Joe - install the J6Cs and run it. If you note anything wrong - funny noises, knocks, etc., then go further, but otherwise, if it has good compression and nothing visibly wrong, it's not likely there's any damage.

 

[bonito1]

Re: Johnson 1956 15hp Flywheel Jammed! After turning fine with good compression!

Okay. It's time to remove that pesky flywheel in anticipation of installing the new ignition system parts. I have read the "top secret files" section on removing using the harmonic wheel balancer. This is a real leap of faith for me! Anyone have any additional comments, tips, cautions, etc. Should I WD40 it up real good first?

Thanks!

 

[lindy46]

Re: Johnson 1956 15hp Flywheel Jammed! After turning fine with good compression!

WD40 probably not necessary. Just loosen the flywheel nut (leave it on loosely to prevent the flywheel from launching when it pops), place the puller with the bolts screwed in 7/16" and tighten the center bolt until it pops. Hold flywheel with a nylon ratchet strap to keep it from turning. Don't worry about tightening too much - sometimes it takes a little force to get it to pop. It may require a tap with a rubber mallet to get it loose. Take your time - tighten it, tap it, tighten a little more, tap it. Sooner or later she'll pop.