1955 johnson 25hp compression, NOt Good?

[FishyMan]

ok after getting some info from here I checked the compression on a 30 yr old sleeping beauty. the motor was cold and after screwing in the gauge and gave it a pull, 60 on the top 35 40 on the bottom, so now what do I do? I was on the way to replaceing the coils and points and cleaning her up for start soon, should I countinue on? what does the lack of compression mean? can a novice like myself handel something like that? please help...

 

[tashasdaddy]

Re: 1955 johnson 25hp compression, NOt Good?

take some marvel mystery oil, turn the fly wheel so the both piston are at the lowest point possible. then prop the motor face down with plug holes up, and fill the cylinders with oil, and let it sit 3 days to a week. it may just free up those rings. afterward drain, pull thru several times to get oil out. then retest. you want the to be as close to equal as possible, and higher than they are.

 

[steelespike]

Re: 1955 johnson 25hp compression, NOt Good?

Put a couple of squirts of oil in the plug hole and try again.Give it 2 or 3 pulls.If compression goes up then it is likely the rings.If no change then could be a head gasket or worse.Could just be carbon sticking the rings.
Get some decarb like Sea Foam follow the directions.If not running you will need to simply soak it.But you will have to be sure the exhaust ports are covered by the piston.You may have to do one at a time.
This may solve your compression problem.You are looking for about 100 psi.
It will work on less but but 100 psi is considered ideal minimum.

 

[Walker]

Re: 1955 johnson 25hp compression, NOt Good?

Its a rope start motor? Unless you can pull hard enough to get at least 3 full revolutions then you are not getting a true compression reading.

 

[FishyMan]

Re: 1955 johnson 25hp compression, NOt Good?

thanks for the info , you guys are great, not knowing anything about these kinds of motors I feel comfortable working on it with your help. after checking the compression last night a took head coveer off to watch the movement of pistions I did put oil in spark holes first and let soak 1 day. I will put cover back on and check again. Everything looked ok to me but I ve only opened up car and truck motors befor, Pistons look totaly diffrent and there is no play in it like the rings were in bad shape, but lik I said I never have been this far in outboard before. Headgasket looks really good to ( according to me) ???
please keep the Help comming, IM pretty much working on motor and typing to you guys at same time thanks.

 

[F_R]

Re: 1955 johnson 25hp compression, NOt Good?

Take the bypass port covers off the side of the cylinder block. You will be able to look in and see the rings (well, one side anyway). See if they are free in the grooves by poking them with something. Your comment about no play in the pistons makes me think the rings are stuck. Considerable slop in the head end of the pistons is normal. If the rings are stuck, they won't let the pistons slop.

While you have the bypass covers off, use a flashlight to peer down into the crankcase end. If you see evidence of rust, you got trouble.

 

[FishyMan]

Re: 1955 johnson 25hp compression, NOt Good?

ok cover back on and checked compression again same as before, when I pull it 2 or 3 times it goes up and stays up top at over 90 and bottom 65 70 range, so Im putting it on the bench and soakin in mystery oil for as long as my patience will allow, please keep the info comming...

 

[FishyMan]

Re: 1955 johnson 25hp compression, NOt Good?

Thanks Import Ill try thatright now, your right there was no play at all, i thought that would be the way it should be . Im gllad you guys can tell me HOW it should be, I ll go investagate right now...

 

[FishyMan]

Re: 1955 johnson 25hp compression, NOt Good?

OK bypass covers removed top piston 2 out of 3 rings free , bottom piston 1 out of 3 free , no signs of rust in crankcase, as far as I can LIMITED see, so I guess I let it soak as suggested please keep it comming, IM beginning to like this ( so far) thanks...

 

[CATransplant]

Re: 1955 johnson 25hp compression, NOt Good?

That's a good thing. Those rings will free up, and you'll have your compression back. Be patient, and give yourself plenty of time to let the PB Blaster or whatever do its job.

 

[wetfoot]

Re: 1955 johnson 25hp compression, NOt Good?

OK bypass covers removed top piston 2 out of 3 rings free , bottom piston 1 out of 3 free , no signs of rust in crankcase, as far as I can LIMITED see, so I guess I let it soak as suggested please keep it comming, IM beginning to like this ( so far) thanks...

I don't have much 2 stroke experience and have a 67 6 horse Johnson sat for about 6 years.Compression in the 30s after 4+ pulls would go to about 60 lbs.
Figured it was shot, nothing to loose I sprayed choke cleaner from parts house followed with WD40. After 4 days I gave up and ordered a new motor.
By the way this engine would not start.A day or two later I went to remove motor and noticed it seemed to have more compression. 6 or so pulls it fired up. Now it starts first pull and runs great.