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One Cylinder 10 PSI Low

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SwampyZT

New member
Hello All,

I picked up a Johnson 115HP from 83 (J115TLCTE) from a family member. I fixed an old 25Hp Johnson last yea but this is proving to be more difficult.

My cylinder 1 compression is 10 PSI lower than the rest.

1 - 108
2 - 118
3 - 119
4 - 118

Is this a difference I should be worried about? The manual says a 5 PSI difference is too high but found conflicting info online. Don't want to sink too much money into it if its a lost cause.

Is there any tricks for bringing the compression up? Or is the only method pulling the piston and the ring?

Runs and idles (rough but that's probably because I have lots of other tasks on it still to do and its below freezing in the Midwest right now.)

I'm sure this topic has been up before but I couldn't find one with only a small PSI difference.

I appreciate any feedback or advice!
 
Simple.------Remove bypass cover for #1 cylinder.----Inspect piston and rings.---Might cost you a gasket ,$2.00 for $100 worth of learning.--That motor would likely be coming apart here if my tester showed 108 PSI.
 
Try a retest and fully charged battery. If motor is in the water make sure that the throttle is open so it can get adequate air. Do compression test with all spark plugs out and start with that cylinder that gave you the low reading. If still low then I agree with Racer.
 
racerone said:
Simple.------Remove bypass cover for #1 cylinder.----Inspect piston and rings.---Might cost you a gasket ,$2.00 for $100 worth of learning.--That motor would likely be coming apart here if my tester showed 108 PSI.
Click to expand...

Not the answer I was hoping for but sounds right. I appreciate the help and the expertise!

Thank you!

Time to start research I guess.

I assume its worth buying the OEM gaskets vs Chinese ones for 90$ less?
 
Run to your local boat shop.----Most would have those $2.00 gaskets in stock.----My mistake , these gaskets are listed at $3.53 on this site.----Still cheap for what you will learn.
 
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racerone said:
Run to your local boat shop.----Most would have those $2.00 gaskets in stock.----My mistake , these gaskets are listed at $3.53 on this site.----Still cheap for what you will learn.
Click to expand...

So I pulled the bypass. Didn't see any gouges or feel any burrs. But not exactly sure what I was feeling or looking for.
20_small.jpg23_small.jpg26_small.jpg
 
Now you know there does not seem to be the " broken ring " syndrome.----At least not at this time.---It will happen on that motor in the future.
 
Got it, makes sense.

So do I start gearing up to pull the engine apart and replace the ring still? Or do I wait for it to break?
 
If you want this motor to last longer, try this....Amsoil Saber mixed 2 oz. per gallon. Non oxy, clear fuel only. Do not ever use ethanol. Why? Ha! The list is endless, it will bring this motor to an early death. Trust me.....I have almost 50 years of records using Amsoil synthetic 2 stroke oil. Other techs here may blast me, but they have little experience in using Amsoil. I still have my very first chain saw.....041 AV Stihl.....ALWAYS run with Amsoil @ 64:1, cut ice at camps for 10 years and hundreds and hundreds of cords of firewood.....want to see a picture of the exhaust port, showing the rings? How about my Ski Doo Olympic, 12.3. Dozens and dozens of trips deep into the bush, not just on trails.....no trails, with sled and minimum of 2 passengers and weeks supply of grub.....64:1.
 
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I'm not here to guide your steps but just educate you on knowledge I have collected over years and years of experience while operating equipment in demanding situations.
 

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