1969 Johnson 9.5 hp low / no compression on one cylinder

[mdebar1]

Bought this motor about a month ago. Last weekend, I ran the motor on a lake and noticed a lack of power. While on the lake, I pulled one spark plug at a time and the motor still ran. This weekend, I didn't have a compression gauge handy, so I took the plugs out, put my finger in the cylinder head holes, and cranked the motor. Bottom cylinder pushed and pulled air just fine. Top cylinder wouldn't push or pull air at all. I took the cylinder head off and cylinders look excellent - no scoring at all. I'm guessing it's the rings... is there anything else I might be overlooking?

Thanks,
Michael

 

[jeremy_nash]

Re: 1969 Johnson 9.5 hp low / no compression on one cylinder

is the piston moving when you rotate the flywheel? if so, the rings would have to be really shot to not feel any air pressure or suction

 

[Joe Reeves]

Re: 1969 Johnson 9.5 hp low / no compression on one cylinder

Check the piston movement as Jeremy states. If okay, install a new head gasket.... you may be lucky.

 

[samo_ott]

Re: 1969 Johnson 9.5 hp low / no compression on one cylinder

It's virtually impossible to plug the hole with a finger and crank the engine at the same time... Were you pulling it hard enough? That's not much of a test anyway. Get a proper compression gauge and get the #'s.

 

[mdebar1]

Re: 1969 Johnson 9.5 hp low / no compression on one cylinder

is the piston moving when you rotate the flywheel? if so, the rings would have to be really shot to not feel any air pressure or suction

Yes. Pistons move just fine.

 

[mdebar1]

Re: 1969 Johnson 9.5 hp low / no compression on one cylinder

It's virtually impossible to plug the hole with a finger and crank the engine at the same time... Were you pulling it hard enough? That's not much of a test anyway. Get a proper compression gauge and get the #'s.

Ok, you got me... I simplified my post a bit. I actually pulled the flywheel off (I'm replacing ignition as well) and cranked via wrench. At any rate, one cylinder was blowing and sucking and the other was doing nothing.

Is there any way to test it (to determine whether it might have been a blown head gasket) now that I've got the cylinder head off? Could it a leak in another gasket cause loss of compression?

 

[mdebar1]

Re: 1969 Johnson 9.5 hp low / no compression on one cylinder

Bump for answer.

 

[Bob_VT]

Re: 1969 Johnson 9.5 hp low / no compression on one cylinder

You never mentioned how much you have run the motor in the month that you have owned it........

I have the exact motor and year.

Have you done anything to decarb the rings?

I would soak the rings with a penetrating oil for at least 24 hours and use a proper compression gauge. Use the gauge before and after you soak the rings.

It is not uncommon for a ring to get carboned up and stick. You can use the de-carb methods listed here on iboats however soaking the rings may make shorter work of it. I have in the past pulled the plugs, sprayed in a liberal amount of penetrating oil and left the engine tilted up for 24 hrs.

The ultimate goal is to have both pistons at near the same compression (within 10%) and a simple stuck ring will rob you blind.

 

[mdebar1]

Re: 1969 Johnson 9.5 hp low / no compression on one cylinder

Thanks for the reply, Bob.

I ran the motor out in the water on two separate occasions (fishing trips). Each time, the engine was run approximately 4 hours. I ran it on a pelican predator boat with two people. I believe that the motor is underpowered because it went approximately the same speed as my 5 hp Tohatsu (both ~4 mph on the pelican predator according to my GPS), which I sold to buy this Johnson 9.5 hp.

Last week, before I checked the compression with my finger, I did an entire de-carb process (3/4 pint of seafoam + 1 gallon of gas / 1/4 pint in spray bottle to mist carb and cylinder chamber). I'm not sure whether there's a separate de-carb process for the rings, however, when I checked the compression, the bottom cylinder would puff and suck air, but the top wouldn't. I have already taken the cylinder head off. Should I get a new gasket and put the cylinder head back on and go check compression again before messing with the rings - or is there some way to test to determine whether it's the rings without having the cylinder head on?

Thanks,
Michael

P.S. - This motor has been a complete POS from the get go. I tested the spark and it wouldn't jump more than about 1/30th of an inch. Not sure whether that's related to my low-hp issues, but I figured it wouldn't hurt to do an ignition tune up. This forum has been an excellent source of information... I only asked this question because I couldn't find a similar issue that was already answered. So far, I've been learning how to work on this engine and test it based on old posts in this forum. Original service manual should be arriving today.

 

[boobie]

Re: 1969 Johnson 9.5 hp low / no compression on one cylinder

What you should do is install a new head gasket, then do a "real" compression test with a gauge and then report back here.

 

[Rick.]

Re: 1969 Johnson 9.5 hp low / no compression on one cylinder

Well I'm at a loss. A week spark will cause it's own set of problems for sure but low compression isn't on the list. If it had no compression it would not run when you pulled the wires one at a time. If you pulled the exhaust cover you can see the rings (a bit). I would agree with others who have said "do the head" and see what happens. Best of luck. Rick.

 

[mdebar1]

Re: 1969 Johnson 9.5 hp low / no compression on one cylinder

What you should do is install a new head gasket, then do a "real" compression test with a gauge and then report back here.

Well I'm at a loss. A week spark will cause it's own set of problems for sure but low compression isn't on the list. If it had no compression it would not run when you pulled the wires one at a time. If you pulled the exhaust cover you can see the rings (a bit). I would agree with others who have said "do the head" and see what happens. Best of luck. Rick.

Thanks. I'll give it a shot and report back.

 

[mdebar1]

Re: 1969 Johnson 9.5 hp low / no compression on one cylinder

Before putting the head gasket on, I put my hand in a plastic bag and tested each cylinder for compression. Once again, the bottom cylinder sucked and blowed and the top didn't. I squirted some oil in the top cylinder and, sure enough, it created a bit of suction. I was able to get a closer view of the top cylinder and put a flashlight on it. This time, I noticed that it was, in fact, scored. I'm not sure whether I need to hone it out or bore it, but if I decide to bore it out, is there any place that sells an oversized ring and piston kit? I know the part number for the .03 oversized piston is 385867 (good luck finding .03 oversized rings), but I was wondering if some aftermarket manufacturer made an oversized kit, piston, or ring set?

 

[iwombat]

Re: 1969 Johnson 9.5 hp low / no compression on one cylinder

Sea-way marine in seattle has everything you need. And yes, it'll have to be bored out and oversized.

 

[mdebar1]

Re: 1969 Johnson 9.5 hp low / no compression on one cylinder

For anyone reading this post in the future: It is INCREDIBLY HARD / IMPOSSIBLE to find two sets of oversized rings for this motor. I have looked everywhere. You're better off buying a new powerhead and staying with standard rings/pistons....

Looks like I got taken on this motor. $200 lesson learned: bring a wrench, sockets, compression tester, and spark tester when buying a motor.

 

[boobie]

Re: 1969 Johnson 9.5 hp low / no compression on one cylinder

Not to be a smart a##, but the next time you buy a used mtr you'll sure know what to look for. Just don't forget your tools and test equipment. Good Luck.

 

[mdebar1]

Re: 1969 Johnson 9.5 hp low / no compression on one cylinder

Not to be a smart a##, but the next time you buy a used mtr you'll sure know what to look for. Just don't forget your tools and test equipment. Good Luck.

Yep... luckily, the lesson only cost me ~$200.

 

[Bob_VT]

Re: 1969 Johnson 9.5 hp low / no compression on one cylinder

http://www.marineengine.com/parts/wiseco-pistons/catalog.html

If you only have one bad piston that is all that has to be replaced. It is common practice to only replace what is needed with no bad effects.

Above is the Wiseco piston catalog. You can get what you need there.

 

[mdebar1]

Re: 1969 Johnson 9.5 hp low / no compression on one cylinder

http://www.marineengine.com/parts/wiseco-pistons/catalog.html

If you only have one bad piston that is all that has to be replaced. It is common practice to only replace what is needed with no bad effects.

Above is the Wiseco piston catalog. You can get what you need there.

Bob,

Thanks for the link, I've never seen that one before. What I don't understand, however, is why Wiseco doesn't make pistons and rings for 9.5 hp? It's not on that list. The oversized rings for the 9.5 are in incredibly high demand... and some nice money could be made on them.

 

[wolfgang123]

Re: 1969 Johnson 9.5 hp low / no compression on one cylinder

www. boats . net /parts/detail/brp/B-0384073 . html

Isnt that it?