15 hp - no compression on one side

[bison716]

Bought a used '93 - 15 hp Johnson, supposed to be low hours and hardly used. It was a sight unseen private deal and I got taken to the cleaners. Got the motor home, besides being very dirty it has no compression on the bottom cylinder. Called the seller back and he swears it ran great last time he used it but it has been sitting for 2 years since being run. OK, I'm a big boy and it was sold as is. I've rebuilt sled engines before but they have removable cylinders. My question is if you need to remove the entire power head out of the chassis or can you strip it down as is. Looks like you can remove the lower engine covers and get at all the bolts. Not quite sure how to proceed. Any advise would be appreciated. Thanks.

 

[1946Zephyr]

Re: 15 hp - no compression on one side

Well, I would first do a compression test and see exactly what you have. It's possible you just have a bad head gasket. You can also remove the intake bypass covers and get a visual of the pistons and check for any scoring.

 

[jbjennings]

Re: 15 hp - no compression on one side

I agree..... Do a little more inspection and see if you can figure out what the problem is. It's shameful for a person to lie like that, and I'd like to think it would be unlikely. If it has NO compression then the wrist pin has come out or the connecting rod has broken. If the rod has broken there's a good chance it would put a hole or a crack in the block that you could see. It could be a really bad head gasket as was said. It doesn't put any pressure out the spark plug hole when you turn the flywheel???? Compression gauge failure???
I hope it's not as bad as you think....
Yes, you do have to pull the powerhead to rebuild it, but hopefully you won't have to.

JBJ

 

[bison716]

Re: 15 hp - no compression on one side

There is no pressure at all when I put my thumb over the spark plug hole and spin it over. Top cylinder has good suction and push when you do the same. Not very scientific, I will borrow a compression tester and check it properly. I'm hoping it's just stuck rings, I sprayed sea foam penetrating spray in the cylinder and will let it sit for now.

So I'm assuming I would need to drop the bottom end first, and then be able to remove the power head?

Thanks for the replies.

 

[bison716]

Re: 15 hp - no compression on one side

I should also mention the piston is moving in the dead cylinder so it is not a broken connecting rod. I will try removing the bypass cover for a better look. Thanks again.

 

[floatingwoody2006]

Re: 15 hp - no compression on one side

I have the same motor. Sure does sound like it could be a head gasket. any visable scarring of the Cyl. walls you can see thru the plug hole? if you were to put a fair amount of oil in that cyl and put the plug in and spin it, you may possibly see somewhere it's leaking from if not internal..

 

[bison716]

Re: 15 hp - no compression on one side

I checked compression tonight. It's got zero on the bottom cylinder and 75 on the top. I would think it should be 100 - 125? Next is to pull of the inspection plate and have a look. With a flashlight I can look somewhat into the spark plug holes, no obvious holes in the piston that I can see.

 

[The original Smokey]

Re: 15 hp - no compression on one side

75 and zippo? 100 MINIMUM for a decent runner.

Could be a head gasket, but you'd get something if it was the gasket.

Sorry bud, this one's toast. They all ran the last time they were used, some just broke the last time being used.
The powerhead can be pulled quite easily without pulling the gearcase. Screws up through from the bottom.
Find your parts manual (exploded assembly pics) at www.shopevinrude.com

 

[trendsetter240]

Re: 15 hp - no compression on one side

I checked compression tonight. It's got zero on the bottom cylinder and 75 on the top. I would think it should be 100 - 125? Next is to pull of the inspection plate and have a look. With a flashlight I can look somewhat into the spark plug holes, no obvious holes in the piston that I can see.

For a pull start 75 psi is not that bad. Zero psi is obviously bad. Could be a head gasket but could also be a hole through the piston.

As it is now you've got nothing to lose; if you do nothing to it it's unuseable. If you get yourself a service manual then you can pull it apart and find out exactly what you are dealing with. It will not be worth it to pay someone else to rebuild this motor for you. DIY and it could be quite cheap.

A 15hp should be very similar to the sled engines you've rebuilt. Small and easy to work on.

Post back with questions and pictures if you are unsure and the folks on here will help you out.

Cheers~!

 

[raybow1]

Re: 15 hp - no compression on one side

Did you try squirting a little oil into the cylinder for a wet test? It does not sound as if it is useful other than a little more knowlege of maybe what it could be. My guess is a hole in the piston as someone mentioned earlier. I don't think if the rings were stuck you would even have zero compression. If it were a head gasket from cyl to cyl you would get bleedoff from one to the other. Did you test with both plugs out at the same time or one in and one out? If so test while leaving one plug in on the strong cyl. It may not be relivant other than a little more knowlege on what's going on internally. You may want to feel around on top of piston with some kind of wire or something to see if there is a hole you may not be able to see by visual inspection. At the very least, I would pull the head off before the whole motor. Unfortunately it does not sound real promissing other than the fact that you will end up with a rebuilt 15 hp that you know inside and out. Sorry to hear about this kind of a deal because most of us love to do business on a trusting level.

 

[reelnative]

Re: 15 hp - no compression on one side

75 sucks 100 sucks you need 88psi min to have a comp stroke that will fire, pull the head off I bet you have a blown head gasket or warped head, or both, its about 15 bucks for a head gasket, you should have about 120 to 135psi on both

 

[trendsetter240]

Re: 15 hp - no compression on one side

75 sucks 100 sucks you need 88psi min to have a comp stroke that will fire,

I disagree, I had a 1988 johnson 30hp that would only read 80psi on my compresion tester and it ran great. This was a pull start motor and pull start engines give lower compression readings than electric start. Once the motor is running it will be building much higher compression then when you are pulling it.

 

[bison716]

Re: 15 hp - no compression on one side

Tonight I have the head off and the side inspection plate, and everything looks in very good shape. Tops of the pistons look fine, rings from the side inspection port look fine, cylinder walls are dead smooth, in fact I can even see some cross hatch in each. There was a mark on the lower corner of the head gasket, like a pushed in bump into the water passage area, and it appears the gasket was wet with oil in this area. The pushed in bump is actually deep enough that that gasket is fractured on that spot with a tiny hole in the center. I had been pumping oil and penetrating spray into this cylinder so the oil mark makes sense if it was leaking there. So what now? Replace the head gasket and try it again? Could this actually create zero compression? Wouldn't I hear it hissing at the gasket when I would spin it over? I'm scratching my head a bit, would appreciate more expert opinions. Thanks to all.

 

[bktheking]

Re: 15 hp - no compression on one side

Throw a head gasket on it and torque it down properly, that's your $10 answer. If compression is low after replacement then the rings are most likely the issue.

 

[reelnative]

Re: 15 hp - no compression on one side

I disagree, I had a 1988 johnson 30hp that would only read 80psi on my compresion tester and it ran great. This was a pull start motor and pull start engines give lower compression readings than electric start. Once the motor is running it will be building much higher compression then when you are pulling it.

pull start motors give the same comp reading as elect start motors, if not then you would have a very bad leak down problem it sounds to me like you have a bad comp gauge, all 2 cycle motors need a min of 88psi to make a fire stroke really im not making that up its the truth

 

[tx1961whaler]

Re: 15 hp - no compression on one side

pull start motors give the same comp reading as elect start motors, if not then you would have a very bad leak down problem it sounds to me like you have a bad comp gauge, all 2 cycle motors need a min of 88psi to make a fire stroke really im not making that up its the truth

I'm sure you believe that, but it's not the truth....

 

[bob johnson]

Re: 15 hp - no compression on one side

if it is a short shaft, it is definately TOAST, ruined, shot, garbage waiting to be taken out..


.how much you want for the drive shaft?????

Ill buy it from you because i want to offer financial assistance to you in your time of crisis!!


bob

 

[ezeke]

Re: 15 hp - no compression on one side

pull start motors give the same comp reading as elect start motors, if not then you would have a very bad leak down problem it sounds to me like you have a bad comp gauge, all 2 cycle motors need a min of 88psi to make a fire stroke really im not making that up its the truth

Nonsense!

 

[Whoopbass]

Re: 15 hp - no compression on one side

75 sucks 100 sucks you need 88psi min to have a comp stroke that will fire, pull the head off I bet you have a blown head gasket or warped head, or both, its about 15 bucks for a head gasket, you should have about 120 to 135psi on both

This is nonsense. I have a 25hp Rude with electric and pull start and the compression reading with the rope is about 10-15 psi less then with electric.

I've had a bunch of 15 hp motors and none of them read close to 120-135 psi. They usually read anywhere from 80-100 psi.

If you can't figure out what's wrong with the motor then part it out on ebay. You will probably make anywhere from $300-$400.

 

[bktheking]

Re: 15 hp - no compression on one side

This is nonsense. I have a 25hp Rude with electric and pull start and the compression reading with the rope is about 10-15 psi less then with electric.

I've had a bunch of 15 hp motors and none of them read close to 120-135 psi. They usually read anywhere from 80-100 psi.

If you can't figure out what's wrong with the motor then part it out on ebay. You will probably make anywhere from $300-$400.

Agreed, my 15 had 95 psi and starts first pull, my 9.9 has 100. Jeez if I went with that theory i'd be reringing every single motor in my garage, that includes all my power equipment!