15 hp - no compression on one side

[bktheking]

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

LOL your funny Bob!

 

[jbjennings]

Re: 15 hp - no compression on one side

If it were me, I'd check and make sure the head is flat by placing it on a pane of glass with 400 grit sandpaper on it and rubbing the head in a figure 8 motion until it is flat. If the head is warped, that could be the problem with the head gasket going bad.

As to the 88 psi thing......... Where did this exact figure come from?
My 50's 7.5hp OMC motors consistently run with 80 psi and knowledgeable people with reliable gauges have motors running good with even less, some down to 65psi. Even older, smaller hp motors consistently run great with 60psi. on one or both cylinders.

I have found the rope start motors giving lower compression readings of about 5 or so psi lower to be normal. You just have to pull them over a few more times to get the highest reading. Not 15psi difference that I've seen, but I guess everyone's arm strength varies.....

I do believe a newer 15 hp johnson would have higher than 110 psi in good shape, although it would run ok. with less. My '56 15hp I believe even has 105 psi. well used, compared to my highest compression '57 18 hp with 125 psi on both cylinders. MY '99 johnson 25hp purchased new only has 125psi as well.

just my 2 cents.....
I think your motor has a good chance of being a really nice one.
Good luck,
JBJ

 

[trendsetter240]

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.

Check the surface of the head for warpage with a straight edge. You can use a straight edge and a feeler gauge to determine how much it is out of spec.


If the head is still good then try a new head gasket and torque it down properly as posted. If you don't have a manual for this motor then now would be a great time to make that investment!

Cheers~!

 

[trendsetter240]

Re: 15 hp - no compression on one side

ha..JBJ you beat me to it.

 

[raybow1]

Re: 15 hp - no compression on one side

There is an absolute huge difference and variation in many compression testers. It does not surprise me that you guys aren't agreeing on the minimum compression it takes to run a motor. The single biggest factor is both cylinders need to be within a certain percentage of each other. The reason for wet and dry tests are to give you a better idea of the condition of your rings. Again this is based on a percentage of climb from dry to wet. And are the two cylinders consistent with both wet and dry tests. The end result is a better knowlege of the condition of some of the internal parts in your motor. A cold compression test should not register as high as a warm test. Expansion I believe plays a role in this. I personally would not get too caught up in the compression other than for diagnostic at this point. Let's first figure out why you have such a variaton in one to the other. Don't worry about the one being only 75 at this point but rather what can be done to get the other consistent with that. Somebody mentioned a $10.00 head gasket and that may at this point be the best way to see. The fact that it looks good is a huge step in the right direction.

 

[jbjennings]

Re: 15 hp - no compression on one side

Dang Raybow,
We had a perfectly good compression squabble brewing here and you go and ruin it with good advice!

Agreed, compression gauges stink for consistency from one gauge to another.
Hopefully the head gasket will do the trick!
JBJ

 

[reelnative]

Re: 15 hp - no compression on one side

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

hahaha ok tell me why a pull start motor is going to have less comp then an elect start motor, ive been a cert omc mecanic for over 20yrs and been working on motors for 35yrs and they never told me in omc 1, omc 2, omc fuel inj school, or on my omc master classes that a pull start motor has less compression then an elect start motor, when you do a comp test on a motor every time you pull the rope the comp is gonna climp till it hits its max unless you have a 20 dollar harbor freight comp gauge that wont hold pressure, the only way you would get a diff reading is if you are checking a motor like a lawn mower that has a comp releese so its easyer for you to pull, no omc pull start motors have this on them. hahaha some of you guys crack me up no wonder we ended up with oboma for our pres

 

[reelnative]

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.

sounds like you need to buy some better testing eqp its the basic laws of physics you need 88psi to make a firing stroke in a 2 cycle motor, and if you had 15hp motors that only were getting 100psi for real well then they are not long for this world and are very tired

 

[71Windsor]

Re: 15 hp - no compression on one side

hahaha some of you guys crack me up no wonder we ended up with oboma for our pres

harsh toke dude....

Your on your way to completing something and being very proud. Dont give up. Do be afraid. Take your notes pictures draw on cardboard and poke parts through. When you get this running you will feel proud to take it on the water.


I built my first 15hp 11 years ago. I still have in on a horse in the basement.

Yes its frustrating. Be patient! Your on the right forum with the right guys who have the ability to deliver the knowledge you need.

 

[tx1961whaler]

Re: 15 hp - no compression on one side

hahaha ok tell me why a pull start motor is going to have less comp then an elect start motor, ive been a cert omc mecanic for over 20yrs and been working on motors for 35yrs and they never told me in omc 1, omc 2, omc fuel inj school, or on my omc master classes that a pull start motor has less compression then an elect start motor, when you do a comp test on a motor every time you pull the rope the comp is gonna climp till it hits its max unless you have a 20 dollar harbor freight comp gauge that wont hold pressure, the only way you would get a diff reading is if you are checking a motor like a lawn mower that has a comp releese so its easyer for you to pull, no omc pull start motors have this on them. hahaha some of you guys crack me up no wonder we ended up with oboma for our pres

Sorry I wasn't clear: I was referring to your assertion that 88psi is some kind of theoretical requirement for combustion. It's not, no matter what you think you were told. There are many happy little outboards putting around on 60-70 psi compression readings that didn't pull an 88 psi measurement when new.
You're correct, the pull start motors and the electric start motors have the exact same theoretical compression. Same cylinders, same stroke, same rings. You do tend to get higher compression gauge readings on an electric start motor, only because the motor will turn over faster and you'll get a better measurement. If you want to prove it, get a small two stroke and measure the compression using the pull start. Then measure it again using a drill motor chucked up with a socket spinning the flywheel. You'll get two different measurements.
Yes, some old OMC motors have compression release mechanisms. But you, being a certified OMC guy would know this, of course. Must have slipped your mind....

Since you are a newbe here, here's a word of advice: keep the troll crap and political stuff outta here, or you'll get banned quick. And please learn where the shift button is for capital letters....

 

[bktheking]

Re: 15 hp - no compression on one side

Come on reelnative, you were on another post telling a guy with 110psi on his triple that his motor is almost done. Are you basing your measurements and conclusion to the people on this board based on a measurement of a new motor or is it what's learned after 30 years in the business? The motor in question is 20 years old, how can you not expect it to be in that range for a used motor? Like I said, if I followed that logic i'd be reringing every single motor in my garage, 100psi on a 20 or 30 year old outboard is stellar reading for it's age.

 

[jbjennings]

Re: 15 hp - no compression on one side

sounds like you need to buy some better testing eqp its the basic laws of physics you need 88psi to make a firing stroke in a 2 cycle motor, and if you had 15hp motors that only were getting 100psi for real well then they are not long for this world and are very tired

news to me!!:redface:

 

[reelnative]

Re: 15 hp - no compression on one side

Sorry I wasn't clear: I was referring to your assertion that 88psi is some kind of theoretical requirement for combustion. It's not, no matter what you think you were told. There are many happy little outboards putting around on 60-70 psi compression readings that didn't pull an 88 psi measurement when new.
You're correct, the pull start motors and the electric start motors have the exact same theoretical compression. Same cylinders, same stroke, same rings. You do tend to get higher compression gauge readings on an electric start motor, only because the motor will turn over faster and you'll get a better measurement. If you want to prove it, get a small two stroke and measure the compression using the pull start. Then measure it again using a drill motor chucked up with a socket spinning the flywheel. You'll get two different measurements.
Yes, some old OMC motors have compression release mechanisms. But you, being a certified OMC guy would know this, of course. Must have slipped your mind....

Since you are a newbe here, here's a word of advice: keep the troll crap and political stuff outta here, or you'll get banned quick. And please learn where the shift button is for capital letters....

you dont have to worry about me posting anything in here ever again, you guys are way too smart for me, I just had to sit back and rem its people like all of you that put bread on my table, yall have a good one

 

[floatingwoody2006]

Re: 15 hp - no compression on one side

Hey..This was just starting to get good..I was just waiting for you to post some sort of publication to this effect to validate your statements..But rest assured, you would have no bread from me friend..I didn't always know better, but thanks to the fine folks in this forum, i do now. What i really want to know is if the head gasket is going to solve the OP issues.

edit.. Hey..Im a chief petty officer now!

 

[tx1961whaler]

Re: 15 hp - no compression on one side

Hey..This was just starting to get good..I was just waiting for you to post some sort of publication to this effect to validate your statements..But rest assured, you would have no bread from me friend..I didn't always know better, but thanks to the fine folks in this forum, i do now. What i really want to know is if the head gasket is going to solve the OP issues.

edit.. Hey..Im a chief petty officer now!

Congrats on the CPO!
I want pictures showing the hole in the piston! Hopefully it is just a head gasket, but most of the time that just drops it down to 30 or 40, not 0.

 

[bison716]

Re: 15 hp - no compression on one side

Checked the head tonight as was suggested to see if it was warped. Found a small chunk broken out of the casting right at the very bottom between the gasket surface and the water jacket. That could certainly explain no compression on that cylinder but I wonder what caused it. Dealer is closed today but I will be calling there tomorrow morning to check on a new head. Thanks again for all the advise and I will report back.

 

[OldJohnson6hp]

Re: 15 hp - no compression on one side

"My '56 15hp I believe even has 105 psi."

Mine too. '56 15hp dead on both at a buck & a nickle! Not bad for 54 years young! Must have 88 for combustion? Huh?

To the OP if it looks good in there follow the head gasket advice. DO lay it on the sandpaper on piece of glass and even it out. Pop a new gasket and check it again.

The seller may not have lied to you (I hope) The gasket could dry-rot out. It did on my 6hp. Using the above fix, it now runs like a top.
PS: If you just wanna get rid of it message me..I'll pay the shipping

 

[bison716]

Re: 15 hp - no compression on one side

"My '56 15hp I believe even has 105 psi."

Mine too. '56 15hp dead on both at a buck & a nickle! Not bad for 54 years young! Must have 88 for combustion? Huh?

To the OP if it looks good in there follow the head gasket advice. DO lay it on the sandpaper on piece of glass and even it out. Pop a new gasket and check it again.

The seller may not have lied to you (I hope) The gasket could dry-rot out. It did on my 6hp. Using the above fix, it now runs like a top.
PS: If you just wanna get rid of it message me..I'll pay the shipping

Thanks, but I'm not ready to give up yet. Will try the head and a new gasket, but thanks for the offer. Will keep it in mind.

 

[tx1961whaler]

Re: 15 hp - no compression on one side

Checked the head tonight as was suggested to see if it was warped. Found a small chunk broken out of the casting right at the very bottom between the gasket surface and the water jacket. That could certainly explain no compression on that cylinder but I wonder what caused it. Dealer is closed today but I will be calling there tomorrow morning to check on a new head. Thanks again for all the advise and I will report back.

If you can, post a nice close up of the broken part of the head. It might be able to be welded and machined. A new head is $153. A good used one is probably half that.

 

[bktheking]

Re: 15 hp - no compression on one side

I'm thinking you'll be gold once you do that.