15hp johnson only firing on 1 cylinder (help needed)

[bktheking]

Re: 15hp johnson only firing on 1 cylinder (help needed)

Couple "o" questions...

When you test the "pull the wire and motor dies test" , are you doing this right at cold start or once it's been running a while?

When you tested for spark was it the same time you did the "pull the wire and motor dies test"?




Pull the plugs and inspect, what do the plugs look like, is one plug brown/black and the other new? Swap spark plugs around and restest.


If you have compression and spark there is only one part missing, fuel. As a test, pull the bottom plug wire off and ground it using the plug tester. Remove the top plug and take some 50:1 fuel mix and spray it in the top cylinder (grab a new spray bottle for you testing, beer bottles don't work so well ). Replace the plug and start it up. If it fires and dies out then it sounds to me like you may have a reed problem. You have 2 pairs of reeds on the motor, top and bottom that feed fuel to the cylinders. If one set of reeds is bad you may not be getting fuel to that cylinder or too much.

 

[cubmixit]

Re: 15hp johnson only firing on 1 cylinder (help needed)

Im testing withing about 5 minutes of starting...

I did separate tests...

You're right... The top plug looks brown/black and the bottom plug is looks much newer!

I dont understand the test... Ok- pull the bottom plug and ground it. Then pull the the top plug and spray fuel in the cyliner? I'm sure the bottom cylinder is the problem.
Oh yeah-- there's plenty of beer bottles to chose from in the workshop at this point.
Thanks for your help...

 

[bktheking]

Re: 15hp johnson only firing on 1 cylinder (help needed)

Im testing withing about 5 minutes of starting...

I did separate tests...

You're right... The top plug looks brown/black and the bottom plug is looks much newer!

I dont understand the test... Ok- pull the bottom plug and ground it. Then pull the the top plug and spray fuel in the cyliner? I'm sure the bottom cylinder is the problem.
Oh yeah-- there's plenty of beer bottles to chose from in the workshop at this point.
Thanks for your help...

Ya sorry I read it wrong, reverse the test, the bottom plug is the issue. Ground the top plug wire, pull the bottom plug and spray the mix, replace the plug and wire and see if the fires. You may have a reed issue or bad lower crank seal. To inspect the reeds remove the carb and the intake, the reeds sit in behind on a plate. For the lower crank seal it involved removing the powerhead. Does the motor spit fuel out the carb at all?

 

[cubmixit]

Re: 15hp johnson only firing on 1 cylinder (help needed)

I manually checked the compression by pulling both plugs and putting my thumbs over the cyliners, wife cranked engine... The top cyliner pushes back very hard.. The bottom is very weak.. Does this mean something internal?

I had the compression checked 3 weeks ago.. The guy told me 111 and 110, that's why I thought the compression was good..

I'll try the fuel test in a few minutes. Headed to the bottle shop to get the hard stuff.. It's gonna be a long day!

 

[bktheking]

Re: 15hp johnson only firing on 1 cylinder (help needed)

You had the compression checked???? Did you see it happen??? More and more it's sounding like either a broken ring, wrist pin retainer let go, bad head gasket / cracked head, I bet the old coil is good. With one clean plug and one dirty and spark, reeds rarely go bad and a clean carb it's mechanical for sure. Don't even bother with the fuel test, when you are out at the bottle shop go to the "compression tester" shop and pick one up.

If you have low compression on the bottom plug remove the head and inspect, if it comes apart nicely you'll be able to tell if the head gasket is blown. If it is the motor more than likely overheated. If the issue is the gasket put the head on piece of glass to make sure it's not warped.

 

[kahuner]

Re: 15hp johnson only firing on 1 cylinder (help needed)

Here's a suggestion that on one hand is the longer road but would save time in the long-run, especially when trying to determine if the problem is a blown lower seal or the head gasket.

If clubmixit's local dealer has a leak-down tester, you can isolate which of the possible failure types you're dealing with. Just trace the path of the leaking air.

I'm struggling with how to isolate a bad lower seal other than the process of illimnation (after head gasket replacement). Engines after 30 years of operation, you'd think both head gasket and lower seal would have a high degrees of probability for failure.

bktheking, your thoughts?

 

[cubmixit]

Re: 15hp johnson only firing on 1 cylinder (help needed)

Ok... on the way back from the bottle store, I rental OEM compression tester from autozone...
Hooked up and tested top cyliner= 80-85psi.
Hooked up and tested bottom= 0 compression reading..?? Oh no, that cant be good.
I've promoted myself to a captain from a cadet.. captain morgan that is...
What do I do now, and what is a leak down tester?
Thanks!

 

[bktheking]

Re: 15hp johnson only firing on 1 cylinder (help needed)

Sure leakdown would work too but there is much less at play for components than a 4 stroke. If the tester is available there is no harm in performing it.

 

[bktheking]

Re: 15hp johnson only firing on 1 cylinder (help needed)

Ya that was my fear all along , A zero reading is the motors complete inablility to hold air, 99% sure it's a blown head gasket , if not you'll see the damage when you pull the head off, cross your fingers it's a $10 gasket.

 

[cubmixit]

Re: 15hp johnson only firing on 1 cylinder (help needed)

Ok thanks! Where can I find information on how to pull the motor apart and replace the head gasket?

 

[bktheking]

Re: 15hp johnson only firing on 1 cylinder (help needed)

Ok thanks! Where can I find information on how to pull the motor apart and replace the head gasket?

According to the parts break down there are 6 bolts holding the head on. Pull out the plugs and remove the 6 bolts (the head is what the spark plugs are in, it's around an inch thick), the head comes off next. My repair manual only goes back to 1990, if someone else has a newer manual they could post the torque specs and pattern. I would hold off dropping $90 on a manual until you determine if the it's worth it. If you have a d camera, sign up for imageshack, upload the pics for message board size and post pics of the gasket and bottom cylinder wall once the head is off.

 

[cubmixit]

Re: 15hp johnson only firing on 1 cylinder (help needed)

OK.. I pulled it all apart.. The piston is a mess... The cyliner is smooth to the touch.
http://img210.imageshack.us/img210/7779/piston1.jpg

I tried to pull the flywheel, but cant get it off.. Dont want to put to mess pressure on it... Now what?

I can pretty much look at it and pull it apart... I'm sure I can get it back together as well.. Should I buy a manual spefically for this engine? Do I buy a piston, rings and gaskets?

 

[bktheking]

Re: 15hp johnson only firing on 1 cylinder (help needed)

Eee gads, that piston is kaput.

You're going to need:

Manual
Flywheel puller
New piston and 2 sets of rings
The block taken to a machine shop to be at least honed, have them inspect it may neeed to be bored out, if you have a hone you can do it yourself
complete gasket set
IN and ft lbs torque wrench
possibly a bottom and top crank seal
etc etc etc, you won't know all of what you need until it's apart.

 

[cubmixit]

Re: 15hp johnson only firing on 1 cylinder (help needed)

Ok.. Thanks for all you help... I really appreciate it!
I'll order the manual and start getting the parts...

 

[bktheking]

Re: 15hp johnson only firing on 1 cylinder (help needed)

NP, they aren't hard to rebuild, just read up on it and take your time and be precise and take pictures if you are unsure about reassembly. You are also going to need a small tube of OMC gel seal or equivalent to reassemble the crankcase.

PS- if you take the side cover off, the cover on the left of the pic you'll be able to see the condition of the rings (sort of), there should be one on the right as well.

 

[cubmixit]

Re: 15hp johnson only firing on 1 cylinder (help needed)

Hey-- where can I get a flywheel puller that is relatively cheap? Or is there an alternative to a flywheel puller?

Thanks!

 

[bktheking]

Re: 15hp johnson only firing on 1 cylinder (help needed)

Autozone should sell one i`d think, Canadian Tire does too up here in the North if that`s where you live.