18hp coughing

[gearheadinWI]

73 18hp ongoing problem, have replaced points, condensor, one at cylinder coil, found lower main seal to be bad and replaced carbonseal, inner o-ring and the spring/washer/clip, rebuilt carb, replaced cracked vacuum line from top cylinder to intake, fresh plugs, top seal, maybe more.<br />It coughs even at idle, the fuel is OK because I ran 2 differnt 6hp motors on it and they were great.<br /><br />The repair shop had some orings and he thought they might go above the bearing beyond were I could reach but sent them home with me to see if I could find a place for them. I did not and the Seloc manual ONLY detailed that the carbon seal had a small oring in it and that the raised side goes up. At this point I am guessing that at least one of those larger orings I had does indeed belong in there somewhere and I am probably taking it all back apart. The shop I got the parts from said they varied a bit and he only knows exactly how they go together by how they came apart. Therein lies my problem, the whole carbon seal assembly had self destructed before I even opened the thing up it was shavings in the exhaust housing. Hopefully someone can give me some better info on placement of the large o-ring at the carbon seal. or if those are above the carbon seal out of my reach point me at what else might be the problem.<br /><br />Part of me hates throwing parts at it like this but it was used for years without any work atall the tuneup and carb work were just a good idea even with no problems and the upper and lower seals were obvious problems.

 

[Paul Moir]

Re: 18hp coughing

Lets make sure you have all the parts for the carbon seal. It shouldn't fall apart for no reason on it's own. There should be:<br />1) Carbon seal<br />2) O-ring that goes inside it<br />3) A large metal washer that protects the carbon seal. Lip should face spring<br />4) Spring<br />5) Small metal washer that protects the snap-ring. Lip should face spring<br />6) Snap ring to hold it all in place.<br />If you've got all that then something is really amiss. The seal is supposed to turn with the crankshaft - what kind of condition is the bottom crank bearing that it wears against in? Usually those carbon seals are very reliable so there's got to be a reason why it shredded.

 

[gearheadinWI]

Re: 18hp coughing

Best I can tell the snap ring came off and that was the reason for failure. I already got it tore down again since my last post. I looked through my old parts and found one piece that the shop had not given me a new one of it was the spring cup. I also played around with the large orings and found room for one between the bearing and carbon seal. Any chance it belongs there? <br /><br />I did run it for a minute or so without the spring cup and that was when I was suprized by the coughing even after the new seal. I know I screwed up there but I don't think that would have caused that problem I think if left it would have destroyed the carbon seal in short order though.

 

[Paul Moir]

Re: 18hp coughing

No, there's not supposed to be any oring between the carbon seal and the bearing. Just to be really clear about this, the entire carbon seal is supposed to turn with the crankshaft. An o-ring stuck in there would prevent that from happening.<br />Here's an exploded diagram so you can see for yourself: Click here for a '73 18hp crankshaft and dressings. <br /><br />But all this might be neither here nor there. Are you saying that the engine coughed with the seal intact but just missing one of the washers? If so, perhaps the carbon seal failure is a symptom rather than a cause. Coughing/Sneezing is actually (violent) combustion occuring in the crankcase itself. I've never seen it blow out a carbon seal before, but I have seen it blow out a chunk of crankcase wall, so I suppose it's possible.<br />Do you think this may be what we're looking at?

 

[gearheadinWI]

Re: 18hp coughing

What is part number 22 then? I think this is what I am asking about as far as the mystery o-ring.

 

[gearheadinWI]

Re: 18hp coughing

Oh and thank you very much you are being a big help and I had no idea diagrams like that were avaialable online those will continue being a big help for a long time.

 

[Paul Moir]

Re: 18hp coughing

Ah, that's a large o-ring that fits over the bearing before you put it in the block. It seals the crankcase halves from the outside of the bearing. It is totally unservicable unless you completely disassemble the engine. Since it's a static seal, it is never a problem. 23 is the one that fits in the carbon seal naturally.<br />You're very welcome, I hope we can figure out this problem for you. Those online diagrams only recently became available. I've been saving a few of them for myself - a few years ago there was another retailer with J/E diagrams, but they disappeared. They're a huge help when you need specifics.<br />Would you mind answering that first question I asked? No sense going down that path if the answer is negative.

 

[gearheadinWI]

Re: 18hp coughing

Sorry about that, the bearing looks great at least what I can see of it, I also see no sign of crankcase damage on the outside.

 

[Paul Moir]

Re: 18hp coughing

My point is that maybe it's sneezing for another reason, and that sneezing is blowing out the bottom crank seal. I just wanted to give you an idea of how violent it can be. It was sneezing with the seal properly in place except for one spring washer?<br />Also, it's sneezing at both idle and full throttle?

 

[gearheadinWI]

Re: 18hp coughing

Before this work it was sneezing at both throttle anbd idle though less under throttle. At this point I was just idling out of gear in a barrel and it was sneezing. Brought the rpms up a little but still no load and it still sneezed, if I allow a low idle it will sneeze and die.

 

[Paul Moir]

Re: 18hp coughing

Well, here's a couple ideas then:<br />Pull both the spark plugs and have a look at their firing ends. Is there any differences? There may not be if the leak isn't bad.<br />What happened if you richened up the idle mix?<br />On your engine, the fuel pump is mounted on the lower bypass cover right? Is it's gasket sealing well?<br /><br />EDIT: Actually, I suppose question 1 will just show the bottom seal leak. It's probably inconclusive.

 

[gearheadinWI]

Re: 18hp coughing

Just reran it and it acts slightly better with the knob full rich and is better in gear at a high idle than with no load. Again just a barrel so I dare take it no further. The plugs were replaced the end of last season and show nothing not even the lower seal leak, before that they were different heat ranges. It is my Dad's motor and he does not take good care of it.