Home › Forum › Ask A Member › 1987 Johnson 9.9 upper crank seal
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davesko.
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May 2, 2018 at 9:05 pm #9805
Hello all. Just finishing up a 87 johnson 9.9 this is the late production model with the plastic topped carb. Got it all dialed In, idled great in and out of gear. Took it out for a boat test and it won’t idle unless the hood is off. So I adjusted everything so it would idle well with the hood on and off I went, ran great all day. I took the hood off and it idled way to fast. Put the hood back on and it idled back down. Upon inspection at home I found a good amount of fuel/oil on the top of the motor. I’m thinking upper crank seal but just wanted some confirmation. Thank you in advance
May 2, 2018 at 11:48 pm #75242If the mag plate and top of the motor are wet, you can be quite sure it’s a leaky seal. Here’s how I test them with a bit of oil or fuel mix:
May 2, 2018 at 11:54 pm #75244Well, sure could be a seal, but haven’t seen many failures on these engines…
There were some crankcase sealing issues back then, so it may be a failure of the gel seal as well…
Only takes a moment to pull the flywheel and have a look at the seal…
If it looks "OK", you may want to clean the powerhead off, then run the engine again looking for the source of the leak(s).
I’m not sure if any of those slick OMC seal pullers will work on this engine, hope so because that makes seal replacement easy…May 3, 2018 at 12:35 am #75250Im failing to see how installing the hood would affect the crank seal? Not saying that may not also be a problem, but perhaps not your immediate issue.
Sounds like an exhaust leak if anything to me.
Also, you know they are made to tune with the hood on? Just slight differences but something to note. Don’t want you chasing a demon that isn’t there. How much RPM difference would you say there is between hood on and hood off? How much adjustment are you doing to compensate?
May 3, 2018 at 12:48 am #75252I agree it sounds like an exhaust leak, unless some bug or rodent managed to plug up the air intake hole below the carb with a nest.
DaveMay 3, 2018 at 1:00 am #75253Check for an obstruction in the cowling behind the handle in the cowl you use to pull the motor up to a tilt. The air passage has to be totally free for the motor to breathe.
I believe Richard A.White is making the upper seal puller for a 9.9/15. As Fleetwin said, that’s the best and easiest way to get the seal removed.
Mumbles- that is a good video of the seal failure, shows exactly what to look for."Some people want to know how a watch works, others just want to know what time it is"
Robbie RobertsonMay 3, 2018 at 1:14 am #75256Thanks guys for all the input. I pulled the flywheel and it’s definitley leaking. I ordered a new one. There are no obstructions in any of the air inlets. Chris P asked rpm difference and I checked with my tiny tach and it was 375 rpm difference. I wouldn’t have been concerned had I not seen the oil mixture. I looked around for any signs of a exhaust leak and found none. I have no history on this motor it was part of a 50 motor gift from a mentor who past away. Thank again Dave
May 3, 2018 at 9:04 pm #75292The upper engine mounts go bad on those quite a bit. When they do, they could leak exhaust around the mounts. I seem to remember that the cowl air intake is under the carb, just above the swivel bracket. If all the stars are in alignment, you could be sucking exhaust from the mounts, in through the bottom cowl….? Grab hold of the installed engine cover and try to move it fore and aft, while it’s on a rack, boat, etc. It shouldn’t move very much. Too much play means bad upper mounts.
Long live American manufacturing!
May 4, 2018 at 8:59 pm #75353Bill raises a good point, those upper mounts can surely make a mess in many different ways…One other possibility might be that the engine might be breathing the raw fuel vapors leaking out from the upper seal/leaky crankcase halves, causing it to run richer with the cover on….
May 4, 2018 at 10:09 pm #75357Thanks Bill and Don, I put the new seal in today and just came back from a test run. All is well, It now runs great with the hood on or off, very happy with it. The seal was not fun to replace but the crank looked good and went back together easily. Very happy with it. Not sure I’m a fan of the “newer” 9.9-15’s but I’m going to go thru them one at a time.
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