What are the symptoms of a bad upper crankshaft seal on a 25hp johnson?

c-dubb

Seaman
Joined
Aug 1, 2016
Messages
54
I have a 25 hp Johnson J25ELCTD that ran good until the other day. It got extremely difficult to start and wouldn't idle, however it seemed to run fine at WOT. When I got it home, I noticed alot of oily fluid coming out from under the flywheel. I am sure the upper crankcase seal needs to be replaced, my question is do these symptoms sound like they are because of this seal being bad? Thanks for any input.
 

F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,195
Yes, that makes sense. Could also be something worse. See if you can move the flywheel fore and aft. A microscoptic amount of movement is normal. A more noticeable slop back and forth is not normal and indicates a bad bearing.
 

c-dubb

Seaman
Joined
Aug 1, 2016
Messages
54
There is no noticeable movement in the crankshaft. I know that the upper crank seal is bad and have one on the way, just trying to figure out if my symptoms point to this or something else. Thanks.
 

raczekp1

Lieutenant
Joined
Mar 30, 2010
Messages
1,327
look under the hood. layer of oil inside the hood or some oil under the flywheel indicates bad upper seal
 

jimmbo

Supreme Mariner
Joined
May 24, 2004
Messages
12,944
The hard to start and poor idle is common when the seal goes bad, At higher speeds there is enough oil to act as a seal and maintain crankcase compression
 

F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,195
A badly leaking crankshaft seal lets crankcase pressure escape and air entry into the crankcase. A sealed crankcase is essential for two-stroke operation, especially at cranking or slow speeds.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,047
Possibly the oil line from bottom of block to top bearing is loose / cracked.----Those upper seals rarely fail.
 

c-dubb

Seaman
Joined
Aug 1, 2016
Messages
54
Thanks for the input guys. I will double check the oil line and the new upper seal should be here in the next day or two. I'll post my results.
 

c-dubb

Seaman
Joined
Aug 1, 2016
Messages
54
Ok guys, new crank seal in and now it will start but will hardly run. Checking spark by grounding a spare plug and see no spark on top cylinder. I will swap coils around as soon as I get time and see if the coil is possibly bad. What else should be tested and how?
 

c-dubb

Seaman
Joined
Aug 1, 2016
Messages
54
The old seal looked like it wasn't sealed completely to the shaft and had oily residue all under the flywheel. It was damaged badly trying to remove it so I couldn't compare it to the new one. The new one appears to seal a lot better to the crank visually though.
 

boobie

Supreme Mariner
Joined
Nov 5, 2009
Messages
20,826
We know you have ignition problems but what's the compression on it ??
 

c-dubb

Seaman
Joined
Aug 1, 2016
Messages
54
100 on both cylinders. Tested stator and tried swapping coils around last night, the problem moved with the coil. Put the meter on the coil and it was shorted to ground on the primary side. The bad coil was a CDI that I purchased a couple of months ago because the old one seemed to be leaking a lot of clear sticky film, but was still working.
 

oldboat1

Fleet Admiral
Joined
Apr 3, 2002
Messages
9,598
For information: https://forums.iboats.com/threads/w...per-crankshaft-seal-on-a-25hp-johnson.684822/ If you can get it running for a little bit of time, check the lower seal by spraying some WD-40 at the base of the powerhead inside the cover. If rpm change the seal is suspect. Check further by removing the lower unit and shining a flashlight up at the top of the shaft. If fuel up there, the seal is leaking.

You can fix these issues, but a '57 or '58 35 hp will have more power.
 
Top