Topic: ’55 Johnson 25 hp head questions – Antique Outboard Motor Club,Inc

This topic has 16 replies, 7 voices, and was last updated 9 years, 4 months ago by chris-p.

Viewing 10 posts - 1 through 10 (of 17 total)

1 2 →

Author

Posts
September 18, 2016 at 4:35 pm #5291
RICHARD A. WHITE
Participant
Lifetime Member
Doing a complete restoration for this motor, motor ran before tear down to blast, prime and paint. It was advised to go ahead and change the head gasket so there will be no issues in the future.

Here is a photo of the head after I removed it..

So why the carbon build up on the upper cylinder, but very minimal on the bottom? Is this an issue? Is this a warning sign of the future?

Thanks

Richard

http://www.richardsoutboardtools.com
classicomctools@gmail.com
September 18, 2016 at 4:55 pm #44240
1946zephyr
Participant
I would say that your motor may be a low hours motor. What were your compression readings before tear down?
September 18, 2016 at 4:59 pm #44242
fisherman6
Participant
US Member
Richard,
I’m sure someone else will chime in here. My first thought is to check the lower seal. Could be a little water intrusion washing the carbon out of the bottom cylinder. That would be my first thought. Compression variance or possibly spark strength may be a factor? Top cylinder running Cooler for some reason? Not sure I understand that weird line where the carbon stops at the bottom of the top cylinder… The head gasket looks like it was sealing properly so not sure what that’s from.
-Ben

OldJohnnyRude on YouTube
September 18, 2016 at 5:13 pm #44246
RICHARD A. WHITE
Participant
Lifetime Member
Oh, those were NOT the original plugs….. just fillers whilst cleaning…

http://www.richardsoutboardtools.com
classicomctools@gmail.com
September 18, 2016 at 5:29 pm #44250
RICHARD A. WHITE
Participant
Lifetime Member
quote 1946Zephyr:

I would say that your motor may be a low hours motor. What were your compression readings before tear down?

90 + both cylinders….
Yes the gasket was good, but I do NOT want this failing after I am done with it…

http://www.richardsoutboardtools.com
classicomctools@gmail.com
September 18, 2016 at 6:06 pm #44252
frankr
Participant
I suspect water intrusion also. First thing that comes to mind is the lower crankshaft seal. What is the model number? You can tell from that if it has the seal disaster problem. Another suspect is a possible pin hole through the exhaust cover baffle plate, allowing water to squirt in through the exhaust ports. RD-17S and RD-17R have the problematic seal.
September 18, 2016 at 6:24 pm #44253
chris-p
Participant
I agree as well. Change the seal, dress the head/block to ensure it is true, and inspect the exhaust. Should take care of it.
September 18, 2016 at 6:29 pm #44256
RICHARD A. WHITE
Participant
Lifetime Member
It is an RD17, so change the lower crank seal, and remove the exhaust cover to inspect the plate for a pin hole..

Thanks guys

RIchard

http://www.richardsoutboardtools.com
classicomctools@gmail.com
September 18, 2016 at 7:29 pm #44258
frankr
Participant
RD-17 (no suffix) should have the good carbon seal. The -S and -R are the bad ones.

But it does have the aluminum exhaust cover that corrodes through.
September 18, 2016 at 8:15 pm #44260
RICHARD A. WHITE
Participant
Lifetime Member
And corroded it is….., can it be coated with epoxy to ensure no leaks?

http://www.richardsoutboardtools.com
classicomctools@gmail.com
Author

Posts

Viewing 10 posts - 1 through 10 (of 17 total)

1 2 →

You must be logged in to reply to this topic.