1950's mark 25 restoration

[Beats paddling]

Bought a mark 25 to restore and want to remove the lower unit but cant even get the prop or cone off. Is there a trick to it? Update it is a 1955

 

[Beats paddling]

Re: 1950's mark 25 restoration

Isn't there anyone who knows the procedure for removing the prop cone and propeller on this motor???

Thanks

 

[merc850]

Re: 1950's mark 25 restoration

First you have to bend any tabs on the tab washer (they are in those slots in the cone) away from the cone and then insert a rod into the hole. Block the prop with a piece of wood against the cav plate and turn the rod counterclockwise. Make sure that the tabs are not catching in the slots while turning.

 

[Beats paddling]

Re: 1950's mark 25 restoration

Thanks, Merc850 - got the cone off and the complete lower unit off also. I am gonna have to get the lower unit welded at the area where the rear bearing holding ring threads in. The threaded part of the case was cracked away completely. Hopefuly this area can be beefed up a bit as I hear it is a known weak point on these motors.

Thanks again for the help on my first outboard resto. Old MG's are my thing but I am having fun with this motor project. Next step magneto troubleshooting.

 

[Chinewalker]

Re: 1950's mark 25 restoration

That area is only a weak point where water and freezing are concerned. There is a tiny drain hole at the base of the gearcase bullet that is supposed to be clear. Due to it's size, it's usually plugged up by sand, goop, etc. Trapping water in that cavity results in popping the rear of the housing when it freezes. If that is kept clear, and the cavity is allowed to drain, no problem with cracking. Also, make sure the shafts are in good shape at all seal areas, as old Merc shafts are prone to rusting, allowing water into the housing, and that could also pop the case...

 

[merc850]

Re: 1950's mark 25 restoration

I have an owner's manual in PDF format. If you want it contact me at kellerwerk@rogers.com

 

[Beats paddling]

Re: 1950's mark 25 restoration

"There is a tiny drain hole at the base of the gearcase bullet that is supposed to be clear. Due to it's size, it's usually plugged up by sand, goop, etc. Trapping water in that cavity results in popping the rear of the housing when it freezes."

Thanks Chinewalker - With all the holes in this lower unit, how is water kept out in the first place. What exactly are the multiple holes near the threads for the rear bearing keeper on both sides of the bullet for? There are six on each side of the case near the propeller.

Is there a good source for the correct paint scheme on this motor including
under the engine covers. It is a blue and white scheme right now.

Thanks

 

[Chinewalker]

Re: 1950's mark 25 restoration

Those holes are the water intake. There is a cavity ahead of the rear cover plate, with a hole leading up to the waterpump cartridge. The intake holes are on the top half of the bullet, but down low there is a single hole that is supposed to drain any retained water.

The powerhead, lower unit, and recoil etc. are all the same color - likely white (or off white) in your case. The cowling and face are the only parts that would get the blue, with any raised bits getting the paint removed and then polished.

 

[Beats paddling]

Re: 1950's mark 25 restoration

Everything is starting to make sense now. I will post some pictures tonight of the motor.

Since I will have to repair/weld the rear of the bullet I am wondering if you would have to remove the drive shaft and pinion gear and forward gear that is still in the lower unit. It looks like there is a bolt holding the pinion gear to the bottom of the drive shaft but I cant get it to move and dont want to strip it. Thanks again for all the help.

 

[Beats paddling]

Re: 1950's mark 25 restoration

Iwill attempt to post pics of this motor

 

[Chinewalker]

Re: 1950's mark 25 restoration

The bolt holding the pinion in place should have a tab washer locking it in. Bend the tab back and then you should be able to undo it. Put the driveshaft in a wood-blocked vice to hold it from turning - that bolt is in their pretty tight... Being that yours already popped once due to water issues, it's not a bad idea to disassemble completely, inspect and reseal...

 

[Beats paddling]

Re: 1950's mark 25 restoration

Closely inspected the driveshaft gear bolt and there is no tab and bolt is not coming out. Tried penatrating oil and heat still no luck. Do you think it would be ok to weld the rear of the bullet with the shaft and forward gear left in place?

One other crazy question - There are a number of holes drilled on the centerline above the water line in the rear of the drive shaft housing into the exhaust chamber - is this factory or some idiotic performance mod?

PS success on the magneto - all I did was clean up all of the magnet and coil passing surfaces and used a point file to clean up the points and now have spark at both plugs12bhnq

 

[Chinewalker]

Re: 1950's mark 25 restoration

The holes in the rear of the leg are supposed to be there - they're exhaust relief holes. When idling in neutral, a mist of water and exhaust should exit those holes.

I would recommend getting the driveshaft out as you will be doing a fair bit of filing to clean up the broken area after it's welded. You'll need to have the unit fully apart to clean it properly and get all metal filings out...

 

[Beats paddling]

Re: 1950's mark 25 restoration

Thanks Chinewalker for all your help. The drive shaft bolt is pretty buggered up - I may have to try one of those sockets that grips tighter the more force you put on it.

Checked the compression today and have 90 psi on both cyls - how does that sound.

Was looking at parts diagrams and it looks as though I may be missing a needle valve for idle speed adjustment. This is the one that is shown to go in the hole to the right of the carb intake. There is a large needle valve at the bottom of the carb. If I need a needle valve can you still get one?

Thanks again for all your help!

 

[Chinewalker]

Re: 1950's mark 25 restoration

What carb do you have? Should be an AJ-XX number on the carb bowl... I may have a parts carb on the shelf...

 

[Beats paddling]

Re: 1950's mark 25 restoration

Was out of town for a couple of days - I will post a picture of the carb tonight. Do I have to remove the carb to see the AJ-XX markings
Thanks

 

[Chinewalker]

Re: 1950's mark 25 restoration

Nope, they're right on the front of the bowl - should be visible if you pull the starboard side cowling... Might be hidden by the choke lever, but that's easy enough to move.

 

[Beats paddling]

Re: 1950's mark 25 restoration

The number on the carb bowl is AJ-43B. Can you tell in the attached picture if I am missing an idle adjustment needle? Also spark is intermittant I think I need to renew everything in the ignition to be safe. I have no idea on point gaps or the procedure for static timing. I sent an e-mail to MERC850 about his manual but have not heard back.
Thanks for all your interest in my Merc project.

 

[Chinewalker]

Re: 1950's mark 25 restoration

Yes, it looks like you're missing the low speed needle valve. Ignition parts are readily available. There's a guy named OldOutboardJim who posts frequently on the AOMCI site's Webvertiser who has good deals on the ignition components.

I will look around for a needle valve...

 

[merc850]

Re: 1950's mark 25 restoration

I've just emailed the manual, if you don't get it maybe you have a size limit on attachments (it's 8mb). I have a carb.