Rebuilding a Mark 25 and 55

[gkabot]

I'm a newbie to old merc rebuilds. I now have a 1956 Mark 25 and a 1957 Mark 55. What will my rebuild limits be without specialized merc tools for these engines? Besides e-bay, are there any other sources for these tools? I have purchased owners manuals and parts manuals for both engines and I'm waiting for my copy of the service manual. Any general tips as to specific problems I should know about would be greatly appreciated.<br /><br />Thanks,<br />Gary

 

[Yepblaze]

Re: Rebuilding a Mark 25 and 55

I guess it depends on how much of a rebuild you intend to do.<br /><br />Most of the repair processes use standard tools.<br />There are some instances where a spanner type wrench is required to disassemble the lower unit and such. Then some pullers and presses, but those are somewhat standard mechanic fare.<br /><br />There are other times when you can make due with creative mechanic'in.<br /><br />I, myself have never had need to totally tear one down for a complete rebuild. But I've done my share of disassembly for repairs.<br /><br />You may have more difficulty finding parts if you really want to overhaul them completely.<br /><br />I guess Oldmercs.com<br /><br />and the antique outboard motor club message forum might be good places to look <br /><br />I might also suggest you weigh your intentions in the end. <br /><br />Do you intend to just run these motors? Display? <br /><br />Even with a top notch rebuild and restoration they probably won't bring much money when you decide to part with them.

 

[gkabot]

Re: Rebuilding a Mark 25 and 55

Thanks for the response yepblaze. I do intend to use them both maybe 5 to 10 times per season and possibly for some shows. I'm in this for love (LOL) not the money. But I do intend to do a fairly complete rebuild without opening the powerhead if I can help it as I think this will prove to be fun (but I'm sure also frustrating). I've seen oldmercs.com and they seem to have most of the required parts.<br /><br />What type of puller will I need for the flywheels? I believe the impeller might pose some problems also? Any hints on repainting? What about painting the blocks on these?<br /><br />Thanks again for the info

 

[Yepblaze]

Re: Rebuilding a Mark 25 and 55

Head over to John's Old Merc forums for detailed info on paint codes and the like. Most of the guys that frequent that site can be quite helpfull. <br /><br />Search what's there before asking the samo old questions.<br /><br />I have seen posts over there telling how to make a pin spanner wrench for the water pump covers and the like.<br /><br />Changing out an impeller doesn't have to be a big deal. Remember heat is your friend. I use a propane (mapp gas) torch liberally along with copious amounts of flaming smoking oils applied to stuborn parts and usually will prevail.<br /><br />Your best tool right now is a compression tester.<br /><br />Run a compression test on all cylinders and look for less than 15% variation. That will tell you right away if the motors you have are going to be good candidates.<br /><br />Wouldn't hurt to pull the lower units, drain off any lube and pressure test those. It's pretty common for the seals to need attention. That can be a tough job sometimes. There is one guy over at John's that does lower units. Once you check the seals and they are ok you can run normal gear oil in that Mark25 rather than lubriplate grease.<br /><br />Best of luck to ya.

 

[gkabot]

Re: Rebuilding a Mark 25 and 55

Thanks for all the help yepblaze. I'm looking forward to the process and will post specific problems here as I progress.