digging into a '56 mark 25

[shoestring]

hi all. i was just given a 56 mark 25. i think it would be kind of cool to get this old girl up and running again. compression is good, but spark to only one cyl. i pulled the flywheel and seen that the coil covering is split pretty bad on both of them. so new coils are in order, along with points, plugs, and condensers. but lets dig a little more before we go spending money. tore the lower unit down to find the impeller is shot. no evidence of over heating that i can see. the bearings seem to be in great shape along with the sealing surfaces on the shafts. except with the drive shaft sealing surface below the impeller. a 0.625 speedi-sleeve would fix this right up. gears are in great shape, it dosent look like this motor has ever seen much use, the prop has about 90% of the original sunset orange paint still on it, i hardly think it has been replaced. carb is clean but should have some new parts put in it along with the fuel pump. the only damage i see it the casting on the side of the motor below the tiller handle. there is a block of aluminum that the tiller haldle rests against when you fold it down, well it is broke off allowing the handle to lower down too far. probably fell over in someones garage. a scrap of aluminum, drill, tap, 2 screws and maybe a little jb weld could fix this right up. i would like to get a new impeller housing but seems they are NLA. some fine steel wool should smooth things out enough for a new impeller to last. other than that just a little cleaning and some lube on the moving parts and i should be in business. I have my parts list here and am ready to order but would hate to spend the money to find another problem that i didn't notice. if any of you guys have any experience with these old mark motors, i'd sure like to hear from you, and learn of any inherent problems they might have. I hear they could use new crank seals from time to time. crank bearings seem nice and tight with no noticeable end/side play. area under flywheel is clean and dry, no oil here so i'm thinking that seal is ok. no idea on the lower one though. the thought of having a good reliable 20HP!!!!!! outboard makes me all warm and fuzzy inside. i'm up to about $300 bucks on my parts list and willing to do it. i think i'll do a little more tinkering and inspecting while i wait for a reply from you guys. thanks

 

[shoestring]

Re: digging into a '56 mark 25

bump, maybe no news is good news?????????????????

 

[coolguy147]

Re: digging into a '56 mark 25

check gear oil. compression should be within 10% of each cylinder.

 

[lindy46]

Re: digging into a '56 mark 25

If compression is good, invest in new coils, points, etc. and replace the plug wires. Do a carb rebuild and change the fuel lines. Change the oil in the lower unit. Replace the impeller. Then try to start it. If it runs good, you're good to go! As far as other things go, if it ain't broke, don't fix it!

 

[daveswaves]

Re: digging into a '56 mark 25

except with the drive shaft sealing surface below the impeller. a 0.625 speedi-sleeve would fix this right up.

First off congrats on bringing an old merc to life. You are on the right track replacing both coils, dont forget to change the spark plug wire, you can still get copper core solid spark plug wire at tractor supply stores if you cant find it in a marine store. You should change the fuel lines as well, the older lines will not stand up to the ethanol in todays fuel. If the mag plate is nice and clean then the top seal is ok. Your comment on the shaft sealing area below the impeller does not make sense to me, very unusual area to wear . Are you sure its not just smaller in that area, not worn. Post a pic of the area in question if you can.

 

[shoestring]

Re: digging into a '56 mark 25

the sealing surface below the impeller is not worn, it is pitted. it happens when small drain holes get plugged and water can't drain out when you pull the motor out of the water. water can get trapped there for a long time. speedi-sleeves are awesome for just such a problem. not only am i changing the lower unit oil, i am doing a complete disassembly, clean and re-seal to it. i haven't fooled around with merc's this old and was curious if they had any inherent problems. and yes i plan on relplacing the plug wires. it is a cool old motor! I can't wait until the old timers come up to me at the lake and want to B.S. about it. 1956 is going back a ways. the motor was 14 years old when i was born. back when tv's were black and white, cars had fins, and politicians were crooks, well some things don't change much!

 

[daveswaves]

Re: digging into a '56 mark 25

the sealing surface below the impeller is not worn, it is pitted. it happens when small drain holes get plugged and water can't drain out when you pull the motor out of the water. water can get trapped there for a long time. speedi-sleeves are awesome for just such a problem. not only am i changing the lower unit oil, i am doing a complete disassembly, clean and re-seal to it. i haven't fooled around with merc's this old and was curious if they had any inherent problems. and yes i plan on relplacing the plug wires. it is a cool old motor! I can't wait until the old timers come up to me at the lake and want to B.S. about it. 1956 is going back a ways. the motor was 14 years old when i was born. back when tv's were black and white, cars had fins, and politicians were crooks, well some things don't change much!

Hey, I resemble that remark...seems I have 20 more years experience than you. Pitted makes sense.