Rebuild kf7

[Mallett]

I think I blow up my kf7 it died as I was running the river. It stopped with a rattling clunk. Is there a manual that will help me take down the motor, any advice on where to start, or is there someone that will rebuild it? Thanks

[green-thumbs]

Mercury Service Manual for 1965 and Prior Models plus Illustrated Parts Manual that covers KE7,KF7,LG7 and KG which will be well worth having and close study. If you need parts the parts manual will show you which models share the same part number. Before doing anything, diagnose the probable cause of problem, Do not fix things that are not broken, There are a lot of people in AOMCI who will know the ins and outs of work on this series who will chime in .

Louis

1 user thanked author for this post.

Mallett

[dave-bernard]

Call Me 1 914 310 7086 Dave.

[billw]

Does it now turn over, or is it locked up? If locked up, remove the recoil and see if you can turn the flywheel all the way around by hand. If you still can’t turn it, remove the power head as a total assembly and see whether the power head or the lower unit is locked up.

Do you think it could have overheated?

Long live American manufacturing!

[Mallett]

Yes it still turns over, it’s not seized. It feels different when pulling the starter cord. Less compression and not as smooth. Any thing is possible what are the effects of over heating?

Thanks for your time and advice

[Mallett]

Thanks Louis, I’ll try and find that manual today. I want to get this back on the water,it’s so much fun on my flyer. any advice will be helpful. I’m a decent mechanic just never turned wrenches on outboard’s new or seventy year’s  old.

[green-thumbs]

There is a member with cylinder blocks for sale now. It might be a good idea to look into as the symptoms you describe indicate rings and or cylinder bore damage. My first place to look would be water pump impeller. If the impeller is not known to be good , assume it needs to be checked and usually replaced. While it is possible in theory to bore cylinder to a standard oversize and fit oversize rings and pistons….The problem is oversized rings and pistons are hard to come by, You may be able to source a complete powerhead…that would get you back on water sooner. Lower crankshaft seal should be renewed even if all else looks good on a donor powerhead. I believe KE7,KF7, KG7 and KG4 powerhead will bolt right up. KE7 are common and I have seen then sell for $10.00 at swap meets. Not as much power, but, an option that can be swapped out when you have worked out issues with your present KF7 powerhead.

Those who KNOW are invited to chime in and correct me if I am in error or expand upon subject…Not often do Mercury fans suggest less power.

Louis

Remover INTAKE port covers to check pistons for scoring AND to push on rings with a probe to see if they are stuck in grooves or mover slightly when pressed.  A very experienced friend fried a Mark 30 when water pump impeller failed  at speed. He was too eager to try it out. It ran real well until it didn’t. He found block and parts to do a rebuild plus a new impeller. If you check impeller and find it has failed, take a look at piston and rings thru ports to confirm. Most likely the impeller failed and the powerhead seized up due to overheating. Not a big deal to rebuild the second one, but. all things done for the first time have a learning curve, thus my suggestion to look into a powerhead for now, Things go better when not under pressure.
The large plate on side of block is the EXHAUST manifold cover…NEVER attempt to remove without a good reason for doing so. One or more of the fasteners are stuck and will snap off, Assume all of the cover fasteners are stuck …use torch and gentle technique NOT force.

 

 

 

 

 

 

 

 

 

 

t

 

• This reply was modified 2 years, 10 months ago by green-thumbs.
• This reply was modified 2 years, 10 months ago by green-thumbs.
• This reply was modified 2 years, 10 months ago by green-thumbs.

1 user thanked author for this post.

Mallett

[billw]

I guess my next move would be a compression check. You should have minimum 110 psi.. I’d like to see 125. After checking compression, remove the complete power head and see if it still turns with difficulty. What you’re trying to determine is whether the power head or the lower unit is what failed. (These Mercs have very fragile lower units and do not tolerate lack of good lubrication well, AT ALL.) When the motor stopped, did you immediately pull the starter cord to try to start it? Was it free-turning at that moment, or bound up? If it was stuck at that moment, then became free to turn, albeit badly, it probably over-heated. As Tubs said, either way, you’ll need a known good impeller, going forward. Also, what fuel/oil ratio were you using? Stupid question, but with so many four strokes on the water these days, you DID mix oil in the fuel, right?

Long live American manufacturing!

[Mallett]

Thanks for all your input. I’m going to start getting into this morning as soon as I get the manual down loaded. I’ve ran 6 or 7 tanks of gas through it, do you mix the the fuel the way it says to on the motor with a pint of 10/w30to the gal or go with regular outboard two stroke oil? I have been running 8 oil to the gal.
yes of course I tried to start it again, it pulled over it didn’t feel the same 3-4 pulls and it did try and start I killed it right away.

[Mallett]

I have a line on a mark 20 is that a faster better motor then the Kf7?

 

[Author]

Posts