'89 Force 35hp scored Cyl Repair

[timmeraw]

Hi,

Just picked up a pair of ?89 Force motors. One 50 and one 35hp. The 50 is running great but for a pretty loud knock/tap. In any case I sold it cheap to a kid who was aware and willing to figure it out.

Now for the 35. Fired it up and it ran but would only stay running on an advanced idle. Checked compression and sure enough the lower cyl was low?real low. Like 40-50psi. Thinking maybe stuck ring or something?warmed up?doused the cyl with seafoam and marvs mystery oil and let set for a bit. Compression increased some to 70 psi so I know something is wrong. Pulled the head and found this:



It is a gouge that something has worn into the cyl wall. Do you think it could be bored out and then use an oversized piston?

Any suggestions would be greatly appreciated.
Thanks,
Tim

 

[gm280]

Re: '89 Force 35hp scored Cyl Repair

Hi,

Just picked up a pair of ?89 Force motors. One 50 and one 35hp. The 50 is running great but for a pretty loud knock/tap. In any case I sold it cheap to a kid who was aware and willing to figure it out.

Now for the 35. Fired it up and it ran but would only stay running on an advanced idle. Checked compression and sure enough the lower cyl was low?real low. Like 40-50psi. Thinking maybe stuck ring or something?warmed up?doused the cyl with seafoam and marvs mystery oil and let set for a bit. Compression increased some to 70 psi so I know something is wrong. Pulled the head and found this:
View attachment 185654
View attachment 185655

It is a gouge that something has worn into the cyl wall. Do you think it could be bored out and then use an oversized piston?

Any suggestions would be greatly appreciated.
Thanks,
Tim

WOW that is hard to say not seeing it with my own eyes. Can you actually feel that area? If so I say bore and go with new pistons and rings is your only way to bring it back to specs. However, if you can't actually feel any gouge or surface irregularities then maybe a cross-hatching of the cylinder and new rings could work. It could even be a wrist pin that came loose and scoring the wall. More info needed before a final decision could be made. If you do further disassembly, measure the ring end gaps to see how far out they are. You may take it to a reputable machine shop and have them do measurements on it for out-of-round or wear problems for peace of mind too...

 

[timmeraw]

Re: '89 Force 35hp scored Cyl Repair

Oh yea you can see and feel the gouge/trough. When turning the crank you can also see and hear the air/oil leaking past the piston on the compression stroke(obvious why the compression is low). Guess I am gonna have to get the wrenches out and tear it down.

 

[Frank Acampora]

Re: '89 Force 35hp scored Cyl Repair

As far as I know, aftermarket pistons are not available for the smaller Force engines. You would best first go to your local Mercury dealer and see if stock oversized pistons are available and check price. Then, if they are available check prices on boring. You may find that the work and cost will make it economically not feasible to do an overbore. Thus, the engine will become a parts engine.


The bottom cylinder does not look bad in the photo. It is possible that the engine has broken a ring. Honing and ring replacement can be done without disassembling the engine. ---Again, if stock rings are available.
Edit: Never mind, just read your last post.

Typically, these engines are worth more in parts than as running engines.

 

[tater76]

Re: '89 Force 35hp scored Cyl Repair

I know I have seen oversized 40hp piston/ring kits on eBay for $78+shipping. However, I can't remember what size your pistons are? Frank? So they may or may not work. You can also pick up a used powerhead on there for around $300 shipped, however, it may not be worth it to you. Sounds like the 50 might have been the way to go