95 Force 70hp Rebuild

[atengnr]

Well, as I wrote in the other thread, I pulled the powerhead today, and found cylinder 2 and 3 with localized scoring and broken top comp rings. cylinder 1 was actually the best looking.

So, what is the best route for getting pistons? Does a complete gasket kit include the spacer to exhaust housing and the engine block to spacer gaskets?

Thanks alot,

Pic is of cylinder 2 and 3 appearance. Actually there is a missing piece of the top ring cylinder 3. Perhaps it was sent out the exhaust?

 

[atengnr]

[No message]

 

[flyingscott]

I would look for a different motor. There are better 70 hp motors out there than that one.

 

[racerone]

I often see folks posting----" the motor has 100 PSI compression so that is all good "--------This kind of proves that many folks are misled by this test.

 

[atengnr]

Yes. I never doubted my gauge readings. It is amazing to me that this engine ran quite well. Started with ease.

I am leaning towards rebuilding. I like the simplicitiy of these engines. Single carb. Smooth runner. I also have been through the gearcase, and have a new tilt motor on it. I also fear buying a $2000 used replacement motor that is not far away from having the issues I found here. I welcome everyone's thoughts. If I rebuild this right, I ought to be able to get 500+ hours of service out of it right (even if it is a force)?

Ive got a beautiful 68 55hp omc that was a fresh rebuild 10 years ago, but it doesnt have power tilt, and doesnt run as well as this force did.

 

[atengnr]

Can anyone suggest a machinist in the Michigan area? Safe to go to a local shop for this work?

 

[jerryjerry05]

My dad had a 68 model 65 hp Johnson, used primarily in salt water.
Normal maint would include new head gaskets every 6-7 years.
He showed me the cyl. before trading up to a 88 70 hp.
The wear/grooves was substantial, yet it ran great just REALLLLLY hard on gas, thus the upgrade.
Some motors run good with some wear!!! Some don't.
My fishing partners 2005 200 Yam OX66 the top cyl. has grooves and lower comp but runs like a new motor.

That being said the Force 70 was a poorly designed unit prone to fail because of the carburation design.
Usually the top cyl would starve for lubrication and eventually fail, yours is the exception.

Myself I would really think hard about a rebuild on this motor.

But if you do Wiseco pistons with their wrist pins and rings.

Depending on the serial# there are 2 gasket kits
Not sure if either has a gasket for the spacer.
Saw a running 120 Force on FB Marketplace for $400

 

[atengnr]

JJ I trust your opinion. I live up here in MI, and any boat I own doesnt get alot of use, maybe 30-50 hours a season. Can I get 500 hours out of a fresh rebuild? I use the pricey 100% full synthetic oil in my motors. If so, Im inclined to do so, because I know that the odds and ends that come up will be easy to diagnose and fix because of its simplicity.

 

[atengnr]

BTW, I am not sure what serial this motor is, both because the sticker is sun faded, and because it seems to me that this powerhead was off before (possibly a swap?).

 

[racerone]

If you do your own work then rebuilding is the best option for you.-----Should not be hard to find a shop to do blind holes.-----But look around for a 70 HP Johnson / Evinrude 1980 /85 in similar condition.-----Just as simple and easy to work on.

 

[atengnr]

Do u all generally replace main bearings and rod needles?

can I get away with filing high spots off scored area on the two pistons and reuse?

 

[flyingscott]

You cannot re-use those pistons if the rings have broken, the ring groove will be shot. Your motor will probably need to be bored out so you will need a complete rebuild kit.

 

[racerone]

???------Filing off bits of pistons ??-----Blunt answer is-----You may not be fully aware of how important the fit of a piston is !!-----Piston skirt has to do with crankcase compression !----So , no you can not re-use them.

 

[atengnr]

Thanks alot. Also looking at used powerheads too. was the 75hp the same motor other than a carb diameter or something (or exactly same)?

 

[jerryjerry05]

JJ I trust your opinion. I live up here in MI, and any boat I own doesnt get alot of use, maybe 30-50 hours a season. Can I get 500 hours out of a fresh rebuild? I use the pricey 100% full synthetic oil in my motors. If so, Im inclined to do so, because I know that the odds and ends that come up will be easy to diagnose and fix because of its simplicity.

The expected life after a rebuild??? Maybe 10 years? Maybe a week??
If you use the expensive oil? I wonder why the motor lost 2 cyl??
Before I'd rebuild, I'd try to figure out why it or what went bad??

Someone said cutting blind holes? Go to a machine shop that works with outboards.
Replace all 3 pistons.
I'd really think twice about a rebuild on that motor

I'm from Flint originally, ended up in West Branch before the last move to Fl.
There are LOTS of junk boats in millions of back yards in MI.
That's how we financed a trip to Alaska. Collect junk boats and break them down and sell the parts.

The simplicity of the Force. I agree completely just not the 70 your fixing.
Paid 125$ for a running 125/1988 The flywheel key had sheared and the owner couldn't figure it out

You can get away without replacing the bearings unless somehow they get rusted.

 

[atengnr]

Ahh, i just bought this motor in spring 2019, so who knows how it was treated before me.

 

[atengnr]

What about buying a powerhead woth good compression for $600 ish? Reasonable thing to do?

 

[atengnr]

Aha, i see why the top cylinder was good - its got a wsm piston in it meaning someone has reworked that cylinder.

 

[flyingscott]

What about buying a powerhead woth good compression for $600 ish? Reasonable thing to do?

Where are you located? In the states the whole motor in good running condition is worth maybe $600

 

[The Force power]

Same here :canada: