1992 Force 70HP wont start

Jiggz

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Oct 23, 2009
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Can you post pics of the #2 cylinder with the piston at BDC. I understand it is rusty which is an indication of water intrusion. With a broken head gasket, we can surmised it is due to the broken head gasket. But now with new gasket the compression is still quite low. Could it be the rings are already worn out or rusted also.

It all depends how much time and effort you want to spend on this to fix it but it is fixable unless the cylinder is seriously gouge. if it is just the rings or the piston, yup you can fix this for less than $200 or maybe $300 tops.

Search the forum on how to replace piston to give you an idea on how to do it.
 

jerryjerry05

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Where you located?
​Post that and maybe some one can help.
The rebuild/replace one piston can be done while still on the motor.
Depending on the damage.
It's tricky but can be done.

Myself I like to redo all the gaskets and rings and start with a "kinda new" motor.
 

brianq

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I am in Lavellette NJ.


I ran the compression test with a tester I got from Auto Zone since I was questioning the harbor freight one and I got 80, 40 90.

I took more pictures of the piston I dont know what BDC is?
 

jerryjerry05

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The comp results are WAY!!!! low.
Post the pics.
It sounds like a rebuild is in your future.

Look around there are lots of motors for sale.

Sometimes the controls are sold with the motor.
Your controls only fit the Forces.
 

brianq

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Messages
145
The comp results are WAY!!!! low.
Post the pics.
It sounds like a rebuild is in your future.

Look around there are lots of motors for sale.

Sometimes the controls are sold with the motor.
Your controls only fit the Forces.



After taking off the summer I have finally started the motor rebuild! I did budget for a new one so I decided to put in the sweat equity. I dont have a clue about motors but I am very handy around the house so I hope with everyones help I will get the boat running again! So far I have taken everything apart removed the power head, got to the pistons and found the compression issue! There are pieces broken off from the rim of 2 pistons (pictures below). Now the questions:

The cylinders seem really smooth but should I still have them honed since everything is taken apart? If no, should i reuse the rings which are intact? I have to assume its worth a hone and new everything?

Is there a rebuild kit which will have each gasket since they pretty much all fell apart. The one in the exhaust cover on the port side, between the power head and the case. Sorry for the lack of technical terms I cant find my Selco book at the moment.

There was no gasket between the bow side cover and the block, seems strange that you would have a head gasket and not one on that side?

There are four panels on the starboard side of the power head on where the fuel line was connected, any reason to open those, I see they are gasketed.


It was a lot of work breaking everything down I would like to replace everything now then risk it not starting after reassembly. Any suggestions? Thanks!
 

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brianq

Petty Officer 2nd Class
Joined
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Messages
145
The comp results are WAY!!!! low.
Post the pics.
It sounds like a rebuild is in your future.

Look around there are lots of motors for sale.

Sometimes the controls are sold with the motor.
Your controls only fit the Forces.


The crank shaft seems to have a good amount of surface rust, any issue with that?
 

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jerryjerry05

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The rust on the weighted side of the crank is nothing to worry about.
Just wire brush it and oil it to stop further rust.
​BUT!!! Look under the bearings and see if the rust got to the bearing mating surface??

The damage on the piston means a new piston is needed.
​The wear on the side of the piston, if it doesn't come off with a brush? Replace the piston.

​With the damage to the rings and the piston? your sure there is NO damage to the walls??
NO? then get them honed and install the new pistons.
From the pics it looks like there is some scoring??
Never use old rings.

​Wiseco has piston assembly's they come with rings and a wristpin kit.
Their rings won't fit the OEM pistons.

​To change the pistons with OEM you'll need special tools.

The intake side uses silicone and a spaghetti seal(depending on year).

​Yes remove the ports under the fuel pump.
​There could be pieces of the rings there??

Ebay for the gasket kits.FG1037-1
 
Last edited:

brianq

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Jerry,

Thanks for all the information I have a few more questions, I appreciate all your assistance

- Should i get a machine shop to hone the cylinders or can I use an attachment for a drill with no experience?

- Any recommendations on cleaning the power head while its all taken apart, perhaps for a quick coat of paint? Lots of pieces of old gasket stuck to it and paint chipping.

-Wiseco has three different boresizes is this a published value or should I get a caliper and measure?

- When I take any bolts out of the outside case some rust/ dust sediment material comes out, is this normal? Will i have to do an tapping of these holes, I am hoping that material isnt the threads inside the block. (terrible description)


While all apart I will replace all three pistons, I dread putting this all back together and having low compression still.
 

jerryjerry05

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Good idea on replacing all 3!!
Yes get a machine shop to hone.
The shop can tell during the boring, if the bore has gotten damaged or egg shaped.
Now if the machine shop says the bore is ok .
​And the pistons are the original size?? then buy standard pistons.
I don't have the specs on the 70hp bore size.
You'll probably need a factory manual or maybe someone here can get it for you??

​I use an air powered hand die grinder , kiinda like a dremel but stronger.
I use a wire wheel to remove the remaining gaskets and carbon/crud.
​Be careful the wheel can remove aluminum if pressed too hard.
Paint after the block is re-assembled and the head bolts tuorqed,
before the electronics are installed and cover all the open screw holes.

The powder is a reaction of did-similar metals. I/E aluminum block and steel screws. "Normal"
​I use a thread chaser(Snap-on) on the holes and on the bolts and screws and nuts.
​Then during reassembly I use thread locker on the rod caps.
​The head bolts gets a light coat of grease.

Think about starting a new thread with the rebuild as a topic and include lots of pics along the way??

Good luck.



 

brianq

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Joined
Jul 15, 2012
Messages
145
Good idea on replacing all 3!!
Yes get a machine shop to hone.
The shop can tell during the boring, if the bore has gotten damaged or egg shaped.
Now if the machine shop says the bore is ok .
​And the pistons are the original size?? then buy standard pistons.
I don't have the specs on the 70hp bore size.
You'll probably need a factory manual or maybe someone here can get it for you??

​I use an air powered hand die grinder , kiinda like a dremel but stronger.
I use a wire wheel to remove the remaining gaskets and carbon/crud.
​Be careful the wheel can remove aluminum if pressed too hard.
Paint after the block is re-assembled and the head bolts tuorqed,
before the electronics are installed and cover all the open screw holes.

The powder is a reaction of did-similar metals. I/E aluminum block and steel screws. "Normal"
​I use a thread chaser(Snap-on) on the holes and on the bolts and screws and nuts.
​Then during reassembly I use thread locker on the rod caps.
​The head bolts gets a light coat of grease.

Think about starting a new thread with the rebuild as a topic and include lots of pics along the way??

Good luck.





Found a local machine shop to check, hone and clean up the cylinders, guy thinks it will be about $50 hope to bring it over there tomorrow, says he can turn it around in a few days. I will wait to order pistons until I get it back from him, just in case.

I showed pictures of the pistons to a mechanical engineer friend of mine and he says that the cracked ringlands indicate pre-ignition that their may have been a timing issue that caused this damage?

The cylinders were stuck and I used a socket, bar and penetrating oil to unstick them. When it wouldnt start I used starting fluid to try and get it to start. Perhaps these are reasons for the damage?


He says the head bolts are usually torque to yield as in they cant be used more then once as they can only stretch a certain amount?

Jerry do you agree do you think I need new head bolts? From what I have seen on youtube and on here it looks like everyone is reusing their bolts.


I like the idea I will start a new thread.

Thanks as always!
 

jerryjerry05

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No on the new bolts.
They only get 20# so the stretch is minimal if at all.
​The rings and other damage could be from timing? the carb not set right? the recirc system clogged?
​Possible overheating? Low oil in the fuel/oil mix? Or too much oil in the mix?
​The starting fluid? probably not. That damage looks like it's been there?
If the exact reason can't be figured out? It's best to completely dismantle the whole block and go through everything and change all seals and gaskets.

Remember silicone's cheap. use a lot when sealing a joint.
 

brianq

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Joined
Jul 15, 2012
Messages
145
No on the new bolts.
They only get 20# so the stretch is minimal if at all.
​The rings and other damage could be from timing? the carb not set right? the recirc system clogged?
​Possible overheating? Low oil in the fuel/oil mix? Or too much oil in the mix?
​The starting fluid? probably not. That damage looks like it's been there?
If the exact reason can't be figured out? It's best to completely dismantle the whole block and go through everything and change all seals and gaskets.

Remember silicone's cheap. use a lot when sealing a joint.


Jerry is there any risk that I rebuild and the damage occurs again to the new pistons?
 

jerryjerry05

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May 7, 2008
Messages
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Like I said in the last post:If the exact reason can't be figured out? It's best to completely dismantle the whole block and go through everything and change all seals and gaskets.
Then yes you can possibly have the same damage occur.

Some just replace the bad piston and don't do anything more.
Not me.
 
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