1997 90 hp rebuild project

[CAPTKEV85]

So my winter project was to replace the frozen pivot arm. Since I had to pull power head off, I decided to disassemble and perform a power head service. I found cylinder number 1 piston skirt to be scored. The cylinder wall has no grooves though.

My plan is to order a WSM rebuild kit .10 over. I’m going to send the block and crank to machine shop. Any recommendations on what i should have them do? I saw somewhere the intake and exhaust ports should be worked? Also mill the head down for some more compression?

These are such a simple engine to work on I can’t see spending 15k on a new motor.

Any opinions would be great

See pictures.

 

[The Force power]

So my winter project was to replace the frozen pivot arm. Since I had to pull power head off, I decided to disassemble and perform a power head service. I found cylinder number 1 piston skirt to be scored. The cylinder wall has no grooves though.
Any opinions would be great

My question; what do you mean by "pivot arm" & why send-out the crank???
My opinion; I would clean-up/hone the worst cylinder-wall first & see if you actually need to get a Re-bore.

Also I would only replace one piston (providing the rest are good, what were your compression-readings on them?)

 

[racerone]

Is there a ridge at the top of the bore ?----If so then 3 new0.020" O/S pistons is the path to happiness.

 

[CAPTKEV85]

The main steering pivot shaft had froze. In order to replace it the power head needs to be removed.

Crank looks fine but figured if the block is going to shop maybe have them look at it.

No noticeable ridge at top of bore. Maybe catch a little with my nail.

 

[racerone]

Put in 3 new pistons at 0.020 O/S.

 

[CAPTKEV85]

I ended up ordering a .020 kit from WSM. I remember reading somewhere but can’t find it, that milling the head .065 and mill exhaust will help improve flow. Block is at machine shop and they are also chamfering the intake and exhaust ports.

Anything else I should do to block?

 

[Nordin]

I do not think milling the head will increase power, maybe raise the compression. Check that the pistons not touching the spark plugs if you will mill the head.
If not milling the head and it is my suggestion, check the head from warping (it used to be a little warped anyway) and grind it flat with a piece of water sandpaper at a piece of window glass.
Pull the fuel recircual cover (dogbone) and clean the screens. Put new gaskets on the cover.

 

[CAPTKEV85]

I do not think milling the head will increase power, maybe raise the compression. Check that the pistons not touching the spark plugs if you will mill the head.
If not milling the head and it is my suggestion, check the head from warping (it used to be a little warped anyway) and grind it flat with a piece of water sandpaper at a piece of window glass.
Pull the fuel recircual cover (dogbone) and clean the screens. Put new gaskets on the cover.

Ok good to know thank you.

 

[flyingscott]

I ended up ordering a .020 kit from WSM. I remember reading somewhere but can’t find it, that milling the head .065 and mill exhaust will help improve flow. Block is at machine shop and they are also chamfering the intake and exhaust ports.

Anything else I should do to block?

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