Johnson "70mod"

[hupiveneilija]

Have another problem now.#1 stuck like it was before when I opened PH. Think it has to be something with cooling. And salt&water, no good. Might put another PH on place.

If it have 2 stock pistons and middle .020 over should I jet it different?

But hey, atleast older electronics work! No rev limiter😂. Think I put that head to stock PH as planned originally and see how it works. Have to get some driving hours for setting the boat as good as it can be.
Maybe a little chamfer on the export😬.

Cant load pictures.

[filthy phill]

when I tell people there are bigger carbs out there they dont believe me.
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[filthy phill]

you probably have the same problem because the bore was scored from the last piston damage.
you honed it, but could still see the score lines from your pictures, and if its number one then yes maybe a water problem.
have you taken the exhaust cover off and made sure the hole in the top is free into the water jacket ? its a small hole about 3mm up in the very top.

some of the early 56 motors did not have good water cooling and there was a service bulletin about it, dont remember the number of the bulletin, but here is a diagram I
got sent to me showing about a water modification to the 56 motors pre 1986 to 1994, showing where some need to be drilled .
maybe someone on here knows a bit more about this.

I think this was mainly due to number 1 (top) and number 2 getting the pistons scored up ? maybe a proper OMC guru can help more with this bulletin.

ALSO there is a bulletin about changing the thermostat and cover, and the exhaust cover plate due to bad cooling..
The improved exhaust side cover plate part number is 343864 also needs the correct gasket to fit this.
ALSO there is the service bulletin about the water pomp and thermostat.
pics below

maybe these need to be done on your motor, you are definitely running early thermostat housing.

hope it helps
.


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[LittleCharger]

Have another problem now.#1 stuck like it was before when I opened PH. Think it has to be something with cooling. And salt&water, no good. Might put another PH on place.

If it have 2 stock pistons and middle .020 over should I jet it different?

But hey, atleast older electronics work! No rev limiter😂. Think I put that head to stock PH as planned originally and see how it works. Have to get some driving hours for setting the boat as good as it can be.
Maybe a little chamfer on the export😬.

Cant load pictures.

Did you blow another head gasket?

Regardless of the piston size you jet each cylinder on it's own.

Are those needle bearings dirty or on their last leg lol

[filthy phill]

they look like the original old roller bearings to me, and that piston has been sanded down to get old score marks off it.
I am also wondering if any little metal particles are still floating around in the block after port work.

[hupiveneilija]

Did you blow another head gasket?

Regardless of the piston size you jet each cylinder on it's own.

Are those needle bearings dirty or on their last leg lol

No I didnt. Was on its way to seize like before. Ive used this engine around 5 summers and when opened head in the winter it was also like that. I think its cooling related.

Those bearing are little dark because of that gasket/water problem. Havent disassembled ph yet to see how bad crankshaft bearing is. Dont know if I can use those.
Sad I dont have any used .030 piston, that one is gone now I think.

Ive got 2 extra powerheads, one with that oversize piston and one allmost like new inside wich I dont like to use for now.

Have disassemble that oversize one and clean up then put together and running. Must solve cooling issues too.

[hupiveneilija]

you probably have the same problem because the bore was scored from the last piston damage.
you honed it, but could still see the score lines from your pictures, and if its number one then yes maybe a water problem.
have you taken the exhaust cover off and made sure the hole in the top is free into the water jacket ? its a small hole about 3mm up in the very top.

some of the early 56 motors did not have good water cooling and there was a service bulletin about it, dont remember the number of the bulletin, but here is a diagram I
got sent to me showing about a water modification to the 56 motors pre 1986 to 1994, showing where some need to be drilled .
maybe someone on here knows a bit more about this.

I think this was mainly due to number 1 (top) and number 2 getting the pistons scored up ? maybe a proper OMC guru can help more with this bulletin.

ALSO there is a bulletin about changing the thermostat and cover, and the exhaust cover plate due to bad cooling..
The improved exhaust side cover plate part number is 343864 also needs the correct gasket to fit this.
ALSO there is the service bulletin about the water pomp and thermostat.
pics below

maybe these need to be done on your motor, you are definitely running early thermostat housing.

hope it helps
.


.

That 5/16 hole, where does it go if drilled?

[hupiveneilija]

That 5/16 hole, where does it go if drilled?

It goes behind the exhaust cavity and there to middle wall cylinder side.

[filthy phill]

the hole that gets drilled goes into water cavity between cylinder and block. it would be there to make sure water gets in and not just trapping air.

this modification was later improved on even more, by putting the hole up even higher inside the exhaust cavity.

I will take some good quality pictures today of the hole on my later model to show you where it is best to be for the cooling...

because on the later oval port motor the hole is right up the top in the corner.
I will take pictures of it later today for you, I checked it out recently on a old spare block I have same as mine.
it is there so no air gets trapped and lets exhaust side of the pistons correctly.
on the 1994 onwards all this is done at the factory to solve all the cooling issues.
if you put a torch into the top toy can see light at the side, and if torch at the side you see light between cylinder sleeve and the block.

also the large exhaust plate gets later one to also improve the water flow/cooling and must be fitted with the new gasket also.

I have got to get to my garage to move a few items and the engine block is at front, so will definitely take pics and post them for you.

there is lots of service bulletins , but nobody seems to share them enough on the internet..

would of been nice if someone put up lots of bulletins for people to see.

[hupiveneilija]

Done this. IMO has to be enough flow but there is not.
But how much pressure is too much? Where is that pressure relief ment to be to flow past thermo? If I make pressure relief lower by softer spring or some kind of a bypass hole next to thermo?