Johnson "70mod"

[filthy phill]

just because your English dont come across good, do not think I am an idiot.....you should try to explain a bit more what your problem is.

you say the thermostat hole ? wtf is that supposed to mean ? why are you worried about thermostat when you only use a butchered one anyway ?
do you mean thermostat will not fit now ?
or do you mean the recess has been shaved away letting the thermostat fall though ?
or do you mean the thermostat itself has a hole in it ?

As said I would do earlier I Just measured Original 56 later style cylinder head part number 339221 the pocket depth is 0.5315 (13.5mm) and the volume of the chamber is 32.1cc.
CC was measured with the plug hole taped over and filled to be exactly level with top of the head surface inc the chamfer.
this is standard from factory never been touched since it was new.
also measured across the chamber and it is 54 mm at bottom of chamfer ( 2.12598 inches ) and 58mm at the top of chamfer ( 2.2834 inches ).
chamfer is 4mm deep (0.1574 inches).

used medical syringe to find the volume and used accurate and calibrated Steel Vernier Caliper and then checked with cheap digital vernier gauge.
amazingly the cheap digital was giving exactly the same dimensions..

" You should open once one of these engines and have the parts on Your hands to look at them properly. Then You understand."

As for me taking one of these engines apart and looking into the internals, I only got down this far on the top bit..

[hupiveneilija]

just because your English dont come across good, do not think I am an idiot.....you should try to explain a bit more what your problem is.

you say the thermostat hole ? wtf is that supposed to mean ? why are you worried about thermostat when you only use a butchered one anyway ?
do you mean thermostat will not fit now ?
or do you mean the recess has been shaved away letting the thermostat fall though ?
or do you mean the thermostat itself has a hole in it ?

As said I would do earlier I Just measured Original 56 later style cylinder head part number 339221 the pocket depth is 0.5315 (13.5mm) and the volume of the chamber is 32.1cc.
CC was measured with the plug hole taped over and filled to be exactly level with top of the head surface inc the chamfer.
this is standard from factory never been touched since it was new.
also measured across the chamber and it is 54 mm at bottom of chamfer ( 2.12598 inches ) and 58mm at the top of chamfer ( 2.2834 inches ).
chamfer is 4mm deep (0.1574 inches).

used medical syringe to find the volume and used accurate and calibrated Steel Vernier Caliper and then checked with cheap digital vernier gauge.
amazingly the cheap digital was giving exactly the same dimensions..

" You should open once one of these engines and have the parts on Your hands to look at them properly. Then You understand."

As for me taking one of these engines apart and looking into the internals, I only got down this far on the top bit..

Its about material thicknes, how much you can shave before head starts warping.
And hey, nice to see engine torn apart.

[filthy phill]

SSt60 head has pocket depth of just 11.178 mm from surface to plug hole.

I just measured the thickness at the bottom of the head, total thickness as can be seen in the pic is 36mm = ( 1.37795 inches ).
thickness of metal at the hole for thermostat is 6mm = (0.2352 inches)...
I have been told these particular heads can be shaved safely 80 thou and that would take pocket depth to 11.45mm = (0.4514 inches), some have gone that
little bit extra and shaved it by 100 thou to make it 11.1 mm (0,440 inches) same as sst60 head.
thickness at the hole in the head where thermostat sits would then be just 3.46mm =(0.13622 inches).

I dont know the thickness of the earlier cylinder heads, maybe they were thinner or thicker I dont know.
maybe someone who has done this can tell you the thickness of the head before they started shaving it.


my engine got taken apart a long time ago, about 1.5 years... been finding and making parts ever since to finish it .
waiting on engineer to set up his machines. plus illness has kept it all very slow work.
will eventually get done but not to sst60 specs, as I dont have a lightweight tunnel for the motor to go on at those specs.
my priority is not racing just wanting to go from 6,00 to 7,000 rpm on same prop. maybe.

pics below of where I measured the total thickness of the head.

[LittleCharger]

Well I have 2,6mm there and pocket depth is that 0,513=13mm. If I take it to the 0,440=11,2mm that leaves 0,8mm material thicknes there. Is that too little?
I measured psi under 130 on every hole with 1,2mm gasket. Now my small head with 1mm gasket 145to147. Was with 1,5mm gasket, quite squish!
Remember i have ex dur 180*.

.

Think could use little more fuel?

8 mm is too thin in my opinion. Heads vary so much from the factory, I have one head with a .375 pocket and the thermostat area is 1.25 mm.

Yes your compression will be down some with that kinda duration but may also be down due to wear, a leak down test would let you know where your at .

Is that wash on the cylinders all from run time with the current porting. If it is your good on the fuel, fat for racing but good for the lake, the middle cylinder tends to run the leanest on that particular block. Give each cylinder what it wants.

[Hevi Kevi]

Those are i think from older 2cyl 60hp. Have removed chokeflaps and modified needlescrew in place of idle jet. Original with 56 jets. Those up pipes inside the bowl has much to do every invidual carb model i guess. But what size to start?

If they are from an older 2 cylinder, I would try what LC said and try 72's, 73s. All depends on how much compression you are planning to run it with and how much power it's making. The more power it makes, the more jet you'll need. If you're running at 180 psi and your mods are working well, you may need more than that... like 76's or more.

[hupiveneilija]

SSt60 head has pocket depth of just 11.178 mm from surface to plug hole.

I just measured the thickness at the bottom of the head, total thickness as can be seen in the pic is 36mm = ( 1.37795 inches ).
thickness of metal at the hole for thermostat is 6mm = (0.2352 inches)...
I have been told these particular heads can be shaved safely 80 thou and that would take pocket depth to 11.45mm = (0.4514 inches), some have gone that
little bit extra and shaved it by 100 thou to make it 11.1 mm (0,440 inches) same as sst60 head.
thickness at the hole in the head where thermostat sits would then be just 3.46mm =(0.13622 inches).

I dont know the thickness of the earlier cylinder heads, maybe they were thinner or thicker I dont know.
maybe someone who has done this can tell you the thickness of the head before they started shaving it.

Good morning,
It seems that sst60 and newer oval port heads are same allready lower combustionchamber cast and can be shaved even further. Older ones are cast with deeper chamber and can not be shaved to 0,440in because there is no material for that.

[hupiveneilija]

8 mm is too thin in my opinion. Heads vary so much from the factory, I have one head with a .375 pocket and the thermostat area is 1.25 mm.

Yes your compression will be down some with that kinda duration but may also be down due to wear, a leak down test would let you know where your at .

Is that wash on the cylinders all from run time with the current porting. If it is your good on the fuel, fat for racing but good for the lake, the middle cylinder tends to run the leanest on that particular block. Give each cylinder what it wants.

Yes its all from start with that block. It is quite worn so i dont expect more psi from it.
Jets are 56, 57, 56. Middle could be even bigger because 0,020 over size.
Im not starting to lean because we drive long periods wot.

Porting is ex 1,382 or 180* and boost level with transfers.

[hupiveneilija]

If they are from an older 2 cylinder, I would try what LC said and try 72's, 73s. All depends on how much compression you are planning to run it with and how much power it's making. The more power it makes, the more jet you'll need. If you're running at 180 psi and your mods are working well, you may need more than that... like 76's or more.

Start with 72, put new plugs on it and make wot pull to see how they look. That 147psi is max what i get now because worn block and those older heads cant be shaved low enough to get higher. CR is ~ 7.0:1 now with current ex timing.

[hupiveneilija]

SSt60 head has pocket depth of just 11.178 mm from surface to plug hole.

.

Thats known. If You have ovalport head in hands, would You measure pocket depth from that piece? I dont have any ovalport head.

[Steves Jem]

With so minimal depth what happens to that thermostat hole?
I would like as much comp with my ex duration as I can.

Youre not using normal pump gas on those psi readings, right?

Ran Leaded and unleaded Av Gas 100 octane. This motor was the 56ci bridge port finger ported block with the Mod 50 straight front and 1 in dual throat carbies and the flex flywheel. Ran on a 14ft racing mono similar to the T850 and pulled 8,000 rpm with the 25in cleaver. Averaged 88mph in a kilo and was clocked at 92mph one way.

Stephen