Hybrid clonesaw 365 with a 390 topend - aka the "86'r from youtube"

[Ketchup]

With a 4.33mm washer high stack (no gasket) it clears the full rotation and puts things at:
Intake - 79,5
exhaust - 96.5
transfers - 123.5
Squish is 0.40mm

In theory (if my math is correct, which I am not sure is so correct me please) 4.1mm(ish) would be the distance needed to be removed/taken off the piston & squishband (or shimmed up) to get a .20mm squish.

I don’t think the maths are quite right. 0.4mm is 0.0157”. Maybe you’re crossing MM and thousanths of an inch?

Those numbers are close though. Maybe make a spacer and set squish with the piston cut?

 

[upstateamish]

I don’t think the maths are quite right. 0.4mm is 0.0157”. Maybe you’re crossing MM and thousanths of an inch?

Those numbers are close though. Maybe make a spacer and set squish with the piston cut?

You're right I had MM instead of inches on the squish (but that was what I was ending up with with that spacer stack)

As I was digging around through my stuff I found an sthil 056 Magnum (part# 1115-030-2003) piston which has the 13mm wrist pin. It's 56mm with a slight dome on it is about 5mm shorter from wrist pin to upper piston edge I this might be a good candidate and more in line with numbers needed without a shim. (although the intake will probably still need to be epoxied...)





turned the diameter down to 55mm and opened up the wrist pin area.


intital fitting was a very slight interferance at TDC. I used some emory paper and 600 gritg to take down the top a bit (may need a bit more)




numbers with a stock gasket and the modified 056 piston:

Exhaust: 96.8
Transfers: 122.5
Intake: 89.5
Squish band: 0.015"* (at the tightest point of the squish band) up to 0.024"

 

[upstateamish]

* there's about a 1mm ridge on in the squish band where some plating is, I'm debating about trying to sand it down, turn the piston a bit more or get some slightly thicker gasket material. or... just send it.



here's the ridge highlighted in red (just didn't get completely cut I assume)


and where the piston falls at BDC

 

[Woodwackr]

* there's about a 1mm ridge on in the squish band where some plating is, I'm debating about trying to sand it down, turn the piston a bit more or get some slightly thicker gasket material. or... just send it.


View attachment 452659
here's the ridge highlighted in red (just didn't get completely cut I assume)
View attachment 452660

and where the piston falls at BDC
View attachment 452661

Looks like a slightly thicker gasket will do the trick

 

[Ketchup]

That’s a pretty thin squish band and 97 is pretty high on exhaust. You might want to drop the jug a bit and cut the squish.

 

[Powerstroke Cowboy]

Nice find with that piston.

Might need to cut the dome off the piston as well. Looks like it could be close to hitting the spark plug.

Of you cut the base and squish band like Caleb said, then also cut the dome off the piston. Should work great! Makes for a lighter piston. Win win.

 

[Outback]

I just wanted to say thank you for the most interesting thread I've read in a long time on here.

 

[Woodwackr]

Nice find with that piston.

Might need to cut the dome off the piston as well. Looks like it could be close to hitting the spark plug.

Of you cut the base and squish band like Caleb said, then also cut the dome off the piston. Should work great! Makes for a lighter piston. Win win.

Just don’t cut too much off the top at center. Pretty thin up there

 

[Shane¹]

Just curious if you have looked into measurements of a dolmar 143 and 153 pistons? They are both already 55mm. Both do have a 12mm pin but a 9000 wrist pin bearing is 12mm id and is the same od as a 395. If interested I can probably get you a few measurements and see if it is something you would be interested in