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

 

[upstateamish]

Looks like a slightly thicker gasket will do the trick

This might be the route initally

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.

Yeah, I was thinking along similar lines. I started thinking about how I want to tackle cutting the squish band. I was thinking of using an indexible boring tool, but my mill setup doesn't have the depth needed (with the vice I have)

so I tested out a piston with some sandpaper glued to it but I only have 600 grit at my house (I'll have to go where I've got some different grits stored)

But I think this approach may work for this iteration of the saw

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.

good point and it might. i'll have to check

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

Thanks for joining and following along on the journey

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

copy that

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

I haven't looked at those, but interesting info! lets see how far this goes but that might be worth following up on.


Also got the seals installed. The 17mm X 26mm X 5mm oil seals appear to work (says it withstands 212 degree F. I've got a higher temp seal that claims 230F in my cart if this fails)

The cheap saw I bought have didn't come with the little o-ring that goes under the top hat. Since I've got this apart I sourced one (Part Number: 503 263 019) which seems to be a lot of money for a small o-ring... we'll see if it matters.

 

[mgr1]

Dolmar 143 piston is 55mm
41,8mm long
12mm pin
Compression height 16,6mm.
Full circle design.

 

[Shane¹]

I know the 153 compression height is taller than 143. Also there is 143 pistons that are not full circle design too. I will look through my stash when I get home

 

[mgr1]

I know the 153 compression height is taller than 143. Also there is 143 pistons that are not full circle design too. I will look through my stash when I get home

The piston I posted is a Nos Kolbenschmidt. All the cylinders I sold where non deco valve with full circle pistons. Partnr from p&c 031 130 004

 

[Shane¹]

The piston I posted is a Nos Kolbenschmidt. All the cylinders I sold where non deco valve with full circle pistons. Partnr from p&c 031 130 004

You got any more to sell lol

 

[upstateamish]

Tonight:
got some heavier grit sandpaper and made some progress on taking some of the squish band down. I'll go in with finer sandpaper to get a better finish once I get things a bit closer to where I want. But have things in the .020 - .024" range with the domed piston (I haven't done anything with that yet)




Also added some jb weld to the intake so I can raise the intake timing numbers

 

[mgr1]

How much more stroke do you have?

 

[upstateamish]

How much more stroke do you have?

well... good question I'm not sure now best to measure that.

I swapped over the 395 connecting rod onto the 385/390 crank but now that I've got the crank stuffed into the case so is there a good way to measure that against the stock 372 crank?
Based on Post 52 roughly there's 6-7mm (ish) more connecting rod than the stock 372 crank

372: connecting rod length: 90.63mm (rough measurement)
385/390: connecting rod length: 91.70 mm (rough measurement)
395: connecting rod length: 96.92mm (rough measurement)

 

[mgr1]

Stroke remains the same with a different conrod.

So a 55mm bore, 37mm stroke but with a different conrod to get the right intake exhaust numbers.

 

[upstateamish]

Ok, spent some time yesterday working on getting the cylinder ready.



Set the intake timing and you can see my divot right in the center but it's showing at 81 degrees so I am gonna run it instead of going further.




Because it was machined down, the piston requires piston rings to be sanded down a bit to fit. I did that and went over the piston a bit to see what type of weight savings I could get (there really isn't much to remove so I didn't go crazy) but after that I weighed it with a single ring, wrist pin and c-clips it's weighing in at 108 grams.


I'm planning to run single ring on top due to how the pins line up on the cylinder skirt, I might (should?) be able to run double ring but a single ring will be easiest to get things together for testing.

In order to get the top cover to fit, the cylinder needs to have a bit of the rear fin taken down (badly highlighted in dying sharpie here) & some plastic removed from the cover in a couple spots where it interferes against the cylinder.

 

[upstateamish]

You can see some of the areas which need clearancing here:

It's overall, its not a ton and things seem to fit together nicely


With this case's impulse line coming out at a weird angle, I've drilled the floor plate to allow it to pass through (vrs using the hole in the boot where it would get kinked)



Overall things are starting to come together and I may put things together tonight.