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

[Mad Professor]

It is dead flat. I got it at a garage sale probably 20yrs ago…just for the purpose of flattening small items.

Handy to have. I went to HS with a friend who owns a glass/window shop. He'll cut me a nice piece of thick scrap plate for free.

 

[upstateamish]

Ok, weekend update - parts have shown up

Round 2 of the cylinder in process: one of my plugs came out when drilling (upper left on this picture, should't matter though, everything still tightens up.)


I decided to replace the 056 piston due to current fitment & there are a couple vertical scratches that would impact compression.

Since I have a few of 390 pistons accumulating here, I decided to to try turning one to a single ring. My thought was taking the top ring portion out would allow it to spin all the way around in the cylinder. As you can see on my first attempt I found out where the top is thin (as others noted) however, it did spin all the way around in the cylinder.

So, in the interest of learning, science (and not haven't another 56mm piston to turn down with this wrist pin diameter) I gave it another shot.



I turned the second one with a slight dome to it starting around where the ring pin ended (hopefully it's thick enough here to not blow out) we'll see.



Weight after all the machine work/ lightening - 108 grams with a ring, the wrist pin & clips (which ended up being the same weight as the 056 piston setup)


got things tightened down the block (no base gasket, but with 1184 so have to wait for it to setup) & I'll do a leakdown test tomorrow

The numbers (without a base gasket): which from the threads I've been digging through on 390 porting sound like it may work ok as a base to work from.

- Squish: 0.025 (I was limited with where things ended up by taking off the 1st the ring)
- Exhaust: 96
- Transfers: 120
- Intake: 79

If this works, this approach might be better. (less machine work to get things to fit & you're able to use a standard 55mm ring.) I think without the 395 connecting rod on the 390 crank, you probably could just use the regular piston as the connecting rod is about 7mm shorter.

Assuming the leakdown test passes, I hope to put everything back together and test fire it. fingers crossed

 

[upstateamish]

Pressure test failed (expected failure point at the clutch side seal) I trimmed down my crank sleeve bushing a bit to better fit an o-ring under it and replaced the seal, and it passed. We'll see if (or how long) that works. Proceeded to put it back together, it runs!

Grabbed a video of it running, the carb needs more tweaking on the high end, but want to check how things look before I let it rip for to long here.

As a side note: I just replaced the tinytach's battery. (It seems extremely sensative, freaks out and resets when I get it remotely close to the spark plug...) I was hoping the new battery would fix it, but it's still doing that. I'll reach out to see what they say but I'm not holding my breath I've had this quite awhile and I'm well out of warrenty phase.

 

[upstateamish]

ok, cut a bit on my lunch break. Was fighting the saw overfueling at WOT (which you can hear a bit in the above video) it would barely get over 9000 rpm out of the wood.

I did a bit more research on it, lots of what I found pointed to a metering lever being out of adjustment (but I had just checked that) so I decided to look a bit closer at the choke lever setup. The linkage actuator I had drilled out on the 395 carb for the x-torq choke lever is to long, it's got to much throw in and doesn't allow the choke plate to fully open. So the effect was running at WOT on partial choke.

I've replaced that with a choke actuator from a 372/390 style carb




Now we have full swing operation and it's spinning quite happily in the upper rpm range (watch your ears, I didn't adjust the levels in this one)

I'm pretty psyched about how it's running now and hope to give it a shot in the wood pile over the next few days.

 

[upstateamish]

Over my lunch break I got some vid of the prototype 2 run against my 500i with a west coast air filter. Same length bar, same chain setup.

But only got three cuts because the chain loosened up on the P2 saw (you can see it in the last cut) then I ran out of time and wasn't able to address it/get more video.

But, seems to be responsive, idling well and feels strong overall. I'll work on tuning the high end a bit (once the rain we have projected the next few days passes)

Here's some side by side comparison test cuts (Standing dead dry ash with the skip tooth chain)

 

[upstateamish]

Prototype number 3:
I'm happy enough with how the prototype #2 is running (and it's been a bit rainy so I haven't had much time to continue running it.) so tonight I decided to start working on the 3rd prototype with the parts I have started to accumulate for 3rd and 4th prototype.

I started by pulling apart the AM 372 short block (I picked up for a spare case) knocked out the bearings, etc

Took a couple rough measurements on the AM 390 crank to see how it matched up against the 372 crank, especially on the flywheel side to figure out number of 25x35x1 mm spacers needed to take up the space on the flywheel side with the thinner SKF 6003 C3 bearing (and crank shoulder that's also not as wide)

372 crank with 6202 bearing


390 crank with a 6003 bearing & four 1mm spacers is about right


Comparing the 390 crank diameter to the case the lobes, it shouldn't require machining the crank to fit. Though it will take some (about 0.10 mm) of case trenching for the connecting rod to clear in the center (Note: this is similar to what I ended up having to do for the 2nd prototype)

 

[upstateamish]

and started laying / measuring out where the crank rod will be rotating in the case and have a rough area figured out of where that clearancing needs to occur between the crank lobes. That is as far as I got tonight.