MS390 / 039 pop up piston

[beaglebriar]

Is the goal here to see what this custom piston can do for a 039/390 or to see how strong you can build said saw? My point is that if you don't work from a known baseline, you have no idea what the piston actually did.

I'm starting with a straight gassed 310. The guy just wants it to run and I'm certain that I can make it run way better than stock.
I'll clean up the 310 cylinder and keep it handy in case the am cylinder has issues but for as much as this saw will run I doubt there will be an issue.

 

[Lightning Performance]

I'll clean up the 310 cylinder and keep it handy in case the am cylinder has issues but for as much as this saw will run I doubt there will be an issue.[/QUOTE]

I roasted my 310 some years ago and parked it. It should be rebuildable with a piston. I'm betting with the larger transfers than a 390 it should run better with a short bar and short blow down. Only have one 310 jug. No piston yet.

Who knows what piston can be turned down for a pop up in the ms310?
47mm small pin
Single ring preferred.

 

[94BULLITT]

This one is advanced 1/2 key.

I might try going half a key and see if it picks up.

 

[MustangMike]

You guys are nuts!!! 020 is all I did, and all I would recommend. You are playing with fire and don't seem to realize it.

You do understand the consequences of too much advance???

 

[Terry Syd]

The stock timing is between 23.5 and 28.5 degrees. Where does yours fit in that spectrum before you mod it?

I elongated the mounting holes on the coil and removed the threads on the bolts above where the threads are active. It gives me about 2 degrees of timing movement. I then trimmed a bit off the flywheel key and tried it, then I did it again, on the third trim it was in the ballpark and I could tweak the coil if I wanted to.

If someone wants to trim 1/3 or 1/2 off the key and call it good - that's a matter for them, but I'm not doing it.

 

[94BULLITT]

You guys are nuts!!! 020 is all I did, and all I would recommend. You are playing with fire and don't seem to realize it.

You do understand the consequences of too much advance???

As long as there is no detonation, the only consequence is going to be harder on the operator and the recoil assembly when it kicks

 

[Lightning Performance]

You guys are nuts!!! 020 is all I did, and all I would recommend. You are playing with fire and don't seem to realize it.

You do understand the consequences of too much advance???

Hey Mike flywheel keys are BS when your scratch building and retrofitting custom parts. It's not that hard to find the sweet spot.
Plus I like popping sounds

 

[MustangMike]

If you guys want to advance timing 20 degrees or more, instead of just 5 or 6 degrees, best of luck to you.

I don't think you will always hear pre ignition until it gets very bad. I think it can be harmful before that point, but that is just my opinion.

 

[T.Roller]

If you guys want to advance timing 20 degrees or more, instead of just 5 or 6 degrees, best of luck to you.

I don't think you will always hear pre ignition until it gets very bad. I think it can be harmful before that point, but that is just my opinion.

All my saws that are ported I have advanced the timing more than .020 other than my 395.

 

[MustangMike]

All my saws that are ported I have advanced the timing more than .020 other than my 395.

OK, but on an integral flywheel the key is often about .140, so if you go half that is about .070! I doubt you have any of your saws advanced that much, but I could be wrong.

My ported 046 was advanced about .050. I pulled it back to .020 and I think it picked up some torque, but it did seem to run fine with the addl advance.

I think Randy did tests in the past and did not find addl gains past .025.

If you are building a work saw instead of a race saw, I would err on the side of safety.

 

[94BULLITT]

If you guys want to advance timing 20 degrees or more, instead of just 5 or 6 degrees, best of luck to you.

I don't think you will always hear pre ignition until it gets very bad. I think it can be harmful before that point, but that is just my opinion.

I doubt that we are getting 20* advance. The flywheel key on a saw with a removable key is .060'' a 1/3 of that is .020.'' I was going to figure up how much 1/3 and 1/2 key advance the timing on one of these saw but I did not get a chance today.

 

[MustangMike]

The keys I have measured for 044/440, 046/460 and 066/660 are usually .078.

The integral flywheel keys I have measured were about .140 (362 C, etc).

Never seen a key as thin as .060, what saw is that from?

 

[huskyboy]

My little 024 super came alive when I advanced it. A 044 I advanced couldn’t get enough of it either. Most huskies don’t seem to like it, my 385 seems to like a small advance. Have to experiment and find out what they like and don’t like. Timed cuts and a tach on the saw to read in cut rpm are your friend.

 

[beaglebriar]

Started rebuilding the 310 today with a Hyway cylinder and the Cross piston.

The cylinder looks quite nice and is a closed port variation. Squish was right at .029 and the port heights measured the same as the stock 310 cylinder.

I'll get some timing numbers tomorrow before it goes back together. Just cleaned up the ports a little on the Hyway, no widening.

 

[Fruecrue]

Started rebuilding the 310 today with a Hyway cylinder and the Cross piston.

The cylinder looks quite nice and is a closed port variation. Squish was right at .029 and the port heights measured the same as the stock 310 cylinder.

I'll get some timing numbers tomorrow before it goes back together. Just cleaned up the ports a little on the Hyway, no widening.

Pics of the closed port cylinder?

 

[beaglebriar]

Pics of the closed port cylinder?

Lol My buddy that has built several of these asked for pics also. Hell I thought all the 390's were like the Hyway cylinder.

I don't remember to take pics while I'm working. Here's the best I can do..

 

[beaglebriar]

It's together and back in the saw otherwise I'd get some better pics.

 

[beaglebriar]

Exhaust cleaned up and muffler mod finished just needs a squirt of paint. Also advanced the timing about 1/3 of the key.

 

[kkemp]

Here's some pictures of the highway cylinder I had. I'm guessing it looks same.

 

[Fruecrue]

View attachment 102929 View attachment 102930 Here's some pictures of the highway cylinder I had. I'm guessing it looks same. View attachment 102931

I remember that. That’s the first time I had heard of the closed port 039 cylinder.