395xp Single ring?

[Plebbers]

Hi all,

Long time lurker, first time posting.

I'm rebuilding a 395xp for a mate who wants to put it on his chainsaw mill. I'm not planning on doing loads to the cylinder in terms of porting but i was wondering about only using one piston ring to reduce friction and therefore heat.

Is that a completely stupid idea or is it worth a punt? I obviously want it to have a good amount of longevity but also want to make the best saw i can for him.

Id love to know your thoughts!

 

[huskihl]

Hi all,

Long time lurker, first time posting.

I'm rebuilding a 395xp for a mate who wants to put it on his chainsaw mill. I'm not planning on doing loads to the cylinder in terms of porting but i was wondering about only using one piston ring to reduce friction and therefore heat.

Is that a completely stupid idea or is it worth a punt? I obviously want it to have a good amount of longevity but also want to make the best saw i can for him.

Id love to know your thoughts!

It works the opposite. Larger Husky saws have a 2nd ring to help get rid of heat. The ring transfers heat from the piston to the cylinder for cooling

 

[Plebbers]

Ah ok no worries! Thanks for getting back to me and clearing that up.

2 rings it is!

 

[huskihl]

Ah ok no worries! Thanks for getting back to me and clearing that up.

2 rings it is!

Yep. Particularly on a mill saw. And to me, that is the perfect mill saw.

 

[jacob j.]

Yep. Particularly on a mill saw. And to me, that is the perfect mill saw.

It's hard to beat a 395 on a mill. The Stihl 075/076 were good on a mill too.

 

[Plebbers]

Agreed. That's why I'm keen not to screw it up for him!

Thanks again for that!

 

[TheWizard]

stay standard, it will last longer

 

[Nutball]

It works the opposite. Larger Husky saws have a 2nd ring to help get rid of heat. The ring transfers heat from the piston to the cylinder for cooling

Interesting. How did you come to learn that?

 

[huskihl]

Interesting. How did you come to learn that?

Common knowledge I guess. Idk.

 

[beaglebriar]

Interesting. How did you come to learn that?

Mostly luck...he occasionally puts a few words together that form a sentence.

FYI- It takes four good sized deer hides to make a pair of mittens in the UP.

 

[huskihl]

This guy gets it ^

 

[Outback]

I've heard that too, but common knowledge is as questionable as horse sense. There are a lot of old single ring saws and some pretty thin on ring and large on displacement saws. If that were true those old saws wouldn't have put down on the ground that left coast monster growth. The piston is largely cooled by the evaporation of the fuel charge. Your tune is more important that the number of rings to avoid burning up a saw. My experience is that if you leave a ring out on a double it will be a little bit more spicy if you don't dog on it too hard. The twin rings seem to help with being able to go down to dog town and not have the saw fall on its face, especially before the rings seat or if the saw has a ton of hours on it. Two rings also help maintain compression if any crap is ingested that could scratch the rings. I would stick with both rings for milling and in most other cases except racing.

 

[huskihl]

I've heard that too, but common knowledge is as questionable as horse sense. There are a lot of old single ring saws and some pretty thin on ring and large on displacement saws. If that were true those old saws wouldn't have put down on the ground that left coast monster growth. The piston is largely cooled by the evaporation of the fuel charge. Your tune is more important that the number of rings to avoid burning up a saw. My experience is that if you leave a ring out on a double it will be a little bit more spicy if you don't dog on it too hard. The twin rings seem to help with being able to go down to dog town and not have the saw fall on its face, especially before the rings seat or if the saw has a ton of hours on it. Two rings also help maintain compression if any crap is ingested that could scratch the rings. I would stick with both rings for milling and in most other cases except racing.

Well, when you hang a ring using only the top ring, and it runs fine with both rings, you tend to think a little bit differently

 

[Outback]

Care to elaborate. I assume you mean stick a ring. Hanging a ring usually refers to tearing it out on a port that's too large, poorly shaped or poorly chamfered. I've never had a problem running a single ring or a double ring piston, or a double ring piston with 1 ring in the top of a saw that was tuned right.

 

[Powerstroke Cowboy]

In the snowmobile world guys that are doing a lot.of wide open throttle runs up the side of a mountain like the dual rings. Why? They transfer heat from the piston to the cylinder a lot better since you have twice the surface area to transfer the heat. Single ring pistons tend to have a problem in that situation, power fade due to heat being transferred to the fresh intake air. Also, since the piston gets hotter you have a higher chance of piston to cylinder contact.

On Edit: The bigger the bore the quicker the problem shows up. Yes, a richer mix can help negate the problem. But, why hold the engine back?

 

[huskihl]

Care to elaborate. I assume you mean stick a ring. Hanging a ring usually refers to tearing it out on a port that's too large, poorly shaped or poorly chamfered. I've never had a problem running a single ring or a double ring piston, or a double ring piston with 1 ring in the top of a saw that was tuned right.

I was referring to a saw being designed to run on 2 rings and running it on 1 ring heated and expanded said ring until it stuck out into the exhaust port and was too large to get tucked back in. With a .011” ring end gap. It previously ran fine with 2 rings.

 

[Powerstroke Cowboy]

I was referring to a saw being designed to run on 2 rings and running it on 1 ring heated and expanded said ring until it stuck out into the exhaust port and was too large to get tucked back in. With a .011” ring end gap. It previously ran fine with 2 rings.

Do you think there's any transfer of what works in a two stroke snowmobile to a chainsaw? Or not so much since ones Liquid cooled vs air cooled?

 

[huskihl]

Do you think there's any transfer of what works in a two stroke snowmobile to a chainsaw? Or not so much since ones Liquid cooled vs air cooled?

I’m sure the basics are the same. An iron bore would hold more heat yet so clearances need to be larger I believe

 

[Outback]

Ah, previously......

So to clarify. A 371xp with a 1.5mm ring, is vastly less able to cool itself than, the twin ring 372xp with two 1.2mm rings, ie. 2.4mm of ring surface width. That increase of 37.5 percent of ring surface is necessary? Any idea how a performance piston with a single 1mm ring is still able to work with even less surface area in the same cylinder? Any idea why husky didn't delete a couple of fins on the cylinder to save weight when they went to a twin ring as it didn't need that additional cooling anymore? It boggles the mind that I didn't melt my saws using them in 95+ degree weather this last year with only 1 ring. I guess its better to be lucky than right. I'm ok with being lucky. However if more parasitic drag makes a saw work better who am I to argue. Guess its time to cut open the ring lands and add a pair of 1.5mm rings for superior durability in the face of bad tuning or hot weather.

 

[huskihl]

Ah, previously......

So to clarify. A 371xp with a 1.5mm ring, is vastly less able to cool itself than, the twin ring 372xp with two 1.2mm rings, ie. 2.4mm of ring surface width. That increase of 37.5 percent of ring surface is necessary? Any idea how a performance piston with a single 1mm ring is still able to work with even less surface area in the same cylinder? Any idea why husky didn't delete a couple of fins on the cylinder to save weight when they went to a twin ring as it didn't need that additional cooling anymore? It boggles the mind that I didn't melt my saws using them in 95+ degree weather this last year with only 1 ring. I guess its better to be lucky than right. I'm ok with being lucky. However if more parasitic drag makes a saw work better who am I to argue. Guess its time to cut open the ring lands and add a pair of 1.5mm rings for superior durability in the face of bad tuning or hot weather.

You’re free to believe whatever you like, I’m not here to change the minds of those who already know they are right. So carry on with your narrative if that’s what suits you