dual ring pistons vs single ring piston

[chainsawworld]

when the 371xp first came out they were single ring pistons. later they became double ring pistons. now the 372xp's are all double ring pistons. they are not by any means a low grade saw.
and i agree about the higher octane in saws assist them in running cooler. i forget the exact numbers as far as octane rating but i do recall the differance in the octanes we tested being at least 12 degrees cooler on the jug of a working saw in the cut. i will look the results up. marty

 

[Dagger]

to keep piston side walls and skirt parallel with cylinder wall.
prevent rocking motion assoiated with short skirt pistons.
the same motion we know of as piston slap, or skirt slap in a highly worn engine.
This motion is detrimental to a saw achieving higher rpms, and is simply a function of bore diameter and skirt clearance and OAL of piston.
think of it as angles, or angle of piston in the bore.

 

[bwalker]

forget the exact numbers as far as octane rating but i do recall the differance in the octanes we tested being at least 12 degrees cooler on the jug of a working saw in the cut. i will look the results up. marty

In a motor that is not detonating or pre igniting there is no differance in burn temp between premium and regular. I know people swear that premium burns slower but this is simply not the case. Check these refferances if you doubt me.

Hydrocarbon Chemistry - Author George A. Olah - ISBN 0-471-11359-x

Automotive Fuels Reference Book - Authors Keith Owen & Trevor Coley - ISBN 1-56091-589-7

The Chemistry of Hydrocarbon Fuels - Author Harold H. Shobert - ISBN 0-7506-0384-4

 

[bwalker]

to keep piston side walls and skirt parallel with cylinder wall.

Sounds like pretty crappy production tolerances. I work in QC and if I let crap like that make it inot the field my butt would be chewed ragad by the powers that be.

 

[chainsawworld]

DARN!!! i spent all that money on a laser dot thermometer and it lied to me all this time.

 

[bwalker]

You honestly think aiming a laser thermometer at a cylinder in a uncontolled manner will give you any data worth a darn? I dont think so. You cant argue with the facts i have layed out. All gasoline has about the same btu's hence it's burn temps are the same.

 

[chainsawworld]

yeah,ok. LOL

 

[joemarty]

win i was drag racing motor cycles we would run low octang gas. it has bigger bang more fire in the hole. but it dose run hotter. evening races where the best to run low octane gas. always two to three rings close to top .140 to .150. you get alot more horsepower heat transfer when using low grade gas two, three rings. and the motors would last a season longer.

joemarty my two rings worth

 

[bwalker]

Why dont you provide me with some data other than anecdote to back your point? Because there is none. Keep in mind the caveit to my statements was that detonation and preignition where not present. Regards bw

 

[Fish]

How many of these saws are rebuilt because they are worn out?
These saws are rebuilt because of lean seizures, not because of
number of rings or octane.
I do not join this disscussion to try to compete at your level
of bu[[8kitting, but to reflect reality.
I have never blamed a saw failure to octane or number of rings,
so I think fighting over the topic to be silly

 

[chainsawworld]

i can't say i got my information from someone else's books i read. just my experiance. i hate to say any more here. if i find out my digital tach is lying too i'm gonna tape both to a log and cut them in half. NOT!!!

 

[bwalker]

These saws are rebuilt because of lean seizures, not because of

I wager many are in need of rebuild from simple neglect of maintenance. Dirt will wear a engine out in hurry, thats why aclean filter is important on a two stroke. bTW its not a pissing match. Just a technical discussion. The problem with the net is that people tend tthihnk you are being hostile when your not. Has something to do with not being able to see facial exspressions and hear different tones of voice. So. saw world no hard feelings. just trying to keep technical subjects factual in basis.

 

[bwalker]

i can't say i got my information from someone else's books i read. just my experiance.

Saw world, not to slite you, but your observations dont hold water when put to the test by proven science. Sorry.BTW those digital temps gauges iMO leave alot to be desired.

 

[chainsawworld]

Originally posted by bwalker

Saw world, not to slite you, but your observations dont hold water when put to the test by proven science. Sorry.BTW those digital temps gauges iMO leave alot to be desired.

perhaps so. but, when changing the octane rating, the temps also changed.

 

[bwalker]

perhaps so. but, when changing the octane rating, the temps also changed

If they did infact change(assuming your Gauge was accurate) I can assure you it was not from the octane rateing of the fuel. Perhaps the premium had a higher end point which led to more heat being leached out of the combustion chamber. I tend to believe however that the 12 degree drop you saw was a result of a less than precise measuring device.

 

[motorhead]

Wecome back Dagger

Hello Dagger, where yea been? Welcome back. For the newer members out there, Dagger has was once employed by one of the 'Big Two' power equipment companies as both a product engineer and as a manufactures rep. (correct me if I'm wrong or only partially right). I always enjoy reading your posts as they are normally based on fact and provide an 'insider's viewpoint' on various topics (I'm still going to continue to run my premix ratio at 32:1 with a premium synthetic oil though for the sake of my crankshaft and crank bearings lol).

Regarding the effect of piston-to-cylinder clearance and it's effect on piston stabilization, Honda CR 250 motocross bikes run a nominal piston-to-cylinder clearance of .0025" but they still use two piston rings (btw, the bore diameter is 66.4mm and the engine is liquid cooled - I provide this info. since larger bore/piston diameters normally require larger piston-to-cylinder clearances). I always thought that this was to help reduce blowby and improve power at low engine speeds (since the power stroke occurs over a greater period of real time at low RPM's) but I never really knew for sure. Wiseco makes a high performance racing piston for this bike and it uses only one piston ring - the primary benefit of the Wiseco piston is that it weighs less than the stock unit which results in quicker engine acceleration.

Regarding piston slap, not only is it detrimental to high RPM power, it is also detrimental to engine durability as piston slap causes increased piston wear rate especially at the piston skirt. Piston slap will also fatigue the piston skirt area which leads to fatigue cracks which leads to broken pistons which leads to 'engine don't run'.

Steve

 

[jokers]

Hey bwalker, I`m not looking to pick a fight with you here, but since you threw it out that you are in QC, as if that makes you preeminently qualified to be an expert on this topic, why don`t you share with us a little info about what your educational credentials are, and what field you are in. I know, I know, I`m pissing in your Wheaties, but whenever someone comes out with the implication that they are more expert, or just plain smarter, because of what they do for a living, I like to know if they are telling the truth. Often you can gauge a persons intelligence by their grammar, spelling, and speech patterns. Sometimes it`s their unfailing attention to detail. Sometimes you just have to ask a person to back it up. Since we are not communicating face to face, or even verbally, so that we could use tonal inflections to fill in the gaps, could you please add a little more detail for us. There is likely no way that you could possibly list all of your academic achievements or life experiences or observations to back up your "fact based" statements anymore than Marty can at this moment, but you do have to concede that Marty is making an honest attempt at generalized observations, which I believe are fair in the context of this forum considering all of the potential varibles at play. I also believe that on the surface, btus are btus are btus, and it would appear simple that burn temps would be the same, and I`m not saying they aren`t. But there again it seems as if the potential effect of any additives is not being considered. If this argument is valid at all, you must consider all variables. So like Fish said, this argument is a waste of time and brainpower, but if you want to sway us with statements, you better be able to back them up. BTW, portable thermal sensors, both contact and non- contact are reliable enough for trending and monitoring safety related component temperatures in nuclear power plants under the watchful eye of the NRC, so they are probably good enough for me. Safety Related components are the "absolutely must not fail" components of a nuke plant that will shut it down with minimal to no human intervention in the case of a postulated design basis accident, in case you didn`t know. Russ

 

[Fish]

Dirt ingestion will wear out an engine, obviously, but is not
really relevant to this, as the bearings are usually shot as well,
making rebuilding a saw impractical {cost-wise}. Pistons
and ring{s} damaged, saws burnt up, etc., are not because
the number of rings or octane but due to a lean condition
in the fuel/air area. I am not entering modified saws/engines
into it because I know little about them, and they may have a
compression ratio high enough to need a higher octane.
I just fix saws and trimmers, and a burnt up saw is a burnt
up saw, whether 1 ring or 2, and something caused that failure,
whether a leaky fuel or impulse line, seal, crap in the carb,
or an idiot playing with the mixture screws.
I worked on an old Green Machine trimmer once {made by
Shindaiwa}, It ran but with low power. Since it had been used
hard on a horse farm for 15-20 years, with mowing crews
using it all day, I pulled the muffler. One ring was in two pieces
the other intact but thin on one side. I pulled the cylinder
and found no damage as the ring pieces stayed in their groove,
the bearings were good, so I installed 2 new rings and it ran
as good as new.
One question, what does QC mean? It may be obvious
but I am not in the industry.

 

[sedanman]

Quality Control

 

[bwalker]

what your educational credentials are, and what field you are in

I have a BS in enviro science from Northern mi u. I know im going to get the tree hugger comments,IM NOT. I have been working in quality control at a tier 2 automotive supplier that bulids fuel sytem parts. I also have been a motohead my whole life. BTW I never implicated that my work expierance make me a expert on this subject. I just commented that sloppy tolerances would not be tolerated in my line of work. I hope my intellict is not based on my grammar/verbage, because it sucks.LOL