Confirmed piston replacement solution for the 340s engine

[HoosierDeereMan]

The skirt corners had to be clearanced on the 2012PS to clear the counterweight of the crankshaft.

The skirt length of the aftermarket slug I have here is actually .047" shorter than the stocker, as measured from pin center of piston pin axis, so counterweight clearance shouldn't be an issue.

It's funny you mention this because we had to cut .040" off the skirt of the Wiseco's to match the 340/s pistons.

As far as what is acceptable for a lower ring land height, I never measured this as the Wiseco piston ring lands were closer to the crown (higher up on the piston) than the original 340/s piston so I knew it would not be an issue.

.004" larger diameter piston is good as the Kioritz cylinder max wear specs are .004" to .005"

Troy

[ICCSF 108]

Intake tear drop isn't it?

Kenny

[pjr2011]

Yep....that's what I meant. Freudian slip.

[400brian]

My question is, with regards to what you found~ What was the max allowable difference in measurement that was acceptable to still allow the lower ring to be captured by the exhaust tear drop?

PJ, that is the $64 K question.

Hang a piston on a rod, and slide a jug on and look...I'm squeezing my left one here.

If this works, AND the pistons are available, my prayers will have been answered.

[pjr2011]

My question is, with regards to what you found~ What was the max allowable difference in measurement that was acceptable to still allow the lower ring to be captured by the exhaust tear drop?

PJ, that is the $64 K question.

Hang a piston on a rod, and slide a jug on and look...I'm squeezing my left one here.

If this works, AND the pistons are available, my prayers will have been answered.

I'm at that point tonight- at least on the primary engine, so I'll do that mock-up this evening sometime.

For all of you part number junkies out there, here is the part number info I found on the piston box. Hopefully, these are still available and hopefully someone can identify what these are for based on the numbers~

# 09-035 is hand written on each box
# 49640000 is printed on the label
There is also hand written text on the box that says, "Parts Unlimited- Central Snowmobile Motosource". These guy's maybe? >> http://www.themotosource.com/

PJ

[Matt]

PJ, the 49640000 shows up in an old 1972 CCW parts manual on vintagesnow.com. 09-035 is a PU/SPI/Sno-Stuff type number, but it must be long discontinued.

[pjr2011]

PJ, the 49640000 shows up in an old 1972 CCW parts manual on vintagesnow.com. 09-035 is a PU/SPI/Sno-Stuff type number, but it must be long discontinued.

Thanks Matt.

The only 1972 340 CCW 2-stroke engine model I could find any info on using that part number was originally fitted into the rear engine'd Raider sled back in 1972. If this piston works out like I think it's going to, that part info will be great for guys to know what to look for at shows or swap meets, so they can get the alternative replacement pistons they need for these 340s engines.

I wonder if the Raider 340 or the Raider "Bandit" 340 pistons can be found or had anywhere these days? If they are and if these pistons fit like I think they will, I'd guess the cost and availability of "Raider 340 Pistons" will spike all of a sudden as everyone rushes out to get what they can, while they can for the 340s junkies.

Maybe this would be a good biz opportunity for NewBreed Parts? Dunno...

PJ

[Sprailfire340]

According to google search "1972 Raider Bandit" is the second most popular search tonight right behind
"Demi Moore + Danica Patrick"
I think I speak for every one here when I say...update please
Except Linder, he's been squeezing his left one so long he is getting

[pjr2011]

I just came back from the garage, where I measured the position of the second piston ring in relation to the apex of the "tear drop" in the intake port. The second ring is approx. .038" lower than the apex at BTDC and the top ring is fully enclosed within the cylinder walls and transfer ports, where it doesn't intrude into the intake port cross section area at all.

At first I thought...awwww crap...there goes that idea, but then I looked at two different Polaris engines I have here, a Yamaha 540 engine and two other Kawi fanner engines- taking note of where the second ring position was located in them. Every single one of them has the second ring exposed in the intake port at BTDC whether the port had a bridge or not, so obviously that design trait isn't a "bad" thing.

I did notice after looking at them however, that each of them had a slight chamfer on the leading, exposed edge of the port to prevent ring snagging and that obviously works quite well for all of these models of engines from different manufacturers.

My question is...why can't it work for these engines also, provided the chamfer is correctly implemented in the same manner??

Personally, I don't see a mechanical issue with the combination if it's done right and the "chamfer mod" seems to be a very easy one do- especially in light of the lack of other viable options out there as an alternative. I'd run them in my stuff if I had one.

EDIT- Photo added and note, the "shadow" of the flash on the tear drop apex makes the gap appear wider than it really is.


PJ

[pjr2011]

According to google search "1972 Raider Bandit" is the second most popular search tonight right behind
"Demi Moore + Danica Patrick"
I think I speak for every one here when I say...update please
Except Linder, he's been squeezing his left one so long he is getting

Uhhmmmmmm...... TMI sir...TMI

[Sprailfire340]

Uhhmmmmmm...... TMI sir...TMI

OK, OK, you are probably right.

AS for this "camfer mod" is it as simple as a die grinder to take off the leading edge or am I missing your point entirely?

[pjr2011]

Uhhmmmmmm...... TMI sir...TMI

OK, OK, you are probably right.

AS for this "camfer mod" is it as simple as a die grinder to take off the leading edge or am I missing your point entirely?

Yep, a die grinder with a fine tooth, cross-hatch burr or a Dremel tool would probably work just as well.


PJ

[Sprailfire340]

That sounds A LOT easier than all the effort Troy went through with the 2012 slugs.
I'll be the guinea pig. Go for it!

[pjr2011]

We'll do Mr. Sprailfire sir....

Oh..I'll try to take macro pictures of the modification if I can, but it's pretty tight in there and I don't know just yet if I can get a camera shot in there or not.
PJ

[Sprailfire340]

We'll do Mr. Sprailfire sir....
PJ