Confirmed piston replacement solution for the 340s engine

[400brian]

So if I read this correctly, what you have here is an aftermarket early production engine 340 piston.

We have considered running OEM NOS 340 pistons for several years. The rings are indexed differently ( as these are ), but everything else seemed to fit. A difference would be the meat on the piston. The 340/S pistons are heavier and beefier in the pin area than the production pistons, and PJ is saying these SPI pistons are heavier than the 340/S slugs.

The reason no one has tried this, is because we've assumed the bottom ring must stay above the teardrop in the port.

A list member has had contact with the original manufacturer, ART Piston, and they were willing to do a run of pistons, 1000 piece minimum ( and that seems to be the deal breaker ). SPI wanted the same minimum run from what I've been told. I've wondered why we couldn't just have them cut the ring grooves higher in a run of production blanks, but are they still making them, or just selling inventory?

[pjr2011]

Don't know about the inventory consumption, but I do know, from what I've directly seen, measured and test-fit here myself, this appears to be a viable, relatively inexpensive solution to the replacement 340s piston issue that's been plaguing everyone for years. As I've said before in previous posts, I'd run these without a second thought if I had this model or engine of sled and anyone who knows me already knows how rediculously anal and picky I am about anything mechanical. It's just my way...

As long as they are either still manufacturered by someone or there are still some stock out there on a shelf someplace, I'd say there is a definitive option available for you 340s guys. Get the port chamfered correctly and I'd say you're in business. Engine test fire to commence in a few days.

Hopefully this accurate info is useful and helpful for those that can use it.


PJ

[HoosierDeereMan]

I'm not trying to nix your idea. These RS/2 engines are hard to find. We don't have a good piston source and we are trying to find alternative crankshafts to run in these engines. If this experiment goes south how much of this rare engine will be salvagable? Im my opinion, If this is your only piston option, I would omit the lower ring and only run the single top ring. There is an awful lot of unsupported ring area showing in the port area. Over time as the cylinders wear it allows more opportunity for the piston to try to cock in the bore. When the crank is swinging around the throw and the piston is at BDC that exposed ring is going to flutter in that wide open port. I think that over time that flutter would wear the ring land in the piston wider and allow more ring movement in the land area. Once this happens the ring will most likely catch in the intake port and break. If this happens at 8,000RPM it will be ugly! That tear drop is there for a reason.

If you had to resleeve the cylinders could a longer tear drop be left in the sleeve itself to allow these pistons to work?

Troy

[pjr2011]

First off, this is NOT "my idea" here...

I was given these pistons to install into these engines and I was asked if they would "fit". Rather than blindly stabbing them in and saying "yes" to that question without regard to the potential consequences of that statement, I took it upon myself to once again donate my time, resources and expertise in professional engine building, by doing my due diligence in measuring nearly every measurable trait of these pistons as a direct comparison to the stock parts, in order to "qualify" them to work. In other words, I did NOT, nor have I EVER "shot from the hip" with any of this as I've sorted it out. To date, NO ONE that I know of has provided ALL of the inclusive (actually measurable) info I've provided here at one time, in one setting, at one place. Even when I went to bat for you guys' before with Wiseco, I spent considerable time and effort on my own dime through my company with the piston manufacturer to get you folks the information you wanted. It was all to no avail and a waste of time, for both myself, my company and Wiseco.....

You can bet, as sure as the day is long, that I've already thought of and pondered everything you said in your post- as that's what I do in my area of expertise everyday in the performance industry I work in. I even went as far as to even sample other engines from three different manufacturers to see what they do in an effort to confirm what I believed- for which they do the very same thing.

As I said before, I believe this to be a viable option for the reasons stated in this thread. If you or anyone else doesn't want to do it or feel as if the data presented is bogus, than fine, don't choose this option. However, if that's your choice, than you or someone else better step up to the plate and finally pony-up the big coin it takes with a given manufacturer to get the *EXACT* piston you want. You can't use "cheap", "custom" and "low volume" in the same sentence....

Good luck.

[HoosierDeereMan]

PJ,

If my opinion or comments offended or insulted you in any way I trully apollogize. That wasn't my intent at all. Our common goal here is to find a viable replacement piston for these engines.

Last year I had talked with Wossner piston about making us 340/S replacement pistons in oversize. They would make any quantity we wanted. 2 to 1,000 if need be. The rub was their 60mm forging uses a 16mm wrist pin and the stock 340/S piston uses a 18mm wrist pin. I did some research and found a needle cage bearing that would adapt the 16mm pin to the rod journal. The cost Wossner quoted was going to be just over $200 per piston for under a order of 25 units and $150 to $175 range for 50 units. That would be a kit which would consist of a piston, rings, curlips, and wrist pin. Additional rings would be available. We would have to supply the needle cage bearing. I had sent Wossner a drawing and was in the process of sending a piston when I found the 2012 option. So I dropped it. I figured their pricing would be more than most wanted to pay.

Troy

[Sprailfire340]

A few thoughts. (*Edit - sorry this is longer than I anticipated)

1) Let's remember it is much more difficult to have a discussion via the inter-google than it is in person. I'm sure if we were standing around a garage drinking a barley pop the "what about this" questions wouldn't sound nearly so critical.

2) I had heard horror stories of the 2012 option. Obviously Troy identified some of the issues before simply dropping them in. That was new info to me, but it also sounds like a lot of expense to make work. At this point I'm not willing to do that IF another viable option is available.

3) PJ has spent considerable time with these slugs working with Wiseco a few years ago to reproduce slugs to OEM specs and in the end the price wasn't something we could collectively get behind. Because of his familiarity with the 340/s I sought him out to explore another option because I don't have the expertise to do it myself. He is not doing this for nothing, rather as service to me. The info presented is on my and his dime. I've gotten a lot of info from this site and have no problem sharing, that is not my point. I see this as adding to the discussion, but in the end what you do with this info is up to you.

4) There are probably other options out there, but how many modifications you want to do determines your choices. For example GPX pistons have been put in a Dator with modifications. Jet ski pistons will work in an Interceptor, but also require extensive (i.e. Expensive) mods. Because of the expense, rarity and desirability of these sleds someone repopped the originals, BUT THEY ARE NOT CHEAP and are difficult to obtain even though they are repops. Until someone does that with 295/s and 340/s we must continue to search for viable alternatives.

5) I also had a former ETD mechanic review this piston. He didn't provide detailed specs like PJ, but after 20 mins of intently comparing these to the originals and slipping them in and out of the jugs he said "I'd run them all day long if it were mine - that is a good piston you've found."

In the end I'm going to try it because I've done all the due diligence I can. This is the best option FOR ME. If I grenade this sled I will absolutely share any additional information I can provide. Nothing ventured, nothing gained as they say. Thank you to all who have contributed to this discussion. The level of active, passionate, and experienced members here is second to none.

[HoosierDeereMan]

PJ & Mitch,

Im sharing my lesson learned on the 340/S piston. This is what forced me down the road of the Wiseco 2012 piston. This was my mag side piston. It caught the top ring in the port. It broke the edge of the crown off but didn't break the ring and luckily blew it out the exhaust. I didn't even know it happened. I pulled the exhaust to repaint it and that's when I found it. This is why I commented on your piston.

Troy

[Sprailfire340]

Thanks for posting Troy. I figured there was a "personal experience" driving your questions. Not sure how to address that potential issue. Chalk it up to sh$t happens, just like Don's snapped jackshaft I guess. Old iron does funny things sometimes.

[pjr2011]

PJ & Mitch,

Im sharing my lesson learned on the 340/S piston. This is what forced me down the road of the Wiseco 2012 piston. This was my mag side piston. It caught the top ring in the port. It broke the edge of the crown off but didn't break the ring and luckily blew it out the exhaust. I didn't even know it happened. I pulled the exhaust to repaint it and that's when I found it. This is why I commented on your piston.

Troy

Troy

Was the leading edges of the port(s) chamfered in the engine where that piston broke due to ring snag that you have shown in your photo?

PJ

[HoosierDeereMan]

PJ,

What got me in trouble was excessive clearance. Mag cylinder was worn .012" and PTO was worn .014" from stock bore size. You could still see some chamfering at the port edges but they had to be worn beyond what they were designed to do. The ironic part is the mag side piston failed but the PTO jug had the worst wear. I learned a valuable lesson. Two strokes don't like clearance they like tight tolerances.

Troy

[pjr2011]

Good point and that is a very good lesson that everyone should learn from, as no piston, no matter who manufacturers it or how it's made, will live very long in the wrong mechanical environment. It would behoove everyone to take the time to actually measure bore clearances to make sure whatever piston they choose, fits as it should so the thing lasts.

[lwb140]

hey guys , here is my 2 cents worth , i found these pistons for sale while surfing ebay a couple years ago while i had my first 340/s apart in my shop . as usual i bought all the pistons the guy had thinking these things would work in 340/s motors . in my opinion they are an oem replacement ccw brand part . i assumed they were for 340/5 or something but matt has figured out possibly what they are from. i used wiseco "340s" old school pistons in my mill , we had to shorten the skirts to get them to clear the crank about .075 if i remember correctly , i didnt have stock pistons to comare them to so i made sure i had plenty of clearance . the wiseco piston was considerably larger than the stock pistons evidentally because we were able to hone out some major nastyness out of the bores and still be within spec .in my mind these pistons would work fine but my thoughts were to leave out the bottom ring . not suggesting in any way you would have to . all other major measurements concure with pjs . id use them wade

[pjr2011]

Ohhhhhhh, so you're the "Wade Bennet" Mitch spoke of.... Well, heck, I know you then, but I guess I only knew you as just plain ol' "Wade"....
Duhhhhh!

Sorry buddy, I just failed to connect 2 + 2!

Send me a PM if you have any other info for these parts.

PJ

[lwb140]

Ohhhhhhh, so you're the "Wade Bennet" Mitch spoke of.... Well, heck, I know you then, but I guess I only knew you as just plain ol' "Wade"....
Duhhhhh!

Sorry buddy, I just failed to connect 2 + 2!

Send me a PM if you have any other info for these parts.

PJ

yep im the culprit!! no other info but ive got a few left!! wade

[400brian]

PJ, thanks for taking the time to make this post, we are appreciative. While most of us do not have access to the measuring tools you have, we had largely identified the problems of running production 340 pistons in the 340/S engine. So no one was trying to be dismissive of your thoughts on the subject. This is just well trodden ground for some of us, and no doubt we have formed some opinions on the issue. It will take more than one post ( and probably some real world testing ) for us to change our views. Kind of a "Show us the Money" kind of deal. No disrespect intended.

There has been an effort to reproduce these pistons since before your efforts with Wiseco, and it has continued since. If there was enough interest we probably could get it done. It doesn't seem that we have reached a demand for pistons that shakes the dollars loose yet. I have a pair of NOS 340/S pistons sitting here on my desk, where I can keep a close eye on them. I was hoping that they might reproduce, but so far no such luck. Probably too old.