295/S & 340/S pistons

400brian · Post by **400brian** » Thu Mar 12, 2009 2:33 pm

Plus, the 340/s piston has a raised pin height over the other pistons "like" it, allowing for an assumed longer rod that improves rod angle ratio for greater high RPM durability and power output from reduced piston skirt side loading, reduced frictional losses, reduced mean piston speed and increased piston TDC dwell time in the combustion cycle.

i'm not trying to muddy the waters here, But...

The 340S piston and the production piston are very similar. As far as I can tell, the pin location is the same. The rings are higher on the piston on the 340S, and the lower ring is indexed to the opposite side of the port.

Attachments:

pistons_001.jpg (819.04 KB)

Post by **WinnipegStPaul9** » Thu Mar 12, 2009 2:48 pm

Brian, that goes against what I've been told. I've always been told that the pin of a RS/2 is higher in the piston than other CCW 340cc engines. I'm pretty certain we even have a comparison picture somewhere on this board. Couple of other comments I have are that 100 pieces doesn't seem out of the question since I for one would like four and I just want a piston that will be a replacement for any 340/S piston that I may "burn down". Right now no such piston exists. What's wrong with a piston that Wiseco builds for us. None of us are going to race these sleds anyway are we?? DA

400brian · Post by **400brian** » Thu Mar 12, 2009 3:07 pm

As far as I know Don, the comparison photo on the site, is the one that I took.

In the previous photo, both pistons are sitting flat on the table, and the pin fits snugly and squarely in both. Production piston port, and 340S.

pj sportfire · Post by **pj sportfire** » Thu Mar 12, 2009 3:48 pm

My head hurts.... I'm letting W. figure it out.

pj

Post by **ICCSF 108** » Thu Mar 12, 2009 6:03 pm

One thing I think that is confusing is that the first CCW replacement Wiseco pistons were CW-340-S for CCW std 340 motors which I'm sure stood for CCW - 340 cc - Std bore. I don't believe they ever produced a RS/2 340/S replacement although I have been told that the CW-340-S pistons will work in the 340/S motors.
I hope this clarifies some of the confusion

Kenny

400brian · Post by **400brian** » Thu Mar 12, 2009 7:49 pm

I'll post some more photos later.

I just threw this in because the Wiseco guys are telling PJ this stuff is weird.

Generally you hear that kind of talk when you are looking at 35 year old parts, and talking to a 30 year old engineer.

Like I said, the 340S pistons are not that much different from the production versions.

pj sportfire · Post by **pj sportfire** » Thu Mar 12, 2009 8:28 pm

37 here, but body feels like 87.... LOL

400brian · Post by **400brian** » Fri Mar 13, 2009 2:59 am

OK, here are some photos.

Production piston AM52370 on the left throughout. This piston was used on all production piston ported 340 engines, with PN subs. 340S piston AM53541 on the right.

You can see the the similarities and some differences. Slightly different cut outs in the skirts, ring placement is higher in the 340S, wrist pin location and size seems the same.

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400brian · Post by **400brian** » Fri Mar 13, 2009 3:04 am

Top view shows how the ring locator pins are differently located.

View of jug has lines drawn down so you can see the path of the ring gap.

On the 340S piston, I measure the lower ring pin at 50 degrees from the top pin.

One piston puts the gap to the left of the exhaust port, the other the right.
Anybody know why?

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400brian · Post by **400brian** » Fri Mar 13, 2009 3:09 am

A look inside. There are some differences here. The 340S piston seems a bit thicker in places, and the wrist pin bores have two oil holes rather than one.

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340Spistons_006.jpg (183.88 KB)

Post by **WinnipegStPaul9** » Fri Mar 13, 2009 6:10 am

Great pictures and explanation Brian. Perhaps I was thinking about the rings when I said the pin was closer to the top of the piston. Just proves why I'm not a mechanic. DA

mikestrat · Post by **mikestrat** » Fri Mar 13, 2009 11:43 am

I am just trying to get up to speed here, but to my understanding, Wiseco is having trouble building something that they used to build at one time? Very strange. I will take 4 .020 over for the 295/s, 2 standard, and 4 .020 over for the 340/s. Somebody please get ahold of me with who I should send a deposit to. P.S. I am planning to drag race my machine!!!

pj sportfire · Post by **pj sportfire** » Fri Mar 13, 2009 1:07 pm

TakeItToTheLimit wrote:As I stated earlier...I do not see any concern with a build of 100 for each model. One question...how does the oversize fit into the tooling...is it an issue or does that come when they machine it (forged oversize & machine it down to standard)?

(forged oversize & machine it down to standard)?

Correct.

pj sportfire · Post by **pj sportfire** » Fri Mar 13, 2009 1:13 pm

mikestrat wrote:I am just trying to get up to speed here, but to my understanding, Wiseco is having trouble building something that they used to build at one time? Very strange. I will take 4 .020 over for the 295/s, 2 standard, and 4 .020 over for the 340/s. Somebody please get ahold of me with who I should send a deposit to. P.S. I am planning to drag race my machine!!!

Nope, you've miss-understood the text presented, as Wiseco isn't having "troubles" with anything. At the end of the day, it all boils down to money and quantities, which is what everyone is trying to work out here. When that info is gathered in its entirety and presented here, you guys' can then make the final decison to "Go" or No Go" on the project. I have no dog in the hunt, nor am I making one single red cent from any of this effort, so it matters not to me which way you folks' choose to go, as I've done my part either way.

That's it, easy-peasy..

pj

400brian · Post by **400brian** » Fri Mar 13, 2009 2:17 pm

And we very much appreciate the effort you are expending on our behalf PJ!

As a dumb farmer, I must say, I really do not understand the mentality of scrapping or getting rid of tooling that was engineered, bought, and paid for. You just never know when someone is going to want a run of 1937 Studebaker pistons!