Wossner pistons for modified Superjet 760 engine

[Barmaley]

Hi,
I think about installaiton of 86mm Wossner pistons (part # 6012D200) in my modified Yamaha Super Jet engine (760 sleeves and ADA Billet head with 760 Domes, Factory B pipe). Early I used Wiseco 85,5 mm pistons (757M08550) in this engine, but I had a problems with over temperature. Now I want to try Wossner pistons, I heard roumors that they are better with high temperatures. Is it really so?

I use 95 octane fuel. I use 38 domes in ADA Billet head and a specific carburetor's tune-up. Usage - is racing on high RPM. I hope that Wossner's pistons will work better in high RPM with temperature than Wiseco. Can anybody advise suitable (proper) bore clearance for Wossner pistons 6012D200 for such modified SuperJet's engine?

 

[Big Kahuna]

@Jr.

 

[Ducky]

I can tell you from talking to @Jr. that 760 sleeves are super thin, and I'd probably be scared to go to 86mm on 760 sleeves. I actually was about to send my stock bore 760 cylinder out to have it build, but as I was packaging it, I noticed a super fine crack in the sleeve wall. So be careful and inspect those sleeves!

Wossner pistons are awesome though!

 

[Big Kahuna]

I think 85 or 85.5 is the largest you can go on the 760 jug.

 

[mikidymac]

This is from Group K if it helps at all...
With all this done, you must understand that the 760 cylinder has only two bore oversizes...that is .010" and .020". The base sleeve of the stock 753 cylinder is not thick enough to safely sustain any larger size pistons. In the event that the cylinder wall was significantly damaged, the sleeves (or cylinder itself) would have to be replaced.

 

[Jr.]

Hi,
I think about installaiton of 86mm Wossner pistons (part # 6012D200) in my modified Yamaha Super Jet engine (760 sleeves and ADA Billet head with 760 Domes, Factory B pipe). Early I used Wiseco 85,5 mm pistons (757M08550) in this engine, but I had a problems with over temperature. Now I want to try Wossner pistons, I heard roumors that they are better with high temperatures. Is it really so?

I use 95 octane fuel. I use 38 domes in ADA Billet head and a specific carburetor's tune-up. Usage - is racing on high RPM. I hope that Wossner's pistons will work better in high RPM with temperature than Wiseco. Can anybody advise suitable (proper) bore clearance for Wossner pistons 6012D200 for such modified SuperJet's engine?

please explain “over temperature” better? Are you referring to Detonation? Or seizure?
neither are the pistons fault?
Later in your post your asking about clearance? So im guessing your experiencing seizure issues?
Both Wiesco and Wossiner are forged pistons and have greater thermal growth than a cast piston.
Both require the motor to be set up with proper clearance given the motors parameters. Even when properly clearanced, if not tuned correctly. Seizures can still happen
An 85.5mm Wossiner piston to wall clearance should be .0055-.006”
For a race motor.
Also note as covered by others in this thread. 760 /64x sleeves are very thin! I would not run 85.5mm bore in them.

ski ya, Paul

 

[Barmaley]

Guys, thank you very much for your kind replies.

I do not have standard sleeves, I understand that standard sleeves are too thin. My sleeves are custom made, thick-walled and made of gray cast iron.
As for the pistons: there is no detonation problem.
Problem with seizure when the engine runs at full throttle for a long time.
The air/fuel mix in the carburetors was nice tuned, the color of the plugs was perfect. Carburetor jets: high - 155, low - 67.5.
Thermal bore clearence with Wiseco pistons was 0.0055

 

[Barmaley]

In my opinion, Wiseco pistons have a very thick aluminum body at the top above the piston pin. This fat body accumulates an elevated temperature, not having time to cool down enough. I suppose that in the top part of the piston above piston pin it is necessary to mill a "cooler" in this place.

I did not take in hands Wossner pistons. I would like to understand if there is a difference in the pistons Wossner (6012D) and Wiseco (757M), or they are the same in quality? Please, advise

 

[Jr.]

I like your train of thought here. Both Wiseco and Wossiner are both very good quality.
Major aftermarket builders, DASA, TPE, X-Scream, Et all use Wiseco exclusively in their motors.
PHP and myself, use a lot of Wossiner in our smaller motor builds. If more sizes were avail? I would probably use them elsewhere also. For me, Its also common practice to weigh and balance pistons in much of my performance motors builds. I have done this on both Wiseco and Wossiner on typical size and brand motors. Both are within a couple grams of each other. That said, Im not sure your correct in the Wiseco being significantly thicker than the Wossiner?
They are fairly close to each other build dimension wise.
Please realize, A race ski has many factors it endures while running. Fuel mixtures / lean mix, hotter burn. Advanced ignition timing. Cooling water, ambient temps, and water conditions. Front runners, enjoy clean ”wet” water, while, back in the pack has rougher, aireated water. So cooling efficiently is somewhat compromised By air concentration in the cooling water.
You are also correct, that high RPM running does not offer time for the piston to cool between strokes. Plus the air speed thru the motor is so fast, not much time for any heat transfer anyway.
All this said, having experienced these type seizures myself over the years. I would again go back to looking at clearances as an option to longer piston life? You stated .0055” clearance? This might not be enough?
Case in point. 550 limited, back in the day. 220# cranking compression, Iron cyl. High heat soak application.
Running Wiseco 76mm pistons. Std clearance for the application .0035” - .0045”. In order to make these pistons last in race application, we had to run .0075” clearance. Made sure we had a solid warm up before the race to build heat into the motor! Otherwise, we probably would have snapped the piston skirts off with all the slap in the motor!
all the things that have to be considered in Race applications!

P

 

[Vortex]

One thing I noticed was 95 octane. You probably should run 98-100. ada recommends 98 for 38cc 760 domes. Some may say that's not enough of a difference to make a difference but I am of the belief that you shouldn't skimp on fuel/oil. And that said there are many factors involved in why the engine was getting hot and seizing as jr mentioned

 

[Barmaley]

I like your train of thought here. Both Wiseco and Wossiner are both very good quality.
Major aftermarket builders, DASA, TPE, X-Scream, Et all use Wiseco exclusively in their motors.
PHP and myself, use a lot of Wossiner in our smaller motor builds. If more sizes were avail? I would probably use them elsewhere also. For me, Its also common practice to weigh and balance pistons in much of my performance motors builds. I have done this on both Wiseco and Wossiner on typical size and brand motors. Both are within a couple grams of each other. That said, Im not sure your correct in the Wiseco being significantly thicker than the Wossiner?
They are fairly close to each other build dimension wise.
Please realize, A race ski has many factors it endures while running. Fuel mixtures / lean mix, hotter burn. Advanced ignition timing. Cooling water, ambient temps, and water conditions. Front runners, enjoy clean ”wet” water, while, back in the pack has rougher, aireated water. So cooling efficiently is somewhat compromised By air concentration in the cooling water.
You are also correct, that high RPM running does not offer time for the piston to cool between strokes. Plus the air speed thru the motor is so fast, not much time for any heat transfer anyway.
All this said, having experienced these type seizures myself over the years. I would again go back to looking at clearances as an option to longer piston life? You stated .0055” clearance? This might not be enough?
Case in point. 550 limited, back in the day. 220# cranking compression, Iron cyl. High heat soak application.
Running Wiseco 76mm pistons. Std clearance for the application .0035” - .0045”. In order to make these pistons last in race application, we had to run .0075” clearance. Made sure we had a solid warm up before the race to build heat into the motor! Otherwise, we probably would have snapped the piston skirts off with all the slap in the motor!
all the things that have to be considered in Race applications!

P

Thank you for your kind adviсes.

I meant that there is a fat aluminum body in the top part of the piston, which accumulates heat.
In these "hot" places we milled the cooler-holes, as in the photo with Wiseco piston. In many kind of 2-stroke pistones these cooler-holes are present from "factory box", but they are missing in case wth pistones Wiseco 757M-series.
Can you say: Are such cooler-holes present on Wossner pistons 6012D-series?

 

[Barmaley]

One thing I noticed was 95 octane. You probably should run 98-100. ada recommends 98 for 38cc 760 domes. Some may say that's not enough of a difference to make a difference but I am of the belief that you shouldn't skimp on fuel/oil. And that said there are many factors involved in why the engine was getting hot and seizing as jr mentioned

Unfortunately 98 octane are missing in my country. 100 octane is very rare. ADA has only 40cc domes for 91 octane and 38 cc domes for 98 octane in a suitable range. I use 38cc, Like a compensation: fuel/oil ratio 35:1 and carburators tune up

 

[Jr.]

Thank you for your kind adviсes.

I meant that there is a fat aluminum body in the top part of the piston, which accumulates heat.
In these "hot" places we milled the cooler-holes, as in the photo with Wiseco piston. In many kind of 2-stroke pistones these cooler-holes are present from "factory box", but they are missing in case wth pistones Wiseco 757M-series.
Can you say: Are such cooler-holes present on Wossner pistons 6012D-series?

What your referring to as “Cooler Holes” really they are not. I would agree, if they were open into a fuel charge path to allow any heat buildup to escape? The brief timing they cross over the transfers would not be enough to reduce any thermal buildup. The hole are merely to reduce mass and weight. To answer your question, yes, they are present in Wossiner pistons. See attached photos of the 84mm size I have in stock

 

[Barmaley]

What your referring to as “Cooler Holes” really they are not. I would agree, if they were open into a fuel charge path to allow any heat buildup to escape? The brief timing they cross over the transfers would not be enough to reduce any thermal buildup. The hole are merely to reduce mass and weight. To answer your question, yes, they are present in Wossiner pistons. See attached photos of the 84mm size I have in stock

Thank you, Jr.

 

[kevbo]

Wiseco got away from making pistons much lighter than stock. Their new ones seem to expand less than older ones and the skirts don't collapse much anymore.

 

[bored&stroked]

So your running lower then recommended octane in a high rpm/constantly building heat race application. That's the problem.

Run the right octane, or let off the throttle every few seconds to let things cool. Ada recommends 100octane for my 760 compression. I run like 93-94 depending how carefully I mix it. 2 season later my pistons and domes still look new, I've never siezed or overheated it. It only gets full throttle going up waves to jump....

 

[mikidymac]

So your running lower then recommended octane in a high rpm/constantly building heat race application. That's the problem.

Run the right octane, or let off the throttle every few seconds to let things cool. Ada recommends 100octane for my 760 compression. I run like 93-94 depending how carefully I mix it. 2 season later my pistons and domes still look new, I've never siezed or overheated it. It only gets full throttle going up waves to jump....

Whatever, owners manual says 87 octane,