Inside the Exploded JMS 064

[Al Smith]

They called the Mac a BP-1 for balanced piston but in reality it had a scavanging air piston that worked like a super charger .Thought to be new and innovating ,Cooper Bessemer had basically the same thing on large stationary engines used to pump well head crude oil about the turn of the century,the last century . I've seen several BP-1's but none that ever ran

 

[Al Smith]

Okay busted piston .It's been said a two cycle engine at least in theory always has some degree of compressive forces on the piston head .Obviously it does on ignition but also on the up stroke of compression .
So if that's true it would be logical to conclude the only way to rip the bottom of a piston off would be if it hung on the down stroke .It would make sense the area above the pin would be the strongest and that below the pin,the skirt portion would structurally be the weakest .

 

[TreeLife]

RUSSIANS !!!
WikiLeaks ?
Darn Deplorables....

And don't forget the dreaded millenials

 

[Fruecrue]

That pic of the top of the piston shows some clean breaks along the exhaust side., left and right of center.
To my logic, this would suggest a hung ring on the downstroke, exhaust side top of piston shattered, causing the other marks we see on top of the piston.
After a couple strokes, debris enters transfer ports.
Once transfers interfere with the downstroke, wrist pin pulls out of the piston.
After the wrist pin shears from the piston, whatever piston chunks remain in the path of the wrist pin interfere off center to one side and cause a clean break in the connecting rod.
Crank continues to rotate carrying what is left of the connecting rod with it, until finally the con. Rod is swung threw and out and pierces the case.
Huge energy dump there, muffler steel absorbs the final momentum.

And that's how I sees it.

 

[mdavlee]

Blue piston is made by Wiseco and coated by someone else. That's what I'm remembering. I can ask if there's more I'd anyone is interested.

These pistons aren't cast by Wiseco. They are from a saw builder in Canada.

 

[Sleeper]

These pistons aren't cast by Wiseco. They are from a saw builder in Canada.

And Wiseco rarely casts a piston... they specialize in forged pistons...

 

[mdavlee]

And Wiseco rarely casts a piston... they specialize in forged pistons...

I guess cast was the wrong word. I've had several wiseco and have 2 in use right now.

 

[Sleeper]

I guess cast was the wrong word. I've had several wiseco and have 2 in use right now.

Normal mistake... wasn't trying to slam you or anything. I plan on a 372 forged piston at some point... whether it goes into a 50mm cylinder to retrofit my XT or into a different 372 OE or 2172... not sure yet.

 

[Jswanson]

Sexy blue pistons cast or forged?

 

[Deets066]

Sexy blue pistons cast or forged?

Forged

 

[Deets066]

These pistons aren't cast by Wiseco. They are from a saw builder in Canada.

I didn't remember them being Weisco

 

[mdavlee]

I didn't remember them being Weisco

I couldn't remember who He said made them. I know the coatings were done in Canada.

 

[Jswanson]

These pistons aren't cast by Wiseco. They are from a saw builder in Canada.

EHP, Luke, or Bertrand?

 

[Deets066]

EHP, Luke, or Bertrand?

Pretty sure it was Bertrand

 

[wcorey]

What are your records for the two stock? I have two that seem to be the same.

My notes have 390 ex at 97 and 385 at 100.

 

[Chainsaw Jim]

My notes have 390 ex at 97 and 385 at 100.

So one or both varies. The two I have are the same port timing.

 

[mdavlee]

EHP, Luke, or Bertrand?

Bertrand

 

[blsnelling]

My notes have 390 ex at 97 and 385 at 100.

That sounds right. The 390 will sometimes even be at 96°. IIRC, the 385 has more intake as well. I've never seen a 390 with those numbers.

 

[Chainsaw Jim]

That sounds right. The 390 will sometimes even be at 96°. IIRC, the 385 has more intake as well. I've never seen a 390 with those numbers.

Well now you know there are some out there that match numbers.

 

[Sty57]

I thought maybe I could talk you into being the test dummy.

I'm a big dummy.......and your a doodoo head. [emoji6]