Piston speed?

In reply to Robbie (Forum Supporter) :

Define 'everyone'.

Driven5 said:

In reply to Robbie (Forum Supporter) :

Define 'everyone'.

I don't discriminate! It's inclusive of LGBTQ, Vegans, cat-ladies, women and children, Canadians, politicians, Bob Costas and Wal-Mart employees, Starbucks employees, and Starbucks-inside-a-Wal-Mart employees. But not that damn rabbit trying to steal children's breakfasts on TV. 

In reply to Robbie (Forum Supporter) :

So you can see/read my posts... Don't mind me then, as I'm just 'no one'.

Robbie (Forum Supporter) said:

 

But not that damn rabbit trying to steal children's breakfasts on TV. 

Somebody just let that rabbit buy a box of cereal with his own money.

On the original topic, my slant six has a 4 1/8" stroke (about 105 mm) and I had run it to 5,500 RPM. Stock cast pistons, and the rebuild is also going to use stock replacement parts.

You're correct.  Weakness was the wrong word. 

Driven5 said:

In reply to Robbie (Forum Supporter) :

So you can see/read my posts... Don't mind me then, as I'm just 'no one'.

Well, upon further review,

'No one' is smarter than me!

I crack myself up.

Driven5 has some good words here.

It's not speed, it's acceleration/inertia.  An 80mm piston moving at 4000 fps is not the same as a 90mm piston.  You also have to look at rod/stroke ratio.  A 5" rod throws a piston with much faster acceleration than a 6" rod and does so with more side-loading on the cylinder.

Tom1200 said:

frenchyd said:

In reply to Tom1200 :

So the "weakness" is the rings?    Hmmmm interesting.    I had a set of Forged pistons  that I took to 5400 FPS regularly and occasionally to 6150 FPS. after 20 years of racing the rings were the only significant area of wear.  
  A fresh set of rings and a light redressing of the valve seats was all it had done to it the rest of the time until it went into the Packard museum about 2016. 

There are no weaknesses in the motor; purely a case of the rings wearing first. They don't actually break things till you regularly spin them past 9000 RPMs. From memory: I think the crank doesn't start breaking till you spin it past 9800, the stock rod bolts around the same RPM.  I've also been using the stock push rods but people running them past 9000 are using titanium push rods. The motor is really over engineered.

Back when I read Cook Nelson's 2-Stroke Tuner's Hndbook (Maybe like 40 years ago) I seem to recall him offering the opinion that 4000 fpm was the mximum for a reliable 250cc stroker, that above that speed ring flutter would cause a reduction in power and land damage. Don't ask me to try to find my copy of the book If I could it would be greasy and dog-eared.

The ofher reference I had was a big weak link on rpm is the exhaust stroke on overrun, and it's affect on the rod bolts. But then again, most people torque 'em well past guttentite so the bolt us well on it's way to yield, rather than using  stretch gage and keeping deformation in the elastic range.

In reply to Curtis73 (Forum Supporter) :

That not only is good to know but since the rod is about 6&1/2" center to center on a 3 inch stroke  explains why I can safely go 500 rpm past factory red line without fear. 

twentyover said:

Tom1200 said:

frenchyd said:

In reply to Tom1200 :

So the "weakness" is the rings?    Hmmmm interesting.    I had a set of Forged pistons  that I took to 5400 FPS regularly and occasionally to 6150 FPS. after 20 years of racing the rings were the only significant area of wear.  
  A fresh set of rings and a light redressing of the valve seats was all it had done to it the rest of the time until it went into the Packard museum about 2016. 

There are no weaknesses in the motor; purely a case of the rings wearing first. They don't actually break things till you regularly spin them past 9000 RPMs. From memory: I think the crank doesn't start breaking till you spin it past 9800, the stock rod bolts around the same RPM.  I've also been using the stock push rods but people running them past 9000 are using titanium push rods. The motor is really over engineered.

Back when I read Cook Nelson's 2-Stroke Tuner's Hndbook (Maybe like 40 years ago) I seem to recall him offering the opinion that 4000 fpm was the mximum for a reliable 250cc stroker, that above that speed ring flutter would cause a reduction in power and land damage. Don't ask me to try to find my copy of the book If I could it would be greasy and dog-eared.

The ofher reference I had was a big weak link on rpm is the exhaust stroke on overrun, and it's affect on the rod bolts. But then again, most people torque 'em well past guttentite so the bolt us well on it's way to yield, rather than using  stretch gage and keeping deformation in the elastic range.

I'm pretty careful when I torque the rod bolts.  First I run a tap and die over the threads, then carefully lube them.   I use I high dollar (Snap On ) torque wrench that regularly gets calibrated. 
    The con Rods are forged EN40 steel and the bolts look like ARP copied Jaguar. While a stretch guage would really add a belt and suspenders approach.  In all of the V12's I've worked on or read about. I've never read where the bottom end is a weakness or ever heard of a rod bolt failing.