Long stroke cranks and their materials/limits.

[ianh1968]

What I cannot understand is why all long strokes
have got 1.625" journals. Wouldn't it be MUCH better to use the 1.75" ones?

The reason why the non-'S' rods were made bigger was
because the material specification was lower. The larger
diameter was intended to compensate for the lower spec
steel.

The 'S' ones were/(are?) EN24V
The 1300GT/Innocenti ones were EN19
The non-'S' ones were EN19 then later, EN16
The A+ ones are EN15
(According to Mr Vizard...)

The 'S' type rod is said to be "over-engineered" anyway, so
it would probably have been OK to have downgraded the spec
and left the journals the same size.

Ian

[Vegard]

I don't for a second doubt that the S rods aren't strong enough.
You hear so much talk about crank flex on long stroke 3 journal cranks. Wouldn't a 1.75" big end reduce flexing?
Don't mind the rods, mind the crank

[In the shed]

Whilst we are here, I am considering my piston situation. I'm wondering what my starting pistons actually are.

They appear to be formed in 2 halves at 90 degrees to the pin (floating) both "halves" are stamped "Omega". The height from the centre of the pin to the crown appears to be 1.5" and the top of the top ring to the crown appears to be 1/4". The ring configuration is top, second and oil and there are 4 holes in each side (8). The centre of the dish is stamped 735 and this looks as if it has been done by a man with a punch. The "flat" outside of the bowl is 3/16" wide and the bowl "looks" as if it is 5mm deep. There is an "m" ripple under the crown of the piston. The total distance between the skirt (below the pin, rather than the "maximum" bit is 2/1/4" (using crappy old wooden ruler! ) The pistons are barrel shaped with no wasting or "flat bits" for the pins.

293g without pin 398 with.

The pistons do not appear to have been turned in any way.

Oddly, I noted that I have 3 midget rods and a 177 rod mixed. All beautifully worked and appearing to be in very close tolerance. Was this engine built by a hillbilly?

Vizard says the minimum about long strokes and compression heights.