Monty Piston

[facthunt]

Can anybody tell me which models this fits?
PN 3460074J

[cappra]

The box says a 2nd oversize for a 34M (King Scorpion) but the piston
appears to be for the 43M, 53m motocross model.  It was the only
models to use the worm ports on either side of the piston.

[facthunt]

Thanks for the quick reply.
Anyone want to buy a piston?

[JC]

I would have tho't the part no indicated 34M King Scorpion.

Jared, didn't the 34M use the extra 'finger' ports that line up w those holes in the piston?

[cappra]

The 34M uses a standard style piston.  No boost port or
finger port of any kind.  Cylinder is very basic, two transfers,
one exhaust, one intake.

[mike1948]

just to confuse things, I pulled apart an old 44m motor, and it's a strange setup.  It has 3 transfer ports and 2 inlet ports, one of the transfer ports separates the 2 inlets.  The piston has a port cutout to fit in with that central transfer.  How long did they run with that design, seems very restrictive for the intake.

[JC]

Yeh Mike,

Thats standard porting for the VR/V75 based engines, inl 44M & 54M. Early 63M cappra was like it too.

Much better & more effective porting than the small 'finger' ports.

Jared, Did the optional kit barrell for the 34M have the 'finger' ports?

[cappra]

From what I can deduce from the 34M parts book
on the "racing kit" page, it calls for the 4360.027 liner
and the 5360.074 piston assembly, which uses the worm
ports.  Problem with using the 34M cylinder for anything
high performance is the intake tract.  Same size as the Cota 247!.

If you think the 44M cylinder looks strange, check out the later 414
cylinder, you would be shocked......

[JC]

JB,

Yes I remember the 34M has same size carb as Cota (27mm??), but doesn't the 34M use an intake manifold that could be presumably replaced w a larger one for a larger carb?

Or is the entire intake tract (inside the barrell) too small to be enlarged?

Re 414 porting - I've never seen a 414 barrell

[cappra]

You could enlarge the 34M's intake passage, but stll not very large
compared to the 43M, 53M intake passage.

[cappra]

Here's a pic of the 414's cylinder.
The boost port cavity extends in to the
intake trac, with a big hump in the middle.
Notice the very narrow transfer ports.

[JC]

Thanks J,

Thats very similar to some 370 Bul barrells

[mx250]

You want ports, you want Monty ports? Count these; 9 ports .





Name the barrel (its bog stock (I think ))

[JC]

Nice shots. Never seen one like it before. (I haven't seen any monty barrells post VB)

My guess is H7 reedvalve or late cappra reedvalve. Probably 250.

Am I close?

[mx250]

My guess is H7 reedvalve ....................... Probably 250.

Am I close?

Close? Spot on. Well at least as far as I know. I got the motor with a 'box of bits' which included H7 sidecovers so I assumed.......