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Re: B33 long rod piston?

As Ron notes, the long rod pistons only work with the M21 crank and there wouldn't be enough material in the crown to machine the piston flat, or even nearly flat anyway...The low compression short rod B33 piston would be the one if the crown heights work out...However, 85mm on an M20 crank will only give you 533cc so little real gain for the effort..Ian

email (option): ian@wright52.plus.com

Re: B33 long rod piston?

My lack of knowledge on this topic is beginning to show, but I'd like to do some more digging on this. Where could I find out the pin to crown length for both the M20 and M21?

email (option): cas.vanderwoude@gmail.com

Re: B33 long rod piston?

Michiel W Quotes the M21/B33 crown height in one of his posts in this thread. Perhaps he also has the M20 measurement written down? Ron

email (option): ronpier@talk21.com

Re: B33 long rod piston?

I haven't measured the M20 crown height lately but the stroke difference between an M21 and an M20 is 18mm (.708")...So the difference in the crown height between the two pistons would be half of that figure (9mm/.354")..Using Michiels dimension for the M21 you should be able to work out the final figure for an M20 by adding the two figures together...

I'd get that figure confirmed absolutely at some point but it will give you a pretty accurate figure to work with...Ian

email (option): ian@wright52.plus.com

Re: B33 long rod piston?

Yes, from the Hepolite catalogue:

M20 comp.: 1 19/32"
M21 comp.: 1 7/32"

They call it the 'compression height', distance from center of the pin to top of the piston.

Surprisingly the difference is 0.375" / 9.53 mm instead of the 9 mm as you indeed would expect.... So it looks the top of M20 piston gets 0.5 mm higher up in the bore than the M21 piston.

BR Michiel

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