250 Magnum Piston sizes

[250 Magnum]

The piston size in the 78 250 Magnum I'm restoring is 67.55, the piston size in the spare engine I have is 67.75, both are Mahle same as stock parts.

The piston sizes in the Maico parts list are 66.95 - STD and three oversizes 67.10, 67.25 and 67.40

Now, if the factory only lists pistons up to 67.40 then where do the 67.55 and 67.75 pistons come from and what effect, if any, does this bigger bore have on the barrell sleeve etc and has anyone else got piston sizes different to the factory specs? Was this a common occurrence back in the day?

Danny

[Mick D]

Hi Danny, all of the associated parts lists at the time that came with the owners operators manual only went to three sizes over for some reason. They always latter added larger size options as bulletin releases, for some strange reason

Don't worry about it. You can get pistons now all the way up 2.5mm sleeve savers, Although I have had a cracked 250 sleeve, it is very rare for a 250 sleeve to crack.

Call Les for a 68mm woosner for the 67.75 bore cylinder that you have. He is now got them down to $149.95. Your engine will be a little snappier too. Their reciprocating mass is a lot less than original Malhe choice.

A Woosner is teflon coated. I like to bore them neat and take it easy for the first three hours. And as usual make sure you chamfer your ring leadins on your ports and set your ring end gap. Machinists are only paid for boring and honing, so that is all they do.   

[250 Magnum]

Thanks for the info Mick.
Maico were renowned for making changes any time during a model run so that make sense.

Danny

[Mick D]

Maico were renowned for making changes any time during a model run so that make sense.

Danny

Yes Danny, so true. Just about every year of production has "half" models for Maico.

Some of the changes are very significant too, although not all visible, but allot very significant.

The ever evolving struggle to compete toward the top of the heap, without waiting for another marque to get the drop on your marque. I have found so many differences within models, sometimes it is just the little things