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Dan Davis

I’m back!
Well, it’s been a year since I’ve worked on my case induction CR250 project….it’s just been sitting there patiently waiting on me to get back to it while I drove a 125 and a TZ250 kart at select events last year.   I am currently working on resolving my cylinder head issue for a 2004 CR250 cylinder for which I intended to fit a 2005 domed piston.

As I began modeling a combustion chamber to cut into a 2004 cylinder head to use the domed piston, I realized that I would need to cut the chamber excessively deep into the OEM head to obtain a 20cc CCV (without spark plug hole, approx. 22cc’s with) and a 1.2-1.3mm squish clearance.  This is mostly due to the piston dome consuming approximately 7cc’s of volume keeping in mind that my chamber must begin flush with the cylinder deck rather than inset into the bore due to the existing porting in the cylinder. The piston depth in the cylinder at TDC then is equal to the squish clearance value.
I have concerns that this will make the combustion chamber casting thickness too thin and possibly even break through since I have not cross sectioned a head to verify casting thickness.

This leaves me with a couple of options to use this cylinder:
1. Use a flat top piston to gain approx. 7cc’s of volume.  This is probably the easiest option but I really would like to use the 2005 single keystone ringed piston.
2. Explore a different head.  Expressly, the 2005-2007 cylinder head for which I know nothing about except that it was designed to be used with the domed piston I would like to use.

Based on previous posts by our favorite technical expert on CR250’s, I think I already have a clue as to the answer of my question….which is no but don’t have a definitive answer, so here it goes:
Can a 2005-2007 cylinder head be fitted to a 2004 cylinder?   I’m guessing the answer is no because of the offset bore/chamber relative to the stud pattern on a 02-04 cylinder (assuming that the pattern and or bolt circle is even the same) but I haven’t seen one to be able to tell.
Thanks in advance,