Just finished going over my CR250 port measurement notes.I ran the numbers...it is crazy mild!! 178/119 if you decked it .040 or 1 mm to keep it simple, you would need to lift the transfers .080 or 2 mm to get 128° timing. And the exhaust...you would need to lift the exhaust .200 or 5mm to get 193 and 6mm to get 196!!!
got me thinking....trx piston 3mm shorter, you could cut .020-.040 off the base and 4mm ish of the top and the transfers would be 128-130 and the exhaust would still need to be lifted 2-3mm, crazy! Or she would love a stroker! Lol
Like what was said .So with the piston, 1.5mm in the hole, your timing would be 182/126 and that would put the transfers even at the bottom of the port, 2mm in the hole 184/128, I am guessing it’s 1.5mm in the hole. If it’s 1.5mm in the hole, I would deck the cylinder 1.5mm lift the transfers 1mm and the exhaust 3mm, that would set you up with 191/130
how thick is your head gasket?
I wouldn’t remove the exhaust bridge, you can and will run fine, rings aren’t an issue, you just can’t make the port as big. No wings, and without sub exhausts, I don’t think it preforms as well.
So seeing my CR250R piston is 1.5mm in the hole and timing at 182/126.So with the piston, 1.5mm in the hole, your timing would be 182/126 and that would put the transfers even at the bottom of the port, 2mm in the hole 184/128, I am guessing it’s 1.5mm in the hole. If it’s 1.5mm in the hole, I would deck the cylinder 1.5mm lift the transfers 1mm and the exhaust 3mm, that would set you up with 191/130
To do the equivalent of a one mill spacer, you’re basically just doing a three base gasket stack unless you find custom .010 gaskets, I have done the three base gasket set up before, and just Honda bonded the three gaskets together it works well.So seeing my CR250R piston is 1.5mm in the hole and timing at 182/126.
I'm looking at the complex roof profiles in the transfer ports. Rather then raise the transfer ports 1 mm and the exhaust 3mm, I'm thinking better to raise cylinder 1mm then raise exhaust port 2mm.
Then finish with lowering transfer and exhaust ports floors 1mm and deck 2.5mm off the top of the cylinder.
I’m not to sure about that, kind depends on your definition of chamfered? Your rings will die if you don’t bevel or chamfer the transfer ports, it may not need to be as much as the exhaust port, but you need to do more than debur, the sharp edge will wipe the oil off the rings and cause scuffing. Can you explain how radiusing the port would cause short circuiting? I can see how a small amount of the charge could get lost for a milasecond, and a small amount of the case compression lost, if the chamfer was extreme it would change the port timing and roof angle, but that would be extremeBit of good info I learned.
Don't chamfer transfer ports, only remove burs off the transfer port window edges.
Reduces short circuiting.
Not that I mod 2T engines like the guy's here do but myself I always chamfer the sides of ports.I think on forums like this chamfering ports gets taken way overboard. You definitely don't want chamfer in the port sides as it encourages the ring to sink into the port thus making them more vulnerable. The top/bottom and be done with a finger and some 320grit. But I suppose feeling the window edges with your finger tell you a lot too. But the deep bevel chamfers you often see people do are poor & unnecessary. Just my thoughts on the issue.