Gio X31 build-up thread

[Weldangrind]

I think that Wiseco makes among the best aftermarket pistons. Once you have measurements, I'll be happy to compare them with a few pistons I have around here.

[goofyexponent]

Thanks Weld...I am going to the shop tomorrow to get my calipers and my precision measuring tools.

I know we are at a 65mm bore.

[goofyexponent]

Ok Mr Weld!

I got those measurements:

I used a mastercraft digital caliper to give me my readouts.

Piston bore size : 64.84MM (65MM bore)

Top of piston to bottom of skirt : 42.58MM (42.5m

Wrist Pin : 14.97MM (15MM)

Top of piston to top of Wrist pin : 14.64MM

Top of piston to center of wrist pin : 22.12MM

I think I gathered up 0.072" clearance at TDC from the piston top to the edge of the cylinder head where the piston would first contact if it centered too high.

Can I plain 0.035" off my culinder's deck to gain a little on my CR?

[Weldangrind]

I'm measuring an old XR200 piston with a Performance Tool digital caliper. $5.00 at a garage sale, and worth every penny.

The wrist pin is 14.97mm, so we're off to a good start. The measurement from the bottom of the skirt to the piston top depends on whether you include the pop-up; 49mm without the pop-up, 50.20 with.

Center of wrist pin to piston top: 25.45mm / 27.05mm (approximate)

Top of wrist pin to piston top: 18.20mm / 19.77mm (approximate)

It looks like a Honda piston would be considerably higher, so I sure wouldn't plane the cylinder. Wiseco pistons to match the XR200 are available in 65.5mm, 66mm, 66.5mm and 67mm. Do you plan to bore out the cylinder?

Do you have an OHC engine? If so, perhaps a Honda cylinder would fit, which would allow you to run a bigger bore without machining costs.

[goofyexponent]

YEP! She is an OHC engine.

Currently there is no market for a high compression piston for the Zongshen CB250 (overhead cam engine) but apparently it is in the works..

What I might do in this case, is just plain the cylinder down, try and find a thinner head gasket (if not, plain the cylinder own some more to compensate) and stick it back together.

Maybe I can save a little more coin and go with a bigger bore cylinder like the XR200's and throw an oversize bore kit in THAT to REALLY pump up the CC's and compression.

I am not sure what to do here....any suggestions?

Should I put an XR200's cylinder and piston in it? What is the bore and stroke of an older XR200?

[goofyexponent]

1992 XR200R

65.5MM Bore and 57.8MM stroke

MY engine is a Zongshen CB350

65MM bore and 67MM stroke.

My TDC clearance is roughly 0.072" ot 1.84MM

The honda piston is about 3.56mm taller than my stock Zongshen piston.

I wonder is I can mill down the piston to make it work. I am near the top of the cylinder now when the piston is at TDC. I can reassemble and take a definite measurement of the piston when it is at TDC.

At best, I think I have 0.085" clearance when assembled with the stock head and base gaskets.

Is there a thicker base gasket I can run?

[FastDoc]

Whereas I respect the effort and the thought and the engineering I can't help but think that the cost/benefit thing is not going to work out on this...

With that said you could be the first to put a 4 valve XR200 engine in a CB :P

[Weldangrind]

It seems to me that the easiest route is to use a Honda cylinder and Wiseco piston. Does your engine have an automatic decompressor? You'll need one, or you'll break the kicker shaft.

You could certainly fly-cut a Honda piston to work with a China cylinder, but it would be way more advantageous to use an uncut Wiseco. I might even have an extra cylinder laying around.

Another thought is to use a piston designed for a 200cc Honda Big Red. They had a 65mm bore. You cut fly-cut that to zero deck and have a nice day. The wiseco version of the Big Red piston is available in either 10.25:1 or 12:1! 8O

[Weldangrind]

BTW, if you want a thicker base gasket, just stack two of 'em.

[goofyexponent]

I don't think she has any type of decompression valve. None that I can see anyways.

I am going to try and dig up info on a big red piston, but it appears that I might be going with the honda cylinder and piston route.

[Weldangrind]

Can you show us a close-up pic of the right side of the engine?

[goofyexponent]

ummmm....I can try. I got the whole thing apart and on the desk. There is no manual d.c. valve, and I am postitve there is no auto d.c. valve. Just an intake valve, exhaust valve and a spark plug in the head.

[Weldangrind]

I believe you. I'm wondering if Honda bits can be adapted, since the motor in "inspired" by Honda stuff.

[FastDoc]

I believe there are generic decompression valves available. People install them on high compression Harleys and the like to help save the starter motors. They install through a small hole drilled and tapped into the head.

I agree the kickstart mechanism is a weak point on this motor design, as it is on the XR200's in general.

[goofyexponent]

Ok, I have taken all the measurements, and taken pics of all the parts laid out on the computer room floor....yea, I know...I am a redneck for a reason lol.

What I am thinking of doing is buying a complete gasket kit, and then just a base gasket.

Putting the cylinder on with the piston inside and measuring clearance from TDC of the piston to the top of the deck.

THEN measure the head gasket thickness, factor in compression when it is torqued down. Measure for valve lift and see if the piston will impact any valves if I plain down the head.

Then meaure out how far I can plain the head down safely and have the piston valve reliefs cut accordingly. Then I think I am going to slap it all back together with the new gasket kit, rings and some synthetic oil and call her good for now.

What I might do is try and locate a blown up XR200R engine and build that fron the ground up. Seems to be a lot more of an aftermarket base for that engine than these overhad cam Zongshen ones.

http://www.facebook.com/media/set/?s...3&type=3&saved for pics