GZ 250 Forums - Convert your GZ250 into a 346cc!!!

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Re: Convert your GZ250 into a 346cc!!!

Quote:

Originally Posted by motorhedfred

since the gz250's engine is so close to the DR250S engine, which gave birth to the DR350S engine......how about this ?

Without even looking I can say: Go for it and let us know how it turns out! :whistle:
We will be forever greatful. :biggrin:

PS I like your tag line. :2tup:

Re: Convert your GZ250 into a 346cc!!!

Quote:

Originally Posted by motorhedfred

I'm in the market for a leftover new, or clean complete GZ250 close to northeastern Ohio. Hmmm, I wonder how often the MSF trades them out........

Keep an eye out for LS650/S40 too. Some of the older models have buckhorn bars; had I known that, I might not have the GZ. Now that I do, I probably won't change but I think that "CC envy" is a chronic disease that one never quite gets over completely. :cool:

Re: Convert your GZ250 into a 346cc!!!

Quote:

Originally Posted by motorhedfred

Hmmmm, 40 cubic inch single....belt drive.....what year did they start putting 5 speeds in them ?

Don't know. I have been avoiding looking at them TOO closely for fear that I might decide I HAVE to have one! :roll:

Re: Convert your GZ250 into a 346cc!!!

I think it existed, it is just that he didn't ever actually do all this stuff he claimed he was gonna do to his bike and he didn't want to come on here and have to admit that he was full of S#@t. But he has been back a couple of times since, he just has commented on this thread, he also claims that he now rides a Ducati, as if that is supposed to mean something to us.

Re: Convert your GZ250 into a 346cc!!!

Quote:

Originally Posted by motorhedfred

This weekend I'm going to shop around and see if I can find a GZ and spend some time at the parts counters comparing cylinder base gaskets and head gaskets if I can find someplace that has them on the shelf for both engines. That's one more piece of the puzzle.

I called JE pistons today to get the compression distance for thier DR350 piston kit. It's .987 and 89mm (3 1/2") diameter which is a 10mm bigger bore size than the DR350 so no doubt it's also a re-sleeve situation on even that barrel. I seriously doubt there's enough meat in a GZ barrel to take a sleeve that size, so it's back to "will the DR350 cylinder fit on a GZ250 crankcase?". Apparently the DR350 has a wrist pin diameter of .787" (20mm) and I've yet to find out the connecting rod length, so that's another search. Does anybody know what these numbers are on a GZ motor ?

I'd better start bringing coffee and Mickey D's to the Zook dealer's parts guys so they don't get sick of seeing me and answering my dumb questions. I can almost hear them now as I walk out...."why the hell does that old dude want to waste his money on that thing ?"

For the same reason a dog licks his junk.....because he wants to, and he can.

MHF

BTW, I thought I hit paydirt with the website below but most of it's pages are under construction.....maybe someday

http://www.suzukidr350.com/

In addition to those parts you may well have to use a different/larger carb. More $$. Maybe a custom exhaust pipe and aftermarket fit-all air filter. Might be more advantageous to look for a nice used S-40 for the extra grunt and only weighs 60 lbs more. A bit larger than the GZ overall with only a couple factory gremlins. One being a lean carb mixture(easily fixed) and the other being a valve train piece that is replaceable with better aftermarket product if needed. The bike as a whole is really just a big GZ with a belt drive IMHO.

Re: Convert your GZ250 into a 346cc!!!

motorhedfred,
first off I'm not trying to discourage you. I'd love to have a 300 or 350 to ride. I think it would take some serious machining and custom work to shoehorn a 350 piston on the GZ250 engine. Even supposing that you could simply replace the top half on the engine with that of a DR350 there is the problem that the DR350 engine has a 10mm longer stroke. 71.2mm vs 61.2mm. You would have to shorten the barrel by 10mm yielding you a 300cc engine. Comparing the bore of the DR350 to GZ250, 79mm vs 72mm. I think the best probability for an improvement would be if there's enuff meat in the GZ250 barrel to do a resleeve to a 79mm bore Which would yield a 300cc engine. An awful lot of work for maybe an extra 3-5 HP. I'm keeping an eye out for a DR350 engine to see if I can shoehorn it on the GZ250.

Re: Convert your GZ250 into a 346cc!!!

Quote:

Originally Posted by Quimrider

An awful lot of work for maybe an extra 3-5 HP. I'm keeping an eye out for a DR350 engine to see if I can shoehorn it on the GZ250.

If there is any practical way to increase the displacement, I think that is probably the only way.

After you do ALL the other checks on the piston, etc. then there is the SHAPE of the piston dome for valve clearance. Those spec's are often VERY hard to find.

Re: Convert your GZ250 into a 346cc!!!

Was just doing some thinking about what would be necessary to convert the GZ250 to a 350 Using DR350 parts. This is of course assuming the parts would physically fit. You would definitely need the following from the DR350 engine:
Piston
Cylinder sleeve
Crank shaft
you might need the following from the 350 engine:
cam chain
cylinder head.
The way I would envision this is that you'd have to swap the crank shaft to add the extra 10mm stroke. the 350 sleeve would be necessary to accommodate the increased stroke and then obviously you'd need the 350's piston. I'll assume the connecting rods are the same. I would think you should be able to use the 250's cylinder head. This would make it easier to not have to do any custom exhaust work and worry about the carb fitting. I also would think the cam chain could be reused from the 250, but you may have to use the 350's cam chain if the 250's chain doesn't fit due to increased stroke distance.

This would seem to be cost prohibitive and time consuming. A more economical approach would only get you a 300cc engine but would have more likelihood of success. This would be to have a machine shop bore and resleeve the GZ250's cylinder jug to accommodate the DR350's piston. The only problem would be whether or not there is enough material in the GZ250's cylinder jug to fit the larger piston sleeve.

I hope this give you some food for thought. Motorhedfred, I see you're in Ohio too. Depending on how far away you are if you do decide to attempt this, I'd be willing to offer a hand.

Give these guys a call maybe they could come up with something.
http://kustom-kraft.com/SUZUKIKITS.html

Re: Convert your GZ250 into a 346cc!!!

There are clearly forms of entertainment that I will never understand. Doesn't Suzi already make a bike that's about the same size as the GZ but with a bigger engine? Also, I think I could appreciate the thinking behind a retrofit that took it from 250 to say 500 or 600 but to 350 seems pretty unimpressive. Still, I will probably be just as curious as everyone else if you actually make it work, or even if you escape without embedding piston or cylinder shrapnel in your behind.

Re: Convert your GZ250 into a 346cc!!!

Quote:

Originally Posted by alanmcorcoran

Doesn't Suzi already make a bike that's about the same size as the GZ but with a bigger engine?

I think so but not available in North America. Next one here is the S40/LS650.
Some days, I wish I had one; most days not.