2 Valve gs750 basket case

[NBraun]

Hi there,

I have a bit of a basket case of a motor i'm trying to decide if it's worth to rebuild. I pulled it apart a couple years ago to go through it and it ended up sitting. The bottom end stayed together, but the jugs and head were pulled. It was always kept inside but the jugs have developed surface rust, and that's really why i'm hesitant to try and rebuild it. The head is freshly rebuilt, which is why it was taken apart in the first place.

What's the best plan of action here? I've tried looking online to get some prices for the cost of an overbore/piston set, but can't seem to come up with anything.

Thoughts?

 

[Guest]

A bit of surface rust can be cleaned up, sleeves can be honed. Measure the sleeves, if everything is within specs I’d just put in some new rings and run it.

 

[Fjbj40]

what azr said! De-glaze, re-ring and run it!

 

[Chuck78]

Wiseco K844 kit with head gasket will run about $420 if you find the absolute cheapest Rock Bottom internet price. + $130 to $200 depending on what machine shop you go to, get the cylinders bored and honed.

Depending on how the rest is, you can likely just own the cylinder out. You can probably rent a three Stone spring home at an auto parts store. Oil it up really good and run that thing in and out as fast as you can plunge it back and forth with a hand drill. That is the key to putting a 45-degree crosshatch cut pattern that the phone is supposed to have into the cylinder walls. Stop and check the angles of the hone marks to see if you need to slow down or speed up the drill or same with your hand motion.

Having a dial bore gauge would be very nice at this point to measure the cylinder, but if you are able to very rapidly get rid of the rust patches, you should rest assured that it is probably not too far out of spec from where you started at least. You can measure the ring end gap to get an idea of the cylinder bore dimension. As long as the rings aren't too far worn out this will give you a fairly accurate indication. This just takes the same feeler gauges that you need to adjust the valve shim sizes.

Or if the idea of adding a whole lot of low-end torque to it appeals to you, eBay some gs850 cylinders, and have them bored out to CruizinImageCo ( Japanese eBay store) 870cc cast OEM style pistons. This wont give you the high compression ratio that the Wiseco Pistons well, nor the ability to run a big aftermarket camshaft as the Wiseco will, but they cost less than half at around $185 with rings and pins, use OEM style head gasket. eBay can get you an old New Old Stock Suzuki gasket for $50 and a base gasket for the 850 cylinders for less than $20. Same cost for boring 850 cylinder out to 70 mm piston spec, but you will be at 870 CC instead of 844 CC.

Carb jetting won't be too far off from a modified stock bore 750, within a couple sizes of main jet. The mid-range throttle position quarter to half throttle will be a little more rich than stock bore. o-4 needle jets from 1979 gs850 carbs solve that, but this is a workable issue, better to be slightly rich than too lean. A dynojet kit may also solve that if you find a needLe with a slightly fatter diameter. Most people ignore this tuning step and just run with them slightly rich and talk about how much more power they added. Better a bit rich than lean. The fine line of being too lean makes the most power, however.

 

[NBraun]

Thanks guys, I appreciate the comments.

Chuck, that answers a lot of my questions.

I think i'll try to go the cheaper route, but if the jugs won't work, i'll go the 870 route. Luckily I have a buddy that works in a machine shop, so I can get use of a bore gauge just to check everything out.