Thread: Super Stock GP1200R
05-19-2009, 05:11 PM #1
Super Stock GP1200R
Im buyin a tripple piped GP1200R from a friend, but it has some issues, the craft is equipped with Magnum Pump "14 Vein" R&D Ride Plate & Intake Grate, Riva Mechanical Trim Tabs, Ported Crankcase, Race Gas Ported 80mm "STD" Cylinders, Trued & Welded Crnakshaft, M16 Reeds & Manifold, Riva 37ccc Heads, FPP Triple Pipes, Novi 48mm Carbs, Aftermarket Ignition System from Japan i forgot the brand, craft ran 77MPH all day, ok the issue is the cylinders had some scores, they rebuild the engine completely New T&W crank, & Complete Top End Rebuild "Pistons, Rings ect" the guy took the cylinders to the machine shop to get them honed to remove the scores & appearantly his telling me that the machinist over honed it, i dont know how he manage to do that but this is the deal after rebuild, & he gived it a 10hr break in period after the breaking in he did a GPS & the craft was runing 65-66MPH not as fast as before doin the rebuild (77MPH all day" he did a compression test & before he was getting a 180-190psi on all 3 cylinders, now his reading between 105-110psi right across, so oviously something is wrong, he told me its loosing compression due to the over honed cylinders, engine getting blow by ect....has any of you guys run across something like this before?? any suggestions?? i was thinking on finding 3 GP800R cylinders "80mm STD" & put it in, also change the domes on the riva head to 42cc's that way i could prob rung a mix between 93 pump gas & 104 race gas "50/50"...any suggestions??
05-19-2009, 05:22 PM #2
mate that sounds a bit weird to me
10 hrs run in?
on a race motor?.....hell we do 10 minutes !
"over honing" will strip the nikasil off the bores, if not stripped, the comp shouldnt drop to 105 psi, you would just get piston slap which will eventually cost another top end. you may lose a couple of psi but not 90 !
By changing the domes, your not sorting the gas issue, the port timing and ECU timing will need changing too, ports will be sorted by changing to STD 1300r barrells, sizing new pistons to match, however the ignition will need sorted.
Then, rejetting the Novi's, changing the pop off pressure, adjusting the gas valves.
after all this you'll have a 65mph ski.......
i'd get the barrells looked at and get some pistons to match, start from there, see if you like 77mph
05-19-2009, 05:36 PM #3
have to watch the piston to wall clearance as well.....with over bored cylinders and OEM sized pistons the rings will have enough room to jump the locator pins and rotate the gaps to the exhaust port. This WILL destroy the cylinder/piston/rings.
...you should have the cylinders measured and re-coated ...then check the piston clearance and get the correct piston/ring combo to stay within spec....
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