Big Bore!

yamaman · Posted: January 5, 2007, 12:58 am Post subject: Big Bore!

Just to let you all know-TX750 pistons-with 80mm sleeves- go straight into a 447 motor-presto XS750, easy hey!
I have road-raced my XS in this config the last 3 outings with no problems
Cheers Yamaman

jayel · Posted: January 5, 2007, 9:36 pm Post subject: Re: Big Bore!

yeah 650central has a kit with everything you need, but 700 (400 kit / 300 liner replacement) bucks for a extra 100cc on a 30 year bike that goes fast enough to get you pulled over on any highway I dunno maybe if you can justify it that's ok, think I'll have to stick with a slow old 650

yamaman · Posted: January 6, 2007, 3:08 am Post subject: Re: Big Bore!

Ahh yeah jayel-that would be with wyseco pistons at a guess?????
Thats why I thought I'd mention the genuine yamaha TX 750 pistons. A much cheaper way to go if you can access them. My bike needed a rebore at the time this became available so I thought why not!

If your bikes already fast enough, why are you reading Performance Parts anyway Embarassed

jayel · Posted: January 6, 2007, 10:22 am Post subject: Re: Big Bore!

yes wisco pistons, replacment liners, gaskets ect. don't forget to check/change your cam chain and adjuster guide while you're in there

If your bikes already fast enough, why are you reading Performance Parts anyway?

aways looking for that magic screw you give a quarter turn and it you 40 more hp lol

royfisk · Posted: January 6, 2007, 6:51 pm Post subject: Re: Big Bore!

yamaman
this is interesting, did you bore your cylinders to 80 . Or resleeve? I have a tx-750 parts bike. That may be what I do, Ill have to see what the pistons look like. Another cool trick is if you want to keep a tx-650 till year 77 looking original is to use th tx -750 forks which are 36mm over the original 34mm and then the rear wheel and swing arm. This is a huge handlein gain over the stock parts and allows you to use the original dash and keep the appearance of the original bike. Which the 35mm forks of the 77 and up you must either modify or update to the newer style dash.

grizld1 · Posted: January 6, 2007, 7:52 pm Post subject: Re: Big Bore!

Roy, max. bore with stock liners is 77.5, yielding 700cc, and if you have a stash of salvage cylinders on hand it's a good way to go. The engine in my D-model has a pair of 77.4 mm Venolias in it; had to have the crowns milled to get compression down into the pump gas range. I recently bought a pair of Shell's JE pistons for the build in progress on my bench; they're produced to yield much more moderate compression and are quite light for a forged piston--with rings and pins, each piston assembly is about 0.6 oz. heavier than stock.

yamaman · Posted: January 6, 2007, 8:25 pm Post subject: Re: Big Bore!

I'll take that on board for my future road bike, mine is a 1962-1972 post classic racer (see my gallery), and therefore must be in keeping with a pre 72 bike. I run 35mm forks, the biggest allowed in this catogary.
I run wire wheels

Is the 750 swing arm longer or stronger?

Yes you must resleeve to get 80mm, just as the wyseco kit. Mines actualy 80.25mm TX750 1st oversize, as they were the pistons I got!

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

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yamaman · Posted: January 7, 2007, 4:39 am Post subject: Re: Big Bore!

sounds the go, now to find one............!

royfisk · Posted: January 8, 2007, 8:49 am Post subject: Re: Big Bore!

yamaman I hve them when your ready. The rear wheel brake drum is about a half inch bigger in diameter and a quarter inch wider then the 650 drum, all meaning more shoe to surface contact and better brakeing. Im sold. My findings are that the stock rear disc brake has to big of a rotor and when hot has a tendancy to lock up prematurely. Of course you could have it ddrilled and cooled a little but Im not real impressed. The 750 wheel on the other hand is a good compromise. Im not positive but I think that wheel would be legal in your class. This might cut down lap times by allowing you to go further into the turn before getting into the brake.

yamaman · Posted: January 8, 2007, 9:05 pm Post subject: Re: Big Bore!

Cheeers royfisk-might try and get one in Oz first, I think the frieght could be a bit of a killer! Unless your coming down under any time soon, you can put one in your suit case!
Regs state I can only run a drum rear brake and min 18" wheels, to be honest my rear brake is more cosmetic than anything!

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