750 kit, engine stress

nuklearzelph · Posted: November 14, 2008, 2:10 am Post subject: 750 kit, engine stress

hi, i am wondering given all the stuff i have read on the overbuild stuff i have read on these motors and hipo crashing an engine faster.

how stable/long lasting would a 750 kit be for a regular use town/highway bike that is not abused? i like the look of mikes long fins and it sounds like i might need that extra power from my bike since i am not a small guy. i weigh about 250. i want a good looking bike and a well working engine, but i don't like blowing money to lose my work before i made it worth the effort and time in use. i am one of those who try to make it last till there ain't much left.

Nuklear

metalredneck · Full Member Joined: Aug 04, 2008 Posts: 308

I did a Wiseco 752 kit on an '84. I had to put in Barnett clutch springs & plates, and then wound up spinning a crank pin. DEFINITELY get the crank welded. And throw the electric start away, 'cuz it ain't gonna make it fire.

Then you can do your carb & exhaust stuff to make it flow.

xsjohn · Posted: November 14, 2008, 10:48 am Post subject: Re: 750 kit, engine stress

After playing with this 80 of mine for 65k.....and many others Yamaha's in the past .....I got smart and went the other way and mellowed it out......what a nice ride now......but I am one of the few that see's things that way.....everybody is on the more more more thing.....

xsjohn

jimmythetrucker · Full Member Joined: Mar 12, 2008 Posts: 1283

I weigh 275. I'm beefing the suspension on my own machine. Heavy-duty shocks on the back, Stiffer springs with emulators on the front. A tweak bar.

All I'm doing for horsepower is a set of round-slide Mikunis. I figger that'll give it enough extra power to haul my lard ass around.

xsjohn · Posted: November 14, 2008, 11:40 am Post subject: Re: 750 kit, engine stress

You guys with the weight do have a catch 22.......being a 135 lb wimp like me does have it's advantages.......not many though.....If I couldn't hide behind this computer screen I would have surely been strangled by now............right Jimmy......

xsjohn

Retiredgentleman · Posted: November 14, 2008, 1:58 pm Post subject: Re: 750 kit, engine stress

I find the 650 is the just the right size for my weight of 169 lbs. It has enough power and yet the bike is still nimble. Maybe you lads that are of larger frame and weight should just look into getting an XS1100?

xsjohn · Posted: November 14, 2008, 2:17 pm Post subject: Re: 750 kit, engine stress

Some ole fart theories on the 750 kit.....if built for me.....and I am sure that no one will care but here it is............ .050 thou shim under the barrels........reducing the compression from 9-1 to around 8-2 to increase longivity and reliability and smoothness........a used chain would be required and they are everywhere and retarding the cam 2.5 degrees would be a must do........that's easy..........the larger fins would really make this cool........should pull a heavy weight like a stocker pulls a lite weight ........even with some taller gears..like 18/30.....might have something that would be around a while then.........

xsjohn

xs1961 · Posted: November 14, 2008, 2:43 pm Post subject: Re: 750 kit, engine stress

Nuklearzelph, these motors are bullet proof, no issues re. reliability,no mods needed if over-boring..One of My 840's covered 23,000 miles, thrashed it everywhere inc. dozens of sprints at the Ramsey sprint Isle of Man , no crank welding was ever needed (though it cant do any harm, insurance ) my 750's covered big mileage too without probs. In fact both the 840's & 750's seemed to run smoother !

nuklearzelph · Posted: November 14, 2008, 8:44 pm Post subject: Re: 750 kit, engine stress

ok, sounds like good news. what equipment does it take to weld on the crank and where do you weld? do you use the stock cam still? is it a good idea to change the connecting rods for the build or is stock fine?

what suggestions for port work to make it breath better? how "dangerous" is it for a total newbie to do the port work? or could i even?

thanks for the info.

Jake68 · 650Rider Supporter Joined: Mar 23, 2007 Posts: 841

Crank welding needs to be carried out by an engineer. The crank needs to be precision balanced afterwards. Adding metal and grinding back changes the overall balance of the rotating forces.

xs1961 · Posted: November 14, 2008, 9:56 pm Post subject: Re: 750 kit, engine stress

Stick with stock cams for overall 'sweetness'..use your original rods of they are in good condition. As for 'porting' I think you may mean gas-flowing - smooth/'clean' out the inlets & exhaust portswit a dremel if you feel up to it - its a great mod. Take note of what Jake says about the crank mate .

Jake68 · 650Rider Supporter Joined: Mar 23, 2007 Posts: 841

What I wanna know is what Jets People are using with the 750 Kit and 38CV Carbs, standard cams and free-ish pipes....:-)

Where do I start? Hopefully someones got an idea..of something on the rich side I guess? Smile

xs1961 · Posted: November 15, 2008, 7:24 am Post subject: Re: 750 kit, engine stress

Depends which 38's youve got mate. Whats your main jet & pilot at the moment ?

moondog · Posted: February 4, 2009, 6:10 pm Post subject: Re: 750 kit, engine stress

I'm looking to build a 750 too. I've been saving for the last 4 or 5 mos to get Mikes complete kit, only to find out yesterday afternoon that he's gone up 20% on it! Evil or Very Mad

Are the bigger fins really worth $150 more than a Thomas Racing re-sleeved 750 kit?

Also, does anyone have a place they recommend to do the crank...or buy one already done?

I have a Shell cam & R&D springs, Mikuni 34mm roundslides & a set of fishtail drag pipes waiting on some cubic inches.

xsjohn · Posted: February 4, 2009, 7:30 pm Post subject: Re: 750 kit, engine stress

It's not so much the 750 per say...it's the CR..........

xsjohn

xs1961 · Posted: February 4, 2009, 8:33 pm Post subject: Re: 750 kit, engine stress

With you there John..
Standard bottom end will cope easily with big-bore kits , my 840's & 750's were thrashed mercilessly for thousands of miles without any crank mods.. They ran smoother than standard 650's which I find to be pretty harsh. . Fitting a 750 wiseco again soon as I can afford it .. My 650 is & going to be 'de-compressed' this spring after hearing of johns success with a spacing plate/gasket method..

xsjohn · Posted: February 4, 2009, 8:44 pm Post subject: Re: 750 kit, engine stress

Speaking of balance (smoothness).........I think the backside of the crank is a bit heavy causing more vibes........when I started the needle thing and got some more power out of my stocker it ran smoother....the heavier pistons of the bigger bore may add to the front side of the crank (big end side) smoothing them out........all theory of course but what else can I go on........and watch the CR of some of those wisco kits unless your racing...hard enough to make 8-5 into 8-1...someday I'll build a 750 at 8-1 CR........

xsjohn

yamaman · Posted: February 4, 2009, 9:57 pm Post subject: Re: 750 kit, engine stress

xs1961 wrote:

With you there John..
Standard bottom end will cope easily with big-bore kits , my 840's & 750's were thrashed mercilessly for thousands of miles without any crank mods.. They ran smoother than standard 650's which I find to be pretty harsh. . Fitting a 750 wiseco again soon as I can afford it .. My 650 is & going to be 'de-compressed' this spring after hearing of johns success with a spacing plate/gasket method..

ines got stock crank, not welded, the cheapest 750cc you can get, new liners & Yamaha TX750 pistons with Repco (best there is) rings, straight in no nonsense, goes like the clappers! Stock cam, 34mm VM's. 2 seasons old & looking forward to a third! Sweet

moondog · Posted: February 4, 2009, 11:14 pm Post subject: Re: 750 kit, engine stress

Thanks for all the input, guys.

Hey Yamaman, any problem with heat? I live in Atlanta & I ride everyday it's over 50 degrees...which, down here is most of the year...and lots of days its over 100, with traffic jams. That's the only reason the bigger fins of Mike's 750 jug kit were appealing.

xsleo · Posted: February 5, 2009, 4:36 am Post subject: Re: 750 kit, engine stress

moondog, you might want to look into an oil cooler. it will help a bunch on keeping the thing cool.

650skull · Support Staff Joined: Jul 19, 2007 Posts: 1186

Moondog, Mikes 750 kit has been $599 for a long time now and is still good value when comparing against the cost to pay some one to resleeve and bore the new sleeves to fit the 750 pistons..........also end up with a spare set of original barrels..................

xs1961 · Posted: February 5, 2009, 6:03 am Post subject: Re: 750 kit, engine stress

YAMAMAN , those TX slugs fit straight on to the rods - same gudgeon pins etc ? Not sure we can get them over here, the TX was never imported..

650skull · Support Staff Joined: Jul 19, 2007 Posts: 1186

My understanding of the TX750 pistons, in the 650 motor was not a good combination...........Don't the TX750 pistons have a flat top, lowering the compression to much to be of any value?

xsjohn · Posted: February 5, 2009, 8:36 am Post subject: Re: 750 kit, engine stress

XT750 (1974) piston doesn't look totally flat......xs1961 is smarter than the average bear.........wish I had a few of them......looks 8-1 ish to me...

xsjohn

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