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Hey all.
Thought I'd pick your brain on something. My xs650 is old and tired.. Never been rebuilt. So I'm thinking, is the XS Performance big bore kit worth spending the money on?
Have any of you done this yourself? If so, I'd love to hear your thoughts.
I have found through research, when it comes to kits like that when you need boaring, pistons, crank work? head work, cams and etc... Go big or go home.
I've been looking into this kit as well. Well I should say I've been meaning to look into this kit. I've read about the kit, what I'm not sure about is how well the bottom end holds up to the larger top end. Kind of worried about my 34 year old bearings that might be in the bottom end.
Nicholause,The bottom end on the xs650's are bullet proof and very reliable. My XS(TX)650 is about 39 years old and going strong still. Nothing to worry about on the bottom end IF you know everything is good. The 750 kit for sale however is for the 447 engines made from 1974 and up. So if you have a compatible year I would go for it.
Garage rat, the 750 kit comes with the whole top end, pistons, rings and the juggs as well. So it is basically a straight up swap.
If I could do it all over again and eventually will. I will get a 447 type engine, get the crank and cam rephased and get the 750 kit all at once. total cost to rephase a crank and cam about $500 maybe a little less.
The old TX750 twin was an entirely different animal from the 650. It used dual balance shafts and a completely different design- it was state of the art at the time. Was a miserable failure sales wise and very short lived (I believe only 2 model years). Very little available as far as parts these days. When running well they are a great looking and riding old twin, just had some teething issues the first year with the balance shafts and oiling. Yamaha fixed it, but the rep killed the bike. That's also why Yamaha killed off the TX model identifier and returned to XS after the 2 years on the 500 and 650.
For more info on the 650's and big bore install, etc. try here:
Everyone I've spoken to is happy enough with their big bore. I'm planning on one for this winter. As far as rephasing is concerned it seems like more power faster revving. But am I the only one who thinks the bike would lose a lot of its appeal if you took away all those gooooood vibrations?
I personally would never rephase my 650. There's something about the sound of a 360 deg. twin that I just love. Sure it makes my winky go numb and tingle after just a few miles, but I still love it!
I think Rossicle means why wont the 750 kit fit on the 1973 TX650.
He was not talking about the TX750. The TX750 was a whole different motor yes, but the TX650 motor is very similar to the XS650.
The cam, the crank and the pistons where different. and the sleeves were different, so you could in essence install the 750 kit on the TX650, but you have to swap the crank and cam from a 447 motor to a 256/306/366 (1971 to 1973) motor, if you wanted to keep your cam you had to swap the cam gears from a 447 onto the cam off your pre 74 motor. T kit was designed for the 447 type motors because there were more of them made, from 74 on to 83. It's just more work and parts to get if you want to install a 750cc kit onto a pre 4 XS650
Xulf is correct. Though I enjoyed the reading material, Wahoo .
Well that's a bummer to hear.. But I'm glad I now know. Looks like I need to start searching for a new crank and cam.. :/. Not what my wallet wanted to hear.
What would happen then, if i used the tx650 cam and crank?
Ross,
It is a good read regardless. My next build will be a full blown built for speed 1976 XS650.
I am not 100% sure what would happen If you tried to use your TX650 crank and cam. I can only assume that the rods and the stroke is slightly different and the pistons would start to hit the valves. But ask around on XS650garage.com
I've read that there was a lot of work involved, but that it can be done. Not surprisingly so, it is easier to get a 447 type motor, rebuild that and then install that on your tx.
But just so you know. the 1973 TX650 Was the one year that carried the hot cam as some call it and the one that produced 52-53 HP over the 42 hp of later years. A lot of people actually seek the 1973 cams and mod them to fit on their 447 engines by putting their cam sprokets on it to fit and be compatible with their crank.
That leads me to believe that is all in the stroke of the crank and the size of the rods. let me know what you find, and it is nice to see another TX650 owner on here.
These are big HP motors, rule of thumb is that 70hp is the limit before the cases become unreliable.
A lot of modifications seemed to be focused around cost effectiveness. If your rebuilding the top end, go big bore, if your redoing the bottom end, do rephase.
I think its silly though to spend thousands of dollars for 20-30hp that'll make your once reliable bike not so, when a modern triumph twin makes 70hp and probably would only cost $3000 or so in the right areas.
I'm easily confused these days- 12 hour shifts since I don't remember when and a whole lot of Saturdays and even some Sundays... You are all correct though on building a 447 motor, and parts are easier to come by for them as well. I also agree with not pushing it to the point of unreliability. Mine will probably need ringed here in another season or two and I'll just do a one over, but will clean up the head and possible go to a hotter Webb cam- in my mind a cheaper/easier alternative to finding and modifying the elusive '73 cam. Best thing you can do to improve your '76 (same as mine!) is put it on a diet- whch is a big part of cafe treatment anyway. I even put myself on one a couple years back- it's amazing what losing 70lbs will do for your bikes performance! Keep the 650 faith!
Stroke is the same on all XS650's, (74x75mm)
The rod length changed 3 times (4, if you count my 'long rod' motors )
The piston pin position is different to account for different length rods (so the top only comes to top of cylinder )
I think (but can't remember for sure) the rods are 136mm, (early models) 130mm (447) and 140mm (European) and 'mine' 144mm (I heard the factory OW31 race motors use 144? 8) )
Race motors made around 100bhp but they couldn't stop cranks breaking in the center at 10,000rpm
447 crank shouldn't be too difficult to find?
Early cam has 34t sprocket and late 36t, swap sprockets (they are pressed on and a bit of a pain to degree properly)
Eventually I'm going to shrink/weld a sprocket mount to make life easier (when I finish screwing round with CB378's ;D )
Thanks for all this knowledge! It's great to hear!
I'm thinking I might just have to do a one or two up on the bore this winter.. Even a simple rebuild to stock would improve it I'm sure.
The compression was about 115 give or take a few.. And that was after many many kicks. I do have highway sprocket on it.. So it's a little lacking on the bottom end. I might need to try going back to stock.
Ross,
I had 95psi on my left cylinder and 100 on the right. I still got around, but was lacking the power needed when I wanted to pass other vehicles. Once I did my rebuild, it was night and day difference. I got the 2 over pistong and ring set. Took the juggs to a local machine shop and also installed new valves and timing chain. My timing chain was so stretched I could not adjust my timing and the bike would give up at top end.
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