Power

Agreed, Jack, the lighter the piston assembly the better. I should have limited my comments to aftermarket piston assemblies available for the XS 650, all of which (JE, Venolia, Wiseco) are substantially heavier than stock; I'd post the weight comparisons for OE 75 mm./JE 77.5 mm./Venolia 77.5 mm., but the manual with my notes in it has gone missing. My comments were meant for the guys who are building for enhanced street performance on a budget, not the guys who know their stuff and are going all out with custom components--they'll balance the rod and piston assemblies and blueprint the crank as a matter of course!
 
... I'd post the weight comparisons for OE 75 mm./JE 77.5 mm./Venolia 77.5 mm., but the manual with my notes in it has gone missing...

Coupla years ago, I started collecting member posted weights.
Two postings for Stock/STD pistons are not in agreement.

Stock 650 piston - 301.1 grams - with pin/rings - 395 grams
Modified XV750 piston - 326.3 grams - with pin/rings - 420+ grams
Rocky XS1 750 piston - 298.5 grams - with pin/rings - 433 grams
ForgeTrue 650 piston - 159 grams
Isuzu 880 87mm piston with pin/rings - 540 grams

75mm 650cc std bore: Piston 268g, pin 84g, Rings 20g = 372 grams

Ross 80mm 750cc LR: Piston 298g, pin 65g, Rings 21g= 384 grams
 
Thanks, 2M. ForgeTrue 159 g.--wow! How'd they do it? Too bad those aren't made any more! I'd bet whatever alloy they used to achieve that weight put the price in the stratosphere.

I pulled the Venolia 77.5's out of the stash and weighed them. Didn't record the original weight, but after milling .030" off the crowns to reduce the 11:1 CR to ~10.25:1, lightening, and balancing, weight of piston, rings, clips, and pin is 421 g. Still can't find my notes and the JE 77.5's are in the motor, but weight was very close to the lightened Venolias (they're the low compression version, made for ~8.6:1 with stock deck height). Maybe Hooser will chime in on that. Might be worth noting that the Venolia and JE pistons referred to are for the 447 motor with 20 mm. rod end, and that the wrist pin used and weighed with the Venolia piston is a tapered pin by Wiseco.
 
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Thanx, Grizld1. I added your pistons to my list.

Thanks, 2M. ForgeTrue 159 g.--wow! How'd they do it? Too bad those aren't made any more! I'd bet whatever alloy they used to achieve that weight put the price in the stratosphere...

I'm clueless about that. Simply pulled those from postings. Maybe worth searching.

Otherwise, Don't you believe a word of it, pilgrim...

Edit: Have a look at hotdog's postings:

http://www.xs650.com/threads/long-rod-pistons.23581/page-3#post-270164
 
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I am a newbie with a question for the members that have Mikes Big bore 750 kit from Heiden Tuning. Can you kick start this puppy with the high compression? Well any way higher than stock.. I am asking because it looks like Mikes Big bore (Big Fin) 650 kit comes with standard pistons and I am assuming stock compression.
I put a big bore 750 kit and went 0.80 right away and have no problem kick starting it. Just remember to think in your mind that you are gonna drive through with your kick, or it will crack you back .....use heavy shoes or boots .
 
Thank you for the reply Micha7el, I read the discussions on the Big Fin Big Bore 750 kit and have decide to go with Mikes Big bore (Big Fin) 650 kit. My main objective is to reduce the cylinder temperature and hopefully improve the hot neutral issue I am having with the bike. I am running low compression so i have to tear into anyway.
 
Great advice and input by a lot of folks on here . 81-650 is bang on about the ports.
Mine is a Heiden 750 cyl blk& slugs, pamco ign. Mik vm34 carbs,mildly portednew rockers/shafts, valve spring kit,tried 3 cams a 447,XS1, and Heiden. they all work, XS- 760 .. I have the same problem with the Ign. on tdc deal too. It kicks back Hard even rolling it up slow. So turn off , set, turn on.
I am going to install a Man. decompressor set up off a partsbike xs1 I have and see if that helps.
Get a stout clutch for sure. Make sure The e-start is gone thru when Your doing the motor.
I did a new relay, new Spring, stripped ,cleaned, rebuilt starter and it still has to work to spin 'er
over.Did the xr500 filter cooler do-dadd and run only Yamalube20w50 mineral based oil. only got about 2,000 miles on it this summer as I was riding my other vintage Yams . as well. As for H.P.
this pulls almost as hard as My old /72 Norton combat street tracker I had. It was real light and had a well assembled motor. I can leave a stop in 2nd gear with 3 less teeth on the back sprkt and the torque pulls it easy. I broke it in real easy for 3 tanks of fuel before I started to work it. No smoke
or bad signs so far..
 
Coupla years ago, I started collecting member posted weights.
Two postings for Stock/STD pistons are not in agreement.

Stock 650 piston - 301.1 grams - with pin/rings - 395 grams
Modified XV750 piston - 326.3 grams - with pin/rings - 420+ grams
Rocky XS1 750 piston - 298.5 grams - with pin/rings - 433 grams
ForgeTrue 650 piston - 159 grams
Isuzu 880 87mm piston with pin/rings - 540 grams

75mm 650cc std bore: Piston 268g, pin 84g, Rings 20g = 372 grams

Ross 80mm 750cc LR: Piston 298g, pin 65g, Rings 21g= 384 grams
I'll add a few to your list
CR500 Long Rod Wiseco Kz 900 78mm piston 256 grams, heavily modified 235 grams
pins 17mm 60 grams ,rings 19grams
CR500 L/R Arias KZ1000J 80mm pistons with dome mod 272 grams,18mm pin 60 grams,rings 20 grams
 
Jack, hope you got the phone message re. my screwup giving you weights for a 256 piston and pin! If not, here are the numbers for the 447 units, and 2M, this may resolve some of the discrepant data you've found on OE piston weights; pre-74 pistons and pins are heavier than the items used in 447 motors. All I have to work with is a cheap set of spring scales, but these numbers will be accurate within a couple of grams. 447 piston: 275g. 447 wristpin: 82 g.
 
Jack, hope you got the phone message re. my screwup giving you weights for a 256 piston and pin! If not, here are the numbers for the 447 units, and 2M, this may resolve some of the discrepant data you've found on OE piston weights; pre-74 pistons and pins are heavier than the items used in 447 motors. All I have to work with is a cheap set of spring scales, but these numbers will be accurate within a couple of grams. 447 piston: 275g. 447 wristpin: 82 g.
Got your message and thanks for helping me out. I'll be using the 78mm slugs,it's just a no brainier giving the weight loss on the top end to aid vibe reduction.
 
I'll add a few to your list
CR500 Long Rod Wiseco Kz 900 78mm piston 256 grams, heavily modified 235 grams
pins 17mm 60 grams ,rings 19grams
CR500 L/R Arias KZ1000J 80mm pistons with dome mod 272 grams,18mm pin 60 grams,rings 20 grams

Thanx, Jack! Added to my list.

...here are the numbers for the 447 units, and 2M, this may resolve some of the discrepant data you've found on OE piston weights; pre-74 pistons and pins are heavier than the items used in 447 motors. All I have to work with is a cheap set of spring scales, but these numbers will be accurate within a couple of grams. 447 piston: 275g. 447 wristpin: 82 g.

Thanx, grizld1! Added to my list.

I plan to eventually put these into a readable spreadsheet.
After I dig out some more old '256' stuff...
 
i am a big guy, i run 6'4 and 265lbs

I love my xs650 but i struggle keeping up to my friends on bigger jap bikes.

Do you guys think the 750 kit would give me that extra nudge i need to help me keep up and such?

Yes. Lots more torque. I hardly downshift on hills. I have Mike's 750 kit, 75 crank and cam, lightly ported. I love it. I've got 10K miles on it so far. I am very satisfied.

For my next engine rebuild, I will do it again.
 
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Port matching is definitely part of the equation. I have some pics below of a virgin, NOS/OEM military surplus 6-cyld. Jaguar head ( the nos car heads were long gone) converted to a duel /twin plug head by a high spec machinist friend I used to help with his jag race car. The racers loved them, what few he built. Has same hemi-dome chamber as the XS 650 type. I had this head ported by the same fellow who this week ported my xs 650 head. The Jag head's been sitting in my garage for 7 yrs as I sold my street E-type (modified) befor the head went on. Was shooting for an easy 11:1 CR using pump gas. I don't have an exhaust port gasket pick here but on this application with a long duration cam, there is a +- 3/8" lower ledge on the exh. port so the overlap gas doesn't totally go back into the port. Also, the engine designers specifically looped around a 'swirl' path intake >exhaust to better mix air/fuel...That said, eveything is smooth. We creeped up on where I wanted to be on the flow bench for the street app. so there is more meat in the ports to work with. I just sold the head to a racer less than 10 days ago for good $$. The Yamaha application, this same port-R, who was a 'known' bike racer in the 1970's, was in and out of my head in an hour. I see some little cast pimples he left on purpose. Point is as mentioned in this thread, a good, knowledgeable metal worm will do what is necessary for the specific application and only that.
 

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Not to discredit your friend in any way,I'm sure he does excellent work on the Jaguar heads but when it comes to porting the XS head you're better off sending the head to a porter who know the ins and outs of the Xs head extracting power for your money. Even when running a stock cam,there was a lot left on table when looking at your intake ports. Besides increasing CFMs,more power can be yielded in the barrier finish to increase atomization of the fuel mixture which helps to improve combustion efficiency.
The exhaust ports on the XS are the number one culprits that holds back the engine from breathing,performance and to insist in helping port scavenging.
Just looking at what was done to your exhaust ports, only a valve job was done. There was no effort to eliminate port turbulence which will yield big results when ported correctly and is the biggest game changer over all in how the engine pulls through the power band.

To give you an example of how I port the XS exhaust port ,whether it's for a stock cam or a shell#1 cam, the flow curve of the exhaust port is well suited with these cam profiles for street use or racing. You have to eliminate port protrusion of the guide and unshroud the side areas of the guide boss,etc.
xs ep finished 1.jpg
 
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TY for the photo Jack. My guy did exactly what I asked of him. I'll tell him what you said...
Browse through this thread, there's info how on the steps I use to eliminate exhaust port resistance and how I turn the flow on the roof around the guide boss. These ports can be tricky to port depending on casting and core shift. Observe the short turn on both ports as they will most likely be cast differently and just match them up as close you can on the short turn radius.
Changing Intake ports to a D shape for better flow.
 
NOW, that I found interesting. TY. 1st I heard of D shape ports was was right where my '72 / 650 head is now when I brought that 12 twin plug Jag. head in. Asked me what I wanted to do? How fast I wanted to go and for how long? Then went on about (long story..they guy's from N.C. too..long stories) if they had another head they could slice up like a loaf of bread, how much materials they had to work with around ports and where they could add material, that a D shaped port could do, has done wonders...pointing up to a shelf with a little Daimler V-8 hemi race motor. Said they spent allot of time optimizing the head work for flat out racing. Engine belonged to a fellow I knew and he'd forgotten he had left it at the shop...for years. So, this time after the what possessed you to buy an XS 650 Yamaha was out of the way I answered that if I do ride this bike, it will probably be on a weekend, in the dry winter < 75 degF, not in town and as I had a bad wreck on bike as a teenager and have not been on a bike since (except 700mi on a 1978 650special) around 1980...that I will not be looking to race anyone, just ride around a bit.
 
Since we're talking hp, a simple calculation, if hp is directly proportional to displacement, (and it is, somewhat), the ratio of increase from the old displacement to the new, in my case 650 to 750, is approximately 15%. If Yamaha's claim of about 50hp stock is correct, then there's a gain of about 7hp. I like to think that with the port cleanup, Pamco Ignition, iridium plugs, smaller, (louder), mufflers, foam filters and an overall seat of the pants feel, I estimate my power to be about 60hp.

Someone mentioned that all dynos are not alike, (I can believe that), well, in maybe 1974, when my brother owned my bike, he had it dyno tested and it showed 23hp at the rear wheel. I still have the graph somewhere. I'll post it if I can find it.
 
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