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xs750 build step by tedious step, "build-along" with me

Discussion in 'The Garage' started by billy icon, Apr 20, 2020.

  1. billy icon

    billy icon test pilot,gunnie pig, and all around experiment

    ok Kids, I've been collecting parts for some time now to do this build ,I'm not sure where they all came from as time has passed, and I would like to build this together, today I'm just sharing what's collected so far but here is a list of components I'm going to attempt to use

    447 bottom end, case and everything never taken apart (year to be identified soon)
    xs1 cylinder prepped for 80mm pistons, (bridge removed in between bores to use 447 chain guides)
    slightly ported 447 head (valve springs to be determined I have xs1 and 447 springs)
    xs1 camshaft with 447 cam gear allready swapped onto it (cam timing to be redone during build)
    new DID cam chain
    750 pistons ( manufacturer unknown help me out here)
    rk rings
    athena full gasket set with 81mm head gasket
    two more head gaskets one 0.38mm fiber and one 0.45mm multi layered steel.. 3 diferent to chose
    complete seal kit
    boyer mini electronic advance setup with coil
    two new 32mm roundy slideys
    new ebc clutch kit with new EBC springs
     
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  2. billy icon

    billy icon test pilot,gunnie pig, and all around experiment

    help identify pistons? who makes these?
     

    Attached Files:

    TW200guy, Wulfbyte, Jim and 1 other person like this.
  3. Bushyeyed1

    Bushyeyed1 Cafe Racer XS650.com Supporter Top Contributor

    I think I have read somewhere that the max safest bore for stock cylinders is 78 mm because after that the wall is too thin. Are you resleeving the cylinder for the 80 mm bore? I ended up doing the cruzinimage 78 mm pistons for 706 cc. There is only one machinist shop here on the island, but even with double the price of that from the states it was a cheaper option than most. They bead blasted the cylinder, honed, and bored it for around $250 and the piston kit from cruzinimage was $120.
     
  4. Excited to see this step by step build! I'll probably end up seeing something in your build and realizing I forgot to do it on mine lol.
     
    TW200guy, Wulfbyte and Jim like this.
  5. billy icon

    billy icon test pilot,gunnie pig, and all around experiment

    I have also heard about boreing a stock cylinder to 78mm, and Im not sure if that is only aplying to 447 clyinders, this cylender cam off a engine I got from a race guy, I cant remember if he said it was a flattrack or if it was a sidecar race bike, but it had allready been run with wiseco high cmpresion pistons 14 to1 I belive, the head I had offered up here was also ON the race bike, and I belive now with some inspection that the head had virago750 valves... but here is the kicker:I know it was ok at 80mm at least for a race bike because I recived it used and the pistons(wiseco tha I sold) and its still in great condition...it actually seems a little tight with these new pistons I have obtained (Any one recognise the pistons I have in the photos)...ok gosh im rambling, here is what I have found, I once bored a 447 clyinder out to 80mm myself and found it to be way to thin... and when I recived this xs1 cylinder bor3d out to 80mm I instantly knowticed that the walls where way thicker than the 447 80mm, and I discovered that the OD of the sleaves in a xs1 is larger to begin with, at least with this one I have anyone chime in here and help confirm this, Im going to take some measurements today to see if the amount left of the wall when taking a 447 to 78mm is the same amount I have left with this xs1 at 80mm,,, ya know what I mean..??
     
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  6. billy icon

    billy icon test pilot,gunnie pig, and all around experiment

    bueller... Bueller??... any one know who makes these pistons? the box has a mikes xs feel to the sticker?
     

    Attached Files:

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  7. Bushyeyed1

    Bushyeyed1 Cafe Racer XS650.com Supporter Top Contributor

    They look like they could be cruzinimage, but I can’t be sure? I think they only make the 78mm pistons for the XS650, but they do have TX750 pistons. They do resemble the ones on MikesXS too.
     
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  8. billy icon

    billy icon test pilot,gunnie pig, and all around experiment

    these pistons seem a little egg shaped, not much but the skirts are slightly larger around than the sides of the pistons. anyone experianced this, also the pistons are slightly smaller on top where the rings go than where the bottom of the pistons are? i found this a little strange, but maybe its not, here is a photo of the xs1 cyl. with the brige removed, and a measurment of the wall thickness, I actually dont have a 447 availibe at this time to measure. also some comaprisons of xs1 valve springs and 447 springs, the inner springs are the same, the outer springs are a larger wire dia. that the 447 springs, the xs1 are slightly shorter than the 447, that may be from fatigue the xs1 sping is the one that is NOT progresive wound on the left
    join in with coments, that my hole idea with this thread
     

    Attached Files:

    Last edited: Apr 23, 2020
    TW200guy and Jim like this.
  9. GLJ

    GLJ Never go faster than your guardian angle can fly. Top Contributor

    Pistons are not perfectly round. That's why they are measured towards the bottom of the skirt front to back. Reason for the shape has to do with how they expand when the motor warms up.
     
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  10. billy icon

    billy icon test pilot,gunnie pig, and all around experiment

    so when your measuring the tolorace between the piston and bore wall, you would do it at the top, thats how I have allways done it in the past? i guees I just knowticed more so on these is that the skirts are actually a little to tight in the bores, they will slide with a little presure on the piston, but Im used to pistons just dropping into a clyneder without pushing on them...
     
    TW200guy likes this.
  11. Machine

    Machine Race the wind Top Contributor

    Without very accurate bore measuring instruments aside from a very good feel with the T-style and a micrometer for the skirts I would tend to trust your gut on the piston skirt fitment and measure for correct ring end gap in the bore just below the top of the cylinder. To fault the bore job you would want to prove or disprove taper. Hope for correct alignment.
    So what is the ring gap? In spec?
    -R
     
  12. Bushyeyed1

    Bushyeyed1 Cafe Racer XS650.com Supporter Top Contributor

    If for some reason you end up needing another set of jugs. I have my old one I removed after I got another pair bored to 78 mm. I was thinking of keeping it for just in case, but everything has been solid. They are off a 1980 XS650G so you wouldn't have to remove the bridge.
     
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  13. Machine

    Machine Race the wind Top Contributor

    Rings themselves along with the feeler gauges to measure end gap in various heights of the bore are perhaps the best tools on hand to confirm the bore diameter with up there in that beautiful forest where your shop is
    :thumbsup:
     
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  14. GLJ

    GLJ Never go faster than your guardian angle can fly. Top Contributor

    It sounds like your cylinders have been bored already. If so did the machine shop have the pistons to measure before the cylinders were bored?
     
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  15. billy icon

    billy icon test pilot,gunnie pig, and all around experiment

    ooo weeee lots to answer hehe.. so the cylinder came from a sidecar race bike, and it had wisico pistons that came with it, the pistons fit Perfect, but I sold them, they looked brand new, probobly ONE race on them... so now I have the cyl. that has been bored then run for a short time with wiseco high compresion pistone, (again theere gone) so no the machine shop didnt have the new pistons, I bought out a guy that "THOUGHT" he was going to build a xs, or actually he died and his nephew sold most of the engine parts... thats the answer for mr GLJ , thank you for joining in.

    Busheyed, My question and answer for you is?? you have a 447 cyl that has not been bored right, Im really curious how thick the wall is stock how big is the od of the facctory sleeve.(the reason is I belive the xs1 cyl I have has a larger around sleave from the factory, any how what I want to figure out is how thick the wall on a 447 cly becomes once it is bored to 78mm because we are in agreement that that is a safe wall thickness to go with,, and if my xs1 wall is atleast near that It should be good to go, it is in great shape..

    Machine, How are you man, stop by whenever you feel like it, so tonight right after this Im going to measure the bores with a piston ring, and I will not only be checking the top for proper ring gap but as you said , numerous places down the cly. to check for taper, But i have had this cly, for years and I remember having it checked once before and its strait and round, like I said I believe the cyl,and the pistons I sold were only run for maybe one race, the xs1 head I have for sale in the classifieds was also on that motor, so I will be posting some new parts I got from a member here nice enough to give me a deal and free shipping, some yummy K&N air cleaners,

    and here is a learning moment, K&N filters are the only filters I have bought that don't have a lip inside of so to say get smaller than the clamping surface just inside, that can block the jets on factory xs65 carbs where the inlet is on the carbs, OK kids Im off to take some photos and make some measurement and decode the vin on the bottom end I plan to use

    here is some phots of some new parts put on the kitchen table today
    clymer manual for reference
    factory pipes (very durable they are double tubes or double wall from the factory and usually never blue) possibly restrictive
    I also have tc bro build your own exhaust,(a bunch of 1 1/2 tube bends and strait feels like 0.65 thick) les restrictive and less durable
    KandN filters for the 32 roundy sliders
    bottom end planned to use from (447 - 711***) going to decode it after this post, I also have two more complete engines to use if needed

    if you made it this far I decoded the vin on the bottom end I planed on using it is a....
    76 to77 xs-d
    I also have a complete never been taken apart 71 xs-d , I belive that one has xs1cam? anyone want to comfirm or deny that.
    I also have a 80-81 xs-sh (US) complete never taken apart, those engine are kinda earmarked for future projects, seem like I build 1 bike ever 12 months,ride it for one summer and start the vicious cycle over again lol see waht I did there hehe "vicious CYCLE"
    ok back to the build, measuring ring gap now
     

    Attached Files:

    Last edited: Apr 22, 2020
    TW200guy likes this.
  16. billy icon

    billy icon test pilot,gunnie pig, and all around experiment

    ok so I've done a lot of measuring in different was and with the tools I have on hand, when putting the 80mm rings in the bores at the top of the pistons throw inside the bore there is no gap atoll, but they fit easily, put them in the bottom of the bore (the rings will never be down there but the skirts will) and there is even less of a gap, if that makes sense, I can say this because you can get the 80mm piston ring in there flat and centered and then its in so tight you have to really push it out,

    so after I di that I did my best with a pair of calipers, now I know I should use bore gauges, (machine come over lol) but as i am using one tool to take all these measurements then even if its not accurate in the "TOTTAL" measurements, it will be correct with the size differences between these two parts measured at the same time with the same tool so here is what I got, Also I put some very thin oil on the piston and it does slide in the bore quite well, just snugger than I have experienced<im thinking I can just use my the bar hone tool to open up the bores a tiny bit bore measherments.jpg
     
  17. Bushyeyed1

    Bushyeyed1 Cafe Racer XS650.com Supporter Top Contributor

    Yes I have an unbored 447 cylinder that had around 18,000 miles on it. I don’t have a very accurate way of measuring, but using my caliper the sleeve ID is 75mm and the sleeve is about 5mm thick on the bottom and 8mm at the top. Your cylinder could have been resleeved for the Wisco pistons. Like you already did you need to install the rings on your new pistons and measure the gap to see if it is within tolerance. I can tell you that with my 78mm pistons they were slightly different sizes from one another so the machine shop had to specify which piston went in which cylinder.
     
    Last edited: Apr 23, 2020
    TW200guy likes this.
  18. billy icon

    billy icon test pilot,gunnie pig, and all around experiment

    if my math is right if a factory 447 cly is 75mm id and a 5 mm wall thickness at the botom, and then if you bored it out to 78mm you would be taking 1.5mm off the wall leaving it at 3.5 thickness, mine measures 2.66 . hmmmm thats got me thinkingbhmmm if you took a 447 and bord it out to 80 you would end up with a wall thickness of 2.5 hmmm real close number to my 2.66 , maybe these rent thick enough walls, .. I will use it n the build anya\ways and find out if 2.66 wall has failure,

    can anyone tell what the failure of a cyl with too thin a wall is, what happend=s
     
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  19. gggGary

    gggGary Stop that! XS650.com Supporter Top Contributor

    Just opinion but wall thickness is a concern for the machine shop also, if the wall is too thin, you can't bore it with any amount of accuracy, the boring tools flex the unsupported liner where it extends below the jugs. My engine shop whined about this when boring cylinders for the 706 pistons, said he would have to charge more because he had to take more, thin cuts to keep the bore accurate.
    It was a "back in the day" thing to install bigger liners in factory cylinders but now that the "mikes" big bore cylinder kits are readily available that's seldom done. I don't know who made the oversized liners. I know you like to keep things in house and economical but I feel taking your parts to an engine shop with quality late model equipment that is known for motorcycle (smaller, tighter tolerances?) work would be the only way to fly here. Makes little sense to build a motor that's going to tear itself apart immediately. I'll add my :twocents: that yes cast pistons, like you have are likely from Cruisin image or mikes, who prolly get them from the same Japanese vendor.
     
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  20. GLJ

    GLJ Never go faster than your guardian angle can fly. Top Contributor

    I agree with Gary. Take your pistons and cylinder to a good machine shop. Let them know what you want for clearance and see if they can size the cylinders. When I had my 650 cylinders bored to 2nd over I took the pistons in with the cylinders. When I got them back the pistons were marked for the hole they went in. I other words each hole was sized individually for the piston that was going in it. Then after you get the cylinders back check the ring gap and do what needs to be done.
    I suppose you could hone each cylinder until you get the fit you are happy with. I'm not going to say that cannot work because it could. It's just not the way I would do it.
     
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