Long Rod Big Bore

Olie

XS650 Junkie
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Has anybody used CR500 rods with a 750 kit? I know the stock pistons it comes with will be too tall but has someone found after market (ie cheaper than custom) pistons to use?

I've looked at using oversized gsxr pistons in 80mm and they'd be great except they're about $160 from wiseco and je :eek:
 
There has been quite a bit of discussion on this over at the XS650 Garage..........................
http://xs650temp.proboards.com/index.cgi?board=EngineModified&action=display&thread=78
The CR500 rods are 10mm longer than standard 447 rods and have the same dimension big end and pin, altho the big end pin is slightly longer. Some have used 77mm Suzuki? 650 pistons. If you want to go big bore, get XV750 Virago liners and drop them in, 83mm, but then you will have to do some machining on the Virago pistons to get them to fit the XS head. Lots of work unless you are comfortable with that sort of thing. Or spend $$$ and get custom made 83mm pistons. It will get you about 800cc. to go any bigger you will have to bore the engine cases.
 
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http://xs650temp.proboards.com/index.cgi?board=EngineModified&action=display&thread=78

is with out a doubt the singe most comprehensive discussion on the matter . One early solution was longer better studs , a spacer plate and a longer cam chain . The problem as I remember was with the longer cam chain was a link(pair actually) was just barely not long enough and two was way too long . Then again I never tried it . I really don't see where an increase in rod length to stroke ratio benefits the XS as most gains would be in excess of reasonable piston speeds and rpm . Softening the mechanical approach to and away from TDC/BDC has the companion effect of softening the start and stop of the intake cycle and to a lesser degree the exhaust cycle . Again these effects are more pronounced at RPM that any "reasonable" XS will never see .
Just to point you in a more gains worthy direction . The intake and exhaust ports are marginally too large for 650cc and somewhat better at 750cc . However the turn in the exhaust and the port floor , bowl area and mean velocity of the intake port could benefit from intelligent careful modification .
I'll be blunt . If I can produce significant gains with a shop vac , home made manometer and a mark one mod 0 eyeball the stock ports are horrible :D

~kop
 
I have read that they are plenty large to begin with, on mine I intend to raise the floor and try to achieve more of a 'D' shape to increase velocity. I know there are guys on here that are much more knowledgable than I. Jack? where are you. I have read his and PJ's post's on the Garage several times. The XS may gain some from an increase in rod ratio on a rephased motor as apposed to stock. I'm not sure, but an increase in bore is the easiest and best way to gain power, the head takes a very saavy person to get the best from it.
 
i was at scorsby swap meet a few years ago ,,and i spotted a xs650 motor that was looking a bit different ,, so i asked the seller,,,,his remarks were its a 1000cc ....of course i choked and walked off ,,later i went back for a sticky beek ,,and under the cyclinders they had placed an allot flat spacer10-12,,, what ever it had to be ,,,,and machined the trans out to fit bigger barrels / longer cam chain,,, i think the spacer was the width of 1 link?? ,,, etc etc ..it was going cheap now i kick myself,,, as he was well known in racing,,,, regards oldbiker
 
I saw my first silly huge XS on the continent years ago . It seems that several grass racing hack drivers acquired the taste for big XS . I asked about the parts and was told that they were for a grass racing sidecar rig . I got to see it all apart to be welded up once again . It seems the rotating mass was a bit rough on the cases . I never did get around to asking Heiden tuning how they managed to keep it all together . From what I have seen of their work and ideas if you really want to breathe some fire into the ole XS these are the people that can lighten your wallet . If you never have looked over their site you're missing out .

~kop
 
Even though a silly huge XS would be the sweetest thing to take out every once in awhile when you just need to show someone what old iron can do (and then subsequently tear all back down and rebuild it again after that one demo), I'm hoping to keep the reliablity of the motor roughly the same as stock but with a few extra tricks thown in. The long rods being one of them for their more complete burn, reduces the piston side wall thrust, flatter torque curve, etc. Yes, I've been reading the Garage thread religously but it's been inactive for about five years.

I do have the 750 big bore kit from Mikes which come standard with 80mm pistons. They do have a next size over at 81mm but that's about it and I think it's due to the cylinder side wall-there's just not alot of meat there. The XV750 83mm pistons would be the ticket but if there's already a standard 80mm piston that could drop in with just some slight machining like the XV750's I'm in business! Problem is I can't find/know of any.

Figured the GSXR pistons would work, come in 80mm, 80.5, 81, etc. so if I ever need to tear it down to rebuild there's plenty of aftermarket pistons in whichever size I need. Just some slight machining like the originals and slap it all together and go.

All this is being coupled with a rephase to smooth it out (and potentially save the cases), copper bottom/top gaskets to set the compression somewhere around 9:1 - 9.5:1, and a slight port and polish (definitely a MUST). Might throw in a kitchen sink or two just for good measure.
 
Yes there are. But, if you have adequate piston to valve clearance and quench zone, it really doesn't matter.

1986-1988 GSXR 1100:
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1989-1992 GSXR 1100/Bandit:
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If there's enough material on top you could just as easily machine them down flat or at least even. No problem.
 
Those GSXR pistons won't work period, not enough dome volume to reduce combustion chamber volume from 63CCs to around 45 to 40 CCs, you would need to weld up the chambers and re-work the shrouding of the valves to compensate for flow loses in the 300 to 400 lift range. The XS intakes ports REALLY RESPOND WELL to volume reductions by raising the floor 2mms and laying the short turn back and in doing so really takes some dedication,ability to weld or either lay down really good epoxy,opening up the spigot area is the real key though,then going back to rework the roof section to alter flow through out the the lift range. Small ports= bigger gains in velocity with minimal loses of flow in certain lifts, that you'd never feel in the pants.

For pistons using the CR500 long rod,you need to start looking at the Kawasaki900/1000 pistons using the later style J Head, 18mm PISTON PIN, about the same weight as stock XS piston, maybe lighter after mods. Its the best piston option that I can think of other than going custom.
 
im really interested in this here. I wanna build a long rod engine but don't have the machining skills to modify pistons alot would the Kawasaki 900 pistons drop in with the 500 rods ?
 
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So I take apart a XS650 crank and find this . The one with the slugs in it is the early "256" crank from about '72 an '81 is on the left for comparison . I guess I don't know everything about these engines . The crank shows no evidence of having been apart before . New one on me .

~kop
 
I don't know if I posted earlier but the KZ pistons will work with the long rods . I don't know what you consider "drop in " but so far it's within .050" or so one way or the other .Should be able to worry it in with decking the block or gaskets and spacers . If you are brave or talented or both you could make up the difference with an offset pin bushing but most don't understand the forces on the small end of the rod well enough to pull that one off . You have a bunch of room in the small end of the CR500 rod to play with but if not done correctly the bush will rotate with predictable results ,


76MM
KZ 1000: 6 mm oversize
2.992 In
DRAG
12.5:1
MTC-K1197H

would of course work with the stock liners and CR500 rods if you didn't want to go the sleeve route
1mm over size if you were snoozing (672 ish )

I'll have details soon

~kop
 
I'm still wondering if th kz pistons would work there's gotta be a drop in piston out there

Along with what Kop said, you gotta pay about 4 plus or higher for drop in long rod pistons. The KZ 1100 GPZ 78mm is almost a drop in,gotta recut valve angles and maybe slightly dome reshaping(maybe). Like Kop, my project has been put on hold and I went KZ 78mm 900 pistons,minor decking issues and welding up combustion chambers but that comes with the territory of working outside the box to save a few bucks.

If you want aftermarket pistons Ross would be my choice about close to 5 bills.might be able to help you there,I'd have to search my notes for the job #s.
 
I don't know if I posted earlier but the KZ pistons will work with the long rods . I don't know what you consider "drop in " but so far it's within .050" or so one way or the other .Should be able to worry it in with decking the block or gaskets and spacers . If you are brave or talented or both you could make up the difference with an offset pin bushing but most don't understand the forces on the small end of the rod well enough to pull that one off . You have a bunch of room in the small end of the CR500 rod to play with but if not done correctly the bush will rotate with predictable results ,


76MM
KZ 1000: 6 mm oversize
2.992 In
DRAG
12.5:1
MTC-K1197H

would of course work with the stock liners and CR500 rods if you didn't want to go the sleeve route
1mm over size if you were snoozing (672 ish )

I'll have details soon

~kop

Glads to see your still active on the forums,you're a viable asset to those interested in hod rodding the XS
 
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