Long Rod Big Bore

[xs650dreamer]

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


~kop

with these pistons were talking about here the compression wouldnt be so high with the xs head would it ?

 

[TwoManyXS1Bs]

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

Hi, Kop. Can't see your pics, kinda guessing here, maybe in this thread?

http://www.xs650.com/forum/showthread.php?t=27461

 

[Hairball27]

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.

Hi Jack, im new here and reserching for a big bore, LR, rephased, Flat track project, are the CR500 rods (depending on manufacturer) tough enough for my aplication or is Carrillo the wise choice . imlooking for hopefully a slipper piston won 10.5 to 11. to 1 compresion, is this possible in your opinion?

 

[kopcicle]

joo havs PM

 

[Hairball27]

This is very interesting but the whole long concept is more of theroy but has any body here actually done this?

 

[Signal]

Yes I have a long rod engine. Did not use CR500 rods used the kit that 650 Central made and sold.
The 650 central kit uses KX 500 rods and custom pistons.
Rephasing with the KX rods caused some problems initially with selector claw breakages apart from that it went very well.

 

[Jim]

This is very interesting but the whole long concept is more of theroy but has any body here actually done this?

From Tech... Have a read here.

 

[kopcicle]

Yes

 

[Hairball27]

Yes I have a long rod engine. Did not use CR500 rods used the kit that 650 Central made and sold.
The 650 central kit uses KX 500 rods and custom pistons.
Rephasing with the KX rods caused some problems initially with selector claw breakages apart from that it went very well.

Hi Sig. have you had good luck with this kit , what was the claw breakage?

 

[Signal]

Yes, it is a quality product. The squish band on the pistons is carefully designed to suit the XS head.
No problems at all with the kit.
The motor was rephased (277) and used in a road race XS sidecar. Using a Lillie replica head it was reliable and competitive.

If you want an off the shelf long rod kit this is the way to go.
The problem with the shift claw breaking we think was due to a Harmonic caused by the long rod and the rephase causing the shift shaft to whip around and the shift claw to bounce out of the engagement pins and hit the bolt heads on the rear of the resprung clutch hub.
Probably would not happen on a bike as the forces are all different and racing sidecars break things you never see broken on bikes.

We did solve this problem with a reinforced shift arm and a modified shift claw retainer.
Here is a link to a thread about it. http://www.xs650.com/threads/gear-selector-trouble.51071/
The fix is at post #14.

 

[Hairball27]

Thanks Sig. i did talk to MMM and asked about maybe a 82MM option piston but he only has the 80mm. did you do any dyno runs? would a larger displacement add in your opinion?

 

[Signal]

Yes more cc's is always better, but the real power from these engines comes from head work and design package exhaust, cam, carbs.
What is your intended purpose if it racing there is usually an up to 750 cc class or similar.
We did dyno the engine more out of curiosity than any thing else and we did change the air filter system for a less restrictive type.
See attached image of dyno print out.Sorry about the orientation I have tried to correct several times and gave up. I think the dyno is optimistic.
You will need to do more work than just a long rod 750cc kit to be getting near to 70Hp at the rear wheel.

 

[Hairball27]

this was rear wheel dyno or chain drive / direct drive. its topped out at the 7700 rpm range, is tourque a little over 40 FP ? flat track application is what i am building Sig. and all the above is on the list but i am concentrating on crank rod and piston package right now. The question always is where does higher torque / hp numbers become overpowering and ineffecient ? chassi without engine would be in the 110 to 120 LB range

 

[Signal]

It is a rear wheel driven dyno. The motor has a great torque curve it makes the outfit very quick off the line not sure of actual numbers.
When we were running this motor not many beat us off the line. So far as a engine power to chassis matching I have no clue.