KK 975 with m1000 pistons

[dicey]

My friend has a 2003 900 he is looking to do a big bore useing the pistons for a M1000 ,can anyone who has done this tell me if the piston pin is the same ,basicly I'm wondering if all he has to do is bore it out and cut the head or if machining to the pistons is required.thanks

 

[76FOMOCO]

pm idahocatman1 or 3 they have a lot of time with this motor. the pin is a little of you i think you have to use two base gaskets and a .20 shim?

 

[Idcatman1]

975

Thanks for the plug Fomoco. The piston pin is the same diameter, so no issues there. The M 1000 piston is about .080" taller so you have to raise the cylinder. What I have been doing is using two aftermarket base gaskets and an .050"
thick shim to raise the cylinder so that the piston at bottom dead center is just at the bottom of the transfer ports. You will need to have the heads machined to match the bigger bore and probably the squish clearance taken out to .070" or so.

 

[1Mike900]

Do you have to have the pistons lightened to the 900 piston weight? Is there any extra vibration with this many CC's? Is the 900 crank assy lighter or heavier than the 1000? I would assume the ports need opening up to match the 3.60" bore, Who would you recommend for this? Sorry for all the questions!

Mike

 

[dicey]

Thanks for the plug Fomoco. The piston pin is the same diameter, so no issues there. The M 1000 piston is about .080" taller so you have to raise the cylinder. What I have been doing is using two aftermarket base gaskets and an .050"
thick shim to raise the cylinder so that the piston at bottom dead center is just at the bottom of the transfer ports. You will need to have the heads machined to match the bigger bore and probably the squish clearance taken out to .070" or so.

thanks for the info,this is exactly what i wanted to know.I think we're going to go ahead and order the pistons and go from there.

 

[scoop]

975

I ran the 1000 pistons in a set of 800 twin cylinders that were ported and bored and plated to fit the 1000 pistons, with a rkt head. mine is a efi and it worked real well. I think im gonna run this one more year but gonna try messin with the timing and if I can find a set of pipes, try that as well.

 

[Idcatman1]

975

I could do the porting and head work for you but won't be able to get to it til about September. I leave mine pretty mild but could go more radical if wanted. You do not have to lighten the pistons to the weight of stock 900s, at least I haven't done it. The vibration is no worse than a stock 900, might even be less. I have three twin engines running with the M1000 pistons and a tripple as well. No piston related problems with any of them.

 

[1Mike900]

I am glad to here this, I wouldn't want to make the pistons any weaker. What RPM range do these run at? I bet power comes on hard and strong in the upper 6000 rpm range? Same power band characteristics as the 862 with the mild porting?

Thanks
Mike

 

[Idcatman1]

975

Mine seems to have about the same type of power band, just a little more all the way through. I am running 5 or 6 gram heavier weights than I was in the stock 900 so it is definitely stronger. Run about the same rpm as stock. I have Black Magic single pipe on mine and run 7600 - 7700.

 

[900kingkitty]

I ran the 1000 pistons in a set of 800 twin cylinders that were ported and bored and plated to fit the 1000 pistons, with a rkt head. mine is a efi and it worked real well. I think im gonna run this one more year but gonna try messin with the timing and if I can find a set of pipes, try that as well.

what did you do for extra fuel?what elevation did you runs it at?can a guy run this with the stock pipe( sleeper look) and would it work?

 

[1Mike900]

Will there be sufficient wall thickness left in the bores for loads, cooling etc.. I have the 03.5 version with roughly 1000 mi. I would assume the bottom end wouldn't need rebuilding? Has ran great since new, Never a problem! Is the hotter ignition on this sled OK to run with the larger bore assuming the porting is on the milder side like you have? 3000 to 7000 ft max in WA. This sounds like a hoot if there are no related reliability problems? I would assume I should get a 6 post clutch and balance it, I don't know if I would trust the 9 tower assy too much longer. Is this really a 975? I come up with 988 if the piston is really 91mm?

Thanks
Mike

 

[Idcatman3]

The pistons are 90.3mm.

They make kits up to 1010 on the stock cylinders, so this leaves much more wall thickness than those do. Like my dad said, we've not had any problems related to the big bore. We burned one piston on the triple, because we were running it too lean with too much compression. If anything, we could use a little more timing on ours on the top end, so I'd think you would be fine there. We run the 6 post clutches on all of ours, and we also run the harmonic balance ring on them. Don't know that we really need to, but it dampens the vibration significantly.

On the EFI, you'd need to run any fuel control box. We run ours with aftermarket single pipes, and they work well, I'd think it would work quite well with the stock pipe as well, although not quite as much power.

 

[900kingkitty]

are you guys doing anything to the cranks in these things? do they support the bigger top end in stock form?

 

[Idcatman3]

Haven't done anything to the cranks, they seem to be holding up just fine.

 

[1Mike900]

I can only assume that some sort of porting would be mandatory? I am asking as i wouldn't want someone else to do this without porting, thinking this thing will rip without it? When the bore gets opened up by .20 in. the surface area increases significantly, Thus the porting needs too match the square inches of surface area. Basically a 900 should have been called a 850. We got screwed on this 900 thing, Not any where close CC wise. Do you make the gasket spacer? Or does some aftermarket company? I would like to tie the heads together to combat torque twist. Does RKT make a set of heads too match? Sorry again for all the questions!

Thanks again
Mike

 

[Idcatman3]

I can only assume that some sort of porting would be mandatory? I am asking as i wouldn't want someone else to do this without porting, thinking this thing will rip without it? When the bore gets opened up by .20 in. the surface area increases significantly, Thus the porting needs too match the square inches of surface area. Basically a 900 should have been called a 850. We got screwed on this 900 thing, Not any where close CC wise. Do you make the gasket spacer? Or does some aftermarket company? I would like to tie the heads together to combat torque twist. Does RKT make a set of heads too match? Sorry again for all the questions!

Thanks again
Mike

You do have to have some port work done. On ours, we pretty much just put all the ports back to stock ratios. You can go wild on them if you want to. The 900 may not have actually been a 900 cc wise, but it sure did perform like one, IMO. We had our spacers made at a local company, we can make more for ~$15 each. We use any of the aftermarket mono heads, and just open up the squish band to match the new bore. Scoop did have RKT make a set of inserts specifically for the 975.

No problem on the questions, that's what most of us are here for.

 

[76FOMOCO]

pm turbotator for a great port job and as wild as you would like to go!

 

[1Mike900]

Thankyou for the replies, I might as well start tearing this thing down over the summer. I have the rear bumper mod like the VE set-up to do shortly, Then it will be engine time! Just need to get the right combo head, Pipe and reeds to match. I will either go 153 PC or 156 2.5 extreme. This should make for a good all around sled.

Thanks
Mike