Skorpion sport cup rebuild

[edfmaniac]

You mean connecting rod right? The crank isn't a direct swap because the flywheel has a different mounting system.

[edfmaniac]

Here's a post from Bill J. viewtopic.php?f=3&t=5040&p=25817&hilit=crankshaft#p25817

He says the XT600E crankshaft is the one. But I don't know much about cranks or the rod for the XT600. If you can buy the crank alone and then have the Raptor rod put on it, that would probably be the safest route. I don't know much about that part of the engine because I haven't had to service mine yet.

[samandkimberly]

Yes, Rod kits - crank pin, main bearing, and rod are available from Yamaha as xt600e parts. You have to find a decent machine shop to press/reassemble, but there are plenty around.

If you're feeling cheap I've got a good used rod/main bearing/pin I'd throw in a box and send to you for 30 bucks, including US shipping. But I don't think new rod kits are very pricy.

Sam

[twinlinemoto]

Aha! So the Raptor crank is not a drop in. If that is the case, it would probably be cheaper/wiser to rebuild the current crank with a stronger rod and new crankpin, right? With all the mods done to this motor, I would like to make sure the crank and rod are stronger than the rest of it!

[twinlinemoto]

After that last post, I did a little research on the szr660 and raptor 660 crankshafts. The only difference I could see is in the crank wheels: the szr/mz cranks have full circle wheels with speed holes, and the raptor cranks are pork chop style. Bearings cross over, the primary gear shaft and key match, the flywheel tapers match, etc. Short of having the two in front of me, I would say they are a drop in. Also, the crank currently in my motor has pork chop style flywheels, not full circle....

[twinlinemoto]

Hi All,

The definitive answer is NO: a Raptor crank does not fit in a Skorpion.

The difference is the flywheel side of the crankshaft is longer to accommodate the larger flywheel of the raptor. As you can guess, the raptor also uses a different stator cover.

My course of action has shifted to trying to salvage my current crankshaft and have it lightened, install a carillo rod from a raptor, and have it balanced for a 102mm CP piston. Now I am broke!

Isaac

[twinlinemoto]

Rebuilt MZ crank with Carrillo rod installed! I used the expensive but highly recommended by Bill Jurgensen SKF NU 307 ECJ bearing on the primary side, install was very easy! Hopefully the last time I see the insides of this motor for a long time.

[dandywarhol]

Did you find out what roasted your original piston?

Alan

[twinlinemoto]

I have a fair guess that the small end seized which then held my piston at an abnormal angle for a little while.

This beautiful new CP piston should do better though!

[edfmaniac]

Are you putting a high lift cam in? I had to check the clearance between the valves and piston on my build and needed to take a little of material off of the valve pockets on the piston. I also had to run an extra gasket at the cylinder base to open up the squish band enough for the piston not to slap the head.

[twinlinemoto]

Wow edfmaniac, sounds like you had to do a lot! I have not yet checked head or valve clearance. Im running a megacycle 280-X2 cam, not a high lift race cam. I will definitely check clearance though! Was your head or cylinder resurfaced? Your clearance issues do not sound normal.

[twinlinemoto]

I have run into more complications. As you can see in the photos below, the cam bearings have been welded and repaired before and were not done very well. This, coupled with the cam not having anything in the end to maintain oil pressure, means that my cam bearings are toast. I have sent the head and cam to Engine Dynamics in california to be repaired. ugh.

[edfmaniac]

Wow edfmaniac, sounds like you had to do a lot! I have not yet checked head or valve clearance. Im running a megacycle 280-X2 cam, not a high lift race cam. I will definitely check clearance though! Was your head or cylinder resurfaced? Your clearance issues do not sound normal.

I didn't have to do a lot but I wanted it done right, and without the possibility of the engine tearing itself apart the first time I get the rpms up near the redline. Aftermarket pistons are supposed to be built to exacting specs, but a half millimeter of stretch in the rod and a half millimeter of piston rock and you can kiss your sweet build goodbye without measuring first. It's just the smart thing to do which is why most professional engine builders check clearances. I'm guessing your valves will be ok with that cam but checking the squish would be smart. No less than 1mm is what I was told by Bill J. I fudged a little and stopped at .90mm, and that was after adding an extra gasket at the base of the cylinder to raise the deck height. Without having done this my piston would certainly have been kissing the head at 8000rpms. Head was resurfaced after full rebuild and porting but that won't effect deck height. Cylinder was bored but not resurfaced. Good luck and don't forget to measure the thicknesses of the different gasket sets you use when making your measurements vs. final assembly. My final assy gaskets were just a little thinner than my used gaskets that I used to make measurements. That's why I estimate my final squish at .90mm instead of 1mm if memory serves me correctly.

As for your cam not maintaining oil pressure, did you figure that out yet. I discovered an easy mod that fixes that when you remove the decomp unit. All you need is a tap, set screw and the original piece that goes inside the end of the cam.

[twinlinemoto]

I used the Bill J method of plugging the end of the cam: 8mm OD soft steel tube, 45mm long pressed into the sprocket end of the cam, then press a 1/4" ball bearing into the ID of the tube to hold it in place/seal it. It took much less pressure than I feared it might to install, and I simply drilled the cam bearing and lobe oil passageways through the new tube insert.

I will definitely be checking clearances once I have my head back from repair!

[dandywarhol]

Wow edfmaniac, sounds like you had to do a lot! I have not yet checked head or valve clearance. Im running a megacycle 280-X2 cam, not a high lift race cam. I will definitely check clearance though! Was your head or cylinder resurfaced? Your clearance issues do not sound normal.

I didn't have to do a lot but I wanted it done right, and without the possibility of the engine tearing itself apart the first time I get the rpms up near the redline. Aftermarket pistons are supposed to be built to exacting specs, but a half millimeter of stretch in the rod and a half millimeter of piston rock and you can kiss your sweet build goodbye without measuring first. It's just the smart thing to do which is why most professional engine builders check clearances. I'm guessing your valves will be ok with that cam but checking the squish would be smart. No less than 1mm is what I was told by Bill J. I fudged a little and stopped at .90mm, and that was after adding an extra gasket at the base of the cylinder to raise the deck height. Without having done this my piston would certainly have been kissing the head at 8000rpms. Head was resurfaced after full rebuild and porting but that won't effect deck height. Cylinder was bored but not resurfaced. Good luck and don't forget to measure the thicknesses of the different gasket sets you use when making your measurements vs. final assembly. My final assy gaskets were just a little thinner than my used gaskets that I used to make measurements. That's why I estimate my final squish at .90mm instead of 1mm if memory serves me correctly.

As for your cam not maintaining oil pressure, did you figure that out yet. I discovered an easy mod that fixes that when you remove the decomp unit. All you need is a tap, set screw and the original piece that goes inside the end of the cam.

More chance of valve spring bounce than a rod stretching 0.5mm IMO