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1996 Summit 670 Tune Up

B

Boondockin800

Well-known member
Nov 26, 2007
4,468
123
63
PNW
I'm finally getting around to making my to-do list for the sleds this year and I'm wondering what all I should be doing to my backup sled which is a 1996 670 summit with 7k miles on it. I have no clue when it was last done so I'm thinking a set of pistons may not be a bad idea. Everyone talks about putting the 501 rotary valve in. Is this strictly a performance thing or should the rotary valve be replaced every so often? Having 7k miles on it, I'm not interested in expensive mods, just keeping it running. Any ideas about parts that should be replaced???
 
4
Aug 27, 2009
43
2
8
Laramie, WY
Pistons, rings, and wristpin bearings wouldn't be a bad idea at 7k. Get a piston kit, make sure to get the correct size pistons (i.e. has is been bored out at all). Look at the cylinder base gasket by the oil injection pump and see how many holes there is. That is the gasket thickness you need to get.

I would take the cylinders off and bring them to a machinist or your dealer and have them "mic-ed" to see if they are round and not worn to ovals. You may want to consider boring one size over bore with 7k miles so the piston cylinder tolerances are correct. If you decide to run the forged Wiseco's they should be bored piston per cylinder and to the wiseco specs. Forged pistons expand much more than cast pistons.

Does the 96 have RAVE valves. If so take them out clean the carbon off them, replace the gasket and re-install. I had to make a short allen wrench to get under the diaphrams to get to the bolts, I think its a 4mm (shortened wrench is also neccessary to take the stock y-pipe off the cylinders). Then unscrew the diaphrams off the valve stem.

Another piece of advise I learned the hard way was the head bolt that goes on the front of the engine above the exhaust port is shorter than the rest don't put the long ones in there. I did it once and had to have a threaded insert put in the cylinder= $100.

When you assemble the top end make sure you gap the piston rings for each cylinder. Use an accurate torque wrench, follow torque specs and pattern. The wrist pins slide in much easier if you heat the pistons in your oven just alittle (100F) and throw the wrist pins in the freezer. And use some assembly oil on everything(2 cycle works).

With the motor torn down I would take the injection pump off and check the free play on the rotary valve drive shaft. There is a brass worm drive gear that can wear out.
 
E
Dec 8, 2008
812
36
28
Chelan area
Pistons, rings, and wristpin bearings wouldn't be a bad idea at 7k. Get a piston kit, make sure to get the correct size pistons (i.e. has is been bored out at all). Look at the cylinder base gasket by the oil injection pump and see how many holes there is. That is the gasket thickness you need to get.

I would take the cylinders off and bring them to a machinist or your dealer and have them "mic-ed" to see if they are round and not worn to ovals. You may want to consider boring one size over bore with 7k miles so the piston cylinder tolerances are correct. If you decide to run the forged Wiseco's they should be bored piston per cylinder and to the wiseco specs. Forged pistons expand much more than cast pistons.

Does the 96 have RAVE valves. If so take them out clean the carbon off them, replace the gasket and re-install. I had to make a short allen wrench to get under the diaphrams to get to the bolts, I think its a 4mm (shortened wrench is also neccessary to take the stock y-pipe off the cylinders). Then unscrew the diaphrams off the valve stem.

Another piece of advise I learned the hard way was the head bolt that goes on the front of the engine above the exhaust port is shorter than the rest don't put the long ones in there. I did it once and had to have a threaded insert put in the cylinder= $100.

When you assemble the top end make sure you gap the piston rings for each cylinder. Use an accurate torque wrench, follow torque specs and pattern. The wrist pins slide in much easier if you heat the pistons in your oven just alittle (100F) and throw the wrist pins in the freezer. And use some assembly oil on everything(2 cycle works).

With the motor torn down I would take the injection pump off and check the free play on the rotary valve drive shaft. There is a brass worm drive gear that can wear out.

wow, good info.
 
I do have a template on my powdercoat site, in the links section. It helps for aligning the Rotary valve, but there is steps too that need to be taken. The RV is not keyed, it will go on in a multitude of ways, so care needs to be taken. The 501 does have some good performance with it, but if your just going to freshen up the top end, I would leave it alone. You may just be asking to much of the crank and have a bearing go. After 7K there is no guarantee the crank is going to last another 7K, or even 1K. Rebuilt cranks are around $500.
 
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