Higher Comp pistons compared

[andyvh1959]

I will finally get into the engine and trans on my VN1600 Classic this winter. I have a bunch of Mean Streak parts going into the Classis 1600 to get some more fun from the engine which already has the typical aftermarket mods (Baron intake, smog crap gone, V&H pipes, Power Commander).

I had bought a set of VN1700 pistons/rods, since the bore is the same for the VN1500, VN1600 and VN1700, at 4.030", and I hoped to up the compression ratio with the VN1700 pistons. I figured I'd measure the 1600 and 1700 pistons when I dug into it, hoping the VN1700 piston would fit. But then I also read the Mean Streak 1500 pistons were higher compression than the VN1600, and they shared the same con-rods and wrist pins. So I bought a set of low miles VN1500 Mean Streak pistons on Ebay.

So check out the attached pics to compare the VN1500MS and VN1700 pistons. Some other interesting details. The wrist pin on the 1500 psiton is much bigger/more mass at 0.945", only 0.867" on the 1700 piston. The compression height of the 1500 piston is 1.207" and 1.105" for the 1700 psiton. The overall height of the 1500 piston is 2.500" and 2.040" for the 1700. The 1500 piston has 18 oiling holes from underneath and up to the lowest ring. The 1700 piston has only eight oiling holes. The 1500 pistons has a LOT more mass, longer skirt, oiling holes to the wrist pin.

[Mechaniac]

Seems the 1700 could handle more stroke. I wonder how the connecting rods compare?

[andyvh1959]

Yeah. I'll find out when I take down my 1600. Then I can compare the big ends of the con rods for both engines. I doubt the big ends of the 1600 and 1700 would be exactly the same. IF, if the big ends are the same for both, there may be a chance of using the pistons/con-rods from the VN1700 in the VN1600.

What I find interesting are the pistons and wrist pins for the 1500 are much more heavy and greater mass than the higher powered 1700. Also, the wrist pin diameter for the 1700 is much smaller than the wrist pin for the 1500, 0.867" versus 0.945", 0.078" smaller for the 1700, and the much fewer oiling holes on the 1700 piston versus the 1500 piston. So the Kawasaki engineers were defintiely going for reduced piston/wrist pin cycling mass for an engine that spins up a bit better. Makes me wonder if they also reduced the mass of the crank/flywheel end to compensate for the lighter top end moving parts.

Another difference. The 1500 wrist pin is fixed. I cannot move it side to side or rotate it in the piston. The 1700 wrist pin is a floating style, I can move it slightly side to side, and I can rotate it in the piston/con-rod with my fingers. I assume that is to reduce friction in the major moving parts in the cyclinder bore on the 1700. So, can a floating piston design be applied to the 1500/1600 con-rod?

So if the piston wrist pin boss area on the 1700 piston is big enough to machine the bore to fit the 1500/1600 wrist pin, then the 1700 piston could fit on the 1500/1600 con-rod. Compared to the 1500MS there is the difference of actual piston TDC height in the bore. Given the piston compression height difference, 1.207" for the 1500 and 1.105" for the 1700, it would actually LOWER the piston height (in the bore at TDC on the 1500). But the 1600 has 5mm longer stroke than the 1500, so the 1700 piston on the 1600 con-rod would raise the 1700 piston 0.197" (compared to the 1500 Mean Streak). IF the piston to deck at TDC on the 1600 is not flush, the 1700 piston on the 1600 con rod would actually be 0.095" HIGHER in the 1600 bore.

So the only hope of using the 1700 pistons in the 1600 is IF the 1700 wrist pin bore could be machined to fit the 1600 wrist pin/con-rod, and if the 1700 piston on the 1600 con-rod at TDC is not flush to the cylinder deck, or just below the deck level, and still clear of the valves at full lift. The shape of the 1700 piston crown would definitely raise the compression ratio more than the Mean Streak 1500 pistons. I do like the squaish band style of the top of the 1700 piston, and then the flat dish is only 0.063" below the squish band. I wonder if that would also improve the overall burn at ignition, kind of a swirl action at the squsih band.

[andyvh1959]

Had another thought. IF the con rod big end ID is smaller for the VN1700 than the VN1600, then it may be possible to have the VN1600 crank reground to fit the VN1700 con rod. IF that can be done then the VN1700 con-rod/piston set could be installed into the VN1600. Still would have to check piston to deck height at TDC to insure the piston cannot contact the valves. If the 1700 con-rod is longer than the 1600 it doesn't change the stroke, just the compression, if the piston does not extend past the deck height.

[andyvh1959]

Just dig some OEM parts digging on Ronayers.com. Trying to find out if the part numbers for the con-rod big bearings were the same. And no, they are not. BUT! the parts list for the crankshaft assembly for the VN1600 Classic and VN1700 Classic shows the same assembly group #13251 for the con-rod assembly for both engines. The actual part number for the VN1600 is 13251-1147HH. For the VN1700 the actual part number is 13251-0026. So there is a part number difference, what remains to be checked is the actual difference once I get the engine torn down. At minimum, the con-rods are different because of the smaller wrist pin diameter for the VN1700 versus the Vn1600. Hopefully the big end of the con-rods are closely similar. Hope remains in Muddville for a cool factory parts swap and bump the compression up with VN1700 squish band shallow dish pistons.

[andyvh1959]

Got into the VN1700 and VN1600 service manuals looking for specs on the crankshaft. Found out the VN1700 crankpin journal diameter is 52mm. The VN1600 crankpin journal diameter is 55mm. Those are general dimensions, the real dimensions are very close to those. Point is, the VN1600 does have 3mm larger crankpin journal diameter. Which means if the VN1600 crank can be ground down about 0.060" to fit the VN1700 con-rod big ends, the VN1700 piston/con-rod could be installed into the VN1600 block. Would also have to check the sizes of the various big end bearings for the 1700 to see what size would be best for sizing the crankpin journals on the 1600.

The bore is the same for the VN1600 and VN1700. The 1700 crankpin offset must be slightly more than the 1600 to achieve the larger engine size if the bore is the same. In essence, that's how Kawasaki made the 1500 into the 1600, just by increasing the 1500 crankpin offset 5mm even though the bore remained the same. The overall height of the 1700 piston is shorter than the 1600 piston, so the piston would not hit the crank flyweights during rotation.

So,...once I get into the 1600 engine. if the 1700 con-rod length allows for the piston to not get higher than the 1600 block height, and not interfere with the valves at full lift it might work.