VN1700 pistons to raise 1600 comp ratio

[andyvh1959]

Another wild ass idea: VN1600 bore and stroke is 102mm x 95mm. VN1700 bore and stroke is 102mm x 104mm. The VN1700 comp ratio is 9.5:1 versus 9.0:1 for the VN1600. If the deck height of the 1700 piston allows for valve clearance in the 1600 at TDC then it may raise the comp-ratio. So, if the wrist pin diameter for both VN1600 and VN1700 pistons are the same, then perhaps the 1700 piston could fit if the pin to deck height does not cause valve interference. On Bikebandit the wrist pin part numbers for the 1600 and 1700 are different, but that doesn't mean the pin diameters are different.

Given the bores are the same, the 1700 engine increased displacement is in the con-rod length and crank throw (the 104mm stroke), 9mm longer for the VN1700. I assume the crank offset is also longer for the VN1700. Anyone know the crank offset and con-rod center to center distance for the 1700, and how those dimensions compare to the VN1600?

Some interesting reading here: https://www.motortrend.com/how-to/05...-stroke-ratio/
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[mick56]

You might well gain a small amount of power by fitting them But i wonder if it's worth the hassle ? If it's any help, the 1500's, timing can be the whole 180 degrees out, and the valves dont meet the pistons. Given that they are just a 5mm shorter stroke, than the 1600's, i reckon you are all good regards that . I bet you were you one of those kids, that had to wreck all your toys, because you had to know how it worked

[andyvh1959]

Gee, now how could you possibly have guessed that about me. I was but a wee lad when first I took a spanner to me bikes. I did find though I could reassemble them and ride them after the wrench attack.

Still have some Whitworth spanners in the tool cart too. My dad was a motorcycle mechanic back in Holland. Heh, for years I thought I was all Dutch, born in southern Holland. Then had Ancestry do my DNA, come to find out I'm 24% British Isles! So God save the Queen's left leg!

All that aside, since I am tearing down my 1600 engine to fix the classic 2nd gear issue I'm thinking of easy boosts for more power when I am reassembling the engine. I do have the factory manuals for both the 1600 and 1700, so maybe I can find some details in there.

[DragonLady58]

Face about 0.035 to 0.040 off your cylinder base mounting surface, and a light skin cut off your heads, say about 0.015....doublecheck everything with some clay on top of your pistons to check valve clearance. A nice 5 angle valvejob will help things, too.
Great time to put in cams if money allows, you'll get a really nice suprise with the added compression....
Also add some performance coils, and some plug wires, and you'll really start smiling from your performance gains....Enjoy!

[DragonLady58]

Oh, I forgot, take a smidge outta your ports, too....theres power in them there heads! Hahahaaaaaaa! Light porting job helps....all those little things add up quickly....

[andyvh1959]

I'll be in the engine soon. I'll put my micrometer on the 1700 wrist pin to see if it will fit the 1600 con rods. I hope that the 1700 piston wrist pin will be within 1mm of the 1600 wrist pin. Then, at most I can have the 1600 con-rod small ends sized to fit the 1700 wrist pin and piston. I'll measure the wrist pin to piston deck height to check if the 1700 piston will be higher than the cylinder deck height.

If the wrist pin works out I'll install the 1700 pistons on the 1600 con rods and then install the jugs/heads to check the valve clearance with some modeling clay. At worst I may have to make a thicker set of head gaskets to get the valve clearance.

When you say a "smidge" out of the ports, are you referring to the exhaust ports? Or the intake ports? I already have the 1500 Mean Streak heads/cams/valves so to raise the comp ratio may really bring more life to the the 1600 engine.

Compression ratio wise, it's interesting to compare my BMW R1200RT flat twin versus the much larger VN1600 v-twin. The BMW R1200RT is rated at 12:1 compression ratio, is happy to spin from 4000 to 8000 rpm, and makes 110 hp at the crank, about 95[h at the rear wheel. The torque curve is most fat from 3500 to over 7000 rpm on a bike that weighs at least 150lbs less than the VN1600. The 1600 has a 9:1 compression ratio and makes maybe 75hp at the crank, delivers maybe 60hp to the rear wheel. The BMW is happy to spin at 4,000 rpm all day long. The 1600 is most relaxed at about 2800 rpm, about 65mph.

[DragonLady58]

yea, exhaust ports....they are pretty smooth, but there are some light transitions in the castings....and those will catch carbon over time....
Trim the bottom of cylinder pads, as I recall, your pistons are down in the hole at least that much plus some...
If the 1700 pistons are the same, pin location, piston deck height, and skirt length, you should be golden. Double check your piston weight, too....
I realize its a pain, but dummy up the cylinders and install your valve train, clay up your pistons, check for clearance.
One trick I do is put a really light valve spring on the valves, and at your highest valve lift, zero out a indicator on the spring retainer, get a small piece of wooden dowel rod, or your finger if they're not to fat....press down your valve till you hit. As long as you have about 0.06, you'll be fine. I personally have run them at 0.045 with good results.
Check your clearance at full lift and at overlap....you should be good, unless you float your valves....but your rev limiter ought to keep that in check....

[andyvh1959]

I hope the 1700 pistons are close in pin to crown height, even within 1 to 2 mm tops should prove out with the clay test to confirm clearance. In fact I am hoping the 1700 pistons are actually a bit taller in the 1600 bores to bump the compression up. My 1600 has 33,000 miles on it so I may run a hone through the bores to clean them up and also check for any ridge at the bore tops. The pistons I bought came from a 1700 with 11,000 miles on it. I take as many measurements as I can between the 1600 to 1700 pistons so we can have comparative data for the two engines.

Surprising that only 9mm of extra stroke on the 1700 "makes" the engine that much bigger than the 1600. Only 9mm, barely more than 5/16" longer stroke. Too bad there aren't any options crank wise to bump the stroke of the 1600 into the 1700 range. But if this all pans out I'll have a 1600 with better ommph and lower Mean Streak gearing to move it along. It certainly won't be an equal to a HD 107 or 114, or an Indian 118, but it still should be a fun rev happy big v-twin. My goal is to build out a full dresser that weighs less than 800 lbs. With the extra power and lower weight than comparabel HDs or Indians it should run with them ok.

[Mechaniac]

I'm a new 2008 Mean Streak 1600 owner and found this forum looking for this type of information. I'm following your research very closely Andy and looking forward to this info. If the pistons are the same the only option is connecting rod length difference.

A big thanks to Dragon Lady, MAS, and others for sharing their hard earned knowledge, it's very helpful. I just found a good deal on 1500 MS heads and the intake parts on Ebay so I had to get it after reading through these posts.

I've ordered some head gaskets because warning they are getting scarce. Pistons I'm waiting to see what you find out and going to look into custom made slugs as well with the max overbore.

[andyvh1959]

First off, the pistons from the 1700 are not the same as the 1600, at least by part numbers. The bore is the same, but the piston, wrist pin, clips and rings are all different part numbers for the 1700 versus the 1600. When I pull my 1600 Classic engine apart I'll measure the 1700 pistons versus the 1600 pistons to see where the difference may be. Like I said, I'm hopeful the wrist pin for the 1700 piston is close enough to that for the 1600 piston to only require very minor machining difference.

I am hopeful the 1700 piston wrist pin is within 1mm diameter difference (larger) than the pin for the 1600. If it is I'll get the small end of the 1600 con-rod machined to fit the wrist pin for the 1700.

[Mechaniac]

Right, I am aware. I just spoke to simply. It would have been better to say "useable" as in with some minor work.

Just hypothesizing here, I think the VN1500-1600 was probably displacement maxed out for OEM comfort at 1600 stroke. So a new engine was developed to stay competitive.

Now that doesn't mean we can't go back larger bore and perhaps use thinner rings or move the wrist pin up, use a smaller one or get behind the oil control ring etc. Wiesco has pin buttons now that work well and keep the oil ring under control for high wrist pin piston designs.

I think a custom designed aftermarket piston is going to be the final solution. Thunder used to use the largest bore to bring the engine up to 100 CID so I would like to use the largest bore with any extra stroke I can get including offset grinding of the crank if possible. The limit on stroke is going to be how much further we can go up the piston with the pin and the rod to stroke ratio within reason. These engines are relatively low RPM and low HP per cyl. or low specific output. There's plenty of room to improve power without breaking it every year. At some point the time and money spent making a used piston work would be better spent on making a new piston that fits perfectly and take advantage of every trick in the book right out of the box.

Your measurements will tell a lot. I obtained the factory repair manual and they don't even acknowledge these dimensions. Just basic rebuild tolerances. Us gearhead Yanks are used to this information being readily available. I guess the Japs don't worry so much as there will be an improved model on the showroom soon enough so why bother.

I don't think this bike will rule them all, just having fun and making it as good as I can. It's what I always do if it's worth the trouble. My V4 Magna 700 would destroy this bike in a drag race but the handling and brakes on this Meanie and V-Twin clout are a pretty cool combo. Might as well grab up the 1500 Meanie goodies and put a piston in it.

[andyvh1959]

I agree on all points. I looked in the 1600 and 1700 factory manuals hoping to find details to compare on the piston specs and wrist pin dimensions. But, none to be found, so I'll measure them to compare once I'm into the engine. I was reading up on the engine updates when Kawasaki brought out the 1600. Some interesting details I found in an article from Cruiser magazine.

The 1500 Vulcan actually displace 1470cc, so increasing piston stroke 5mm to 95mm added 82cc, and raised displacement to 1552cc, where it could be rounded off to 1600. I assume that 5mm stroke was done with a change in the crank throw offset. In effect the 1600 crank is the "stroker" version for the Vulcan?

Kawasaki engineers shortened the 1600 connecting rods 2.5mm versus the 1500. That makes me wonder if the longer 1500 con-rods can be installed into the 1600 to further boost the comp-ratio? The stroke remains the same but the increased height into the combustion chamber will increase the compression. The 1600 got new dished piston-crown shapes that retain the 9.0:1 comp-ratio of the 1500. Longer (by 1.2mm) cylinder sleeves were designed to provide better support for the piston and to counter the tendency for greater ring wear created by the longer piston stroke.

So if I read that right, the 1600 got greater offset crank throws by 5mm, but shorter con-rods by 2.5mm. To me that indicates potential for the 1700 pistons to fit even if the wrist pin to deck height is say 2mm taller than the 1600 pistons. Maybe Dragon Lady can pitch in and clarify if I use the 1600 crank with the 1500 con-rods, then with the 1700 pistons will I achieve a higher comp-ratio 1600 engine. If there is valve clearance at TDC to use the 1700 pistons and 1500 con-rods it could make for a decent comp ratio boost. Did some parts research between the 1500/1600/1700 to look for parts matches. Found out the 1500 and 1600 use the same piston wrist pin and the same big end con-rod bushings. That indicates the 2.5mm longer 1500 con-rods will fit the 1600 crank and pistons, so just using the 1500 con-rods would add 2.5mm of squish in the combustion chamber.

Since I already have a PowerCommander and de-smogged air intake I can play the air-fuel ratio to get decent running and hopefully avoid any pinging issues. I agree this 1600 won't rule any current packs, but with a bit of massaging with factory parts it won't be a slouch either.

[Mechaniac]

Okay just reading through what you've shared about rod length.
If Kawi increased the stroke by 5mm then the crank throw is only increased by 2.5mm just like the reduction in rod length. 2.5 on the top higher and rotated to the bottom is 2.5 lower = 5mm overall increase in stroke. This means the only difference between the 1500 and the 1600 is rod length and crank stroke. Pistons are the same. 2.5 higher crank journal with 2.5 shorter connecting rod = same overall height at the top of the stroke in the jug, 1500 or 1600.

Therefore if pistons are interchangeable it would be prudent if all you are trying to accomplish is higher compression to use the readily available 1500 Mean Streak piston. Although it is no longer available in std. bore it is still available in the overbore size, rings too, as a Kawasaki replacement part. The 1700 piston is irrelevant. I was just looking and it said price in cart so maybe the 1600 piston is no longer available in std. size, IDK I was noting that a couple days ago. In any case the oversized pistons are still around both engines.

If one didn't care about a larger bore size this would be the instant way to go.

I have ordered 1500 parts including jugs, good to know the 1600 are longer to support the increase in stroke. I will have to decide how to proceed, easiest would be to use my existing 1600 jugs.

Realizing this, do you want to overbore for max CID with a custom piston and spec'd compression ratio or just use the replacement higher compression 1500 piston on the 1600 stroke since the rod in the 1600 is shorter for it, further increasing compression because of the added displacement?

The 1500 and 1600 piston have different part numbers, both are rated at 9.0 to 1 compression. The 1500 slug used in the 1600 will be higher, not by a whole lot. 9.6 is likely. Still might be better than the 1700 piston made to fit at the cost at $125 each + rings. Order now and it's in your mail in a week.

What do you think? I'm almost ready to say this is the way. A custom piston is likely to be $500 each + rings and someone doing a lot of research and specing with a piston company.

Unless you see a flaw in my reasoning, in that case what am I screwing up on, lol.

Vernon

[mick56]

Bored shitless now. Wake me up if it burns rubber. Otherwise

[Mechaniac]

Another point, the piston travel is was increase only at the bottom of the stroke. On the 1600 the piston travels 5mm lower but goes no higher.

Mick56, funny you say that. I've only had this bike for about a month now and I had the opportunity to try a hard launch yesterday. It burned rubber with tire screech and all, lol. My Magna wheelies.

Vernon