deck height

[kopcicle]

so ...
8.1" = 205.740 mm half the stroke = 37mm Cr 500 rod = 144mm MTC-K1327H compression height = 24.8793 205.740 mm deck -205.8793 assembled height +0.1393 mm or 0.0054" Think I'm close enough to worry it into spec with head and base gaskets ?
8.1" is the distance frome crank centerline to top of the XS650 cylinder
The 1/2 kit price is $255.73 as these pistons were originally meant for a big arsed 1300+cc over bore of the Z1/KZ 903/1015
I think that beats the hell out of $400/pr don't you ?
Then again it took me countless hours to track down the information on the interwebz and on the phone
I am not soon going to forget that brain dead 20's something at Wiseco that told me the compression height was "proprietary"
Or Ross and J&E both wanting minimum orders of 8
Or the nameless ID10T that kept telling me " they have different pin diameters it won't work " no matter how many times I told him it was a CR500 rod with a different small end diameter " That's a two stroke rod " , well yeah , sooooo ...
So my machinist answers the email with the dimensions with " And what was so hard about that ?"
I get him on the phone and the voice of reason tells me " Dennis , not a whole lot of people think like you do . You're just going to have to accept that fact and learn to live with it . I have "

Get it from Mike or do it yourself the price difference isn't enough to quibble about . Any real savings will be from your machine shop of choice and or your assembling the pieces . I will stress for the novice that these discussions are all hypothetical until the assembly is trial fitted and the dimensions/clearances verified .
many thanks to Brett ,Greg , Dick , Bubba , LarryC , APE , Cliff @ MTC and Google Calc for the conversions .
http://xs650temp.proboards.com/index.cgi?action=display&board=EngineModified&thread=17014&page=1 for the original thread .

~kop

 

[angus67]

" Dennis , not a whole lot of people think like you do . You're just going to have to accept that fact and learn to live with it . I have "

 

[kopcicle]

So the included valve angle of the Kawasaki 900-1100 up to 83 was 63 degrees . The included valve angle of the XS was 76 degrees for all but the OW72 head . This results in a 6.5 degree difference . The relative importance of this is that it allows for a continuous increase leading from the limited squish area into the combustion chamber . With the bore increase more area is exposed for modification . One of the things the Stock 650 lacked was little if any squish/quench area .

Just a little information on squish/quench area . It has been said that squish/quench area is a band-aid for poor combustion chamber design . On the other hand moderate but effective squish/quench area increases flame front turbulence during ignition cycle turn around through TDC and promotes slightly better scavenging during exhaust cycle turn around tdc at the expense of a short sharp pressure rise as the intake valve is opening . Originally thought to be an impediment to low lift intake flow further experimentation fount that the resistance to the inertia of the the resonant intake charge tended to compress the charge prior to entry into the combustion chamber .
This eventually leads to a discussion in inlet valve/seat venturi/geometry at low lift and does not pertain to the present thought .
I just wanted to include that little bit of information as I'm sure most are aware that the intake valve is open a significant amount as the piston turns around during overlap .

 

[kopcicle]

The original bore for the XS is 75mm . The KZ bore originally was 72.5 .
So there is only a difference of 2.5 mm between the two or 1.25 mm between the dome of the KZ and the combustion chamber of the XS . That is considering that the clearance between the original pistons and their respective chambers is for now unknown . I still don't have the pistons in my hand . Just these photos offered with an apology by Cliff @ MTC . This after he found them on a shelf , while I was on the phone , taken with the only thing he had and sent via email before we got off the phone . (I will never pass up an opportunity for a shameless plug when someone steps up and outside the norm . Cliff not only represents MTC he , well , he just gets it. )

Looks like I'll be doing a bit of chamber work also . As you can see from the pistons there is a significant squish band that is fortunately tilted several degrees. So from the previous post the angle leading to the top of the chamber created by the valve faces is 6.5 degrees . It should be relatively easy to blend the squish band on the piston to the squish band in the head . What will take a bit of advanced modification will be matching the dome of the MTC to the chamber of the XS , they are bound to be different .

Fortune smiles on the bold , or foolish . The valve sizes are similar to the point where .5 mm isn't going to make much of a difference . I may have made mention of this before . The slope of the back side of the intake valve needs to lead smoothly over the top of the edge of the valve cut out in the piston for as long as possible . The intake valve is opening well before TDC , on the order of .040" @ 30 degrees before TDC and well up on the ramp . Another 30 degrees (15 degrees camshaft) and the piston is dwelling at or near TDC for nearly 15 degrees ,7.5 degrees either side of TDC .

Okay where does this bit of esoteric information come from ? Experience , trust me here , the volume of the combustion chamber changes very little across these 15 degrees because it shrinks to a minimum just after TDC because of centrifugal and inertial forces . It averages out over this rule of thumb 15 degrees in practice .
Again , trust me . The only reason I mention here is as a prelude to the combustion process I'll mention later . Simply , max cylinder pressure needs to occur anywhere after minimum combustion volume . Think on that until we get there .

Now We're at or just after TDC and the valve is well onto the ramp . The object is to "dwell" the valve just slightly inside the the valve cut out in the piston for as long as possible . Initial valve opening may temporarily bury the valve in the pocket but the mean portion of the lobe lift should allow the valve head to track the piston down the hole as closely as possible for as long as possible . This creates problems . The intake can only be open just so long before a late closing point allows the inertia of the intake charge to escape . You can only open the valve just so soon because the combination of exhaust scavenging and the overlap quench spike begin to revert unburned and combustion byproducts back into the intake and poison the incoming charge . These two factors determine the intake duration far more than mechanical interference . Now we add to the confusion , total lobe lift / rocker arm ratio .
I'll not reproduce the math here and now but again , trust me . The inertia of a SOHC /rocker arm/valve assembly easily reaches into the several tons of force region . What determines how fast the valve can open is the limits of how well the assembly can track the camshaft without departing the cam lobe .
I've chosen titanium valves not just to say I have titanium bits in my engine but to allow steeper ramps without prohibitively heavy valve springs . To extend the valve and keep it near the surface of the piston as long as possible the last bit of lift has to happen fairly quickly as the piston begins it's acceleration away from TDC . Now those of you capable of visualizing these demands on the profile of a camshaft I commend you because It took me months to realize that what I've described is nearly square with the exception of the base circle and corners leading to and away from max lift . Fortunately one of the cam grinders I know and has been dealing with me for years understands that I'm a bit "different" and is working with me to provide a modification to an existing cam so that a completely new profile isn't needed . The work continues as I try and get the funds together for the pistons .


~kop

 

[hotdog]

Watching closely kop, I have another engine I thinking of toying with. What cc's are you going to achieve here..?? Keep the details coming.......

 

[kopcicle]

743.93088cc give or take

~kop

 

[hotdog]

I'm going to stir things up a bit here - why.?
I realize the long rod & its benefits are cool as well as the other mods you're doing. Is the result going to be massively different to bolting on a Heiden/Mikes 750 BB kit.? (there's no fun in that).
What HP & rpm ceiling is hoped for.??
eagerly waiting for your reply...lol

 

[hotdog]

thanks for the link/info kop...

 

[kopcicle]

The whole reason behind this is not so much the long rods for , in and of themselves . It was a way of acquiring high compression pistons without having to design them myself , have to order several sets , have to spend one more minute on the phone with a brain dead 20's something that thought the time of day was proprietary information .

All else being equal I would have just as soon used stock 447 rods and crank assembly . I would have already been done with the crank . As it is I had to acquire two CR500 rod kits and have the ends bushed as well as push the crank apart and back together . The crank had to come apart anyway for the re-phase . I'm not really going that much farther and I already know the benefits of the re-phase .

What I get in the end is longer , stronger rods , less expensive pistons , a re-phase , and a significant compression increase .

I'm going to size the plumbing to nose over around 9,000 RPM with useful torque to about 9,400 and be gasping for air around 9,500

On hooch it might make 75/75 by 8,800 without spontaneous catastrophic metallurgical detonation .

It all started with " alcohol is cool , heh , heh , heh ....

~kop

 

[Hairball27]

Kop , got your reply, the rods you used would be strong enoughr sustained high rpm in a flat tracker? or is carrillo the safe choice for this in a repahased LR , if i was boring out to 81mm and uaeing J & E pistons? or are the KZ pistons shorter skirt type?

 

[kopcicle]

Strong enough? Seriously, what can CP/Carrillo offer above and beyond say a Hot Rods part?
True enough the Carrillo parts are top notch but ...

Short skirts are for

umm, well,

A short piston skirt is worse than useless for a large bore air cooled engine. The only worse things you could do would be to shorten the rod and stroke. An air cooled engine at 80mm just doesn't have dimensional stability to support a piston in the bore without significant skirt length. The MTC piston has what I would call "nominal" length to diameter. The above CR450F piston as an example of full silly short skirt.

Let me emphasize that this is in no way a drop in part. Variations in machining, deck height, casting, chamber, phases of the moon are waiting to ambush you. Likely that you will need cylinder base spacers or thicker copper base and head gaskets. Valve clearance will become intake chasing the piston down the hole and piston chasing the exhaust into the head. Cam chain geometry can be affected as well. About all that this has going for it is favorable compression height and similar valve angles. What you do with the added quench/squish area is an area for extensive debate with only one common thread, it's useful. The rest is on you.

Treated as a developmental project I would use the CR rods and the MTC piston in a check for rod stretch, check for various assembled heights and flame travel round and about the dome. I wouldn't get any part of the piston closer than .080" to the head to begin with but in short order start working toward .040" . Running clearance is NOT assembled deck height. You have been warned. Don't start pouring the fuel and advance to it just yet, just get it running. Once you get the chamber sorted you'll be surprised how little advance is necessary to produce consistent, usable, and reliable power without worrying about windowed pistons should you run out of gas at full throttle. I can give you one useful tip in the area of bore finish. Take the rough hone (240) to piston diameter then finish to clearance with 320. Done like this the 320 supports the rings and the remaining deeper 240 leaves room for lube. You would be surprised how tight a piston to wall clearance you can run with this principle. Finish grit and clearance will vary. Last I heard there was a bit of a wait for sleeves so get a "few" and experiment.

When I tackled this initially I had thee engines. One had current modifications in it and was in the chassis. One had current modifications in it and was in pieces. One was being modified. In the end I got two engines. One for all its compression is strictly an alcoholic that can, with significant base gasket run on race gas and a gas engine that could really benefit from the extra cooling of the Hooch. The third engine became spares for the other two as I never finished the 76.5 degree crank* project.

I won't be able to play along at home as all that is and has been packed away for far too long and will remain so for the foreseeable future. I will however stand to encourage, consider, and cheer you on






*Okay now for the nerdy bits ...

Crank offsets
The first article on offset cranks, written by Phil Irving in the early sixties, proposed a 76° offset based on the stroke and rod length of a 650 Triumph. His theory was that while one piston was at TDC the other would be at maximum speed in the other cylinder. Going further, formulas such as shown at right, using a scientific calculator, indicate compromise offsets of 72 (some Norton), 74 (750 Triumph and some Norton) and 76° (long rod Triumph 650). Each offset works best for different engines (see detailed information elsewhere in this booklet).
Balance angle = 90° minus the maximum thrust angle.
Maximum thrust angle: arc tangent, also known as tangent^-1 of (1/(2*rod length)/(stroke length)).
To do this on a scientific calculator:
1. rod length [enter]
2. × 2 [enter]
3. ÷ by stroke length [enter]
4. invert (1 / X)
5. click [Inv] box, then [TAN]
6. subtract 90°.
result is offset angle
(information provided by Jeff Diamond)

 

[Hairball27]

thanks Kop for the info.