KR-1S.co.uk Forum

I assumed he was referring to KR-1Rs post above.

falconman wrote:Hello mj, how are you doing? If you look in the engine section under "cranks" it was determined that the crank would work. There will be 6.5mm space between the OD and pin. Same as a Banshee stroker crank. If those work so will this one. Also the stock KR flywheel fits the RZ taper so stock iggy can be run. I'll post the crank stuff in more detail when I have the primary gear and rods figured out. I'll have this and more ready for Bonneville if you want to give 'em a spin!

Interesting - never really measured it but as you say if it works on a Banshee should work on the KR. Will have to do some digging.

2 heads are better than one...
viewtopic.php?p=29731

Just a quick update. I hit a small snag with the crank. I have never seen a disassembled KR crank and I thought the primary side was 20mm diameter but turns out it is 25 with the end turned down for the press on gear. I had planned on welding keyway material in the RZ crank then grinding it down to size. Once I found out that wouldn't work I had to come up with something else. Now I'll weld in the keyway then grind down for a repair sleeve. That will keep the 25mm diameter for the bearing and seal then reduce the diameter on the end for the gear. The parts are at the machine shop now. I'll post pics of the finished parts when I get them back. Now I'm going to clean and weld the cases. I'll drop them off for redrilling the stud holes when I pick up the crank.

YAY!!! Got the crank parts back today. =D> =D> Also picked up a new 0-1" digital mic and 0-8" digital calipers as my old ones decided to die after 15 years. I'll be giving them a workout tonight when checking the crank parts for correctness. I'll take some pics and post them up later tonight. The parts look real good. Cheap too. Only charged me $200 for all the work. I only took a pic of the 3 pieces as the 2 inner pieces were the same.

Before:


After:


Now to finish welding the cases and redrill the stud holes.

Hi Falconman, just a quick question, what are you doing to balance this all back up?

That is a huge chunk you have taken off the rod counter weight there, are you going to drill the end of the pin to get it all back into balance?

I can't imagine that there is that much difference in the rod weight for the rotating component, so the removal of that much of the counterweight is going to make it shake itself to bits unless you can add some mass with heavy slugs or get rid of some of the pin side. You could probably taper bore the pin ends to get it back into some sort of order. Not sure I'd thin the web down anymore than it is though.

Its good to see someone thinking outside the box. I hope it all comes good in the end.

The balancing is the easy part. Put all the bits in a box and drop off at the balancing shop. A few $$$ later and it's done!!

LOL!


interesting project, watching with interest.

Hi Falconman, it is only easy if there is eough material left on the 'heavy' side to remove I think.

On the opposite side to the pin the reduction in diameter has taken, I would say looking at the thickness etc, about twice as much metal as the pin side. This means that you are going to have to get that amount of mass off the pin side, without making the web so thin it fails, or add heavy material (tanatalum or lead) back to the non pin side.

I saw a similar crank job done for a h***a NSR to get a long stroke out of it. To get it all back in balance there were three very large diameter slugs of tantalum added and it only just came back to a condition where it would balance up. The pin was offset machined on the ends as well.

I'm not sure a few $ will fix it, maybe a lot of $

youre forgetting how easy depleted uranium is obtained in the U.S.
...just buy a few rounds of Warthog ammo off ebay
that should add another kid to balance the see-saw

please correct me...what am i missing?
the reciprocating mass of left rod and piston assumed to be cancelled by righthand side...(180 out of phase but leaves a rocking couple instead)
after rough 3D modelling of mass
the scallops missing in the web around the pin cancel the extra mass of the solid pin...
...doesnt that mean by my reckoning the CENTROID of that web and pin is approximately dead centre down the axis of the crankshaft
(in the bottom photo, the pin has yet to be inserted into the LEFTmost web)
looks pretty balanced to me (but it is Friday here)

If you don't want to twist the crank to buggery then each reciprocating mass must be balanced with with a counter weight.

Unlike one piece cranks which can share the forces (which go up with the square of the speed) along the length of the crank, having huge twisitng forces is a very, very bad thing to have because on a multi piece crank you are relying on the friction in the joints to stop it twisting. Once you exceed the force required to twist it, it will move. Hence the welded up cranks you see in older race engines. Partly these were due to making more power, but mostly because they ran bigger pistons (more weight) and/or higher speeds for longer. As it is very difficult to add weight where you want it cheaply, the simpler and easier expedient of welding them up started.

This sort of helped, the forces did not go away obviously, but they were now distributed along the crank. That is until one or more of the welds cracked and failed. Then all sorts of horrible things happened.....

The issue with welding them is, that you can only access the very end of the joint. This then means that once you have exceeded the force requirement you are applying a huge twisting force to the moving unwelded part of the pin very suddenly.....

Remember also the the force is not evenly distributed along the big end. As this is rotating around the crank centreline the force changes and is greater on the larger radius than the smaler one. So you are trying to bend and twist the pin at the same time.

Early Yamaha's (TZ's YDS7's) had the balance factor all screwed up. They were only about a millimeter out on diameter (where the weight has the most effect) but the cases were impossible to relieve so they added weights to the cranks in the form of lead slugs cast into the webs to get it right.

Without these the engines used to shake themselves into destruction in very short order.

At 10,000 rpm the piston on a KR has an effective mass of about 5 tonnes (give or take a gnats knacker). Start applying this to the centre pin on the crank twice a rev and think about how long that poor little shaft will last before is spits the dummy and breaks into two. You might be lucky and the shaft just fracture, or it might grenade itself and destroy everything around it. I've seen both, neither are desirable.

Remember on an opposed twin like the KR the piston going up to tdc is being slowed down at a different rate to the one coming down to bdc because of the difference in position of the crank pin around the crank centreline and the rod length. (The motion of the pistion does not describe a perfect sine wave form) so although they appear to be in phase, they are not, resulting in large forces within the crankshaft even when things are perfectly balanced. Get the balance factors wrong and these forces go up by the square of the error.

Being even slighty out with your balance factors can ruin your day.

By the way, you forgot the rod and the piston, their mass acts on the crankshaft as well.

If we assume that Yamaha got it right in the first place then removing the metal as it has been will have screwed it up. If you think about the missing bits, as the tool passes over these areas, no material is removed, however where there is metal it is gone. Comparing the missing area to the complete are either side of the centre of the crank (web side to pin side) and you can see that there is quite an imbalance.

This is the problem, you have to either add material to the heavy side to get it back, or remove a lot more material from the light side. As the pin has remained unchanged the pin side is disproportionally heavy to the counter weight which is now lighter. Also the metal has been removed from the place where it has the most effect, the outer diameter, so you have to add more than you took off at a smaller diameter, or remove a heck of a lot more at the pin radius.

On another note, the balancer shaft will have to be looked at too. It was designed to work with the KR crank and masses, but that is all out the window now because the masses are all changed.

do we assume the centre middle bearing is a pin joint so to speak...
there wont be a bending moment in the centre shaft because one side is trying to flex up and the same time the opposite end is trying to flex down? (not a banana like down-bearing-down situation)

the circumference has been turned down resulting in more metal removed (counterweight half) proportionally compared to the big end pin side - does this not mean the pin is where the extra mass needs to be added? the scallops (divets) are there to statically balance the pin half against the counterweght half (the scallop -ve mass counters the mass of the near solid big end pin? (yes something can be in perfect static balance but completely out of balance Dynamically)

yes the balance shaft may also be where some uranium might be added
its there for the rocking couple, offset to one side of the motor a bit like a fat person sitting closer in on a seesaw than a lighter person farther out. when the gross effect of the pistons,rods etc want to roll the motor (about the middle axis of the bike) in one direction the effect of the balacer is opposite direction

the cylinder bore centerline isnt offset from the crank centre line? as some single cylinder motors are?

KR-1R wrote:do we assume the centre middle bearing is a pin joint so to speak...
there wont be a bending moment in the centre shaft because one side is trying to flex up and the same time the opposite end is trying to flex down? (not a banana like down-bearing-down situation)

They are both individually supported in bearings which will distribute the forces equally through the cases. However the acceleration on the downward moving piston is different to the upward moving piston, so there is a twisting moment in the centre pin. When it is all balanced correctly....

KR-1R wrote:the circumference has been turned down resulting in more metal removed (counterweight half) proportionally compared to the big end pin side - does this not mean the pin is where the extra mass needs to be added? the scallops (divets) are there to statically balance the pin half against the counterweght half (the scallop -ve mass counters the mass of the near solid big end pin? (yes something can be in perfect static balance but completely out of balance Dynamically)

No. If we assume that the pin rod and piston mass contribute to the missing scallops, then when we remove more of the 'other half' than the piston et al, then the mass has to go back on the non pin side. The rod piston and bearings have remained unchanged (theoretically only because Falconman has changed those too.) Don't forget that not all of the masses can be accounted for, crankshafts are usually balanced to take into consideration only part of the reciprocating mass, and hence only part of the rotating mass. (you cannot do all of both) So for a parallel twin, typically the balance factors are generally 50% rotating as per a single, and 33% reciprocating.

KR-1R wrote:yes the balance shaft may also be where some uranium might be added
its there for the rocking couple, offset to one side of the motor a bit like a fat person sitting closer in on a seesaw than a lighter person farther out. when the gross effect of the pistons,rods etc want to roll the motor (about the middle axis of the bike) in one direction the effect of the balacer is opposite direction

Correct, but as the crankshaft, pistons and con rods are now all different, the shaft is going to require work. The rocking couple is only there because both pistons arrive at tdc and bdc at the same time. If we messed with the crank phasing say to 90/270 or 76/284 then this would disappear and we would no longer need a balance shaft. However it would then sound like an NSR/RS/RGV/TZR.
Whichever is chosen though the crankshaft must be balanced. The rocking couple comes as a feature of 180 parallel twins, not because of the crank balance.

KR-1R wrote:the cylinder bore centerline isnt offset from the crank centre line? as some single cylinder motors are?

No the piston centre sits on the centre of each cylinder, equally spaced between the bearings.

Hi Love the idea, I've had a similar one for some time but with 4 KR cylinders, would have to be billet c/cases with a stronger g/box. I've got 2 or 3 spare engine so have all the parts.