Adding Crank Weights for a Big Piston (KT100)

yammi pistons

I noticed Mr Burris said his 52mm piston is cast and that his 55mm piston is forged. Just wondering what the weight difference is between casting and forging processes. I do know I have never used a cast piston in hiproformance builds. Iam impressed in the weight of the 55m piston though 120 grahams is very light. But that is a large difference between stock 52 and the 55 around 10+ grahams. That's not nearly as large as the strike but is enough to start creating some problems. From the builds of a stock 52mm yammi piston to a CSI 52.80mm the weight increase for me was large enough to start creating vibrations that I could feel in the engine. I also noticed more wear in the crank bearings and a increase in the cylinder wear in the front and rear sections. I don't know if the stock 52mm yammi piston I weighed was of old or new design but my weights were a little different than what he stated. I used calibrated aircraft scales to do my weights thought. This information is very useful should help many guys going big bore to decide if added weight is needed to run his Burris pistons.I guess the evidence will be seen after his pistons are run for a while, since they are so new to the market. As I stated before that's close to half an ounce difference in a very small piston. Balancing in Harley 3-7/8" or chevy 3-5/8" piston is very good at 1grahm. So how can 10+ grahams in a very small piston turning 14,500 rpms not be a great difference. As rpm increases centrifugal mass increases exponentially, so this weight difference grows enormously.
 
crank weights

Hey Jon great to hear from ya. I did not weld the plugs in but thought about putting a couple tacks on them.I was on the road so much last racing season I didnt get to run but a couple times so didnt put a real test on them. I think when i tear down for a rebuild I will tac them just for added insurance. I was very happy with the change thought it took all the vibes out and allowed the engine to really rap quick. It pulls harder than I ever dreamed it would. The intake mods and the kby-97 work great togather. I ran away from the other kt mods at the track. They were all wanting to know what I had done to my engine. So as I say let the masses know and I told them the mods I had used. Bet it will be a lot closer next season,if some of them use the same mods, hope so love the compatition. Its all about the fun factor anyway.
 
I plan to glue mine in then peen the edge of the hole. I want to know how hard it is to drill a hole in that crank web. Btw if you have a small hole in a big piece of metal heating will shrink the hole so, you might as well press it at room temp.
 
I work at a turbine aircraft engine rebuilder and we do interference fits on many parts and use them same process as i discribed. Heat expansion works on any size hole no matter how big the piece of metal the coefficent of expansion is different depending on the type of alloy. We have high pressure turbine discs that are of very high Nickle chromium content that we sleeve and there is a .020 interference fit and the same process is used except we heat them to 1100F and freeze the sleeve in liquid nitrogen. I guess freezing the plugs doesnt cause them to contract either. You can do yours howevver you want but this is what I consider the correct method fo installing a plug or bushing or sleeve.Just wondering what type of glue are you planning on using. It must be heat resistant and gasoline resistant as well as oil. Let me know how that works for ya. Seems really risky to me relieing on adhesive to hold a metal to metal bond in that type of enviroment. Good luck hope it works for ya. The flywheels are mild steel and not very hard. I used a new drill and and a vertical mill to indicated the 180 degree from the crank pin and orient the distance in from the edge.Drilled about .010 under the used a sharp ream to finish the hole at .004 undersize.
 
Have you ever seen a calibration ring for a bore gauge? They are a certain OD to equalize the ID for any temp. If the OD was larger there is more metal to expand from OD to ID than there is at the median dia between OD and ID so, the hole gets smaller. Hard to believe but it's just physics. Of course chilling a part will shrink it but the change is very little compared with heating, in some cases it does help but for go kart work? My plugs will be pressed in and peened over so the JB weld is just added insurance. I'm an FAA certified A&P mechanic and I work for Boeing on million dollar transmissions.

Sundog
 
oh my just when I thought things were going good.
I am certified to weld up to 6 inch thick iron
I use jb weld as a last resort
Plus I stayed at a holiday inn once;)
 
Iam also a FAA certified A&P tech and I inspect all the engine parts in a 10million$ Rolls Royce turbine. All I can say is I have done the crank project and at .004 undersize my tungsten plugs required no pressing to be installed. All that was needed was a light tap to flush them to the outside of the flywheels. Going by what you said that means the liquid nitrogen shrank the tungsten by more than .004 if my hole shrank from heating. Thats very interesting considering tungsten is such a dense and hard material. I didnt want to press the plugs under that much pressure possible causing any deflection or warpage in the flywheels. My crank was done by Gary Wlojer here in Tulsa and has less that .001 runout, which is excellent for a Yammi. I wish I had tacked the plugs into place or possible peened them as added insurance.So far there has been no problem with about 1.5 hours of run time. Hopefully I will get to race a lot more this comming season and see how they do until the next teardown. Your process will probably work fine but I dont like the pressing technique as well. I intend on reasearching your heating theory thats very interesting. Good luck hope your crank works as well as mine does.
 
alvin l nunley said:
No doubt in my mind you know how to do it, but there are people doing KT cranks with stock pistons and getting very good results with, I think, about the same weight addtion. You would have to talk to Louie Figone about the size of the inserts used. Jeff Nelson lost a first place enduro Nationals trophy because his cranks had lead in them and one came lose. They found it in tech. I think that was about 1986-87. Jeff didn’t build the engines, a guy from Ohio did them.
I think I know why the TKM was so fast; it had inserts in the crank. From my Mc experience, I know what extra balance in the crank will do.
I don’t know, but my guess is those Horstman tungsten weights added more than what you’re talking about. It would be interesting to find out for sure.
Comments, compliments, criticisms and questions always welcome.
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Al, I never installed weights in any of my engines, I think what you are referring to was the 1999 IKF Road Race Grandnationals at Portland, OR when I DQ'ed four KT 100 engines for having loaded cranks, one for a solid crank pin and one for an illegal wrist pin, all were first place finishers and all were built by the same Fresno, CA shop. It appeared that the weights were welded in as there were grind marks to smooth the area down. And yes, they did run fast.
 
Louie, I said ask you because you’ve seen these pins. I was thinking you might have some comment on the size of the pins.
If it sounded like I thought you put pins in your KT cranks, please accept my apologies.
I remember some of that guys customers defending him and his cheating was.
 
I'd send it to crank works, let them do it, they do it for a living, and have balancing equip. to do it at the rpm you plan to run the engine at.. with out the equip. your only guessing.. jmho..
 
alvin l nunley said:
Louie, I said ask you because you’ve seen these pins. I was thinking you might have some comment on the size of the pins.
If it sounded like I thought you put pins in your KT cranks, please accept my apologies.
I remember some of that guys customers defending him and his cheating was.
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Al, no apology needed, I knew what you were saying. As a tech person I was not looking to see what they had done, only to check the legality of the engine.
 
Hi Sundog,

I have not gotten involved trying to balance single cylinder engines, but I have modified a bunch of them and I have noticed that changes in piston weight will effect performance heavy=bad. One note about balancing single cylinder engines, you can compensate for the weight of the moving parts BUT you can not compensate for the cylinder pressure on the piston ( mass=energy=mass ) without extra parts, balancing shaft etc..
Mike Berg
Ok let the comments begin
 
sundog said:
Have you ever seen a calibration ring for a bore gauge? They are a certain OD to equalize the ID for any temp. If the OD was larger there is more metal to expand from OD to ID than there is at the median dia between OD and ID so, the hole gets smaller. Hard to believe but it's just physics. Of course chilling a part will shrink it but the change is very little compared with heating, in some cases it does help but for go kart work? My plugs will be pressed in and peened over so the JB weld is just added insurance. I'm an FAA certified A&P mechanic and I work for Boeing on million dollar transmissions.
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The above is unfortunately incorrect -- growth is growth. It doesn't matter how much larger the OD of the part is vs. the bore.

I'll demonstrate:

Here is the EXACT type of calibration ring being referenced: http://www.muller.net/mullermachine/photos/gauge.JPG

As you can see, the ID is 2.2465" (which is exactly what it measures).

I took my Mitutoyo dial bore gauge which has a .0001" indicator on it, and it set the indicator to zero in my 68°F shop. I then took the calibration gauge (aka: ring gauge) and placed in the oven in my kitchen which was set on 200°F convection. I left ring gauge in the oven for about half an hour.

Here is the math on what the growth SHOULD be (irrespective of the OD):

Most steels grow very close to six millionths of an inch, PER inch, per degree F. e.g. .000006" per inch (of diameter in this case).

So since the bore is 2.2465", we simply multiply .000006 x 2.2465, and that will give us the growth PER degree F. That answer is .00001348. So growth in diameter SHOULD be about 13.5 millionths of an inch per degree.

So my oven was set at 200°F, which means that the ring gauge increased in temperature 132°F. (assuming my oven is fairly accurate, and the gauge was fully up to 200°F.

So to get the total growth, we simply multiply 132 x .00001348, which equals .00178"

That means that if I measure the ring right out of my oven, it should be between .0017" and .0018" larger than it was at room temperature.

And lo and behold.... http://www.muller.net/mullermachine/photos/size.JPG

The camera was at a bit of an angle. Looking at it straight-on, it was right in the middle between .0017" and .0018".

So much of the theory that the bore in calibration rings don't grow. In fact, they grow EXACTLY like any other piece of steel would, regardless of how much material is around the bore (provided of course that the entire piece of material is at the same temperature).

The other piece of incorrect information is that chilling does not do the same thing as heating. In fact, it does EXACTLY the same thing. The amount of movement PER degree is exactly the same whether heating or cooling. Makes no difference. I'm more than happy to demonstrate that one as well.


:)
Pete
 
Hey Pete thanks for the formula that collaberats what i stated in my post. I knew what he was saying was not correct. We use the heating and cooling technique on our Rolls Royce parts and many have small bores in large pieces. We install sleeves and bushing in them according the the heating index from the RR manuel relating to the type of alloy its made from. Some are Titanium, High nickle chromium and steel. Each has a different cofficent of expansion per degree of temp used to heat them. But back to the Yamaha crank using your formula starting temp of 72F heated temp of 450F = 378x .00001348= .005 increase in bore size on mild steel. Now I also froze the Tungsten plugs in liquid nitrogen which has an average temp of -325F but the contraction coffecient will be different becuse of the density of the Tungsten alloy. I reemed the bores in the flywheels at .370 for a .375 dowell, so even without freezing the plugs would have almost droped in. Using your formula for steel plugs would shrink .003 but being Tungsten I probably only got half that. It was still enough for the plugs to drop in with no pressing. Hey Jon just wondering what is the weight of those 7/16 tungsten plugs you were talking about, they must be 4 or 5 grahams heavier than the 3/8 plugs.
 
This line is the key to what is being discussed.

(provided of course that the entire piece of material is at the same temperature).

Of course its a lot easier to heat a piece of metal than it is to freeze metal to the equal temperature change but in the opposite direction. As most know, you actually cant cool steel as much as what you can heat it. Not that its not possible for the steel but the means to drive the temp down below -270C is the problem. Thats why people say heating is more effective than cooling.
 
Ya Mitch , 5.5 grams more with the alloy I was looking at, minus a little more steel with the bigger hole and using a Strike piston that has not been lightened any still puts it at close to 100% of weight added, I don't what to go that far. Not on this first one, maybe when I get some time to do some testing.
 
"So much of the theory that the bore in calibration rings don't grow. In fact, they grow EXACTLY like any other piece of steel would, regardless of how much material is around the bore (provided of course that the entire piece of material is at the same temperature)."

Good stuff Pete!! The truth is measurements that are traceable to the Bureau Of Standards or ISO or........ are all done in temperature controlled environments. Years ago I worked in the Aerospace industry at Garrett as an Experimental/Prototype Machinist involved in extremely close tolerances and the room (and many of the machine tools) were temperature controlled so we had apples and apples when it came inspection time.

Another myth that popped up on here is that "forgings are heavier" than castings. The truth of the matter is with equal mass (especially something like a piston) there is very little difference. The reason castings were lighter in many cases was the shape was more intricate but forged pistons have evolved to where they are near net shape and require very little machining and because of their strength and ductility can have thinnersections cast weaker less ductile castings. We have a forged replacement piston for the cast Rotax and it weighs 15 grams less!!
 
You missed something there.

You have to multiply .000006" TIMES the diameter to get the growth. I calculated growth for nearly a 2.5" bore. Your growth will be a small fraction of that.


fyi: A document I've had on my web site for 15+ years: http://www.muller.net/mullermachine/docs/temperature.html

Pete


ttownwideglider said:
Hey Pete thanks for the formula that collaberats what i stated in my post. I knew what he was saying was not correct. We use the heating and cooling technique on our Rolls Royce parts and many have small bores in large pieces. We install sleeves and bushing in them according the the heating index from the RR manuel relating to the type of alloy its made from. Some are Titanium, High nickle chromium and steel. Each has a different cofficent of expansion per degree of temp used to heat them. But back to the Yamaha crank using your formula starting temp of 72F heated temp of 450F = 378x .00001348= .005 increase in bore size on mild steel. Now I also froze the Tungsten plugs in liquid nitrogen which has an average temp of -325F but the contraction coffecient will be different becuse of the density of the Tungsten alloy. I reemed the bores in the flywheels at .370 for a .375 dowell, so even without freezing the plugs would have almost droped in. Using your formula for steel plugs would shrink .003 but being Tungsten I probably only got half that. It was still enough for the plugs to drop in with no pressing. Hey Jon just wondering what is the weight of those 7/16 tungsten plugs you were talking about, they must be 4 or 5 grahams heavier than the 3/8 plugs.
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