Services for Brough Superior motorcycles and their contemporaries
KTOR crankshaft last update: 1/2006
|After making the crankcase and cylinder drawings I made a drawing of the
original crankshaft. Now, this was nice, and I am a keen engineer, but I did
not dare to make my own conrods. Maybe I should have tried...
I did a lot of investigations as I thought there might be a suitable rod set available from one of the guys stroking and boring Harley engines, but to no avail. I found the Sportster big end fits into the space given in the KTOR engine, but there is no special 7 3/4" Sportster rod in the market.
So finally I turned to Carrillo's, asking if they could make me a set of Sportster rods, albeit with a special length and a different small end diameter. Yes they could, it would take 13 weeks. Well then, we agreed on the specs, I paid a deposit and waited patiently.
After 13 weeks I was asked to pay the rest of the price and the rods were duly sent. When I had paid the freight and customs duty they were finally delivered. Now, when I unpacked them, I thought the finish was very nice, but the shape looked a bit weird. Have you ever seen rods where the beam is not on the centre line connecting the small end and the big end?
I found both the small end bore and the big end bore were offset by some 2mm from the beam centre line. In the picture, you can see this best if you look at the small end of the blade rod.
Now you can call me a nitpicker or what ever you like, but I did not like this shape, as it is technically wrong in my opinion. Of course the rods, which were designed for a tuned Sportster engine, will certainly not cause any problems in a 45hp engine revving 4500rpm only, but that is not my point...
|Well, to cut a long story short, despite all my efforts to discuss this
with Carrillo's, I could never quite find out why the rods had this strange
shape. I was told this is how Fred Carrillo had designed them, and if I
absolutely wanted rods with a 'wrong' shape they might make me another set.
After another half year of negotiations we eventually arrived at a compromise, and I ordered another set.
Maybe you can imagine that I only opened the parcel with trepidation when I finally received these...but this time they absolutely looked the part!
These are the new rods, and despite all the trouble I must say I am very happy with them! To me, they seem to be good for a lot more than the 45hp I am aiming at for the time being, but you never know, maybe I will go for a little more power once everything is working nicely?
So I have made peace with Carrillo's, and whether the whole affair was my fault or theirs, I am now sure they can do a first class job!
|Well, now I need to get a Sportster big end bearing and then I need to
make my own flywheels.
I did a lot of calculations, trying to decide if I should stick with the good old taper ends on the big end and main shafts, or if I should go for a pressed-up assembly with cylindrical fits, which is at least easier to manufacture. I found there is not a lot of safety margin in all the shaft/flywheel joints, and whatever solution I will use, I will need to use a good material for the flywheels. Watch this space....
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