Maxie
Crank Pin Number
Crank Pin Number
Hey Gang, refresh my memory. As I remember from four decades ago, you would go up one number on the pin when rebuilding a crank. Now they have no number. What is going on here?
Maxie
Maxie
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Re: Crank Pin Number
My assumption is that the numbers were manufacturing tolerance sorting numbers so that pins and crank halves were not assembled with tolerance stacking issues resulting is loose pins. Since none have been made for forty years, I doubt you will any longer have the luxury of selecting a pin with the right number. Or maybe not, as only those with an inventory could say with certainty. Another possibility would be that a NOS pin with no number was by default a zero, neither over nor under target size, and as such not worth marking. Machinists are free to establish their own protocol.
Your source for the pin would have to answer where and when the pin was made, but if these are made after the fact (recent manufacture) any number reference on the pin would be superfluous if not misleading. Measure the pin pocket with a micrometer, measure the pin with a micrometer, compare readings. Someone here is going to know how much oversize the pin has to be to stay put once pressed together. Or if you have the two pins, one you removed and one you intend to install, measure both. The new pin should be at least as large as the one removed.
Your source for the pin would have to answer where and when the pin was made, but if these are made after the fact (recent manufacture) any number reference on the pin would be superfluous if not misleading. Measure the pin pocket with a micrometer, measure the pin with a micrometer, compare readings. Someone here is going to know how much oversize the pin has to be to stay put once pressed together. Or if you have the two pins, one you removed and one you intend to install, measure both. The new pin should be at least as large as the one removed.
Re: Crank Pin Number
Hey Max,
General rule is to use the next largest number crank pin when rebuilding.
With that said, I have measured Hodaka crank pins that were one size larger than the old pin and could not detect any size difference. Used a quality Starrett micrometer with tenths graduations. May need more sophisticated equipment to measure the difference. If say you measures a +2 and compared to a +4 maybe the size difference would be more noticeable. I have not had the parts in my hands to make those measurements.
I did purchase some crank pins some time ago from Wiseco for my 03 Wombat and there was only one size available. I can report they had a good tight press fit when assembled.
I try to install the next larger pin when rebuilding Hodaka cranks but sometimes those parts are not readily available. If the pins seem to press in with less force than I am used to seeing I weld the crank pin. So far no problem with loose crank pin.
Also, the rod kits from Strictly Hodaka come with a new crank pin with no size markings on them. All of those I have installed also had a good tight press fit.
Sorry I cant be more specific.....just good ole common sense.
Danny
General rule is to use the next largest number crank pin when rebuilding.
With that said, I have measured Hodaka crank pins that were one size larger than the old pin and could not detect any size difference. Used a quality Starrett micrometer with tenths graduations. May need more sophisticated equipment to measure the difference. If say you measures a +2 and compared to a +4 maybe the size difference would be more noticeable. I have not had the parts in my hands to make those measurements.
I did purchase some crank pins some time ago from Wiseco for my 03 Wombat and there was only one size available. I can report they had a good tight press fit when assembled.
I try to install the next larger pin when rebuilding Hodaka cranks but sometimes those parts are not readily available. If the pins seem to press in with less force than I am used to seeing I weld the crank pin. So far no problem with loose crank pin.
Also, the rod kits from Strictly Hodaka come with a new crank pin with no size markings on them. All of those I have installed also had a good tight press fit.
Sorry I cant be more specific.....just good ole common sense.
Danny
Re: Crank Pin Number
Hey, thanks AZ and Danny. It appears not to be an issue nor did I remember issues from the past. I actually never pressed one, I just sent them to our magic local machine shop.
Maxie
Maxie
Re: Crank Pin Number
My guess would be that pin diameters vary in the tens of thousandths. Of the several micrometers I have, each is graduated in thousandths. Anything smaller than that requires interpolation between the marks, and while the marks are something on the order of a 1/16 inch between each other on the shaft, which makes it possible to see differences, anything between the marks is only broadly accurate, requiring more skill than I have these days. I could perhaps see differences around 2/10,000 but no guarantee.
However, it should be possible to see if one pin is larger than the other, even if the "how much" part is vague. I just don't think the numbers that pins used to be marked with related to actual measures, that is, if marked with 4, it wasn't four somethings, just that 4 was smaller than 5 by some amount that made a difference to the machinist who made them.
Pressing pins in and out of cast crank halves stetches the metal to some extent, which is why one would as a rule choose the next larger increment. But the amount of stretch was never known anyway, so picking a higher number was a relative thing. Good practice, but not science.
Use the parts you have. If not comfortable with the result, take it to a machine shop where someone will have the experience it takes to make better guesses than we can. Or, I suppose, if you are confident that your build is true, you can tack the pins with a spot weld. Personally, if I thought the pin would slip is not welded, I would not use it.
However, it should be possible to see if one pin is larger than the other, even if the "how much" part is vague. I just don't think the numbers that pins used to be marked with related to actual measures, that is, if marked with 4, it wasn't four somethings, just that 4 was smaller than 5 by some amount that made a difference to the machinist who made them.
Pressing pins in and out of cast crank halves stetches the metal to some extent, which is why one would as a rule choose the next larger increment. But the amount of stretch was never known anyway, so picking a higher number was a relative thing. Good practice, but not science.
Use the parts you have. If not comfortable with the result, take it to a machine shop where someone will have the experience it takes to make better guesses than we can. Or, I suppose, if you are confident that your build is true, you can tack the pins with a spot weld. Personally, if I thought the pin would slip is not welded, I would not use it.
Re: Crank Pin Number
So Danny and AZ, when you weld a crank, how serious is it, a tack or what? Is it reversible or permanent? Do you have any pictures of examples? Just curious. When I road-raced a Yamaha RZ-350 it was recommended that I weld the crank pins but I never did. Supposedly the crank could twist on severe down shifts. It was always on my mind but no problems were ever encountered. Anyway, thanks for the input!
Max
Max
Re: Crank Pin Number
Hey Max,
I attached a picture of the grooved crank / pin before welding. I use a stone and aim to grind the groove width half on the pin and half on the crank. I also try to have enough width and depth to lay the weld in the groove and keep as much of the weld bead even with the surface of the crank. I do not have a welder at present so after prepping the crank I take it to a local welder. When I get the crank back I usually have to dress down any excess weld. Of course any welding is done after the crank is assembled and trued.
The crank can be dis-assembled after welding but you would have to grind away the weld. I do not weld many cranks as long as the press fit is good. For serious racers making lots of power and turning high rpms welding seems to make sense.
Danny
I attached a picture of the grooved crank / pin before welding. I use a stone and aim to grind the groove width half on the pin and half on the crank. I also try to have enough width and depth to lay the weld in the groove and keep as much of the weld bead even with the surface of the crank. I do not have a welder at present so after prepping the crank I take it to a local welder. When I get the crank back I usually have to dress down any excess weld. Of course any welding is done after the crank is assembled and trued.
The crank can be dis-assembled after welding but you would have to grind away the weld. I do not weld many cranks as long as the press fit is good. For serious racers making lots of power and turning high rpms welding seems to make sense.
Re: Crank Pin Number
Danny's description is good. I have never had the need, but the photo shows the process as I know it.
Maybe I am just being cautious but if I didn't have confidence that a pin would hold, I would replace it with another rather than weld it, for a variety of reasons. The entire stress of the assembly is supposed to be endured with a pressed pin. Welding would be insurance for racer types operating in the OMG zone.
Maybe I am just being cautious but if I didn't have confidence that a pin would hold, I would replace it with another rather than weld it, for a variety of reasons. The entire stress of the assembly is supposed to be endured with a pressed pin. Welding would be insurance for racer types operating in the OMG zone.
Re: Crank Pin Number
Hmm, all quite interesting, I'd heard about it but I'd never seen an example. Thanks for the pictures Danny!
Max
Max
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