Crank Pin

rainman

rainman

Member
I have been trying to find a crank pin for my open 131 Ital like the one it had and the measures were 46 x 18 mm but the real issue is that I can only find it either solid or with a 6 mm I/D (this is used for the PRD Fireball). Thing is the one I had was 5/16 I/D which is close to 8 mm and I was trying to keep everything as close as possible as it was to keep it balanced. I have tried everywhere, Comet, Riekens, TS, Laukaitis, even RLV and checked catalogues from VERTEX, even the European catalogue and couldn´t find it everywhere. I have oredered the 6 mm I/D in case I can´t find anything else and I didn´t want to but I guess best soluton might be get that I/D done to what I want unless I can find it anywhere that I haven´t tried. Thanks everyone.
 
Got to Italsistem web site and check out their importers, you might find one that has what you are looking for ( UK, South America, Canada ).
Mike Berg
 
I have never seen a big cc PCR without a solid pin. I think someone did not put the correct one in there. You may want to check with your engine builder.
 
TMW said:
I have never seen a big cc PCR without a solid pin. I think someone did not put the correct one in there. You may want to check with your engine builder.
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Thanks Strahl. It was actually built by Joe Torres and rebuilt by John Klutz at CKI, both good builders, and it worked great with no vibration. That's why I am trying to keep it as it was. I have had some issue when I rebuilt top end and found out crank pin bearing needed to be replaced. I think this Ital of mine is a strange combination if parts, including the driver, lol.
 
Magmo said:
Got to Italsistem web site and check out their importers, you might find one that has what you are looking for ( UK, South America, Canada ).
Mike Berg
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Thanks Mike, it is an Ital but many of the bottom end parts are not Ital since it is ab open engine. At RLV I was told some older PCRs had this pin but you can't find it anymore with this I/D. Either solid or smaller I/D is all you can find anywhere in the world I have checked on 18 x46 crank pins. Any experience on modifying I/D?

Mike a twin with 2 twin spark IDKs would calk some attention in UAS. I hace one but you have the other, lol.
 
Hi,
What size is the solid crankpin? length and diameter ( you must get down to .0000" tenths ), I have several from AFAM in Japan they offered replacement pins for Ital engines years ago and I bought some and forgot I still ahve a few left.
Mike Berg
Twin IDK's that would be a odd ball in a parade of interesting karts.
 
Rainman,
Forget about trying to enlarge the ID of a finished crank pin, they are 62Rc or greater and that IS hard, you could damage the pin trying to drill bore etc the ID, the only way you could do that id EDM and that would easily be over $100 for 1 hole.
Mike Berg
 
Magmo said:
Rainman,
Forget about trying to enlarge the ID of a finished crank pin, they are 62Rc or greater and that IS hard, you could damage the pin trying to drill bore etc the ID, the only way you could do that id EDM and that would easily be over $100 for 1 hole.
Mike Berg
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Thanks, Mike. I have already ordered one with a smaller I/D but same O/D and length. It is not difficult to find the 46/18 with a 6 mm I/D since it is used on the 125 PRD Fireball and it also is easier to find it solid, Mike. It is just like if nobody has anymore those old ones with a 5/16 I/D. I was not thinking on drilling that myself but didn´t think it could be so expensive either. My season is only one pin away, lol.
 
I have taken weight off crank pins by grinding a taper on each side leading into the center hole.
The closer you get to the end of the pin, the less strength is needed, so you can run a pretty deep 45 degree taper into it.

I used my lathe, with a tool post grinder, and spray mist for cooling.
The pin never got warm, let alone hot.

You are talking a 46mm long hole, 6mm id, and 1mm per side, so that isn't much steel.
 
I can't believe the difference between an 8mm hole and a 6mm hole would make any change except for internet drama.
 
sundog said:
I can't believe the difference between an 8mm hole and a 6mm hole would make any change except for internet drama.
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I don't know but that's what I am trying to find out. Some tried to help without smart drama comments. Thanks everyone for your help once more.
 
Hi Rainman,
I have replaced crank pins on Open engnes without regard to balancing. FYI It is nearly impossible to balance a single cylinder engine beyond about 60% of perfect balance because of the unopposed cylinder forces ( you can add a balance shaft to bring it closer ).
So my advice is go ahead and install what you have provided it is the correct diameter and when installed has correct en d play.
big end clearance =.001" to .0015"
end play=.005" to .010"
Good Luck
Mike Berg
 
The world is adding more counterweight, and a lighter crank pin can serve the same purpose.
If it was me, and I was sure that the pin would hold the stress, I'd try it. Of course it's not my engine.


Comments compliments criticisms and questions always welcome.
 
Thanks. we are trying with the one I found, so we´ll see. we have already checked for the correct end play,
Mike. We got it right 1 st try. Thanks everyone.
 
"I can't believe the difference between an 8mm hole and a 6mm hole would make any change except for internet drama."

I have to agree. I built reed and rotary valve Euro engines for years and swapped rods, pistons and crank pins around without any adverse effects. According to Pete's calculations its only 8 grams between the 6mm and 8mm hole so I wouldn't bother. A much bigger concern, IMO, is the final clearance between the diameter of the crank pin and the ID of the rod. I have found that some manufacturers build the clearance into the pin and others into the rod. Either way can be big trouble if it's not correct.

Mike
 
8 grams can have an effect but it depends how many rpm you turn. Really only becomes an issue after 15-16k or so. and also depends how much weight the other components add to the assembly that might not be stock weights, eg piston pin and rings. You will only tell on a dyno anyway, at least thats what I found. I wouldnt worry about it unless you were turning 18-20k rpm on a sprint track.
 
I think it will be OK since it is my UAS and it is gonna run on dirt (lower rpms). Thanks anyone. I really appreciate your feedback and knowledge coming from your long experience building engines.
 
The 8 grams difference in the crank pin will have much less effect than 8 grams difference in the piston. Done that and it will shake your teeth out!!!
 
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