Press Fit On Crank

Jimbo

Jimbo

You can fool some of the people some of the time
How much is the press fit on a typical crank?
In other words what would the diameter of the crank pin be and what is the diameter of the hole it gets pressed into?
 
Jimbo, from tips found on the web I recall .003 inch. I'll do some checking today on some new pins and cranks and see what I come up with. I have see quite a few MC cranks with a weld on them.
 
Jimbo, EC tig welded a 4 cylinder crank for me one time, because they were known to twist under extreme HP, but we never had to weld a single cylinder two cycle crank to keep it from moving. If the crank wheels are in good shape, a new pin with the correct interference fit will keep it locked in true. We built some bad singles, including a 440 cc RM Suzuki dirt dragster on nitro and never had that problem. Jon
 
Seems I remember, many years ago, the Europeans tried to make two-piece cranks but they never worked out, for reasons unknown to me. This leads me to believe, maybe, that welding the crank might not work out.
 
alvin l nunley said:
Seems I remember, many years ago, the Europeans tried to make two-piece cranks but they never worked out, for reasons unknown to me. This leads me to believe, maybe, that welding the crank might not work out.
Click to expand...

So who makes all the cranks for the Euro kart engines?
 
I have welded a couple, and in most cases the weld cracked. I was afraid to get the crank mis-aligned when the weld cooled, so I just sort of used 3 small tacks -- bad idea. Bottom line is that a lot of weld is needed for the higher HP beasts when the halves are worn out. You just have to take time to let it cool and check the alignment after each weld section to be sure it does not get too bad. You will have to pull it back in alignment with more welding.... Also, look closely at holes in the halves, I have also seen a couple with cracks and those we just had to scrap. One was on a K-80 and one on a K-35.
 
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