CMB Crankpins - Material

[ids987]

Just wondering if anyone might be able to comment on this please.

I have a number of Evo style .45s and .90s - mostly purple headed, and since the crankpins are now "unobtanium", I was wondering whether something like a HSS drill blank would be suitable material, hardness etc. I believe the correct diameters (CMB used several over the years), may well be available off the shelf, and if so, are probably held to close enough tolerances.

Thanks for any input !

Ian

 

[Jim Allen]

Just wondering if anyone might be able to comment on this please.

I have a number of Evo style .45s and .90s - mostly purple headed, and since the crankpins are now "unobtanium", I was wondering whether something like a HSS drill blank would be suitable material, hardness etc. I believe the correct diameters (CMB used several over the years), may well be available off the shelf, and if so, are probably held to close enough tolerances.

Thanks for any input !

Ian

There are several materials that I have tested which are excellent materials for crank pins in pressed in crank pin assemblies. AISI M-2, M-42 & 52100 are available in drill blank sizes, reamer blank sizes, as well decimal sizes & metric sizes. Also available are gage pins in several different tolerances from .0002" to .00002" which are made of 52100 steel. All of the previously mentioned pins will have a micro inch finish of 8 or less.

The ends of the pins that are to be pressed into whatever hole should have a polished radius. The material into which they are pressd into should also be hardened & the hole's ID ground. Typical press fit amouints of .001" to .0013" prevent movement of the pin once assembled. A fixture should be used for assembly & disassembly. An extreme pressure lubricant such as CMD should be used during pressing operations.

http://gallery.intlw...x.php?cat=10141, page 2

Properly made crankshafts that use a properly pressed in crank pin can last forever!

Jim Allen

 

[steve wood]

Just wondering if anyone might be able to comment on this please.

I have a number of Evo style .45s and .90s - mostly purple headed, and since the crankpins are now "unobtanium", I was wondering whether something like a HSS drill blank would be suitable material, hardness etc. I believe the correct diameters (CMB used several over the years), may well be available off the shelf, and if so, are probably held to close enough tolerances.

Thanks for any input !

Ian

i have made them from a-2.they must have worked fine,as i haven't heard back from anyone

 

[ids987]

Thanks Steve and Jim, for the info.

 

[Jim Allen]

Just wondering if anyone might be able to comment on this please.

I have a number of Evo style .45s and .90s - mostly purple headed, and since the crankpins are now "unobtanium", I was wondering whether something like a HSS drill blank would be suitable material, hardness etc. I believe the correct diameters (CMB used several over the years), may well be available off the shelf, and if so, are probably held to close enough tolerances.

Thanks for any input !

Ian

i have made them from a-2.they must have worked fine,as i haven't heard back from anyone

AISI A-2 is not a bearing steel & would not be used at Rc numbers higher than 62. The steels I mentioned would be considered bearing steels & would be used at Rc numbers above 64. The M-2 & M-42 steels both have high heat hardness with M-42 primarily being used in turbine engine bearings & M-2 primarily being used for high quality wear resistant cutting tools. Both have high shock resistance. 52100 is the steel that is used in most ball bearing applications.

The blanks I mentioned come all ready hardened & ground to size. Cut them off with any abrasive wheel & they are ready to use. They are also very cost effective. Even a short 2" long gage pin blank will make two crank pins in large motors.

Jim Allen

 

[steve wood]

Just wondering if anyone might be able to comment on this please.

I have a number of Evo style .45s and .90s - mostly purple headed, and since the crankpins are now "unobtanium", I was wondering whether something like a HSS drill blank would be suitable material, hardness etc. I believe the correct diameters (CMB used several over the years), may well be available off the shelf, and if so, are probably held to close enough tolerances.

Thanks for any input !

Ian

i have made them from a-2.they must have worked fine,as i haven't heard back from anyone

AISI A-2 is not a bearing steel & would not be used at Rc numbers higher than 62. The steels I mentioned would be considered bearing steels & would be used at Rc numbers above 64. The M-2 & M-42 steels both have high heat hardness with M-42 primarily being used in turbine engine bearings & M-2 primarily being used for high quality wear resistant cutting tools. Both have high shock resistance. 52100 is the steel that is used in most ball bearing applications.

The blanks I mentioned come all ready hardened & ground to size. Cut them off with any abrasive wheel & they are ready to use. They are also very cost effective. Even a short 2" long gage pin blank will make two crank pins in large motors.

Jim Allen

i just used what i had available to me.wasn't going to buy any thing else for i pin

 

[ids987]

Thanks again guys.

Much appreciated.

 

[ids987]

An extreme pressure lubricant such as CMD should be used during pressing operations. http://gallery.intlw...x.php?cat=10141, page 2 Properly made crankshafts that use a properly pressed in crank pin can last forever! Jim Allen

Hi Jim, You learn something every day - as they say. I'd always understood that this kind of pressing should be done dry, because there's no space for the lubricant. In my previous rebuilds (using new - and more recently, used CMB OEM pins), I've just cleaned up, and pressed the pins in dry (pressing methods also distinctly suboptimal - using a vice, carefully, but it seems to have worked ok so far). I've only had one pin failure, and not one I pressed in myself. Probably had more to do with a bent (solid) propshaft. Guess I should invest in some extreme pressure lube though.

Thanks for the gallery link too. I have visited a few times before, but ended up back there again. Truly awesome work, and a staggering level of attention to detail......

 

[Jim Allen]

An extreme pressure lubricant such as CMD should be used during pressing operations. http://gallery.intlw...x.php?cat=10141, page 2 Properly made crankshafts that use a properly pressed in crank pin can last forever! Jim Allen

Hi Jim, You learn something every day - as they say. I'd always understood that this kind of pressing should be done dry, because there's no space for the lubricant. In my previous rebuilds (using new - and more recently, used CMB OEM pins), I've just cleaned up, and pressed the pins in dry (pressing methods also distinctly suboptimal - using a vice, carefully, but it seems to have worked ok so far). I've only had one pin failure, and not one I pressed in myself. Probably had more to do with a bent (solid) propshaft. Guess I should invest in some extreme pressure lube though.

Thanks for the gallery link too. I have visited a few times before, but ended up back there again. Truly awesome work, and a staggering level of attention to detail......

There are many simple things that model boaters can do to improve the realibility & performance of any high performance two cycle engine. The correct application of readily available metallurgy & proper engineering principles can make a significant difference in any two cycle motor. All we need is for engine manufactures to do this before the engine is put on the market!

Jim Allen

 

[Terry Keeley]

Thanks Jim!