Greetings all,
I am just sending my crank out for a big end bearing replacement, received a new assembly via NOC spares scheme. Now I believe the 'new' bearing sleeve (which is pressed into the con rod) should be checked and honed to ensure correct clearance of fit to the new pin / roller assembly, but I have no specifications. As I understand it, old NOS bearings (re 16H vintage and the like) were made with sufficient clearances 'built into' the manufacturing process to fit and forget, but somewhere maybe from Mike Pemberton I believethat the new bearing sleeves once fitted do need a hone otherwise premature big end seizure may occur. I have scoured my library and all I seem to get from a fairly varied source of books, and some vintage publications is "Sent back to the factory / take it to your local dealer!" So any ideas please?
This is urgent as I need to get the monster back together for the Distinguished Gentlemanâs Ride Sunday week!
Regards Steve
No specifics but in genera…
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I got my Model 50 big end…
I got my Model 50 big end from Alpha Bearings but had to send it back (With the rod) because the outer casing was oversized. It would go but too tight.
This bearing assembly was not made specifically for the Model 50. The nut had to be taken down because of its position on the Model 50 flywheel. Not a lot of people know that! (59-63 models in question)
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G'day Steve, I purchased…
G'day Steve, I purchased my Alpha (N3) big end assy from a UK dealer about 10 years ago. When I went to fit it to the rod eye, I found that the outer race was about .003"-.004" bigger than the rod bore. I compared it to what I had pressed out and found it to be definitely too big. There was (I thought), danger of splitting the rod and/or reducing (crush) the outer roller track diameter enough to pinch or jamb the rollers against the pin. Also, there is the additional danger of distorting the rod eye due to there being non uniform metal around the circumference, where the sectionof the rod is formed(which will not stretch compared to the opposite side) which is relatively thin.I had the rod eye skimmed out to allow a crush of around .001" which is amply to hold the outer race in place with minimal distortion. The result is a smooth rotating pinafter I pressed it all up in the rod with no perceivable rock or play. After I pressed up the flywheels, the rod had excellentrotation and now has been back in service for several years.
Martyn Adams could assist.
See you all 'DAPPER" on the 25th. 
Paul.
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Thanks everyone for your a…
Thanks everyone for your assistance. I did warn the engineering shop the ass'y may need to be honed for correct fit, but have added your comments for clarity. Due to Mike Pemberton's excellent singles DVD, I was aware of the bevelled nut situation as the big end ass'y I had recently purchased (actually from the NoC spares scheme, but no complaints) has non-chamfered nuts!
Thank you all anyway.
Rgds Steve.
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No specifics but in general you are looking for a clearance measured in microns, in practise a crude measure is does the big end bearing need to be screwed into the housing, if it does then there is too little clearance. If you can feel any clearance the its too much, you want no detectable clearance but the con rod will rotate under its own weight. Best left to the experts with a precision hone who know the required clearances.