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General => Douglas Motorcycles - General Discussion => Topic started by: Derek on 09 Mar 2005 at 09:03

Title: 1926 EW - bottom end bearings
Post by: Derek on 09 Mar 2005 at 09:03
Dear All
Has anyone had any success in utilizing ball bearing race to replace original roller bearing race for bottom end. I have found SKF 16004 deep groove ball bearing race that is correct dimensions. Basic load ratings are 6 89 (dynamic) and 4 05 (static). fatigue load limit 173 pu and speed rating 17,000 rpm. Though the latter obviously would not be an issue, I have some concern over load bearing of a ball race compared to roller race, noting however that this could be offset by modern materials. I would appreciate any comment or anyones experience. The potential ball bearing race would eliminate the requirement for the spacer rings. If I reuse the roller bearings (with potentially new rollers) I will have to manufacture, harden and grind new spacer rings as .006" clearance I believe is excessive. Thanks for any assistance. best Regards.
Title: 1926 EW - bottom end bearings
Post by: Doug on 10 Mar 2005 at 04:17
Derek,

If you have not seen it, check out this article on the forum about refurbishing these big end bearings.   See here  (http://www.douglasmotorcycles.net/index.php?topic=109.0)

There really is not much difference in modern materials, high chromium bearing steel is pretty much the same then as now chemically.  About the only difference is in purity, most all bearing steel now being vacuum re-melt.  That is assuming Douglas did use chromium bearing steel.  Though the bits and pieces of Douglas engine that I have sent to the laboratory for gas spectrometer testing pretty much indicate Douglas used the quality alloy steels that they claimed in their advertising (particularly the high nickel steels used in crankshafts, connecting rods, and gears.)  Also some gears were in proprietary K.E. steels.  

The info I got off the SKF US website gives 7.28kN dynamic and a ridiculous 38,000 rpm limit!  I have read that racing single engines can develop 9-13kN force on the crankpin.  Racing engine the EW is not, still 7.28 does not sound like enough of an operating margin.  The 42mm o.d. is slightly bigger than the 1.625 i.d. of the EW connecting rod.  You could machine the hardened race out slightly, but pressing a bearing into a sleeve, pressed into the rod is not a great idea.  As mentioned in the article referenced in the link above, the big end eye was prone to stretching and going out of round.  Also it is going to need a bush to fit on the 0.75 diameter crankpin.    And as you know the ball race at 8mm wide is ever so slightly wider than the original, and you will need to shim the inner race each side so the outer race is not pinched between the throws, making it a little wider yet.

I assume what you are calling spacer rings are the inner and outer race for the big end roller bearing.  Besides AISI 52000 chromium bearing steel, I have made these out of AISI D2 air hard chromium tool steel.  Not as good as the proper bearing steel but darn close and easier to work and heat treat in the small bench top non-atmosphere controled furnaces.  

-Doug