The main bearing problems were primarily with a single engine the high-compression Combat which was produced mainly, or only, during the 1972 calendar year.
In fact, premature failure of the main bearings had been a problem even before the introduction of the Combat engined models, as the bearings were first upgraded around October 1971.
Early in the year Norton switched over to producing all high-compression engines.
Not "all", as Commandos with standard spec. engines were still produced during the Combat period.
During the same year Norton reduced compression on their other engines to 8.5:1 to meet NOx emissions requirements like everybody else. These low-compression engines did not produce sufficent torque to require the special bearing and normal, cheaper bearings were then fitted.
After Combat production ceased (around August 1972) two "standard" engine versions became available for late '72 and for '73, with different 32mm carb. cylinder heads giving "High compression" (up to 9.6:1 CR depending on gasket arrangement) or "Low compression" (up to 9.2:1 CR dependant on gaskets) but without the Combat camshaft
therefore the compression ratio was not significantly reduced and it would have been neither sensible nor logical to fit lower spec. bearings to any post-211891 750 engine, and after the serious lesson they'd learnt-it seems highly unlikely that the factory would have been foolhardy enough to do such a thing.
A representative of R&M has told me that the FAG bearing is the equivalent of a normal MRJA30 but not of the special 6/MRJA30.
Unless your Commando engine is a high-compression one the special bearing is not needed and the FAG will do.
The standard replacement bearing for all models from early 1973 (Service Release N2/10) was the "extra high capacity
" (FAG) bearing, "A new main bearing capable of carrying a much higher load than any offered before, has been introduced."
and; "the new bearing, part number 064118[FAG] supersedes the old type 063906[6/MRJA30]...."
The 064118 FAG306E still being the standard replacement main bearing supplied by Andover Norton today.
Well I'm no bearing expert but I expect the folks at R&M are. Here is what they wrote to me a few days ago:
The original R&M (Ransome & Marles) ceased to exist after 1969 when the company merged with Hoffman and Pollard!http://en.wikipedia.org/wiki/Chelmsford"The firm [Hoffman] became Ransome Hoffmann and Pollard (RHP) after an amalgamation with the Ransome and Marles Bearing Company together with the Pollard Ball and Roller Bearing Company in 1969. The factory that once employed 7500 employees over 50 acres in its heyday was wound down during the 1980s and finally closing for good on 23 December 1989.
The company assets and name were absorbed into the Japanese NSK Ltd bearing company in early 1990 trading as NSK-RHP Ltd. at its UK base in Newark on Trent with the historic R.H.P name finally disappearing in 2001."
It would seem the name "Ransome & Marles" is actually being used by: "The Orinoco Bearing Co." of Leeds, which appears to be a shed on a Leeds trading estate! http://www.ransomeandmarles.co.uk/
+44 (0)113 263 1919.http://www.orinocobearings.co.uk/contact.html
+44(0)113 263 1919
The name 'Ransome & Marles Bearing Co. Ltd.' is still retained by NSK, R&M as a company having been dormant for some time.http://companycheck.co.uk/company/02270163