These are the inner bearing spacer(s) that fits between the two driveside main bearings on M30/M40 magnesium crankcase pre-Featherbed crankcases - they are used to provide the correct width between driveside ball and roller inner races - but this should always be checked on assembly, as their were minor variations over the years - as well as many orginal engines over the years having had small modifications or repairs carried out, requiring different width spacers to be fitted.
These spacers are machined from high tensile EN24 steel and CNC machined
Rather than a single piece spacer, I had two slimmer spacers made for this model - if fitted to standard magnesium M30 crankcases they both need to be fitted alongside each other. I made them as a pair, with a view that it may be possible to remove and possibly fit the wider International crank, although I have not tried this yet and cannot confirm conrod will line up in that configuration. Therefore they are sold to be fitted as a pair, with a view to them being used with magnesium SOHC (racing type) crankcases and the corresponding (slimmer) M30/M40/pre-Featherbed Manx crank (which has less width than a Mod30/40/CS1/CSJ crank).
SOHC engines can be found fitted with both lipped and non-lipped roller bearings on the innermost drive side bearing. As the SOHC engine had its crankshaft 'locked' to the Timing side bearing (because of the bevel gears on that side), a small amount of 'float' on the roller bearing on the drive side is acceptable.
This inner bearing spacer fits between the roller and ball type drive side bearings - and when fitted in conjunction with item 0656 (outer spacer) should give approximately 15 thou of clearance on the lip if a 'Lipped Roller Bearing' is fitted. Likewise if a non - lipped roller bearing is fitted, the rollers should run relaively central to the outer track. However, it is essential when assembling an engine with these spacers for the first time to confirm this is the case - as the engine was manufacutred for many years and there can be slight variations (or modifications made by subsequent owners. Added to this - with any racing engine, years of use and rebuilds can mean they have had modifications made - so it is important to check for yourself these will give correct spacing and running clearance for your engine.
When assembling - I normally aim for approx 10-15 thou of side clearance between the driveside of the flywheel and main bearings, and for the roller bearing to be running close to central (and of course the inner part of the roller bearing will have a small amount of 'float'.
If you assemble the engine crank and bearings into the crankcases and it 'locks up' as the engine bolts are tightened - you may have 'negative' clearance', and not sufficient clearance on the drive side mainshaft. If so - one of the inner spacers may need to be slimmed