I have had the oil pumps on my Model 50 & Dommi 99 both refurbished by RGM however, the relative performance seems very different. I am basing my judgement purely on the visual evidence of the flow of oil returned to the tank with the engine ticking over. The Model 50 return is by far the stronger !
Is this purely a matter of the individual oil pumps performing differently, or could there be something else amiss on the Dominator ? Both engines have been completely rebuilt in terms of big ends, mains, piston & seals. Does the pump rotate more slowly on the ticking over Dommi ?
Are the pumps interchangeable ? Such a switch should prove whether or not the pump on the Dommi is suspect.
As the Dommi is likely to get more and harder use than the Model 50 should I consider a new pump ? Is it possible to fit a Commando pump without re-working anything ? If so, is it of sufficient benefit to justify the expense ?
Mike
Get Some Gears
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The Model 50 has a roller…
The Model 50 has a roller big end, this provides no resistance to the oil flow and so no oil pressure builds up. The twin has shell big ends with a 1 thou clearance which resists oil flow and so you can measure the oil pressure which is a function of the resistance. The higher resistance reduces the oil flow but you need the pressure more than the flow. On engine types where the 2 types of big end bearing are fitted the feed gears on the roller big end are narrower to reduce the flow, fit the shell bearing wider geared pump and you risk over oiling the piston and rings and a smokey exhaust.
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Interchangeable ?
Aren't the pumps handed differently for singles and twins ?
These three are 850 Mk3 Commando, 750 Commando and 1936 pattern side / OHV
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Swapping pumps may not be way to go ....
It sounds as if, assuming the information suggesting the pumps are different depending on the type of big end bearing being fed, I shouldn't swap over. Not sure about the 'handed' issue - will need to have a look.
Mike
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The return gears on the singles oil pump are 30% wider than those on a pre-1960 99 Twin. Assuming that is what you have. I would guess that many owners reading this thread are eagerly waiting to see the outcome of you switching the respective pumps over.