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Timing cover external ‘ports’

Submitted by tony_wood on Sun, 20/12/2020
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Heavy Twins

Hi. I hope to fit a later style timing cover to my 1960 Dommie 99. The only thing is I’m unsure about the two external threaded ports (photo below). They are both threaded - there’s one large diameter hole and one smaller diameter hole. I know that the larger one is for the oil pressure relief valve, but what goes in the smaller hole? Is it just a blanking plug with a sealing washer or does something special go in there?

Thanks

Regards

Tony

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Submitted by john_holmes on Sun, 20/12/2020

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It's for the high pressure feed to the rockers, assuming your rockers are currently fed from the low pressure return it can be blanked off with a suitable bolt and sealing washer.

Submitted by tony_wood on Sun, 20/12/2020

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Thanks John. I hadn’t thought about the rocker feed. As my rocker feed is low pressure from the oil tank return pipe I’ll blank it off. Alternatively, as it’s high pressure, would it be a suitable place to use as the connection for an oil pressure gauge? I like to have oil pressure  gauges on my bikes. It’s easy to do on unit Triumphs but I’ve not worked out how to do it simply on a Dommie. Regards 

Tony

Submitted by tony_wood on Mon, 21/12/2020

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Thanks John. Does the oil pressure get really low? On my 60’s Bonneville the lowest oil pressure I get on tickover is around 20psi with hot oil and at 4000rpm with hot oil the lowest it goes is about 60psi. Do Nortons have much lower oil pressures than that? At what point should ‘pressure panic’ set in on a Norton Dommie? Regards

Tony

Submitted by john_holmes on Mon, 21/12/2020

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You have the 3 start pump gears not the later 6 start so half the flow of oil (ignoring the oil going to the rockers), the issue is at high revs with thin oil then the centripetal force applied by the spinning crank at the big end pulls at the oil in the middle of the crank and the pump can't keep up and hence the gauge reduces the pressure it is seeing. But the big end is seeing pressure due to the centripetal forces so it's fine. So fit the gauge and look at what it tells you, at lower revs and cooler oil the pressures at that point are the ones to worry about. 

Submitted by tim_stockdale on Mon, 21/12/2020

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Hi Tony

Don't be tempted by a cheap gauge

I've just had 2 workshop gauges go faulty, easy to shut the engine down, not easy

If you are tooling along a road and lose your oil

 


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