Hitchcocks Forum

This subject comes up for discussion here from time to time. Mystery seems to surround the operation of the push and turn oil filler cap, with its ‘two positions’. A plethora of theories have been floated, some of which always seemed a bit bizarre. It’s been said the Redditch factory said nothing on the subject. But a bit of of information on this subject can be found in the Redditch Owners' Instruction Books. Under the heading ‘Operation of the Motor Cycle’ we read, ‘Oil Filler … operates the same way as petrol filler.’ Under Petrol Filler the book says: ‘To open, turn to left till catch is felt, push down and turn again to left as far as possible, then lift off. To close, push down and turn to right as far as possible.’



The factory explanation clearly implies the ‘first position’ is a safety feature, to prevent the caps falling off unintentionally. The ‘second position’, ‘as far right as possible’, is the regular closed position, for both petrol caps and oil caps of this design.



The interesting bit here is that it was, after all, the factory that gave the definitive answer, in the Instruction Books.

Very true Presto, we have had this silly myth reoccurring on here many times, most makes of old Brit bikes use this method and as you say should be fully closed.

The factory "Fatwa" would be correct; however, experience over time by many riders, including me, has found that loosening the cap to the second position will lower crankcase pressure and reduce oil consumption. A system which proved correct on my Bullet.

The cap was intended to be fully tight, it's quite clear in the original instruction book. However, I've always used the loose position, as Leon says, it does appear to reduce consumption.

I will throw this into the ring - I always fasten the oil filler caps tight, this is the correct way and there is no 'transport position' or anything else to explain a reason for not doing so. However, I have noticed some filler caps have a small vent hole, while others don't - maybe this applies to some models and not others, or maybe it was a design change at some point, I don't know, but the two types are definitely out there! Regards, Paul.

Yes, Paul's right, the early "vent hole" cap was fitted to pre-56 Bullets and Twins. It's a tiny hole (1/64th?) but it makes a huge difference. When I built my 1953 500 Bullet I fitted a non-hole cap (not knowing any better) and it pissed oil out of the timing chest mag drive seal, which on these is a felt and shim sandwich rather than the later neoprene type. I couldn't work out why until I remembered an article in The Gun which mentioned this. Swapped over and leak fixed. I've deliberately put one on my 1966 Interceptor and it helps to reduce sweaty joints (rocker covers, barrel base) to almost nil. Mind you, I nicked it off the Ebay Bullet so I'll have to find another one!

REgards, Mark

Where is the 'vent hole' on 56 on Bullets Mark?

The filler cap vent hole is a vertical hole in the centre of the cap itself, had one on my '94 bullet.

Ric, I meant where is the vent hole on engines with no vent hole in the filler cap.

Hi Chris: To answer your query, click here, I also saves my from typing.
http://www.motorcyclecruiser.com/unders ... le-engines