Oil Tap with Cutout Switch - FAQ
- Andy Marks
- Apr 13
- 4 min read
This page answers the most common questions about our oil tap with cutout switch, designed to prevent wet sumping on classic motorcycles. It covers how the tap works, how to fit and wire it, and what you need to install one on your bike.
How does the Oil Tap with Cutout Switch work?
Our Oil Tap with Cutout Switch can be connected to bikes with magneto or coil ignition. They ensure that, if the oil tap is 'off', the switch will stop any sparks and the engine cannot be started until the oil is switched on.
How big are they?
Full dimensions, thread details and bore sizes can be found here.
Do I need to worry about the hosetails restricting oil flow?
In a word – no. Take a look at what your rubber pipes are currently pushed onto at each end of the line - these will have a smaller ID than the rubber pipe itself. The hosetails won’t add any further restriction to the feed than is already caused by these in the original design.
What if the oil drains through the pump while the tap is off and causes an air lock or vacuum?
If your oil fittings are all air tight (they should be) the oil won’t drain away from the tap as there is nowhere for the air to get in and replace it - the vacuum effect works in your favour here. If there is a leak, and an air bubble appears, there is nothing to worry about anyway.
Pumps are not typically designed to suck oil through anyway. Oil is fed to the pump by gravity from where it is pushed around the engine under pressure. If the oil does drain away from the tap, as soon as you turn the tap on the lower part of the pipe will refill with oil under gravity. If you think about it, if the oil pump allows oil through when it's not moving, it will definitely allow air through.
What size/type of oil tap do you recommend for my bike?
I’m afraid I can’t help much with application. Each bike is so different I’m unable to offer much help on this front. Take a look at the previously mentioned page on sizes and make a decision from there.
The first thing to look at is the size of your existing oil pipes and decide whether you need the ¼ or 3/8BSP version. The 3/8 taps have a 2mm larger bore so will flow more oil.
How do I fit the oil tap into the oil line on my bike?
As above, it is very hard for me to help you on this one. If you have any questions about a specific bike please Contact Us and I’ll do my best to help.
How do I wire the oil tap into my ignition system?
The wiring is simple and depends on the type of ignition system fitted to your bike. The same tap can be used for bikes with either coil ignition or a magneto. The tap comes with three terminals, only two of which are used depending on which type of ignition your bike has.
On bikes fitted with coil ignition
On a bike fitted with coil ignition, the tap is wired into the power supply to the coil. You need to remove the existing wire between the ignition switch and the coil, then replace it with one which goes via the oil tap. By wiring the oil tap in series with the ignition switch, both need to be turned on for power to get to the coil and produce a spark.
On bikes with a magneto
On a magneto equipped bike, the ignition is cut out by earthing the points. A wire needs to be run from the cutout terminal on the magneto to the tap. When the tap is switched off, the points are connected to earth and the magneto will not produce a spark. The tap itself needs to be earthed for this to work. If it is fitted in a rubber hose for example, a separate wire can be run to a convenient earthing point on the chassis or engine.
Some single cylinder magnetos are not fitted with cutouts as standard – for this reason we offer a range of points caps for the more common types of motorcycle magneto which allow a cutout switch, and our oil taps, to be used. Please click on the image to see the full range.
Every oil tap is supplied with a comprehensive set of fitting instructions, if you’d like to see these before buying, they can be found here.
What else do I need to be able to fit one?
As well as potentially needing a new points cap for your magneto, as described in the previous question. You’ll usually need some extra pipe fittings. We sell a lot of hosetails with the oil taps. For the Norton singles our tank fittings are very popular and make fitting a tap very easy and tidy.
Does the oil have to flow a certain way through the tap?
Nope. The oil tap can be fitted either way round to suit your bike and the available space. So although we sell a Male-Female tap, this does not dictate the direction in which the oil must flow.
What’s wrong with a standard ball valve from eBay for £3.50?
Nothing – as long as you never forget to turn it on! What does an engine rebuild cost these days?
The difference is that our tap prevents the engine from starting if the oil is switched off.
My Japanese/American/French/German/Italian bike doesn’t use BSP threads, do you sell a tap for that?
A Japanese bike that wet sumps? Never heard of such a thing! Joking aside, this is predominantly an issue with British bikes so we only sell the taps with British threads. We have sold a couple to Harley owners and they were able to buy adaptors (elsewhere) to make it work.
How do I buy one?
Simple! You can view full details and purchase one here.
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