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BT7 fuel pump

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davidb

davidb

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Evening gents

I'm sure this topic has been kicked around but I can't seem to find specifics in the Search feature. I'm considering renewing my old fuel pump which has to occasionally be "encouraged" with a blunt object (baseball bat, crowbar, large rock) to get it ticking, after winter storage. Is it easier to rebuild an older pump with new points, etc, or replace it with a solid state, or an OEM type? If I decide to re-build the old one, how difficult is it? Also, can you you pretty well use a pump from most models (other than perhaps the very early 100-4s), and are the required pressures similar?

As usual, any of your experiences would be welcome. Always learning from the pros on this website.

With thanks
Dave
 
You can get electronic conversions for the original pumps which retain the original look and also still make a ticking sound while offering reliability, or you can go for a more modern pump which will obviously need adaptation of the mountings and pipe work. Or of course you could just rebuild as is, it's not a difficult job to rebuild.
 
Burlens Fuel Systems sell electronic kits if you are good with a screwdriver https://www.sucarb.co.uk/ProductCategory.aspx?ParentId=16

Their website is a bit of a shambles but they respond to emails quickly.

You can probably get a diaphragm kit and electronic conversion kit to make your original one go again, or jut get a whole new pump. They are remanufacturing using the original SU tooling.

Andy.
 
Hi Dave,

Although you can convert to a transistorized trigger, replacing your points with the inclusion of a TSV will not only extend the longevity of your points indefinitely, but will be, by far, the most economical approach you can take. Additionally, if you experience a failure in a transistorized SU, there is no way of reviving it as you have done.

I would first take a look at your present points to see if they can’t be saved by redressing. Since most points failures occurring after a winter’s hibernation are the result of tungsten oxidation, they can be recovered by simply cleaning. If new points are required, they are easily installed (https://www.mossmotors.com/forum/forums/thread/5665.aspx) and adjusted. In either case, I would eliminate any diode or other components attached to the points and install a Transient-Voltage Suppression (TVS) diode.

Since it is common for as much as 200 Volts to build and pass across the points, it is not hard to imagine this build-up as the cause for point flash and burn. SU has attempted to diminish this excessive voltage through the application of a number different diodes, however, their attempts have only met with marginal success and have imposed a Polarity requirement on our pumps. Keeping the voltage below 30 Volts and well within the tolerances of the tungsten points is the primary requirement for extending point and pump longevity but such a component has only come into being within the last decade.

The TVS is designed to shunt excessive power to ground. Since voltage build-up on pump points can approach 200 Volts and cause point burn and flash, this unit can keep that voltage down below 30 Volts (component selectable) when an appropriately selected TVS is applied. The result, no flash or burn as power across the points will remain well within the limits of the tungsten points yet sufficient to burn off the oxidation after a long rest.

TVS Specification: https://www.digikey.com/product-detail/en/P6KE20CA/P6KE20CALFCT-ND/285933

My choice of a P6KE20CA TVS (manufactured by Vishay), at a cost of around $ 1.50 (including shipping), was made to have a TVS that would pass power below 21 volts and safely allow the pump to operate even if the regulator creates an overcharge situation (could happen). The TVS will react at millisecond speeds to impose a clamping (ground-shunt) voltage at 27 volts to eliminate point flash-and-burn, before automatically resetting for the next points cycle.

The TSV is applied between the top points contact and ground by easily twisting around the mounting screws or by soldering end connectors. Keep in mind that this is a diode and must be installed in one direction. The ground end is sometimes indicated by an arrow but also may be indicated by writing on the component being read from the ground end.

The cost and longevity of a points/TVS trigger on the SU pump has made it difficult for me to justify changing to a transistorized trigger. One last benefit, a points/TSV combination is NOT Sensitive to Polarity.

Hope this helps,
Ray (64BJ8P1)
 
one last benefit, a points/TSV combination is NOT Sensitive to Polarity.

No if the polarity of the car changes the "TVS" will have to be reversed or it will burn out.--Fwiw--Keoke
 
As I understand, the Polarity of the TVS referenced is stated as Bi-Directional. As I'm aware, this means the component is NOT POLARITY Sensitive but handles voltages above or below the reference.

I was mistaken in my reference to how to identify the negative side of the TVS diode as I was referencing the indicators of a unidirectional unit which has polarity. A bi-directional polarity TVS will have no ground indicator as it is not polarity sensitive.

Keoke, I am not expert in the space of electronics and would appreciate any correction or clarification.

Thank you and all the best,
Ray (64BJ8P1)
 
I replaced the original square body pump with an electronic pump for a late model BJ8. They are a lot cheaper than a new square body pump. All I had to do was take the fittings and mounting studs from the old pump and install them on the new pump. It fits perfectly on the old mounting plate and there is no fiddling with the fuel line fittings. The only down side is that it is polarity sensitive. Since I am changing to a negative ground this is not a problem. If you think you may go to an alternator and negative ground in the future just put new points and diaphram in the old pump. It's not that big a deal. A capacitor across the points will extend the life of the points but it will run a long time without it. I ran my original pump for almost 20 years and replaced the points a couple of time as a preventative measure. The fuel pump was one of the few things I never had a problem with.
 
My thanks to all of you who took the time and care to provide your helpful experience/advice/web sources on fuel pump rebuilding/replacement.

Nice to have some options.

Richard - good to know that a BJ8 pump will work and will fit, because you're right they're much cheaper than the square body type on the BT7.

Cheers to all.

Dave
 
Hi Dave,

Yes, you can replace your square pump without any problem. Either way, I would install new points and the TVS in your square body pump and keep it just in case. It is inexpensive insurance and a very good pump.

Ray (64BJ8P1)
 
Hi Ray (RAC68)

Thank you for both your initial and follow up comment. I wasn't aware of the TVS diode. Electronics are a definite achilles heel with me, but having viewed the website you referenced, I will incorporate your suggestion if I go with a rebuild kit. Much obliged. Comments like yours are likely helpful to others as well. The collective wisdom of this website is staggering. Wish I'd had this resource 31 years ago when I dragged home the British mutt that still graces my garage.

Regards
Dave
 
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