Sdi throttle pots

[Meatball]

Hi are the large round SDI throttle pot sensors still avaiable?
Or is there a convertion to use a hot wire one?

Thanks in advance

[honestjohntoo]

Not available commercially, used to be some cottage industry replacements available, not any more, easy to fit an acceptable substitute using a DIY adaptor plate, there is a do-able and lasting repair, everything you need to know from this link: clicky

[Meatball]

honestjohntoo said:

Not available commercially, used to be some cottage industry replacements available, not any more, easy to fit an acceptable substitute using a DIY adaptor plate, there is a do-able and lasting repair, everything you need to know from this link: clicky

Nice one thanks

[sprevett]

engineer mate of mine is making me one the said adaptor plates on his CNCmilllathetreadlepressthingy. it is feasible that he may be able to produce a quantity if there is demand? He builds steam engines (from scratch) for a living so they would be spot on to the drawing supplied.

[Meatball]

I gave up looking for one in the end and modified the existing sdi pot housing to take the hotwire unit.

[sprevett]

aha...that's clever, how'd ya do it?

[Meatball]

sprevett said:

aha...that's clever, how'd ya do it?

It was quite easy its self explanitry once you seperate the two halfs
Bullet points

Dig out the grub screws to seperate the 2 halfs

Remove all the electrics

Drill a big hole in the top of the SD1 pot, stick hot wire pot in big hole two small electrical screws to hold in place

Cut the spike off the plastic dial

I had an engineer friend make me a metal disc with a slot the same size as the prong on the hotwire pot. (you could drill a line of holes into a 10p)

Stick the metal disc to the plastic dial.

It works a treat.

[sprevett]

hmmm...sounds a bit easier than the adaptor plate conversion...anyone done both who could offer an opinion on which is easiest/works best?

[leorest]

Has anyone fitted one of the RS pots?
Link

[Meatball]

leorest said:

Has anyone fitted one of the RS pots?
Link

I thought about this but if you read between the lines it says it may not give you enough voltage at WOT.

[leorest]

Meatball said:

leorest said:

Has anyone fitted one of the RS pots?
Link

I thought about this but if you read between the lines it says it may not give you enough voltage at WOT.

That's why I asked if anyone has tried it.
Just for comparison - how much does a hotwire throttle pot cost and how easy are they to get hold of?

[honestjohntoo]

Meatball said:

leorest said:

Has anyone fitted one of the RS pots?
Link

I thought about this but if you read between the lines it says it may not give you enough voltage at WOT.

I wrote the article you read earlier and had the RS pot fitted to both my Single and Twin Plenum cars.

The single pleum has moved on to a new owner and was never a problem, The Twin plenum is still with me, going strong since about 1997/8. On my Single Plenum, it failed after a year (4/5000 miles) but I found out it was not hermetically sealed being able to suck filthy engine bay air into the working parts contaminating the carbon track.

This was cured by a simple sticky patch to seal it and a set of thin spacing washers at the rear to inhibit the throttle shaft vacuum getting to the pot innards.

Regarding the top throttle voltage, it actually reaches about 3.7 volts (90/105 degrees-worth, or 86% of the maximum 4.3volts)

At one time, I assumed that the full load enrichment circuits were triggered just shy of 4.3 volts but I have since established that they trigger at 75% of full voltage or about 3.3 volts.

Therfor, there is no loss of full load enrichment function triggered at 3.3 volts and the acceleration enrichment function has always worked as expected.

You can see the modified assembly on a TP here



as compared to the original arrangement here



You can just see the thin spacing washer(s) at the top of the first image assisting the denial of vacuum to the component innards.

Although my images show the Twin Plenum, the drawing of the circular plate is correct for the single plenum engines.

Everything mentioned above is in the referenced article clicky

except that the statement:

However full load fuel enrichment (i.e. throttle wide open) may be denied due to the maximum voltage limitation.

is no longer true for the reasons given, and the PDF has not yet been updated accordingly.

Regarding cost, I was looking at the cost of Hot Wire pots and they seem to be around 90 quid, whereas the RS component is still around twenty quid.

I guess it all depends upon the economics once you are satisfied with the explanations above.

Hope this helps.

Edited by honestjohntoo on Thursday 31st December 23:21

[leorest]

Cheers for that.
If my TP gives problems I'll go for the RS replacement then.

[sprevett]

i have bought the RS item to fit my 350i. Does it also fit into the old casing as per the above mod by meatball? or should I stick with the adapter plate method as described on the pdf article?

[deetes]

On a slightly connected subject. I'm in the process of making up a plenum with a progressive throttle body, however it has no throttle pot mounting at all and I was scratching my head as to where and how to mount one.

[honestjohntoo]

sprevett said:

i have bought the RS item to fit my 350i. Does it also fit into the old casing as per the above mod by meatball? or should I stick with the adapter plate method as described on the pdf article?

If you study the following linked data sheet pdf (which includes the drgs for the item with flying leads):

http://docs-europe.electrocomponents.com/webdocs/0...

one could see how the fixing wings could be cut off the RS pot to see it mounted inside the body of the original Rover item.

Whichever method is chosen, the choice is either to copy an existing proven set of drawings/instructions or to reinvent the wheel.

If the latter, be prepared for some empirical engineering to get it fitting right.

Edited by honestjohntoo on Monday 4th January 20:47

[sprevett]

ok honestjohn, message received and understood....

[Meatball]

honestjohntoo said:

sprevett said:

i have bought the RS item to fit my 350i. Does it also fit into the old casing as per the above mod by meatball? or should I stick with the adapter plate method as described on the pdf article?

If you study the following linked data sheet pdf (which includes the drgs for the item with flying leads):

http://docs-europe.electrocomponents.com/webdocs/0...

one could see how the fixing wings could be cut off the RS pot to see it mounted inside the body of the original Rover item.

Whichever method is chosen, the choice is either to copy an existing proven set of drawings/instructions or to reinvent the wheel.

If the latter, be prepared for some empirical engineering to get it fitting right.

Edited by honestjohntoo on Monday 4th January 20:47

Using the original pot body and sticking a hotwire pot on tops not exactly re inventing the wheel.
You pays your money you make your choice

[sprevett]

ok - adaptor plate made, fitted with new throttle pot from RS and set up. All very straightforward - despite a bit of filing on the plate to stop fouling the water pipe and also some filing on the pot to get an easy fit on the throttle spindle - just needs patience and care to get it spot on. Photos attached for reference - note copper washers between plate and plenum as per recent recommendation. Sadly, new pot has made sod all difference to stumbling/faltering engine so replacing the pot was not required - but hey ho, it's done now.




big thanks to the adaptor's creator - nice job as they say stateside....

Edited by sprevett on Thursday 21st January 20:55