Re-bushing SU carburettor bodies

[uphill racer]

Does anyone have any suggestions re re-bushing SU bodies?

A friend in my workshop community has a handful (3x HS4 and 2x HS6) that all apparently need new bushes for the throttle spindle. Apparently Burlen in Salisbury quoted about £60 per carb, and being a bit "short arms and long pockets" he's whining a bit (well, a lot actually).

So I said I'd ask around... To be honest £60 doesn't sound like a bad deal, but when you have five to do (they are alternate set-ups for his TVR Grantura project, and he wants to have both sets complete) I guess it adds up

Many thanks in anticipation.

[tony g]

I would be tempted to buy new bushes which I presume will be slightly oversize and ask a good engineer to ream out the bodies to accept the new bushes. Set up time on the miller is key I suppose but i wonder if 2 carbs were bolted together flange to flange if the spindle holes would be parallel, in which case 2 carbs could be machined on one set up ?

Tony

[Galileo]

When you consider that you can't just drill through but drill in to just before the venturi, on both sides, and be in absolute perfect alignment afterwards, it doesn't seem such an outrageous charge!

There's this seller on ebay who cuts a groove in the spindle and put in an O ring, I like the thinking but I'm not sure in practice.
https://www.ebay.co.uk/sch/wem19520/m.h ... 7675.l2562

I guess the cheapest way is to ream slightly larger and fit an oversized spindle?

[tony g]

Yes youre right! i was thinking of a through hole doh O rings could be a cure I'd like to try it. It wouldnt be so critical on concentricity.



Tony

[Magenta Auto Sprint]

I cant remember the SU spindle arrangement but when I did some strombergs I mounted them on a angle plate, squared up off the diaphram face and reamed both holes through in one go to ensure they were in line and I would think that this would also be how SU make them.

malcolm

[uphill racer]

Many thanks for the replies so far - TBH (as per my OP) I didn't think £60 was a bad price either!

As already noted, the original bushes, once pressed in, are machined to follow the shape of the throttle chamber (which is circular of course) - so replacement bushes go only "almost" all the way in.

I like the O ring idea, you would need to re-ream the existing bushes pretty accurately - but in the workshop we have a slightly odd bloke who runs a bespoke fabrication shop, he could surely ream the bushes out and machine recesses for O rings

Thanks again chaps

And to anyone else with any other ideas, do please chuck them in...

[Emerald Sprint]

Recently stumbled on this excellent blog post where a SU HS6 rebuild is shown in detail, including drilling and honing the bodies in preparation of rebushing.
The writer -who does this for a living- rebushes them with Delrin, a Dupont made plastic, and states that in 20 years he never got complaints about wear. It also reduces the risk of splitting the body should a metal insert be just too large. There's also a reply of someone using Acetal, fwiw.

With that number of carburetters (or is it carburettors?) to do, it might be worth investing in some tools.

[soe8m]

I like the O ring idea, you would need to re-ream the existing bushes pretty accurately - but in the workshop we have a slightly odd bloke who runs a bespoke fabrication shop, he could surely ream the bushes out and machine recesses for O rings

Thanks again chaps

And to anyone else with any other ideas, do please chuck them in...

O rings are a bodge repair. Painted duct tape over a rusthole.

Rebushing is the only right way. 60 gbp when it's done right is a good price.

Jeroen

[GTS290N]

I do like the Delrin idea, there may be even better alternatives to Delrin these days.

[Magenta Auto Sprint]

it is not just the carburrettor body that wears but the spindle too.

so Moss sell oversized throttle spindles, no need to bush the body, just ream them out and fit oversized spindles.

https://www.moss-europe.co.uk/oversized ... ttors.html

Malcolm

[GTS290N]

Suddenly £60 looks a bargain!

[Tom Bryant]

Recently stumbled on this excellent blog post where a SU HS6 rebuild is shown in detail, including drilling and honing the bodies in preparation of rebushing.
The writer -who does this for a living- rebushes them with Delrin, a Dupont made plastic, and states that in 20 years he never got complaints about wear. It also reduces the risk of splitting the body should a metal insert be just too large. There's also a reply of someone using Acetal, fwiw.

With that number of carburetters (or is it carburettors?) to do, it might be worth investing in some tools.

Thanks for the kind words. A few comments:

1. I don't do this for a living; if I did I'd starve. I'm retired, living on my pension. Since I don't need income, I freely share my "secrets", and my blog posts are intended to teach people how to do a job themselves.

2. In my opinion o-rings are not a good idea. You need to replace the shafts and the bushings themselves to provide secure centering of the shaft so that the throttle plate will close reliably and at a consistent idle speed. O-rings would be quite difficult to install, don't generally perform well in unlubricated, rotating, service, and frankly, would not provide any benefits that are not to be more easily obtained with a good-fitting, long-lasting Delrin bushing.

3. It sounds as if the people in this forum are very capable, and some of you should be able to do this type of work. But it does require considerable setup expense, so if you have only a few to do, it's more cost effective to hire it done. Burlen's price of 60 British pounds per carburetor is reasonable. I'm currently charging $125.00 US per pair, or roughly 45 British pounds per carburetor, but because of the expense of trans-Atlantic shipment, it's probably not cost effective to send them to me.

4. Although Burlen's price is reasonable, they're simply not using the best and longest-lasting material for the job. Delrin is that best material.

5. I would be happy to assist any of you in getting set up to do this job yourself; to that end you may contact me with any questions you may have. My contact information is shown on my "About" page:
https://thosbryant.wordpress.com/about/

Tom Bryant

[tony g]

Welcome Tom and thanks for the input

Tony

[soe8m]

You could send an email to info@bccp.nl. I do not know what the normal retail price is for rebushing but you can ask. Hans does it for 25 years now and has the right alignment tools etc. He did teach burlen at the time. From my own experience they do last at least +150.000km.

Jeroen

[tony g]

https://www.directplastics.co.uk/acetal-rod

Tony