General TR Great SU Carb rebuilder instructional Blog.

[GTP1960]

For anyone who is interested in rebuilding their SU's for the first time, Tom Bryant's Blog will be very helpful.
(or at least it is to me)

https://thosbryant.wordpress.com/2014/03/30/su-carburetor-rebuild-h-6/

Though he is not a Triumph guy, he has great pics & step by step instructions, that proved much more user friendly than some of the other sites I visited.

best regards,

 

[TR3driver]

That's an interesting trick, using penetrating Loctite to locate the levers while you drill the shaft. I'll have to try that next time.

Note that all of the hex flats are actually sized for Whitworth wrenches. Probably the equivalents he gives are "close enough", but I prefer to use either the right wrenches, or an adjustable wrench. Much less apt to round those soft brass nuts that way.

If you check the John Twist site, I believe he even shows an example where the domes and pistons were NOT interchangeable. He shows that, by swapping them, the drop rates become very different, and swapping them back makes the rates match.

 

[GTP1960]

Note that all of the hex flats are actually sized for Whitworth wrenches. Probably the equivalents he gives are "close enough", but I prefer to use either the right wrenches, or an adjustable wrench. Much less apt to round those soft brass nuts that way.

thx Randall,

i didn't realize they were whitworth.(13/16 did seem kind of loose)
are there other whitworth's on a 3A?
the space under the carbs is pretty limited (for an adjustable), but I rather make do with an adjustable, rather than pay $50-60 bucks for a combo set I'll rarely use.

 

[Tom Bryant]

That's an interesting trick, using penetrating Loctite to locate the levers while you drill the shaft. I'll have to try that next time.

Note that all of the hex flats are actually sized for Whitworth wrenches. Probably the equivalents he gives are "close enough", but I prefer to use either the right wrenches, or an adjustable wrench. Much less apt to round those soft brass nuts that way.

If you check the John Twist site, I believe he even shows an example where the domes and pistons were NOT interchangeable. He shows that, by swapping them, the drop rates become very different, and swapping them back makes the rates match.

Yes, fasteners on SUs are typically Whitworth sizes. In most cases I have found, and identified in my blog, wrenches that are "close enough". Some are really, really, close, probably closer than the official Whitworth wrench would be. In a few cases, for smaller hex fasteners, I use 6-point sockets that are a bit loose, but not enough so to be in any danger of rounding anything. I believe I don't show any of those in my blog; wouldn't want to suggest anything inappropriate, I guess. There is only one size hex fastener used on SUs for which I was unable to find a suitable "standard" or metric size wrench, so I made my own, also shown in the blog. That fastener measures about 0.525", which is roughly 17/32" or 13.5mm, each of which is 0.531" to the nearest thousandth. Close enough, as the wrench really has to be a smidgen bigger than the fastener.

I measured several of the original Whitworth brass "nuts" used on Type HS carburetor jet tubes and found them to all be about 0.445" across. The new replacement jets that I purchase from Joe Curto come with nuts that measure 0.437" across. So, although the originals were Whitworth, the replacements are actually 7/16" (0.4375"). Fortunately, I have a slightly oversize 7/16" combination wrench, measuring 0.450" across (It came that way from the factory.) that fits both the original Whitworth nuts and the 7/16" replacement nuts, with no significant looseness on either.

I measured several of the jet adjustment nuts used on Type H and Type HS carbs and obtained values from 0.598" to 0.604". My "official" Whitworth jet adjustment wrench (a short and thin thing, like those available in kits from Moss motors, etc.) measures from 0.610" at the root of the flats to 0.650" at the tip of the flats. Yes, it's stretched out a bit. But it fits well enough and works well enough for the purpose intended. The "close enough" standard size wrench is 5/8", or 0.625", which means that it actually fits better than my "official" Whitworth wrench does.

Then there are a whole slew of hex fasteners that I measured from 0.815" to 0.825". Those are in places such as:
Banjo bolts on fuel lines.
Type H jet bearing nuts.
Brass "nuts" at the top of the dashpots, primarily on Type H carbs.

My 13/16" (0.8125") combination wrench fits all of these "perfectly", even the ones that measure a bit bigger than the official size of that 13/16" wrench. So, if your 13/16" wrench is a bit loose, Guy, you probably should check to see just how big that wrench measures; it's probably a bit larger than it should be.

The jet bearing nut on Type HS carburetors measures from 0.707" to 0.710", so the 18mm (0.709") wrench that I recommend in my blog fits that pretty darn near perfectly, also. If anything, it might be a smidgen small for the job, but I've never encountered an instance where it didn't work after a bit of smoothing out of any burrs on the nut.

As for adjustable wrenches, well, I don't own any. My daddy, an old Maine farmer who didn't like skinned knuckles, taught me better.

Regards,

Tom

 

[TR3driver]

thx Randall,

i didn't realize they were whitworth.(13/16 did seem kind of loose)
are there other whitworth's on a 3A?
the space under the carbs is pretty limited (for an adjustable), but I rather make do with an adjustable, rather than pay $50-60 bucks for a combo set I'll rarely use.

Sorry to be so slow to respond. Yes, there are a few other places, mostly on electrical equipment. For example, the nuts that attach cables to the starter solenoid and starter motor are Whitworth sizes.

BTW, the "SU Tool Kit" still available from some sources has a cute little wrench that fits the mixture nuts on H6 carbs (and maybe HS6), but is small enough to fit under the choke return spring.

 

[2liter4cyl]

May I add to the 13/16 wrench needed to fit the jet ass'y , I found that dropping the whole unit into a spark plug wrench socket only, alignment and fitting up is quick and easy without removing other parts. A ratchet wrench if wanted can then snug up properly. The 6 point socket does little harm like a 12 point might.

LeT