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Triumph TR6 - Hole in Intake Manifold?

Another dumb question...I've noted a threaded hole with a bolt screwed into it adjancent to the rear carburetor in the intake manifold on my 71 TR-6. Thinking it to be a bracket attachment point or that a vacuum hose might ought to go there that had been disconnected, I went to my British Leyland Parts Catalogue to ascertain the function of that "port." No luck. The parts catalogue does not show the hole in the manifold nor is it annotated in any of the supplier catalogues I have (Rimmer Bros, Restorations, MOSS, Victoria, TRF, LBC etc). The hole is immediately to the engine side of the rear carburetor and in line with the damper assembly, that is, about 90 degrees to a longtitudial line through the carborators front to rear just at the damper assembly. Would someone kindly enlighten me as to the intended function of this hole and whether a blanking plug should be there for the 71 TR or is some hookup missing. Thanks.
db
D R Baker

DB--That head port is for the EGR system when installed. I have no EGR system, so I simply plugged it with a recessed hex bolt.

Rick O.
72 TR-6
Rick Orthen

Forget last post; I have no idea why a port would exist on the intake manifold at the location you describe. I presume you're not referring to the port that your brake booster servo hose attaches to.

Rick O.
Rick Orthen

Rick,
Thanks for the response. The brake servo hose is ported amidship on the manifold just about between the carburetors. In my BL parts catalogue is a "Plug Core, Inlet Manifold", part number 46172, (Plate E, page 15) which APPEARS to be in or near the location of interest for this mystery port. In the Victoria TR-6 Catalog, there is a "core, plug", part number 12-5130, which is similar in appearance and location to the BL book. In MOSS's catalogue, what appears to be the same part is labeled, "clamp, water hose." So I don't have a clue as to what was intended by this port. I suspect that it had some vestige function, not used on the 71, but have not yet discovered what that might be or have been. Rick Crawford or Roger H., y'all have any ideas?
db
D R Baker

Hi Doug

I think Rick O is on the money.

The brake booster take-off and the EGR take off are possibly interchanged on your car.

Reference to the water clamp could only be a stray goose (!) referring to the water heating pipe which runs longitudinally through the bottom of the manifold on some of the carburetted models - (I have noticed a few errors in part number listings which only serves to confuse the confused even more!)

(PS - check your mail)

R
Roger H

PPS Try to get hold of The Roadster Factory Catalogues (2x) as well - I find them about the best for my failing eyesight!!
Roger H

A 1971 NA spec TR6 would not have an EGR valve. It would be a narrow port head and manifold set up. The only NA spec TRGs with EGR valves were on the later, lower compression, wide port spacing heads. The only possible explanation if it was an EGR take off on a 1971 NA spec TR6 would be that someone had been playing around with some part swapping. Hopefully if that is the case, they have a matching head and manifold in place.

Based on the description and location, it sounds like it is the rear one of the two welch plugs at either end of the gun drilled protion of the manifold that is used as a balance pipe and brake servo vacumm port take off on the early manifolds. Of course, this is operating on the assumption that no one has played around with any part swapping.
SteveP

Hey guys,
The mystery is somewhat solved and deepens...:) I was mistaken; the hole is NOT IN THE MANIFOLD...it's in the carburetor!! It appears to be about a 5/16" tapped/fine threaded hole into the boss on the side of the rear carburetor, about 7/16-1/2" deep just shy of the manifold attachment. It appears to only be drilled into the housing and not through into some working part of the carburetor although I did not inspect thoroughly enough late last night to clearly determine this. This suggests a bracket mounting for something, not clear to me. The carburetor is a Stromberg 175 stock item for the the Spec NA 71 TR-6. The front Carb does not have the same hole! BTW, there are spacers between the manifold and the carburetors each about 1/2" thick. Is this standard?

Any more ideas on the function of the hole??
db
D R Baker

Ahh, mystery solved. That port is blind so don't worry about it. On later year TR6's (starting in '74 I believe), that port was tapped to provide manifold depression to who knows what. The spacers are there to insulate the carbs from conductive heat transfer from the intake manifold. Hot carbs are not good for smooth running or emissions control.

Rick O.
Rick Orthen

Doug, I was going to tell you I have a 71 and would check, but I have SU carbs.

John
JL Bryan

That port supplied vacuum to the vacuum advance capsule on the distributor on the first generation TR6 (1969).

Rick O.
Rick Orthen

Rick Orthen's answer fits. Following Roger Hearne's advice, TRF's catalogue (Vol 1...don't have Vol 2), page 61 in the carburettor Identificication Checklist, states...:
"The will be no vacuum fitting on top of the inner mounting flange, as there are not vacuum advance units on the distributors fitted to this model range; if you find a threaded hole in that position, it will not be drilled through into the throttle passage, and you can plug it or leave it unplugged as you wish."

Neither of my carbs had the metal ID tag affixed, so I'm not sure if they are original (stock) or transplants from other models. Anyway, mystery solved, although, the comment about no vacuum on the distributor puzzles me since my distributor does have what appears to be a vacuum advance module although, the hose that would attach it to a vacumm source is not there and only a short (1 1/2") ninty degree hose fitting is attached at the distributor end. Unfortunately TRF's Vol 2 first page starts with the distributor. Hope that they republish soon.

Thanks to all for comments. Anyone know a source for a blanking plug for this hole. The bolt there now fits, but it's about 3" long.
db
D R Baker

db--Is the capsule on your distributor facing the scuttle? If so, it's a retard unit that takes vacuum ported from beneath the rear carb. No problem if that's not hooked up as long as the rear carb port is capped.

As far as the plug for the hole in the intake manifold, it's likely threaded for a NPT fitting. Go to your favorite hardware store and buy a few of different sizes.

Rick O.
Rick Orthen

Rick,
Indeed the distributor module faces the scuttle. Thanks for the tip. I'll check the port on the carb and either make sure it's blanked or attach a suitable hose to the distributor. Since I eventually plan to install some version of electronic ignition, I suppose that the retard not working will be of no consequence. I'll check for shorter bolts for the hole. I probably have a size that'll fit nicely in my bolt/screw/nut bins.
db
D R Baker

This thread was discussed between 02/06/2004 and 03/06/2004

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