Mis-aligned TR7RV carb and air box - Triumph Forum: Triumph Rat Motorcycle Forums
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post #1 of 9 (permalink) Old 10-19-2019, 03:59 PM Thread Starter
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Main Motorcycle: 1972 T100R, or a TR7RV
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Mis-aligned TR7RV carb and air box

I've a re-build thread just started here:

https://www.triumphrat.net/members-r...storation.html

The frame is a 71 T120R, everything else, AFAIK, is a 73 TR7RV, bought as a non-runner, which I fettled and have done 1000 trouble-free miles on this summer. My intention always was to get it on the road, ride it and then do what needed to be done this coming winter.

So, It's a high seat OiF, with a 73 750 engine and running gear.

The single Amal sits about 20mm too low for the rubber hose connection to the metal airbox, bolted to the main spine downtube. Not too surprising as when they lowered the seat the airbox would have been lowered too. The bike is coming apart for it's mainly cosmetic refurb, so I have the opportunity to do whatever to get the carb to line up. However, moving the airbox mounting down on the spine tube does not work, as I would need to lower the single pin that the side panel mounts on the diagonal seat tube, and that would then leave a big gap between the top of the side panel and seat.

Anyone got any ideas as to how to sort the 20 mm misalignment of carb intake and airbox? ATM I have no connection to the air filters, but I'd like one for next year.

Thx

Andy
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post #2 of 9 (permalink) Old 10-19-2019, 04:13 PM
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What height is the hole for the carb? And distance from the bottom ?

Edit- if you buy a Bonnie 73-77 or so inner airbox, there is no cutaway as the splayed head ran the intakes to the outer covers. Then sell on the older inner

Please check what I said though- I THINK it's right

Last edited by DAVE M; 10-20-2019 at 09:07 AM.
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post #3 of 9 (permalink) Old 10-20-2019, 04:44 AM
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Hi Andy, On my '73 Tiger the bottom of air box hole is about 5-3/4" from top of trans. Hard to say for sure as my boot covers the opening, but 5-3/4 is fairly close.

From bottom of casting to the top of trans is 5-3/8".

The bottom of my carb air horn is rather close to the bottom of the opening such it's very hard to squeeze boot between carb & air box at bottom.

They changed the offset in the hole of the boot from 650 to 750.

The inside of your air box casting looks like mine. Where the screw boss is that holds the 2 halves together. The parts book shows different part # between inner air box halves from '71 to '73. I don't know what all the changes are. Visually in photos looks like mounting point is the same location in the casting.

I think the castings are similar in size. The air box on the lower rear frame bikes is a lot lower & closer to the motor. Looking at breather hose on my '73 you can see how close air box is to rear crank case bolt boss. The entire rear triangle, swing arm etc is different from 71 compared to '73. But I've never measured all this side by side. I posted photos that might give some insight.

One solution is get a "special" old type air filter like the 1970 Tiger had. A special one is made with offset hole to clear the back bone, as a normal one will hit back bone at top. Then get retro side covers.

Do you have enough room at bottom of casting to cut a new hole if that was an option. '73 Tiger castings may be hard to come by, but Bonnie castings are common. You could get Bonnie castings & cut a new opening lower if you have the room. Doesn't look like you have much room to work with.
Don
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post #4 of 9 (permalink) Old 10-20-2019, 11:33 AM Thread Starter
Grand Prix 250
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Hi Don, Thx for the photos - my TR7RV looks exactly the same, except that your side panels are closer to the top of the gearbox - as you say.

I'll investigate both Bonnie and 1970 Tiger parts to see if that works.

My only thought so far is to make up a neoprene foam collar that fits around the inlet port to the carb, and fills the space across to the casting, with a 30mm hole cut through. That would exclude stones etc (or £ coins!) and pull air through the air filters. I have a local supplier of neoprene in all sizes.

Hopefully, after its cosmetic refurb, it'll look as good as yours does! I'm using the same vapour blaster/powder coater as I did for my T100R this summer so I know they can perform a good job.
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post #5 of 9 (permalink) Old 10-20-2019, 04:24 PM
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Hi Andy, Any kind of sealing arrangement you could fabricate that keeps dirty air out would work fine.

I think the casting is aluminum. If you have access to welding you could cut air box & add a lower alloy tube & use rubber section from like a Bonnie to connect carb. If carb & manifold are removed I think you can remove air box as one piece so there'd be no reason to split it. I've never removed an airbox on these bikes before though.

That would look stock like the factory did it.

I'm sure whatever you work out will be good.

Don
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post #6 of 9 (permalink) Old 10-20-2019, 05:32 PM
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post #7 of 9 (permalink) Old 10-21-2019, 04:34 AM Thread Starter
Grand Prix 250
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Hi Don, yes the casting is ali, and I do have an expert welder on hand - he's got international prizes for welding so he's good. I like the idea of cutting and making up a new fitting somehow. I'll need to have the bike re-assembled to get the dimensions right though - I took the head off yesterday and had a look in the barrels. The barrels are fine, except for some minor scoring on the intake side of both barrels - which I assume is due to grit ingestion. I need to fix that air cleaner problem.

Dave M - many thx for the eBay link. Not sure what I'm going to do yet.
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post #8 of 9 (permalink) Old 10-21-2019, 10:07 AM
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Airbox dismount is fairly straightforward, if the carbs are out of the way and the rear of the fuel tank is raised to clear lines., unplug the zener if fitted, leave mounted to RHS. Remove outer lids and filters, the air box section bolts to two straps welded to the Oil spine with welded 5/16 UNF threaded nuts, 1/2" AF socket deals with them, for the time being leave them tight, first slacken the 1/4 unf bolts that fix the rear steel panels to the air box, then slacken the air box 5/16 bolts, if the carbs are out of the way , the steel rear panels have conveniently slotted bolt holes , they can be wiggled free from the air box, you can leave the ignition switch attached if its an early type, the steel panels can remain in situ, remove air box bolts , there should now be enough room to wiggle the air box forward then twist round to the primary side to come free.

its tempting to split the air box halves, dont, they are a pain to deal with, i find it easier to remove the carbs, better left as one unit and are painted as such usually.
You can remove the air box and side panels as one unit , but its difficult, , the motor top end gets in the way. With the top end off , its a doddle.

The air boxes are pretty castings when viewed in isolation, the die maker did a great job on these., my LHS section was cracked at the top and bent a little, it straightened after annealing and the welder made an invisible repair to the crack, your hole shouldnt be to tricky to relocate with a fresh plate in there. At a push, with no handy welder, an Al plate some panel sealer and a 1/2 dozen pop rivets would do it..

The hole in the pics looks almost like it was cut for the flat back headlight rubber bathtub ?

We have no means of establishing reality outside our own frame of reference.
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post #9 of 9 (permalink) Old 10-22-2019, 04:04 AM Thread Starter
Grand Prix 250
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Hi Gavin,

I have the air box off already, but I split mine. When I did what was necessary to get the non-runner on the road earlier this year I bought the rubber bellows (bathtub is a good analogy) that goes between the single carb (it's a Tiger) and the airnox, but of course the misalignment means that it does not fit.

The plating idea may allow me to adapt the shape to use the bellows, so I'll have a think about that. The alternative is Don's idea of a short ali tube projecting from the airbox to take a rubber tube connection.

Something to mull over over the coming long, dark nights - which are even longer given where you live!
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