Throttle/intake tube interference

[Pablo M]

1972 2002tii with 74 aluminum intake plenum/tubes/manifold. 
 

As many of you know I’ve been replacing the rebuilt head. Just about ready to fire it up. Problem. 
 

When it was all back together, before the airbox went back on, I tested the throttle linkage. It was stuck. Didn’t move at all. I checked and checked and once I removed the second intake tube did I discover the linkage is touching the tube when I snug it down. 
Here, where my finger is pointing. 

 

Im tempted to take a grinder to it and shave it down but would rather understand why it’s doing that and I can’t for the life of me figure out why the tube is closer to the linkage now. Are the 4 tubes different? I know they’re numbered but I don’t think I ever had one marked #2.

edit: the only thing I can think of that would change the relationship of the intake to the linkage is the motor mounts are new. That would have shifted the engine relative the linkage perhaps? 
Otherwise it all went back on as it came out.  

 

 

Also, the return spring looks like it’s wearing a slot in the linkage and it looks tenuous. Any suggested fixes? JB Weld? I placed the spring on the further back hole for now but don’t know if that has other adverse effects. Does it matter what hole the spring is in? 

 

With this setback I’m unlikely to make it to SoCal Vintage. Tonight was the last chunk of time I had to work on it. I only have a couple small pockets of time left. 

Edited November 2, 2023 by Pablo M
Added clarification

[Rob Zaeos]

14 minutes ago, Pablo M said:

1972 2002tii with 74 aluminum intake plenum/tubes/manifold. 
 

As many of you know I’ve been replacing the rebuilt head. Just about ready to fire it up. Problem. 
 

When it was all back together, before the airbox went back on, I tested the throttle linkage. It was stuck. Didn’t move at all. I checked and checked and once I removed the second intake tube did I discover the linkage is touching the tube when I snug it down. 
Here, where my finger is pointing. 

 

Im tempted to take a grinder to it and shave it down but would rather understand why it’s doing that and I can’t for the life of me figure out why the tube is closer to the linkage now. Are the 4 tubes different? I know they’re numbered but I don’t think I ever had one marked #2.

 

Also, the return spring looks like it’s wearing a slot in the linkage and it looks tenuous. Any suggested fixes? JB Weld? I placed the spring on the further back hole for now but don’t know if that has other adverse effects. Does it matter what hole the spring is in? 

 

With this setback I’m unlikely to make it to SoCal Vintage. Tonight was the last chunk of time I had to work on it. I only have a couple small pockets of time left. 

Kinda hard to tell but it looks like the orientation is off by 90 degrees.... could just be the drawing though.

 

[conkitchen]

perhaps you need that intake support bracket. 

[dlacey]

Firstly that lever looks wrong, it's normally longer with a stud on the Ned to hook the spring.

Concerning interference, I got a vague recollection that lever is meant to be bent downwards and there was some info-note from BMW back in the day.

 

Edit:

Seems there are two types:

https://www.bmw2002faq.com/forums/topic/125516-tii-throttle-linkages-and-synchronization/

 

And the bent bit is somewhere else...

Edited November 2, 2023 by dlacey

[Pablo M]

9 hours ago, Rob Zaeos said:

Kinda hard to tell but it looks like the orientation is off by 90 degrees.... could just be the drawing though.

 

The bottom of that rod has two linkages connected to it so turning it 90° would be impossible. Also the relationship to the spring would be totally wrong. 
the only thing I can think of now is that it usually sits in a cup/bushing (part #7 in diagram) and that may have gone missing. The rod did come out of the bottom pivot point during the refresh.  That might be enough to make it contact? Having said that I wonder if I couldn’t just slide the pivot a bit higher on the TB and secure the two bolts in that position, slightly higher. 
 

9 hours ago, conkitchen said:

perhaps you need that intake support bracket. 

Not likely. I didn’t have it before and the TB support bracket, as well as the 4 intake tubes, support the plenum in its place. I had been hoping to get that bracket before I reassembled, but didn’t happen. I still want it and will send payment soon, but I’ve been hyper focused on getting this done and running by Saturday. I didn’t want to wait till I received it to reassemble. 
Thanks. 

[stephers]

There are early and late linkages that go with the type of throttle body ( early or late )      If I remember right, did you not have plastic tubes originally and you went with the later aluminum tubes         I would just grind down the edge to clear the tube and at the same time , weld up the spring hole and redrill           Only the late linkage is available new, the older style has been unavailable for quite some time       If you use a later linkage, it has to be modified to work properly with the older systems            Weld and grind      only thing that you can do     no big deal

 

Thanks, Rick

[Mike Self]

4 minutes ago, stephers said:

weld up the spring hole and redrill 

I've fixed ovalized/worn spring holes (and the peg on carburated throttle linkages) by sleeving with a short piece of brass tubing cut to the proper link and pressed into the (slightly) enlarged spring hole or slipped over the worn peg.  While brass will wear faster than steel, it's simple to replace when worn and much easier to work with than a steel sleeve.

 

mike

[Pablo M]

54 minutes ago, stephers said:

There are early and late linkages that go with the type of throttle body ( early or late )      If I remember right, did you not have plastic tubes originally and you went with the later aluminum tubes         I would just grind down the edge to clear the tube and at the same time ,

 

Thanks, Rick

Thanks Rick. That’s right. Mine is a 72 and originally had plastic tubes. When I got the car they had been replaced with aftermarket aluminum tubes but never sealed well. I replaced the plenum, intake tubes and manifold with later style, keeping my TB and linkages. I painted the tubes black for a period correct appearance.
There wasn’t a clearance problem before, which is what has me concerned. The only change is the rebuilt head so I’m guessing decking the head and different HG thickness (thicker) was barely just enough to create interference where it must have been extremely tight already. 
 

I unbolted the linkage and slid it up tight to the TB and that helped but it’s still barely catching, but can get past with some effort. I should be able to grind off half a mm or so and it will clear. I’ll just do that. 
Generally speaking, when things like this happen I want to know what caused it in case it’s something I did wrong and can correct. 
 

It’s just barely touching now. 
 

thanks for the info @Mike Self  I appreciate it. Hadn’t thought of welding and redrilling but a sleeve would be an easy temporary fix as well.