PaulTWinterton

Tii Linkage Gauge. DIY

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I decided to rejuvenate my throttle linkage on the tii.  There is at least 1mm of play on all ends except strangely the pump to intermediate shaft linkage rod with the plastic ends.  There is no play on those 45 y/o ends.  Hmmm.

 

CenterlineAlfa  (dotcom) sells ball-cup linkage ends, #TL441.   I tested a cup on my existing male ends and they fit snugly.  Sold!

Parts1.thumb.jpg.088bdf646e57ff65b1dab65934a42191.jpg

  At the same time I decided to make my own linkage gauge, but with the added length for measuring the 289mm rod.   I opted for light weight L-extrusion aluminum.  Cheap.  I wasn't sure it was beefy enough but once I'd completed the tool I realized that the parts should fit easily without force, therefore the gauge is not being stressed.

Drill_holes1.thumb.jpg.1c5cab772f538840d91c04ea4312328c.jpg 

 

My Faux Pas

Not until I placed the 289mm rod onto the tool did I realize that the ends are rotated 180 degrees! My glorious tool has a flaw.  Oh well, I'll leave that to you guys to solve and build a better mousetrap.  For now I can rest one end on the ball and measure (very close).

Test3.thumb.jpg.f642515ef2278a768444d643b661727c.jpg

 

I threaded 3/16" steel rod.  5mm rod would have been easier but it's not readily available. 

ThreadRod1.jpg.14c5629db0ad83a6f013c822505b0523.jpg

Parts2.jpg.5616ff9437fe3979699be9598b7b62c6.jpgFinished1.thumb.jpg.f6561f56b0b86e411da4da69e7c1e32c.jpg

Call me quirky: I love shrink-tube.  I added a piece in the middle  because I could.

Finished2.jpg.1932a6e5256c7d6cb54a2065234c63ce.jpg

 

Tool cost:

L-extrusion   $7.

Ball ends x2  $8

 

Linkage cost (ea.)

Rod                $1

Cups x2         $14.00

Nut x2           $0.50

 

Adjusting the length of the 85mm rods is tricky.  Having the gauge allowed me to see the variation as the ends are tightened against the locknuts.  Without the tool it's near impossible to achieve an absolute length.  With the tool I was experiencing an overly tight fit after final tightening of the locknuts.  I realized that the threaded rod was moving with the locknuts and changing the length of the linkage +/- 1.5mm.  With the tool I was able to get a precise 85mm measurement and no binding on the balls.

 

A fun and rewarding experiment.

Edited by PaulTWinterton
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Maybe I haven't had enough coffee yet but couldn't you put the ball for the long rod on the other angle of your gauge to compensate for the 90' linkage offset?

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4 hours ago, Son of Marty said:

Maybe I haven't had enough coffee yet but couldn't you put the ball for the long rod on the other angle of your gauge to compensate for the 90' linkage offset?

 

Unfortunately, no.

 

I could have used "U" extrusion, had I done more planning.  Then I could have an "opposed" ball fitting at the far end.  Or I could still add a small opposed L-extrusion piece at the far end with a ball fitting hole.

Test4.thumb.jpg.d92d9f58e89d6d085f31fd7a0cd796d8.jpg

 

Edited by PaulTWinterton
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Paul,

Thanks for the lead on CenterlineAlfa - good resource "in case of". 

 

ColinK

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Does anyone understand the impact of this rod being *not* 85mm? Both the Throttle spindle and the Kugel enrichment lever are moving in an arc...so the linear motion of the rod is varying with butterfly position with some ?cosine? law... is the Kugel lever at some other point in it's arc so that these linear variations cancel-out??  At 83mm do you end up with richer mid-range or anything?? has anyone ever tried this as a variable to improve drivability on a worn engine??  

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Paul maybe in saying this wrong but if you remove the end on the ball now and rotated the linkage 90' so that the end thats off the ball is on it's ball won't the other end face the other angle and put the ball there?

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1 hour ago, Son of Marty said:

Paul maybe in saying this wrong but if you remove the end on the ball now and rotated the linkage 90' so that the end thats off the ball is on it's ball won't the other end face the other angle and put the ball there?

 

Not sure I understand but my existing tool only has opposing connections at 90° (max) variations.  I need 180° for the long rod.   The rod must be attached at both ends to lock the measurement.  I could attach and measure the rod with both ends at the same angle and then rotate one end back 180°.  But then it would change the length by the revolution of the threads.

 

1 hour ago, dlacey said:

Does anyone understand the impact of this rod being *not* 85mm? Both the Throttle spindle and the Kugel enrichment lever are moving in an arc...so the linear motion of the rod is varying with butterfly position with some ?cosine? law... is the Kugel lever at some other point in it's arc so that these linear variations cancel-out??  At 83mm do you end up with richer mid-range or anything?? has anyone ever tried this as a variable to improve drivability on a worn engine??  

 

I too would like to know the answers to your questions. An interesting observation is that the original linkage is variable.  It has reverse threads and a gripping point in the middle of the rod.  Possibly for adjustment or just ease of setting the measurement?  Not sure.  LinkageRod.jpg.95b4aa1813b0edeb668df5e6533a89ae.jpg

 

 

Edited by PaulTWinterton

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Nice, timely tip...since I was going to order some spider parts. Now I can feel less guilty by including some tii parts on the order.

 

Centerline Alfa are good people.

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Effect of the length of the 85mm rod

I took a look at the linkage..and will use a crankshaft analogy...the real situation quite complex as the arcs moved by the throttle spindle and the kugel spindle are in different planes...i guess a serious mathematician could take that into account..

The Throttle butterfly ball/pivot (that the rod clips on to) starts (closed throttle) at~10 ATDC (TDC is 3 o'clock on the GIF wheel below, ignore the red/green/blue) and as throttle is opened goes to 90 degrees ATDC and at full throttle is about 110 degrees ATDC... that means the linear motion of the rod (related to the angular opening of throttle) starts low, rises to a max and then starts to decrease again at WOT (in the GIF its the crankpin moving from ~4 o'clock to 7 o'clock).

The Kugel throttle position lever ball/pivot goes from something like 190 degrees ATDC closed throttle to 270Degrees ATDC at WOT. (in the GIF from just after 9 o'clock through to exactly 12 o'clock). That means that every, say 1mm, movement of the rod is having a decreasing rotational degrees effect on the pump lever as you move towards WOT.

TRUE_piston3_ANI.gif

So, it seems that the linear variations DO NOT cancel out, as the two pivot points do not follow equal/opposite arcs relative to the rod direction.

 

If the rod were shorter and all other Tii setup procedures were followed, the throttle butterfly ball pivot would start closer to TDC, (closer to 3'o'clock), meaning there would be less linear motion (per degree of throttle angle)....that would weaken the part-throttle mixture as the Kugel lever will simply move less...

 

If the rod were longer, then the throttle ball pivot would be further from TDC, meaning more linear motion per degree of throttle angle in the part-throttle period, meaning more kugel lever movement early-on...meaning richer earlier.

 

hope this makes some sense...

 

I am gonna experiment at the weekend...

 

Edited by dlacey

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8 hours ago, dlacey said:

I am gonna experiment at the weekend...

 

Interesting.  Let us know.

 

Something else to remember: the adjustment in the middle of the intermediate shaft is used to change the relationship between the Kfish(fuel) and the tuna-can cam(air).  Where the 4mm tool is used on a factory set up, often the 4mm hole is covered to some degree on older engines to affect the air/fuel ratio.

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Also interested in how the length changes the air to fuel ratio.

 

As for the degree to which the hole in the tuna can is covered, My experience is that it moves the entire throttle range, but does not lean out or richen up the air to fuel ratio nonlinearly within the range. 

 

Was contemplating actually changing the profile of an old spare D cam (by sanding it down) to make mid-throttle a little more rich. Might try that this summer. 

 

Vince

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To follow-up on the effect of lengthening the 85mm rod:

 

I I unscrewed the rod to get to a length ~87.5mm, i then reassembled and went through full setup procedure, locking the pump and setting the throttle butterfly with the 4mm rod etc.

 

After optimising idle mixture it improved my part-throttle weak-mixture situation (hunting) which before was quite bad at 1500 rpm despite idle mixture setup being fine... there's still a little weakness at 1200, but by 1500 its smooth... also appears better-behaved on full throttle when hot (previous some pinking despite backing-off ignition already).

 

so *maybe* lengthening the rod does richen part-throttle mixture as we postulated above.... 

 

Of course, there must be some underlying issue for why the standard 85mm setup doesnt work...wear? fuel? latitude?

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