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Discussion Starter #1 (Edited)
Light at the End of the Throttle Body:

NOTE: This was originally posted to the Throttle Body Rebuild thread but I put it into its own separate thread because a) its long and b) the procedure can be used to sync the throttle body butterfly valves apart from a rebuild. Also, it is important to make a distinction between this sync and the "normal" throttle body sync where you adjust the air needle screws to balance the pressure taps at idle. This thread explains how to get the linkage and stop adjustments set, a procedure not describe in the service manual for K7+ models and absolutely necessary after a rebuild. Caveat: If you mess with your linkage adjustment screws you can wreck your throttle bodies. This procedure is not yet validated as I need to reinstall my TBs to confirm it will work. I will update the thread once I complete that task.

If you have ever done a precise measurement and adjustment procedure you'd know that 80-90% of your time is spent prep'ing and calibrating the equipment and only 20%-10% on actually doing the adjustment. Studying what you are trying to measure and how is really important to avoid frustrating and painful (or worthless) adjustment procedures. I sat down and started to work on what I need to measure and how to measure it. First I need to define some terms so here is a schematic of a throttle body valve positions;

And here are the adjustment screws to set these positions.

Ignoring the secondaries, if you back out the throttle stop so it has no effect and disconnect the linkage to TB#2 then the valves will sit independently at their closed position (black line) due to the springs. Assume that the valves are linked and are perfectly sync'd then when you turn in the stop adjustment this moves the valves a tiny bit off the closed position to its stopped position (red line). The stopped position is where the valves sit when the throttle is "closed". The "cracked" position (blue) is where the valves need to be synchronized and the critical parameter to adjust in order to make it work correctly. The cracked position is the point where the throttle is just coming off idle and transitioning to the main flow in the TB throat which is why it is so critical. So setting aside the question of how to get the valves sync'd, I still needed a target for the cracked and stopped positions.

There are no adjustment procedures for the K7+ models so I read the adjustment procedures for the K5 model and the primary valve sync procedure says to adjust the sync with a stop gap of 0.17mm (pg 5-34 of the service manual). I thought this spec was odd (figuratively and literally) because no one designs things to an odd value. Bolts are typically 10mm or 12mm not 9mm or 11mm. This implied that the stopped value had to be an odd number (i.e. 0.01mm, 0.03mm, 0.05mm) so that the combination of the two would be an even number (i.e. spec + stop value, 0.18mm, 0.20mm, 0.22mm). I didn't think the stop value could be 0.01mm as that is such a tiny amount it would be difficult even for Suzuki to adjust to such tolerances. Moreover, the stop has courser threads than the linkage adjustment screws so its not a super precise adjustment. To determine if the stop value was 0.03 or 0.05 I disconnected the link between the TBs so the valves were independent. The front TB was still OEM stopped and so I shimmed the rear throttle plate with a piece of standard aluminum foil (thickness 0.015mm) and compared the light passing through the gaps by holding it up to a brightly lite white wall.

I then shimmed it with a piece of heavy duty foil (thickness 0.03mm) and a double thickness of heavy duty foil (0.06mm) and it was clear from this experiment that the stop target was 0.03mm. I confirmed this measurement on the K9 throttle body as well so I felt I had the right number. BTW, the Vee spec for sync'ing is 0.31mm so the same argument applies -- the cracked target should be 0.34mm on the Vee. [NB: the stopped measurements are linear but shimming the valve plate with foil is a rotation, so there is probably a Sin(theta) factor but for small angles theta is essentially equal to Sin(theta)].

Sync Procedure:

Based on this information I developed a plan to sync the valves.

1) Back off the stop and disconnect the linkage and measure the tightest valve (i.e. which valve passes the least amount of light when closed).

2) Connect the link and turn in the link adjustment screw until it starts to move TB#1 plate. Back off the screw until both plates return to the closed position as measure by the light.

3) Turn in the stop adjustment in until TB#1 plate just begins to move and backoff slightly so it returns to closed position, gently tighten the lock nut so it doesn't move during the sync.

4) Shim the stop adjustment gap with a 0.20mm feeler gauge and turn the linkage adjustment screw until the valves pass the exactly same amount of light.

5) Remove the stop shim and insert a small strip (about 5mm wide) of heavy duty aluminum foil in the plate of the tightest valve identified in step (1).

6) Gently turn the stop adjustment in until one of the plates just starts to move (it will probably be TB#1), carefully and tightly lock the stop adjustment screw without upsetting the position.

So that's it, your valves are sync'd.

So I had my procedure and all I needed was a way to measure and compare the light between the TBs to complete the job. I started to design a light measurement detection circuit and was going to use Light Detecting Resistors with an LED to illuminate the throat and a Wheastone Bridge to detect and balance the measurements. I even started to order parts (but they were not expensive so no big loss) but I came upon a better idea to accurately measure the light. I realized from my experiments to determine the stop and cracked values that my eyeball is a pretty sensitive detector and I was able to easily measure down to 0.015mm (if not lower) just by comparing light passed through the gaps with the TBs aimed at a white wall. Here is my latest design.

The catch was I needed to somehow get the light to each eye so I could do a simulataneous comparison while I adjusted the screws. Here is my setup;

Does that look like a high precision measurement instrument? It is.

This setup was much easier than designing and calibrating an electronic, high-precision light-detection system. With those tubes I could see the images of both TB throats at the same time while adjusting the screws. I think the accuracy is extremely high and though I haven't installed my TBs yet I am certain that the valves are synch'd and it will work. You can literally see that they are sync'd with your own eyes.

This is the image in the right eye, the left eye has a mirror image and so it is very easy to compare the relative brightness of the images side by side. The accuracy is so fine that I can see diffraction lines in the crescent shape of the gap (too fine to show in the picture). Mine had 6 bright/dark lines but more importantly the eyeball/brain can easily perceive tiny differences in light levels (more on that below) and get the valves right on the spot. This isnt a complicated setup and it really isn't that difficult to get those valves resync'd if you need to rebuild them or resync after touching the adjustment screws. I can't detail all the steps so you'll just need to understand the procedure and build it and then play with it for a while to get the hang of it. Nevertheless here are some tips for anyone going down this path.

Tip#1: Prep: I cleaned and lubed all the stop screws so they would move smoothly when adjusted. I also sanded the stop plates the screws press against to give the stops new, fresh plates to press into and improve the accuracy of my measurements. I also cleaned the throats and plates with rubbing alcohol to remove any assembly lube that would form sticky strings between the plate and throat wall when the valves were cracked opened. I used canned air to remove any stray particles that could wedge the plates and throw off the measurements and I removed the secondary plates to get them out of the way.

Tip#2: Find a way to raise up the apparatus to eye level so you can comfortably look into the eye piece for 30-40 minutes. I had mine on the desk at first and it was killer on my neck and back.

Tip#3: Be sure to use identical flashlights to illuminate the gap and that they are securely attached. During the procedure you'll need to flip the throttle bodies over to insert the plate shim in step (5). If the lights fall off you are back to square one. Old batteries are fine for the daytime practice runs but when I did the final dark-adapted measurment I installed fresh batteries.

Tip#4: After you remove the valves stops the plates are resting on the TB wall. These plates are probably very high precision so be gentle opening and closing the valve when unstopped, don't let them bang shut. Also be gentle when setting the foil shim. Alumininum is not tool steel and will easily deform so set the valve down lightly when shimming the plate. I made a mistake in shimming the stop gap with the feeler gauge resting on the STVA and kept getting weird and unrepeatable measurements. The bending of the feeler gauge was throwing my measurements off so I had to hold the feel gauge in alignment with the gap so it wouldn't bend and impact the gap distance. If I was going to do this again I'd probably sand and mic a brass washer to 0.20mm so this wouldn't happen and I wouldn't lose one of my hands to hold the feeler gauge.

Tip#5: I built mine and used white light and walked through the procedure a couple of times to familiarize myself with the process and get some practice at setting the stops, judging the light, etc. This was good for practice runs but I remembered that Dark Adapted Eyeballs are about 10,000 times more sensitive than daylight adapted eyeballs. For the final measurement and setting I darkened my room and set up a lamp on a dimmer and waited 45 minutes for my eyes to adjust. I tried to do the adjustment with white light but after adaptation the light was blinding, like opening the fridge in the middle of the night, so I had to add the red filters so I could see and not get knocked out of dark adaptation. With dark adapted eyes I could really see a lot more details. At small angles the side of the plate that moves toward the eye is much, much brighter than the opposite side that moves away. The calibration is focussed on the bright side of the plate but when I used white light with day adapted eyes I never saw the dimmer light coming from the opposite side of the plate. With red light and dark adapted eyes I could see two crescents per image as in the photo above. This increase in the sensitiviy is really important when setting the stops and I could detect much more precisely when the plates just started to move in steps (2) and (3).

Tip#6: After the final adjustment I could see that the plates are very closely sync'd at the stops, the crescent images are almost indistiguishably different in brightness, much closer than the K9 throttle bodies (assuming the ebay seller didn't mess with his linkage screws and dump it on me). Don't worry if there is a slight difference between the images at the stops (but it should be very close), the normal throttle body sync procedure where you adjust the needle valves is to correct for that small discrepancy at idle. After I was done I did a validation step and shimmed the stop gap to 0.17mm spec and the crescents were virtually identical so I am certain these throttle bodies are fixed.

Tip#7: I haven't done the secondary sync yet but I don't think it is super critical as the primaries. The secondaries typically operate from 10% to 100% open so the closed/stopped/cracked issues won't arise. I'm still going to sync them using the light but I will do it daylight and not deal with dark adaptation.

Okay, that is the procedure and feel free to ask me any questions or clarification if you plan on doing this. However, I forgot my disclaimer in my original post: Do this at your own risk, YMMV, benefits may only exist in my mind. The next step is to get them installed and adjust the position sensors and do the idle needle TB sync. I have a new procedure to sync the throttle bodies with ISC lockout which I will post in a different thread. The stops are going to settle in like a new bike so I'll do another TB sync (not this procedure but the normal idle needle adjustment) in about 500 miles


879 Posts
Discussion Starter #2

Missing Photos in post #1


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