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Bob Axsom

Well Known Member
I had a vacuum pump failure recently so I had to go through the replacement process in the close quarters of an RV-6A. I was especially careful not to drop anything because of all my lower cowl baffling but installing the hardware is very difficult no matter what configuration you have. I Struggled for hours using every ice cream stick, masking tape, safety wire etc. resource I had to solve the problem and I finally hit on a solution. Sting the flat washer, star lock washer and nut on waxed wire bundle lacing tape like beads on a necklace. Drape them down into position and push the washers on the stud with a ice cream stick or screw driver then press the nut against the end of the stud with something like an ice cream stick and while holding it there use a screw driver on the nut flats to turn the nut and get it started. It will go on right over the waxed nylon wire bundle lacing tape like it wasn't even there. Once you get them started you can cut the string and leave the remnent in there like a nylon locking insert. Of course you have to use the Rapco tool or equivilant to run the nuts down and tighten them BUT THE BIG JOB IS GETTING THE NUTS STARTED. Once I tried this method I had all four nuts started in a few minutes and the rest was routine (with the special wrench of course).

Bob Axsom
 
I used a small ingition box wrench with the end opened up ( to slip over the stud) to tighten at least one. Very tight fit, indeed.

Roberta
 
Very clever Bob - I am going to rememebr that trick the next time I have to get some washers on a tought bolt. I had to change several vacumn pumps in the years I owned my Yankee, and the quarters are tighter than an RV- lots of bad words invovled.... Fortunately, I have left the Vacumn world behind!

Paul
 
Bob, Like I said in your other thread, I just recently replaced my vacuum pump also. I had no trouble re-installing 3 of the 4 washer/nut combos. The 4th one was a real pain. I tried several methods like you described but fell just short of your solution. I was using a precision screwdriver to feed the washers down but every time I tried to put the nut on, I would knock the washers off. The dang oil filter is almost making contact with the vacuum pump. If I was real desperate, I would have just taken the filter off. I finally got it on but it was a real fight. I may try your method next time.

Karl
 
Roger That!

Yes the lower inboard nut installation (just getting it started on the stud) is the problem.

Bob Axsom
 
Torque value and torque wrench access?

Installing an SD-8 on the vacuum pad. All four nuts are started on the studs. Now, to tighten. But how do you get a torque wrench on that troublesome lower left nut? Looks like there would be adequate access if the right mag wasn't in the way. But with it there, I don't see how.

So, is there a clever trick, or a special tool to torque this nut? Or do I just have to bite the bullet and pull the mag to gain access?

Thanks,
-Roee
 
This might be heresy to some, but in decades of aircraft maintenance doing this on vacuum pumps, I have generally used "German Torque" (Gutentight) on that nut and called it fine. Sometimes you have to make risk trades, and the risk of messing up Mag timing, dropping other bolts in bad places, etc overweigh the need to torque that one bolt for me...

Paul
 
Thanks

Thanks, guys. I suspected that was likely the best answer, but was unsure for lack of experience. Notice I say "best" answer (practical), not "right" answer (puritan), agreeing with Paul's analysis of the risk trade-offs. I'll proceed with the "gutentight" method, reassured by the fact that the many heretics that came before me have not been stricken out of the sky.

Thanks again.
-Roee
 
German touque

On vacumme pumps, or any other installation where I elect not to put a totque wrench on a fastener or two, I will run them all down lightly the same amout by feel, then note how many flats or part flats to make tourqe with the tourque wrench. Then I at least have something to go by when I tighten the remainder without the tourque wrench.
 
Update: a tool for the job

Not knocking the gutentight method, I still think it's a reasonable solution here... but I did just a little more searching, and came across this dandy tool:

http://thevacuumpumpwrench.com/about.html

img19.gif


Like the specialty hand wrenches offered by Rapco and Tempest, it's purpose-designed to reach around the vacuum pump (or alternator as the case may be) and get to that elusive nut. But unlike the Rapco and Tempest wrenches, this one has a 1/4" drive at the other, so you can use it with a torque wrench. Getting on that nut with this tool is still awkward, but possible.

Again, I don't think I'd lose any sleep just using my calibrated wrist on that fourth nut (or counting the number of flats as has been suggested),... but since this tool does exist, I figured that $35 was worth the peace of mind.

One caveat: As can be seen in the photo, the tool end is offset to one side, but the drive end isn't offset to match. So orientation of the tool relative to the torque wrench handle matters for getting the torque right, just like with a crow's foot. In the orientation of the photo, the vertical offsets of the tool end and the drive end are equal, just the tool end has an extra horizontal offset. So the tool should be oriented such that the torque wrench is vertical (either straight up or straight down) relative to the wrench in the orientation of the photo, so that the unmatched offset is perpendicular to the torque wrench handle.
 
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