Thursday, December 29, 2011

Two steps forward, one step back

It's a truism in building an airplane that the harder something is to fit/fabricate/install, the sooner it will have to be removed. Normally that's quite a downer, but in the case of the cooling shroud it wasn't so bad since I needed to remove it and patch it. Because of that, "Now remove the cooling shroud and set it aside" was just fine by me, albeit while being fully aware that there would be no immediate setting aside.

The patching job was straightforward and, other than the typical hassles that come with messing around with smelly, sticky resin and fiberglass cloth that's ever eager to shed threads, it went well. It required a half dozen more round trips on and off of the engine to get it trimmed properly, but the result looks okay.

The reasons that the shroud needed to be temporarily removed were primarily to mark its location on the top of the engine to show where the RTV (high temp tolerent goop to seal the edge of the shroud to the engine surface) needed to go, and to make plenty of room for the installation of the engine mount that will mate the engine to the firewall.

For that mount mounting to happen, a few other things had to be moved out of the way, starting with the four coolant hoses. The clown at Van's that was responsible for such comedy gold as "metric Crescent wrench" and some of the meaner little practical jokes (the longerons in general come to mind, metric Crescent wrench included) must have been on vacation the day that these particular instructions were written because the plans clearly warn us that there might just be some coolant left in the hoses from when the factory did the test run of the engine. It must have killed him to let an opportunity like this slide past....

Forewarned, I put a catch tray under the hoses before starting the removal of the clamps.

It's good that I did!

As I worked on these clamps, I soon realized that The Van's Joker hadn't taken a vacation after all. Rather, knowing what a royal pain these clamps are to deal with, he came up with an even more diabolical joke: "Remove the clamps and push them forward off of the hoses to allow the hoses to be removed.". Or something like that; I'm paraphrasing from memory. In any event, those clamps are very difficult to work with, at least without the special tool that surely must exist. Even on the rare occasions when I could get a decent enough grip on one of them to loosen it enough to move it, the area between the end of the hose and an inconvenient bend in the pipe was too small for the clamp to move completely into, leaving a corner of the hose still clamped. In one case, I had to remove the far end of the hose too in order to get enough slack in the hose to remove it from the pump end.

It was later, when I was trying to put the hoses back on, that I realized for sure (I already strongly suspected) that the whole thing would have been much easier if I had slid the clamps back onto the hoses rather than forward onto the pipes.

Ha ha, Van's, you got me on this one!

Literally got me, that is: it is possible (likely, even) that at least once when a clamp snaps loose from the inferior tool in use, the ostensible fancy purpose-built tool probably not available to us mere mortals, it will catch a small fold if your fingertip, resulting in a nice, livid blood blister on your finger.

Here at home, we now call that "the 'OUCH' heard around the block!"

It was the upper left hose (looking at it from behind the engine) that needed both ends removed:

With the hoses finally off, it was back to safer work like removing a big, long, seriously important looking bolt. Van's, perhaps realizing that we wouldn't be in the greatest mood at this point, uncharacteristically tells us why this bolt is being removed: it will be used to hold the engine mount.

Here's a hint: you know something is going to be a frustratingly tight fit when an entire step is devoted to applying a protective layer of tape to the part first:

Further foreshadowing of the difficulty ahead: another entire step that has us removing the powder coat from the areas that will need to fit in a tight space. Although, I suppose, this could also be required to provide a firmer fit or a better electrical ground. Either way, it turns out that my fancy new sander was up to the task.

And, for any remaining optimists, step-by-step instructions for getting the part to fit, complete with a "it will fit if you do it like we tell you to" admonishment.

Like so:

Start at the lower left, fitting the mount around the lower coolant hoses:

Fit the upper right around the ignition module:

And it will now align with the bolt holes.

Unless.... me, you found the packing braces to be a good way to support the engine while its sitting on the work bench, so didn't remove them:

Which will now be hard to do without an awkwardly positioned allen head wrench slipping as the bolt breaks loose, leading to a nasty cut on your inside wrist. Trust me on this one.

Once the braces are gone (and the bleeding stopped), the mount does, in fact, slide into place nicely.

There are four bolts that mount the mount to the engine. I remember reading about these bolts a couple of years ago; there was a big problem with people finding that they had worked loose, in many cases with all four having backed significantly out of the holes. That justifiably scared the beans out of those involved; an engine separating in flight is no different than the airframe falling apart in flight: 100% fatal. So, extra caution required here, over and above the routine high degree of care one uses when building a contrivance such as an airplane that one intends to fly in his very own self.

The plans don't include the all-important torque value, instead having you go try to find them yourself in the Rotax documentation. I'll save you the prolonged search: 26 - 30 foot-pounds. The upshot of the lengthy discussion around how to keep these bolts in place came down to two camps: use some blue LocTite, or buy some fancy wedged lock washers. I used LocTite.

I also marked each bolt with torque lock; this will show at a glance whether or not a bolt has moved.

Once the mount is bolted in, the RTV can be squeezed along the marked lines and the cooling shroud can be re-installed for the final time.

Once the RTV has set up, the coolant hoses can be replaced on the pump. Remember, it is easier to put the clamp on the hose, get a good tight grip on it to open it as much as possible, then slide the hose and clamp over the pipe together. Also note that, as always, 'easier' does not mean 'easy.'

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