Engine Mount Brackets (3 hr)

Next up in front of the firewall are the engine mount brackets. These are big heavy lumps of aluminium that sit on rubber barry mounts that act as shock absorbers for the engine. They come undrilled of course because to give them to me with the holes in them would spoil the potential fun of having the engine fall off in flight. The photo guide for the engine is largely of the “put this on” variety, we’re a long way from the “take out a marker and put a line here” instructions of the rudder days. Fortunately the video has some handy hints and so it was that I rested the bracket on what is supposed to be the top half of the barry mount, made sure everything was level and centered and then back drilled into the bracket from below.
Preparing the engine mount brackets for drilling

Once the bolt hole had been drilled I realised I had to use the mighty step bit to further enlarge the hole for the barry mount to fit inside. Once the front was done I repeated the exercise for the back mount.

Except that you can’t do that because the hole for pax-side is blocked by the frame and you can’t get a drill up through to back drill. Funny how they didn’t show that in the video. So I’m sad to say that my improvised solution didn’t end up with a good result but it was still possible to make the right hole and have the rubber mount fit snugly inside it. I think it fits fine and will work ok though I do wonder about replacing that part and doing it again – that said, I don’t know that I would do a better job if I did.
Both engine mount brackets drilled

After this I drilled three pilot holes in the oil cooler bracket, centred it on the rear engine mount bracket, clamped and drilled through both, enlarging the holes to their proper size.
Oil cooler bracket drilled

The lower radiator bracket goes between the front engine mount and the shelf on the frame below, the shelf having pre-drilled holes (yeah, give me holes where I could made them myself). I realised this could get tricky because you need to drill holes through the mount bracket as well and it wouldn’t be as easy as back drilling because one, you have to drill upside down and, two, there’s a good gap between them giving plenty of room for getting the holes off centre.

In perhaps the first good idea of the weekend I determined the centre of the hole from underneath and used the punch to mark it on the bracket. Removing the bracket I then used the punch mark to drill and slowly expand the two holes that I needed (note that the really good idea would have been to use the drill press for this but I did not). Once they were close to the size of the shelf holes I reinstalled the brackets and enlarged the holes in the mount to match – they were an almost perfect match. I put the radiator bracket in between and drilled the holes to the final size.
Radiator bracket and oil cooler drilled

Looking at that picture I realise that I’m not finished as the front bolts use the same shock mount and penny washer assembly as the others. I’ll need to get on the step bit again for those.

To finish this work, I need to deburr the large holes and (ugh) trim the edges of the brackets and round them off. Then they can have their castle nuts added and tightened. Also, I need to get corrosion protection on the steel brackets that attach the engine to the mount.