Fortune favours the brave, or so they say.
An engine builder on Pelican claims he does the oil bypass mod by hand with no jig, drill press or engineering mill and it takes about twenty minutes.
I started out with a small end mill, with a view to creating a flat surface which would take a drill bit. But even having taken one of the case studs out, the small bits weren't long enough to get the job done before the chuck was interfering with something.
So I ended up with a longer 10mm end mill. It took a while to work out the best way to get it to stay still and cut nicely, was on high speed, touching the case only very gently, and with plenty of oil. It did skid from side to side initially, scratching the inside of the oil tube.
Soon, however, it stabilised and was cutting beautifully and clean shavings dropping on the bench below. When it stopped, it became apparent there is a non-cutting centre to the bit, so I had to reach in and break off the centre nib of magnesium with a screwdriver.
The instructions from Pelican were to start with a small drill bit and work out. So once I had a nice flat surface, I domed the centre with a 10mm bit before continuing with a smaller one, say 3.5 or 4mm.
After a surprisingly long while drilling, I was starting to worry I had missed my mark. In theory (and according to the experienced hands on Pelican), and looking at the job, it's next to impossible to get it wrong. It looks like you're aiming for this oil galley, which you can see plugged at the end of the case.
In theory the spec is i think 28 degrees from vertical and it was hard to imagine I had missed it, but the drill was going ever deeper...
And then I saw this:
Shavings appearing in the vent to the case, exactly what I was hoping for!
I gradually stepped up the drill bits until the hole was 10mm. I may go a little wider later. The spec may be 12mm I think, but I'll check carefully.
Twenty minutes (for somebody who knows what they're doing) includes tapping and blocking off the hole which drains into the case, too. I spent about an hour in all doing this half of the job, going slowly. I think 10 minutes for somebody knowing what they're doing is reasonable.
Saved myself the £200+ I was quoted for doing this job. I don't think that's an unreasonable price, though, for twenty minutes work. You would be paying for expertise, skill, and taking responsibility if they screw it up. On this occasion, no mishaps. But I guess a job like this can easily grow into a day's work. And they'd need to measure, check specs, get the right tap, plug and loctite etc.
Next part of this job requires a 1/4" tapered BSP pipe plug. I couldn't find an aluminium one, which I'd have preferred for galvanic corrosion reasons, so I have brass on order as well as the tap and I'll wait until I have the loctite open for another purpose before doing that.
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