Perhaps it is better to tap the crankcase and use a grub screw up against the undrilled venturi insert rather than tapping and drilling into it and using a penetrative screw.

Worried about tank height with the raised spray bar Tim?

Read Matt's question.

I obviously did, otherwise I would not have come anywhere near an answer.
There was the original question -

"Please see the attachment and give me your suggestions/comments."

I did that and posted a comment.

And there was the postscript -

"P.S: I need a good plug for Magnum 52 XLS. Any suggestion"

And since there is no question within the attachment  which question are you referring to? (Logic would dictate the former since that was the only one I addressed - twice.)

Matt's modification raises the spraybar which may in turn may need a raised tank position to match it and since you advocated the original spraybar position without reasons given I in turn asked why.

Thanks.
P.S. I indeed just found part 1 of this subject but it seems that it doesn't change anything here.

Hello,
The engine will be installed in the "Cylinder Outside the Circle" configuration so the height of the existing spray bar is not that critical.

I would like to use the grub screw method but I do not know how to drill properly this kind of hole.
The drill bit will cut easily through aluminum cast of the crankcase but it will start "cutting air" on one side at certain depth.

The drill bit ( 0.157" max.) may and most likely will bend or break at this moment. The shortest drill bit I can use is about 0.625" and, with 0.157" diameter, may be stiff enough not to bend too much. It can break, though, due to unbalanced cutting forces when the part of it starts "cutting air".

On the other hand, the crankcase material is quite soft and may allow the drill bit of this length and diameter to remain reasonably straight while "cutting air".
The drill bit will, unfortunately, bend while entering the material on the "other side of air".

To sum it up: I have never tried such drilling before. I feel it is too risky and may lead to damaged brand new crankcase.

Possible solution: machine the 6061-T0 cylindrical plug tightly matching the venturi opening in the crankcase and plug this opening. 6061-T0 has the machining resistance similar to the cast of the crankcase making the drilling forces reasonably symmetrical w/r to drill bit axis. Symmetrical forces will not bend the short drill of this diameter and the only concern is discontinuity of materials causing some variation of cutting forces.

Is this variation acceptable in circumstances?  I do not have some already crash damaged crankcase to test the above method and never tried it before so it will be another "first time" but my gut feel tells me the risk is much smaller.

I have only a very basic table drill. Perhaps using the milling machine and proper milling tools having much higher stiffness will get the job done in two minutes?

More questions than answers...

The 4-40 through screw method is easy and does not affect the crankcase. It will, though, affect the venturi flow but to what extent?
The two short, stubby screws method is basically ok but there is very little "meat" for these screws to engage. The venturi wall thickness at this level is only 0.06" and may not provide enough gripping forces for the screws thread. Also: the screws are steel and the venturi is 6061-T3 and we have to remember about vibration.

More questions than answers again.

Thanks,
M

I would like to use the grub screw method but I do not know how to drill properly this kind of hole.
The drill bit will cut easily through aluminum cast of the crankcase but it will start "cutting air" on one side at certain depth.

The drill bit ( 0.157" max.) may and most likely will bend or break at this moment. The shortest drill bit I can use is about 0.625" and, with 0.157" diameter, may be stiff enough not to bend too much. It can break, though, due to unbalanced cutting forces when the part of it starts "cutting air".
Thanks,
M

Matt,

It's really easy to drill this type of hole. Having drilled probably upwards of a couple hundred thousand holes in aircraft, it has to do with bit rotational speed and type of bit. The optimum RPM for aluminum is 2800. It can be done much slower or faster then this, though. The issue of the bit canting as it clears the end of the material is minimized by using minimal pressure, proper (high) speed and the correct type drill bit. The typical "Home Depot" bit is 118 degree. great for wood and works fine on steel using a drill press and reasonable pressure. For drilling aluminum, high strength steel titanium, etc, a 135 degree split point bit is what you need. I can hand drill those holes with absolutely no damage to the case easily, and tap it to 4-40. Drill size for 4-40 is a #43 (0.089"). I can drill it to +/- 3 degree to perpendicular and +/- .005 from center by eye/hand.

Matt also asked for glowplug suggestions. Well, it depends on what you can get in Ontario, but...I'm a huge fan of Ohlsson Corporation products, and I'm ashamed to say I can't tell you all of the brands they make...but none of their own. Thunderbolt (Hobby People is the main source, but Randy Aero and Leonard Neuman also have them in stock, generally)...and I like them a lot. Ohlsson also makes Zinger, RO-Jett and K&B glowplugs. May well make others, but I'm not 100% sure on them. SIG? Sonic Tronics? Dunno.

Brodak sells Merlin glowplugs, and I hear good things about them, but we don't see a lot of them out here. Easy enough to get, of course, if you order from Brodak. As for what ones to get, I'd suggest a 4-cycle glowplug first, but I have also used the normal "R/C Long" with great results. It really doesn't seem to make much difference. I don't think you can run a glowplug that TOO hot. Some prefer NOT to use an idle-bar, because they're usually welded on and if they come adrift, the result is not good. I'm also dubious about using the recent Asian "medium reach" glowplugs, because I've seen how poorly a "short reach" works in an engine designed for a long reach glowplug. I'm not sure if all OS glowplugs are "medium reach", or if any Enya glowplugs are "medium reach", but I'd bolt a Thunderbolt Big Bore/4 Cycle glowplug in there and be happy. Basically, you want a hot or hotter glowplug. I really dislike Fox glowplugs, because quality seems to be variable at best.

I would suggest ordering a few from Randy Aero, along with the NV Assys., and also one of the CNC Tube Mufflers. Add a "rubber ducky" and it should work out pretty good. I'd start with an APC 12.25 x 3.75 and launch about 9,700 revs or so. Might also try the 12-4 and 12-5, and 13-4. I think they make a narrow and wide 13-4. But maybe that's the 14". If you want to experiment, you might block off the boost port and try a 13-6 or something like that. Might be good to try CF 3-bladers, or wood props in that range, depending on what you do to the engine, if anything, and what you can find. As good as my stock XLS .36 ran, I would sure run it stock if I could make it behave. Finding the right prop, muffler and venturi size was important.  Steve