Hi.

I have an OS . 25 FX motor mounted onto a Dave Brown glass filled mount.

I believe I've stripped two of the mounting holes. The right side screws go in nicely and tighten. The left side screws go in nicely, but don't tighten. I can get them snug, but they don't grip down tightly, just keep turning. I put some lock-tite on the screws last night, but I doubt that will hold forever.

Pretty sure they're stripped. Anyway to save these holes? I used a drill and a tap to make the holes and would prefer not having to make new holes or buy a new mount.

just drill the holes all the way through the mount, use longer screws and lock nuts... I personaly never tap a motor mount I feel much better knowing there is a lock nut holding down my power plant.
Good luck

That's my problem. I stuffed an OS . 25 engine into a plane that's suggsts only going up to a .19 (the SIG Wonder). The mount (and I may have been mistaken that it was a Dave Brown) looks similar to this:



The sides prevent me from getting a nut-driver deep enough to tighten the lock-nuts. I busted another mount trying it. There is literally no room to operate. I set the engine to the very back of the mount.

Can't you just buy another mount?

As per the other posts, tapping the plastic mounts is never a great idea.

Consider looking into suitable metal mounts if you need a tapped one.


You could re-tap the existing mount using a larger screw size and tap.

First, Dave Brown mounts do NOT need to be tapped if you use the supplied sheet metal screws. These work perfectly well and replacing them is reinventing the wheel. If you drilled and tapped for a machine screw, your only solution is to drill for a larger machine or sheet metal screw.

Dr.1

The proper Dave Brown for the OS 25 is the DB 2025 not the DB1519.

Dave Brown mounts all have a tapered bottom surface to the beams, You can drill through and use nuts however unless you grind flats where the nuts go the bolt will break every time at some point. This is a very poor makeshift alternative.

Using them as they are intended they are superb and I use nothing else because of the round back face and the non square firewall bolt pattern they can be fit in tighter places than any other mount.

Your mistake was in drilling and tapping the beam holes, will strip every time. Use only the indicated size pilot holes indicated on the back of the packaging. The proper pilot drill size for the 2025 mount is 3/32, use no other size. Now the supplied screws are driven in (Do not tap). The proper size and supplied screws for the 2025 is #4 x 1/2 inch sheet metal screw.

I would reccomend you get a new mount and use it as intended anything else will only come back to bite you.

John

I agree with not using the threaded mount idea and I personally put a regular nut on a longer bolt and then a nylon threaded nut after that. I also use a lock washer between the nut and the mount and then I feel safe it will never come off. Just my opinion. I also fly very large engines too.

Gibbs

http://www2.towerhobbies.com/cgi-bin...?&I=LXB867&P=7

This is a Dave Brown mount, if you drill it for nuts without grinding out great chunks on the bottom of the beam to provide a flat surface for the nuts, washers or whatever you stack on there, the bolt will be forced to bend. They always fail a some point if you do this. Even grinding big chunks out for a flat leaves a very weakened beam.


This is the worst thing you can do to a DB mount and it completely destroys the integrety of a good mounting system.

John

Yep, should have used the sheet metal screws.

For a metal mount (not here) you could have drilled for a larger size and tapped. Could also use a helicoil to repair a damaged thread. But not in this application.
http://www.emhart.com/products/helicoil.asp

you could try to fill the holes with some epoxy and re-drill, but there is no saying if it will hold.

you could try to fill the holes with some epoxy and re-drill, but there is no saying if it will hold.

It won't. Epoxy won't stick to the nylon mount.

Dr.1

Had a similar problem.I used good blind nuts . Shortened the length of the mid screw tube with a dremil to just below the tips of three legs.The three teeth of the blind nut dig in and catch better on the non flat surface of the mount once the screw is tightened .However ,probably one would need to re-tightend the screws once more after a flight or two and then they would do the job .Well in my case ,this kept my 46AX in place for some 20 flights so far.

my bad, i was just guessing. Personally, i would either drill it through and put a nut on or even go to a larger diameter screw that has enought to still catch the mount. I was just throwing the idea about the epoxy out there really. at least i qualified it with the part about "no saying if it will hold". guess that question was answered before it got a chance to fail for real. thanks for the voice of reason Dr1Driver.

Actually, given that these mounts are usually less than $5 at the LHS, I'd simply go buy another one.

Dr.1

why waste time and effort trying to repair a $5 mount when the repair will make the beam weaker by drilling a larger hole or cause the bolt to bend or break,buy a new one

Hi!
The best way of mounting an engine to the Dave Brown mounts is to use the supplied metal screws!
I use them on my Q-500 racer (424) powered by a Webra .40 GT and have done for years.
Never drill trough a plastic mount if you can avoid it...makes it difficult ,nearly impossible to mount the nuts when you have a tight fuselage wraped around the engine.