Hello All
My Sig 4* 40 manual says not to drill and tap the glass filled adjustable engine mount as this is going to weaken it.
But then how can I install my engine? What bollt shall I buy?

Please help, I've never assembled a plane before, and I am stuck at this phase

Thanks
Fadi

just drill it and use bolts w/ nuts and lock tite

i find myself drilling holes JUST large enough to let the bolt start and as i'm screwing the bolt in, it actually cuts it's own threads. haven't had any problems so far. i also follow the backside with a nut and lock tite-------- just to be safe.

Humm... so it is soft enough to allow the screw to cut its own threads?
I will try it, this is really the only thing I could think of if not to drill and tap.

Is there any other ways of doing it?

Hi fadi81,

I always use allen/hex head bolts with nyloc nuts and washers both at the bolt heads and nut rather than loc-tite.

Cheers,

Colin

yup I think I prefer that as well, but do you drill the mount?
This is my problem I want to know how to create the holes in the engine mount without weakening it.

Yes, Put your engine on the mount and mark where the holes should be drilled.
Remove the engine and drill small pilot holes through the mount (Be careful to drill as straight and vertical as possible) at all four marks, change the drillbit to the size your bolts are and drill again through all four pilot holes, enlargening them. (Making these pilot holes first with a small drillbit makes aligning easier than going with a bigger drillbit immediately)

Place the engine over the mount once again, line it up over the holes and push a bolt with washer throught the engine+mount. Secure with nyloc nut and washer under the mount...Done.

You can also use the proper pilot hole and sheet metal screws, similar to the ones provided with the Dave Brown mounts. Quick, easy, and I've never had one loosen.

Dr.1

ok thanks
I will try them... but I really am afraid to damage the mount.

Use a small drillbit first (to make the pilot hole) and don't apply to much preassure, let it take time. Aim straight.

DR, after having an engine actually depart the airplane while in flight [X(]I never use sheet metal screws any more. Alway the screw/washer/locknut method as described above.

I've been using sheet metal screws for years and if done properly (not drilling your pilot hole too large), these are very difficult to remove let alone loosen on thier own.

Lucky!!!!!!!!

i drilled and used the mounting screws to tap the holes for my saito 120,i drilled the holes two sizes under the screw size.once i tightened the screws and let me say a few of them i had to put in by hand wore my wrist out.they have been in now for two years and i checked them every time i went to the field for looseness for about a month,now i will check one screw every now and then.in fact i dread if i ever have to take them back out.lock nuts for peace of mind wouldn't hurt but IMO they aren't needed.

Think about this. In the unlikely event of a crash a mount SHOULD break and protect the crankshaft. Smacking Mother Earth with a durable mount will also dent the piston sleeve with the piston. A glass mount is designed to be a bit fragile.

I've flown several planes of .40 size with nothing more than self-tapping 1" hex head screws threaded into undersize drilled holes, then backed out and Locktited. It's actually easier to visually check them as being tight. A missing nut is hard to see in an enclosed cowl.

The fellers here who don't lose mount fasteners may be the type who carefully balance their props, too.

They said "drill and tap". It's tapping the hole for the screws that's the problem. They don't want you to use the mount, itself. to retain the screws. Drill for bolts and use nylon locknuts. Put a washer under the head of the bolt, and one between the nut and the mount. If you tapped the mount and properly-tightened the bolts, then you've also put a strain on the mount. This would also go for drilling slightly undersized and using sheet-metal screws. Another no-no. That effectively does the same thing as tapping the mount.

And yet both TopFlite and Great Planes (same company now?) instruct this as the method of attachment in at least three kits of theirs: Easy Sport 40, Contender 60, Ultimate 40, and a handful of their ARFs (but that's no surprise as it means less hardware). I had a well campaigned Big Stik 40 with an OS FS70II screwed to the mount. The largest piece of the engine body was still screwed to the mount after a midair and lawn-dart into a rock.

May not be the best method, but as they said at the Mig Plant: "Perfection is the enemy of good enough."

Of course everyone has their opinion, but if you read Dave Brown's tech sheet for thier mounts, they recommend using the sheet metal screws provided.
Tapping the nylon is not the same as using sheet metal screws (in my opinion).

[link=http://www.dbproducts.com/downloads/pdf/mm_tech_sheet.pdf]Dave Brown Engine Mounts Technical Data Sheet[/link]

Hi!
Sheet metal screws is the way to go...and Dave Brown plastic mounts (hard and good mouldings). Have used sheet metal screws for years (31) on many airplanes ...pylonracers, scale ...you name it , always worked good.

As has been said before everyone has their opinion.
I drill a hole and tap it with a tap.
Never once had a problem doing it this way.
I do not like to use sheet metal screws for any application where I may have multilple installations of the screw.
Others have told the the exact opposite, so I guess all methods work.

I always drill two sizes under and then tap the holes,I've been doing this for 20 years and have never had a failure.these are from 20-60 size planes