I finally got to madien my trainer, well I didnt madien it but I was still very pleased, sun. was a learning experence for me, learned that I needed airspeed and to flare or I'll break my prop ( its was my first landing ) but still in one piece, I was told before we madiened it, that I needed longer screws and to use a nut, right now it just 4 40s treaded into the mount, What is longer than a 4 40 but same diameter, or will it be ok not to use a nut? I can get pics if needed

the 4 40 is the thread and diameter, it has nothing to do with the length the 4 is the diameter and the 40 is the threads per inch.
and that is american and not metric

Yep just go to the hardware store or hobby shop and get a longer 4-40 screw.

alright thanks, I had no idea what the 4 and 40 stood for, now i know

Machine screws into a plastic mount is a waste of time, use socket head sheetmetal screws.....they will never back out. If the holes in your mount are wormed out, shift the engine forward enough on the mount to drill new pilot holes for the sheetmetal screws. For .40-.50 sized engines I drill out the holes in the engine lugs to accept #6 sheetmetal screws to pass through.

what do you mean by wormed out? if you mean by treaded yes, if that is not what you mean, sorry Im a lil slow , and its a os 46 la on a debonair

Combatpigg is referring to holes that have stripped, drilled wrong or otherwise made larger than intended. That stuff tends to happen from time to time. The sheet metal screws will work in the plastic mount like he said.

TIP: when cutting bolts to length use a Dremmel tool with a cut off disk. It will not deform the threads...as much.

No matter how many times I cut this it is still to short!

What is really handy for any modeler to have is a numbered drill index. Harbor Freight has been selling them for $10. You can "sneak up" on the best pilot hole size for whatever job or material you are running threads into. It really pays to have tight pilot holes going into the plastic mounts. Make sure that the engine lugs lay on the mount nice and tight before being bolted down so the case doesn't get distorted any.

Not true! I do it all the time.

If you're concerned about it, just don't tap the hole all the way through - then the mount acts like a locknut.

That picture wouldn't happen to be a new Top-Flite T-6 ARF would it?

As for threading the plastic mount, I was always skeptical but I've done it several times and it holds up surprisingly well. I think the trick is to use the correct size drill bit for the particular thread you want to cut and to make sure the hole is straight and round. I have larger 2 and 4 strokes in GP mounts with threads cut in them and so far, so good. The material on those mounts seems to work very well for the purpose; I wonder if other types of plastic might not work as well?

I'm confused, fly boy are you talking about the the mount the engine is on or where the engine mounts to the firewall?...Rog

Boy, you've got a good eye Chuck! Yes, it's the new TF AT-6. I am in the process of doing a review of it. It's now finished and ready to fly, but our weather has just turned to crap! I'm hoping we'll get a break soon so I can shoot the video before the REAL winter hits!

I suspect what you have are not machine screws (bolts) at all but instead self tapping sheet metal screws and number fours are appropriate for your size engine. Sheet metal screws in plastic beams are entirely approrpriate and work well and better in some cases where the bottom side of the beam has no flat for a nutted bolt and must be severely modified to work that way.

All Dave Brown mounts come with sheet metal screws for the beams and it works very well The screws do not generally protude all the way through the beam either. Different size srews are provided for the different sizes of mount from #2 to #8's and the proper bit size for the pilot hole is always indicated.

Its likely you do not need to do anything. Machine screws that have had a hole tapped or self tapping sheet metal screws works great and going through a big hassle just to have nuts is silly and in some cases not even pratical where the bottom of the beam is tappered.

John

Just head on down to your local hobby shop and or the ACE Hardware and get longer 4/40 bolts. The Ace Hardware sells them in the bulk screws department. While there you will need to pick up some 4/40 nuts and lock washers. You can also use a 4/40 nylock nut which has a nylon tip on it so that it will not vibrate loose. You will need to make sure that the new bolt sticks out the bottom of the engine mount at least 1/4 inch to accept the nut and washer. My Ace Hardware has the 4/40 bolts in slotted head as well as hex head which requires using an allen wrench to tighten them up. You might find that the hex head bolts are a little easier to tighten up. My local Hobby shop also sells packages of 4 screws and nuts for about a $1.00. Good Luck, Dave

I use nothing smaller than 6-32 hardware on most engines and just tap the mounts. 6-32 taps and drills are much easier to deal with than 4-40, much less likely to break while tapping the beams. On some engines you may need to open up the engine mounting holes as CP said.

Chuck,

Wouldn't it be better in the long run to drill slightly oversized holes and just use machine screws with lock washers, nuts and threadlock?

It's quite simple really.

Places like Home Depot sell individual taps along with the correct drill in the same package.

Buy the most common sizes (4-40, 6-32, 8-32, 10-32, 1/4-20) and then drill holes in a block of wood so you can put each tap in its hole with its corresponding drill right next to it (And make sure you put them back in the block when you're done using them!).

Lowes sells a small set of taps in the sizes that Minn mentioned above with the corresponding drill bits. They come in a small storage case that keeps them all sorted and ready to use. It was well worth the money as I have them neatly stored and ready to use. And was nice to get just the sizes I use the most for this hobby and not stuck with a lot of larger taps that I wouldn't use too often.

Ken

Drats, so many requirements, so many requirements. Putting something back where it belongs is just too tough a requirement. Where do I appeal?

For engines .45 and smaller I sometimes use 6-32 machine screws tapped into the nylon mounts. I check them before every flying day and after a couple flights.
In metal mounts I tap and use large machine screws. 632 thru .60 8-32 through .90. Larger gets 10-24 or 32 whichever I pick up in the box of screws, nuts etc.

In all cases where screws are tapped into a mount at least ONE long screw goes through and has a self locking nut and washer tightened up on the bottom of the mount. No engine has ever departed the flying machine since I started that procedure, but a few screws have, especially when I was an ardent pylon racer.

I have a number of the old Fox Alum. engine mounts and use them whenever I can. They were and are the best ever produced.

I use one of two methods depending on the installation. If I have easy access to both sides of the mount then I prefer to just drill it large enough for the screw to pass through and use a fiber locknut or double nut with a lock nut in between. If there is limited access, or the fasteners are accessible from the engine side only, then I’ll drill/tap for a machine screw. When I install it I put a flat washer and between the fastener head and engine, and a lock washer between them. I’ve never had a mount screw come loose from an engine mount.

Hogflyer

You can actually get away with pretty small screws on large engines. A 4-40 screw is quite strong. I've used 4-40 screws to hold a YS160DZ to a mount, holds just fine. 1000+ flights, etc. These were however run into blindnuts that were sunk into the bottom of the nylon rails via application of heat. If just tapping the rail, I wouldn't use a 4-40 on a larger engine and would scale up bolt size as Hoss posted. BTW, the blind nut trick on the bottom of the rails is a good solution if you don't have easy access to the bottom of the rails to use a locknut, or if you just don't want to mess with the lock nut method.

I just got through reading a download of the manual so it looked familiar.

That's why all those reviews should be done out here. Can't fly every day during the winter of course but a few decent ones and quite a few more that are "good enough" manage to sneak in.

Yeah Chuck and I would be willing to do reviews out here, yes we have rain and fog and cold but we can usually sqeeze in flights. tomorow is gona be a great flying day!!

I just drill holes large enough for the bolt to pass and nut the other side. drilling and tapping partial way through soinds like a great tip. the plastic beam acts like a nylock, very cool

Wife is gone all weekend. After I take the dog to the vet this morning, I'm going to squeeze in two straight days of flying.