Replacing head bolts with caphead/allen bolts.

Hi all!

This was mixed up with a thread further down but I thought I'd start a new thread in the hope of getting more replies.

What thread is used on the head and crankcase on Enya 35 (model 5224) OS MAX-S and I/II/II 35?

>Hi all!
>
>This was mixed up with a
>thread further down but I
>thought I'd start a new
>thread in the hope of
>getting more replies.
>
>What thread is used on the
>head and crankcase on Enya
>35 (model 5224) OS MAX-S
>and I/II/II 35?
>
>Tony

Tony, I can't speak for the OS Maxes, but the Enyas used a 2.5 mm, I believe, and I think the OS's used the same. On some of the Enya 29/35's I had, I retapped the holes for 6-32, with solid results. You'll have to check the lengths to make sure they don't bottom out, but the 6-32's are most readily available, from several hardware sources. (I bought boxes from Rutland, in 1/4, 3/8, 1/2, 5/8, 3/4 and 1" lengths).

The larger heads of the 6-32 still fit nicely in the screw recesses in the head. From my references, the 2.5mm has a .45mm pitch, which is about 56 threads per inch (tpi). This is a far cry from 32 tpi, but there's enough meat to make a clean thread from this 'pilot hole'.

I haven't gone this far with some ST's I have, but it's my next thought to replace the flat head screws they used.

>I haven't gone this far with
>some ST's I have, but
>it's my next thought to
>replace the flat head screws
>they used.

The ST46, for instance, used a very oddball super-coarse thread metric that just happens to correspond to the midly oddball 5-40 UNF. In general, metric threads used for model airplanes are relatively finer than similar-sized American sizes, and you can't replace them 1:1 without tapping them out.

> The ST46, for instance,
>used a very oddball super-coarse
>thread metric that just
>happens to correspond to the
>midly oddball 5-40 UNF. In
>general, metric threads used for
>model airplanes are relatively finer
>than similar-sized American sizes, and
>you can't replace them 1:1
>without tapping them out.
>
> Brett

Brett,
Thanks for the heads-up! I just had to check on my ST's; I believe that the 35, 40 and 46 pretty well use the same fasteners.

The ST screws appear to be M3.5 X .6, which is about .136 major diameter and (25.4/.6 = )42 tpi. A 4-40 is .112 major dia and obviously 40 tpi. I checked on the fit...it isn't bad, but a wee bit off for my taste and concerns.

I know that Tom Lay substitutes socket head screws for the stock ones in his reworks, but I haven't asked him what he uses.

It appears that a 6-40 (now there's an oddball size, even if it is UNF!) would be a better fit for ST's, at .138 o.d. A 6-40 tap would probably make a clean fit out of the existing threads. I may give this a go on one of my 'carcass' engines to see how it works out.

>> The ST46, for instance,
>>used a very oddball super-coarse
>>thread metric that just
>>happens to correspond to the
>>midly oddball 5-40 UNF.

Brett, re-reading your note, and seeing '5-40' instead of '4-40', it is 'mildly oddball' but a much better fit, at .125 major dia., but still about .010 short of the M3.5. For all intents and purposes, probably ok, but I like the 'look' of the fit on the 6-40.

Do you use these in your ST46?

Here in the USA you can get Metric 60 degree form socket head cap screws from any decent bolt supplier. Locally, I suggest "Tacoma Screw" (no jokes, please) or "Hi-Strength Bolt", both within a stones throw from Mitzels on N. Central, Kent, WA. I understand that in Ol' England they stuck with a 55 degree thread form per previous (Whitworth?) threads. Perhaps they have come to their senses since. In any case, OS, Enya, ST, Webra, etc. would all be metric except for the glowplug (1/4"-32tpi) and about 95% of the prop nuts. The prop nuts are typically 1/4-28tpi, bigger engines like .60's may be 5/16-24, and smaller .09/.15's are the biggest headache, being Metric, SAE, "Special" SAE. "Special", meaning that their engineers rode to school on "the short bus". OS .15's have always been 7/32"-32, which is about as "Special" as they get. If you need a prop nut for an OS .15, call Mr. Ogawa. Basic rule of thumb is that you want to use a fine pitch thread for something that needs to be really tightened, like a prop nut. As a rule, you don't want to use fine threads in aluminum, as they pull out too easy (the screw is steel, remember) and are more likely to gall up either during machining or use. Standard shop/ engineering practise is to use a coarse thread in aluminum. Metric threads do come in both coarse and fine pitch, but are measured "peak to peak" in tenths/hundreths of mm, instead of over a long unit, like SAE threads, "per inch". Hope this helps clear up whatever the original question was;) Steve

The screws in the O.S 35 (nosepiston, end 70th) are 4-40, 3/8 long, I measured them. They are similar with Bernhardt engines
HB20 and Fox 35 (exept the hex.head)
Currently I try to get them here in Germany (100 pcs) but it seems almost impossible to get them (We are metric...)

Hi Richard - your'e not Richard Kornmeier are you?

The head bolts on the older OS's are definitely not 4-40 they are metric.

>>> The ST46, for instance,
>>>used a very oddball super-coarse
>>>thread metric that just
>>>happens to correspond to the
>>>midly oddball 5-40 UNF.
>
>Brett, re-reading your note, and
>seeing '5-40' instead of '4-40',
>it is 'mildly oddball' but
>a much better fit, at
>.125 major dia., but still
>about .010 short of the
>M3.5. For all intents
>and purposes, probably ok, but
>I like the 'look' of
>the fit on the 6-40.
>
>
>Do you use these in your
>ST46?

If I have to replace them, I use a 5-40. Ted put me on to this after I spent the better part of a year looking for metric ones (which to my measurement were 3x.6, which exists but is anomalously coarse {better to bite into soft aluminum}). It seems to fit awfully well. I actually have had no problems at all with the stock slotted screws, so the one engine I have left is still that way.

Is there such a thing as a 6-40? Sounds weirder than a 1/4-32.

The key to keeping them alive (like all screw heads) it to use a screwdriver that actually fits. I got some Proto screwdrivers at a discount store in 1973 that fit the 4-40's in the Fox perfectly, and a flat screwdriver intended for electrical connections that fills the ST slot (which is narrow the long way, and fat the short way) perfectly. It also doesn't "spread" - it's just ground from cylindrical stock, so it doesn't bend the fins.

The Proto Phillips has a similarly narrow shaft for it's point size, so you can actually fit the right size into the hole. The right size is usually one size bigger than you think it is. If it fits properly, it will have a very solid feel and not wobble around in the slot at all.

I'd give the part numbers for these, but it has long since worn off.

Japanese "Phillips head" screws usually strip out (like motorcycle case screws) because they really aren't standard Phillips, but some sort of Japanese standard in which the angle of the "pointy part" is shallower. A standard Phillips bottoms out before it engages the head completely, it just sort of rides the points, and the first time you try to tighten or loosen it it strips the points off. There's a bunch of 60's and 70's Japanese motorcycles running around which cross-head bolts that look like they've got round holes in the head, and have Vise-Grip marks where someone had to grab the outside of the head to get them loose.

I have never gotten a real Japanese standard Phillips screwdriver, but once you realize the problem, it's easy to grind a regular one that's close. Once you do that, the screws are actually just fine, and give a very secure feeling. A standard Craftsman (which are fine for real Phillips Head screws) will almost certainly strip a Japanese standard cross-head bolt.

I imagine there will shortly be 10 posts telling us where to getreal JN standard drivers...

Tony, I am not Richard Kornmüller, but I met him in the early 90th. I remember him as a funny guy, he is a Graupner/ Taifun
maniac (so do I)
The FP and the FSR engines are metric (M3) but not the former O.S. nosepiston (baffle?) engines in size 30/ 35.
I tried a Fox 35 screw and it is definately the same and my thread gap (hope I got the correct name) measured 4 - 40.

Hi Richard.

You're right - much to my suprise 4-40 bolts fit the OS but not the other way round - the OS bolts won't fit the Fox.

So it may not be 4-40 but it's pretty close.

so tell me what common sizes are close to 4 - 40?
I measure approx. 2.9 milimeters dia and approx. 7 mm length for 10 threads (results in approx. 36 threads per inch)on the original O.S. screw

Just have taken the O.S. screw under the microscope.
Definately 36 threads /inch!

What size bolts were you looking for? May want to trade you for os fp bolts.

For Brett: Yes, there is a 6-40. Perhaps the pointed "Phillips" screwdriver is a "Reed & Prince". The point is less blunt, the blades taper in thickness toward the tip, and angle increased. Somebody once said that this was the correct screwdriver for Fox .35's, but I can't verify that.

It sounds like Richard may be employed as a machinist or QA inspector, and may be familiar with a "form tap", AKA "roll tap". They do not cut the thread, they reform the metal into the thread. Because they don't make chips and have no flutes, they are much stronger and less likely to cause difficulty than cutting taps. However, they do require a different drill size (larger), a good lubricant, and cannot be used on plastics or non-maleable materials. The other benefit is that you might be able to reduce the thread size increase. Also, I have a question for Richard...is the Webra .50 used for stunt in Europe? If not, why not? Its weight and general specifications seem close to the popular ST G.51. On the plus side, they don't have ringed pistons but they are ABN, near as I can tell. Getting good information on them is not easy here...the R/C people just don't care. As long as it runs strong and idles well, not much else matters. Steve

>For Brett: Yes, there is a
>6-40. Perhaps the pointed "Phillips"
>screwdriver is a "Reed &
>Prince". The point is less
>blunt, the blades taper in
>thickness toward the tip, and
>angle increased. Somebody once said
>that this was the correct
>screwdriver for Fox .35's, but
>I can't verify that.

Reed&Prince is a third different kind of cross-head screw, that is supposed to push the tool out before you break the bolt, sort of a torque-limiter. I don't know about the Fox bolts, they always seemed to work as normal with regular Phillips.

I found an on-line description of the JN standard and the standard Phillips

http://www.katun.com/products/toolsjis.html

Looks like you can get real JN screwdrivers from Snap-On.

I know the Webra 50 Speed well as an RC engine. It is the direct
successor of the famous Speed 40 and the austrian answer to the O.S. FX 46. Although the power to weight ratio seems to be good for C/L purpose, you have to keep in mind that it is a typical high speed engine so I assume it needs some rework for good C/L engine behaviour. I will keep your question in mind and pass it on to some experts (my C/L experience is restricted to old diesels and old glow engines up to 35).By the way, the engine is relatively cheap.

If I remember right even Duke Fox used 6-40 screws for mufflers at one time. Don't hold me to it but I know one of the engine manufacturers did. You can get Japanese standard screwdrivers at Heliproz, or any of the RC helicopter supply houses at a not to high price for a set. For me I'd love to have a Webra 28 diesel. I've tried unsucessfully for awhile to get one sent over. These were a real sleeper but they were absolute powerhouses. Perhaps our friend Richard in Germany knows a little about them.Even better would be if they are still available there.Dennis

Dennis, the old Webra's are one of my subject. The 28 Speed ABC
was the successor of the Speed 20 ABC. Currently the 28 is replaced by 32 (same case, bigger bore). I have both engines (the 20 and 28) in RC use.
They are typical Webras (classic Bodemann design)
I remember the Diesels from Webra advertisement but never had one.
Although the Diesels are no more offered, I think at least the diesel heads for conversion could be delivered by request. Let me know if you need one (e-mail adress).
A nice weekend to you all - Richard

Rich, thanks for the reply, Sadly I don't have a 28 but only the various 32's and 35 heli, an aircraft version exists of the 35 and would be a good stunt motor I think. Diesels are limited to records, bullies and mach 1's
on the 35 Webra that has to be one of the smoothest steady running motors that I ever had in a small heli. It wasn't the most powerful but it's manners were impeccable, and it was light for the purpose. Anyone using them in Germany . Since our importer refuses to get them in for any reason there is no way to evaluate them here
Oh email is [email protected] forgot to enable it. Thanks Dennis

Have you tried using a roll tap by hand? Does it work?

I know it is the preferred method in our CNC shop and they do alot of small dia work in aluminum. (for all the reasons you listed.)

I sent this bolt off to a small family concern who specialise in 'bolt matching' and they say that the bolt I sent them from an Enya 35 - is a 4-42 UNC and that they can't match it!

Is that likely to be what Enya and OS used?

>I sent this bolt off to
>a small family concern who
>specialise in 'bolt matching' and
>they say that the bolt
>I sent them from an
>Enya 35 - is a
>4-42 UNC and that they
>can't match it!
>
>Is that likely to be what
>Enya and OS used?

No chance. It's some metric size, probably 2.5x.6 or 3x.6

>>I sent this bolt off to
>>a small family concern who
>>specialise in 'bolt matching' and
>>they say that the bolt
>>I sent them from an
>>Enya 35 - is a
>>4-42 UNC and that they
>>can't match it!
>>
>>Is that likely to be what
>>Enya and OS used?
>
> No chance. It's some
>metric size, probably 2.5x.6 or
>3x.6
>
> Brett

Those little "contraptions" that most places use to size up a bolt don't have enough threads. There are a number of metric and SAE bolts that are "almost" interchangeable, and if you don't watch yourself, you will convince yourself that a metric is not or a not is. (Got that?) I have a metal lathe where the tool holder stripped. I went down to the local machine shop to have the hole filled and retapped. He checked the bolt and thought it was metric. (IT screwed right in the metric hole) Guess what, it was a standard US thread.

On the engines in question, be assured they are metric.

Leonard Neumann