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Unusual stabilizer bolt thread pitch printer friendly version
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dannparks
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Posted Tuesday, October 29, 2013 @ 11:46 PM  

In removing my horizontal stabilizer I noticed that the bolts holding it to the brackets on the fuselage were a bit short and decided to replace them with longer ones. Well, odd as it is, they don't seem to be standard M5 .8 pitch. In fact, I can't seem to figure out what they are.

There are 3 of these bolts, a short one with a hex head on the front and two longer ones in the back. They all go into nut plates on the brackets. You can jam an M5 .8 bolt into there, but that's not what they are. It is a coarser pitch than standard metric. I dug through the old parts box and discovered that the original bolts holding the engine mount angle brackets to the firewall are also this same thread. Those bolts are drilled to go into special castle nuts. Again, something a little different from the standard bolts. The pitch seems to be around .9 mm.

An internet search showed something about an old JIS standard M5 .9 pitch used in the 60's. Could these be that? Are they still available? Any ideas?

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Dann Parks • RF4D #4051 N2188 • now flying!
Pictures at: https://picasaweb.google.com/111628310900713778468/RF4D_N2188?noredirect=1

Markku
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Posted Wednesday, October 30, 2013 @ 02:49 PM  

Hi Dann
That sounds strange, I'm quite sure that originally all the bolts in fuselage are metric LN bolts. LN bolts have the same thread as normal metric bolts, I will check tomorrow from my plane.
Markku
eugenio
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Posted Wednesday, October 30, 2013 @ 03:41 PM  

I confirm, all bolts and nuts used are standard metric (ISO) threads, and most of them are not LN but common 8.8 bolts and 8 nuts. If you find something else probably it has been modified, this most probably may happen on US and UK Fournier's, since in all other european countries we all use mostly metric hardware, quite easier to find here, or for US produced aircraft AN/MS hardware (a little less easier).

Eugenio

dannparks
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Posted Wednesday, October 30, 2013 @ 11:12 PM  

Very weird. Here are the aforementioned bolts.

Top is the engine mount firewall bolt and castle nut. Next, the front of horizontal stabilizer bolt, and another engine mount bolt. All these seem to be M5 with a .9 pitch thread. Bottom is a standard M5 .8. You can notice the threads are different. And the top of the bolt head with the P-L-9 marking. I can't imagine these are not the original bolts. I don't see why they would have been changed out, but you guys would know if they look familiar.

Bob G., since you have your plane all apart, maybe you could take a look.

Below are obviously the brackets for the horizontal stabilizer with the nut plates that they fit correctly into -- at least on my aircraft. Does this look original?

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Dann Parks • RF4D #4051 N2188 • now flying!
Pictures at: https://picasaweb.google.com/111628310900713778468/RF4D_N2188?noredirect=1

Markku
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Posted Thursday, October 31, 2013 @ 05:57 AM  

Hi Dann
It doesn't look like the original, I think all the factory installed selflock plate nuts looks the same as in attached picture
Markku

eugenio
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Posted Thursday, October 31, 2013 @ 03:24 PM  

It seem original but it's not. First of all does not exist a M5x0.9 thread, but only the M5x0.8 or the M5x0.5 (fine thread). Second the installation of the bracket on the fuselage is not original because the two fittings originally are bolted with hex bolts, not allen bolts, and more the thru bolt on the side fittings has the thread too long, it should have the solid shank longer, you should not see threads between the two fittings, this weaken the system and can damage the hole of the support on the fuselage.
Maybe everything screw in fine, but in any case does not exist an anchor nuts with the 5x0.9 thread, they may have been threaded.

Eugenio

dannparks
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Posted Thursday, October 31, 2013 @ 11:34 PM  

The oddity continues...

There was a J.I.S. (Japanese Industrial Standard) M5 0.9 thread pitch that was used until the mid-60's, when the J.I.S. standard was changed to match the I.S.O. standard (other bolt sizes also changed). A lot of antique Japanese motorcycles use these bolts and they are almost impossible to find for restorers.
http://www.mottomoto.com/Build_Program/manuals/CB160%20Part%20Index.pdf How some of these bolts ended up here is very strange.

The bolt in the two brackets is too short. That's the problem. I need longer ones with the proper shaft/thread length.

The anchor nut seems to be original. It was attached below the skin level and there is no indication that the wood was ever cut to change the fitting. This fitting fits the .9 bolt perfectly, and not a .8 without forcing it. The front fitting is the same. Why these would get re-tapped from .8 to .9 makes that seem unlikely.

I did find an M5 .9 die on Ebay. I think I can use this to add threads to an engine mount bold to make it fit.
http://www.ebay.com/itm/like/181112010180?lpid=82

I also noticed that many metric tap and die sets include M5 .9., so they must still be around somewhere.
http://www.northerntool.com/shop/tools/product_200512864_200512864

Since I'm going to have both brackets opened up, it might make better sense to try to replace the fittings with .8 anchor nuts.

That doesn't solve the mystery though :^).

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Dann Parks • RF4D #4051 N2188 • now flying!
Pictures at: https://picasaweb.google.com/111628310900713778468/RF4D_N2188?noredirect=1

eugenio
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Posted Friday, November 1, 2013 @ 01:04 PM  

For sure the best solution is to change the anchor nuts and use all ISO hardware. Do not thread the solid shank of the bolts, you will weaken the bolt. All bolt's thread are rolled, not cut.
I did'n know the 5x0.9 thread existed, but I suspected it was like so, a special thread used on some particular applications, not a standard. Is the same as the thread of the Zenith Stromberg 150CD carburetor's spindle, it is not a standard metric, nor a Withwort or a UNF, and I could not find the die to make it, so I use a M7 ISO that is very similar but not the same.

Eugenio

dannparks
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Posted Friday, November 8, 2013 @ 01:44 AM  

Well I decided to just leave the threads as is since I realized I can use an old 0.9 engine mount bolt with a few washers on the rear fitting. Still doesn't solve the riddle though.

If anyone (Bob G., Collin, ?) has their stabilizer off, I would appreciate if you have a moment to examine the small allen-head bolt for the front bracket and compare it to known 0.8 pitch threads. Also (anyone) peak at your (original) firewall engine mount bolts and see if they have the P-L-9 markings on them. Thanks.

Everything is tightened, patched, and painted and I hope to be flying again soon -- although the weather has totally crapped out here for the winter.

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Dann Parks • RF4D #4051 N2188 • now flying!
Pictures at: https://picasaweb.google.com/111628310900713778468/RF4D_N2188?noredirect=1

Bob Grimstead
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Posted Friday, November 8, 2013 @ 01:51 PM  

Hi Guys,

This is the correct bolt (not an Allen screw) from the leading edge of my horizontal stabilizer.

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Flying and displaying Fournier RF4Ds VH-HDO and G-AWGN, building replica RF6B G-RFGB and custodian of RF6B prototype F-BPXV

dannparks
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Posted Friday, November 8, 2013 @ 04:19 PM  

Thanks, Bob. Just for grins, could you also check the thread against a known M5 0.8? And, does it (or another 0.8) go smoothly into the anchor nut(s)?

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Dann Parks • RF4D #4051 N2188 • now flying!
Pictures at: https://picasaweb.google.com/111628310900713778468/RF4D_N2188?noredirect=1

SteveBeaver
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Posted Friday, November 8, 2013 @ 05:55 PM    YIM

Sorry to add to the confusion, but my a/c is completely original, and the Allen head retaining bolt is 5mmx0.9. I have just removed it, measured it on a pitch gauge, and further tested it by running it through a 0.9mm pitch die. It runs through with no resistance, but will not go through the 0.8mm die.

Buckers have lots and lots of 5x0.9 mm hardware. Even the landing wires and cabane wires are of that pitch. The assembly manual lists it, and in my stash of spare Bucker parts I have many 0.9mm pitch nuts and bolts. I understand this thread was common before 1960, but is little used today. That's what the Bucker museum people say anyway.

Steve

Markku
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Posted Sunday, November 10, 2013 @ 01:46 PM  

That Steve's comment is really confusing, in my plane those parts are also original and the thread is normal M5x0,8. I will use a new LN bolt M5x22, threacd lenght 9mm, that one is too long, but it's the shortest available, I will add some spacers under the head.
Markku


SteveBeaver
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Posted Sunday, November 10, 2013 @ 03:06 PM    YIM

Perhaps like British sports cars they were built with whatever was in the parts bin that day
dannparks
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Posted Sunday, November 10, 2013 @ 08:18 PM  

I think Steve might be on to something. There is a subtle difference in the shape of the nutplates. Mine has a pinched shape and Markku's is fatter, and it looks like they have different thread pitches. The factory probably had the older pitch and changed over at some point (or were very aware of it if they were mixed on different aircraft). In any case It looks to be something to be aware of when disassembling/assembling.

--------------------
Dann Parks • RF4D #4051 N2188 • now flying!
Pictures at: https://picasaweb.google.com/111628310900713778468/RF4D_N2188?noredirect=1

eugenio
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Posted Monday, November 11, 2013 @ 03:36 PM  

What seems very strange is that kind of strange threads or bolts are found on British and US Fourniers, why in all those registered in Germany, France, Italy, Finland, Sweden etc. this does not happen? Who can say his RF is "straight original" after more than 40 years and more than one owners? In all drawings from the RF3 on, all thread are specified ISO, so, please, believe me when I say that originally all them used standard metric threads, then for some reason somebody did the change.

Eugenio

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Posted Monday, November 11, 2013 @ 10:25 PM    YIM

A valid point. I know of no changes or repairs to the aircraft, and it appears to still have the original paint in place around the fittings, but I have no way to know for sure.
Donald
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Posted Thursday, June 16, 2016 @ 00:15 AM  

A bit of a necropost, I'm afraid but this thread came up when googling for metric hardware.

Mine is an RF3 and I have the tailwheel assembly out at the moment. That is held in place by four M5 socket head screws and my thread gauge tells me they are 0.9 thread pitch.
The aircraft is half a century old but as far as I can tell the tailwheel assembly is original.
I'd quite like to renew them but they are in not too bad a condition so I'll probably just clean 'em up and refit with some zinc chromate jointing compound for protection, but why is metric hardware so difficult? Probably the result of a multi nation committee.

milnerd
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Posted Saturday, June 18, 2016 @ 04:44 PM  

I just saw this and thought that I may be able to shed some light on it. The Avions Max Holste Broussard is held together with thousands of French Metric Standard bolts and screws. A friend who is restoring a Nord 3203 has hit the same stumbling block with strange thread pitch hardware. These screws were common in France in the 1950's and early 1960's before the DIN standard was adopted. The pitch on these screws are somewhere between DIN fine and DIN course. If you Google "Old French Metric Standard" you will find some tables. M5 x 0.9 was the French Standard.

John Aunins has scoured the world looking for NOS hardware for his Broussard but it has proved easier to look for Unicorn manure. He did find a place in Rhode Island that ran him some small batches of straight slot truss head screws for a price. They look great with high quality plating but of course not to any sort of standard.

I am 99.9% sure that the reason you are struggling is that nobody even lists French Metric Standard hardware any longer. I have seen a copy of an early 1960's Metric & Multistandard catalog that listed a small section that they used to carry but not for decades now.

So the bottom line is that you should not lose or mung up what you have because replacing them is just about impossible.

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