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Rotax ring mount to engine M10 bolts


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Hi,

 

I've been trying to get some information about the M10 x 110 and M10 x 35 bolts that are used to secure the ring mount to the engine itself.

 

Does anyone know the specifications for these?  I'm assuming they have to be some kind of high tensile bolt rather than the sort you buy at Bunnings.

 

Obviously they're not AN because AN don't do metric.

 

Thanks, Marty

 

 

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Marty, An M10 bolt is 0.393 inches, which is a poofteenth thicker than a 3/8" (AN6) bolt.

 

110mm = 4.33", or 4-3/8

 

An AN6-47 will do the job.

 

35 mm = 1.377, or 1-3/8

 

An AN6-20 will do the job.

 

You can quite safely use an AN bolt of the closest diameter to the metric one IF the fit you require is not close tolerance. If you really want to be pedantic, get some Imperial drills and drill your holes to suit the AN bolts you get.

 

Use this chart to identify the type of bolt you are buying if you are buying metric.

 

https://www.boltdepot.com/fastener-information/materials-and-grades/bolt-grade-chart.aspx

 

 

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Marty, An M10 bolt is 0.393 inches, which is a poofteenth thicker than a 3/8" (AN6) bolt.

 

110mm = 4.33", or 4-3/8

 

An AN6-47 will do the job.

 

35 mm = 1.377, or 1-3/8

 

An AN6-20 will do the job.

 

You can quite safely use an AN bolt of the closest diameter to the metric one IF the fit you require is not close tolerance. If you really want to be pedantic, get some Imperial drills and drill your holes to suit the AN bolts you get.

 

 

 

Hi OME,

 

These are bolts that go into the engine itself, so they can't be changed to AN. 

 

 

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Hi,

 

I've been trying to get some information about the M10 x 110 and M10 x 35 bolts that are used to secure the ring mount to the engine itself.

 

Does anyone know the specifications for these?  I'm assuming they have to be some kind of high tensile bolt rather than the sort you buy at Bunnings.

 

Obviously they're not AN because AN don't do metric.

 

Thanks, Marty

 

Definitely not from Bunnings Aero Space, however any good quality nut & bolt supplier is likely to stock (or ordre in ) what you need.  Do not try and substitute with any imperial sizes . Go & have a chat with them they will know what is available (lengths, hex, allen, torxs,  etc) in the M10 high tensile - my guess is that any grade above & including 8.8 will do the job.  Make sure you get good quality flat washers to suit (x 2/bolt if using a nut). One more point - use the aircraft manufacturer recommended or if not available, bolt approved torque settings.

 

 

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Unbrako socket head capscrews are the answer, they are alloy steel that is stronger than 12.9 grade in metric.

 

Under 16mm diameter, they are actually 1300MPa (189,000psi) Tensile strength. Over 16mm dia., they are 1250MPa.

 

Be aware that capscrews in Inch sizes are one standard high strength, 170,000 to 180,000 psi Tensile strength. Unbrako Inch sizes are 180,000 to 190,000psi Tensile strength.

 

But Metric capscrews come in metric 10.9 grade, metric 12.9 grade, and Unbrako grade.

 

The Metric capscrew listing is on Page 38 of the file below.

 

http://www.unbrako.com/images/downloads/engguide.pdf

 

 

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You probably already have the 110mm long one it is a crankcase bolt. Onetrack is on the money. You can get them from most reputable fastener suppliers.

 

Bunnings is overpriced garbage when it comes to fasteners.

 

 

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There isn't a hole drilled in the head of the bolts to thread a wire through. If you could drill a hole in the bolt head, you would have to run the safety wire around a post of the frame to have something to tie off against. I doubt if high strength Loctite would keep the bolt fixed as perhaps the Loctite would soften due to the hot environment of the engine bay.

 

 

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There isn't a hole drilled in the head of the bolts to thread a wire through. If you could drill a hole in the bolt head, you would have to run the safety wire around a post of the frame to have something to tie off against. I doubt if high strength Loctite would keep the bolt fixed as perhaps the Loctite would soften due to the hot environment of the engine bay.

 

They would be quite difficult to lockwire as they are recessed into the mount. There are grades of loctite that would work. 

 

Personally, I would just see what the Rotax installation manual recommends. 

 

 

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Wrapping PTFE thread tape around fastener threads is a simple method that vastly improves fastener retention rates. But you must wrap the thread tape in the direction that the fastener screws in.

 

One of my favourite fastener retention products is Parfix Polyurethane Sealant and Adhesive. It sets, but remains pliant, it keeps out moisture (which causes corrosion), and its grip on threads is second to none (Loctite excepted). It also doesn't melt, when it gets heated, unlike Loctite. Loctite will melt at 250°C.

 

But when you want to remove a fastener secured with Parfix PSA, it unscrews easily - unlike many of the Loctite anaerobic products.

 

 

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Thanks for all the replies.

 

Onetrack / M61, apparently "Nuts & Bolts Tasmania" stocks Unbrako in the sizes I need.  Thanks for the heads up about the 110 one.

 

I've looked at the Rotax installation guide and as far as I can see it doesn't go into detail about lock washers / chemical locking.  It seems like they've devolved that responsibility to the aircraft manufacturers, which isn't much help when you're scratch building and the plans don't go into much detail about it.

 

Anyway if you've installed the Rotax Ring Mount I'd be interested in knowing what you used to keep the bolt from moving.

 

Thanks again!

 

Cheers, Marty

 

 

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Download the Heavy Maintenance manual. Have a look at Section 71  6.1.3.

 

It gives torque of 40NM with lockwashers and grade 10.9 spec. as well other interesting stuff.

 

I like Loctite 243. It's a medium strength locker that will also help keep out moisture, is not too difficult to remove and is good for temps up to 200°C.

 

https://tdsna.henkel.com/NA/UT/HNAUTTDS.nsf/web/96FA02BC2AE06C5E85257E49004D92EA/$File/243-EN.pdf

 

 

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There isn't a hole drilled in the head of the bolts to thread a wire through. If you could drill a hole in the bolt head, you would have to run the safety wire around a post of the frame to have something to tie off against. I doubt if high strength Loctite would keep the bolt fixed as perhaps the Loctite would soften due to the hot environment of the engine bay.

 

 

 

They would be quite difficult to lockwire as they are recessed into the mount. There are grades of loctite that would work. 

 

Personally, I would just see what the Rotax installation manual recommends. 

 

I am astounded at both your comments - What is your problem with drilling the bolt head (hex, allen, torx) to accept safety wire AND since when did you have to have a designated anchor point for the wire - any suitable non moving point will do, including the engine mounting frame itself. Chemical locking agents are not as secure and can not be so easily checked by eye, as to their security, compared with security wire correctly installed.

 

I do not have a Rotax engine ring mount, however I have drilled all four of the mounting bolt allen key cap heads used and secured them with safety wire to the frame itself - easy to inspect for rotation/loosening and if by some miracle came loose, rotation would be limited to a mm or two at the very most - terrific piece of mind.

 

 

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I am astounded at both your comments - What is your problem with drilling the bolt head (hex, allen, torx) to accept safety wire AND since when did you have to have a designated anchor point for the wire any suitable non moving point will do, including the engine mounting frame itself. Chemical locking agents are not as secure and can not be easily checked by eye, as to their security, compared with security wire correctly installed

 

I suggest having a look at a Rotax ring mount. I have nothing against drilling and lockwiring, but have a look at how the allen head bolt sits deep inside a welded tube that completely restricts access for a useful lockwire. Maybe that's why checking the security of the engine mount bolts is part of the Rotax 100 hr engine servicing. Most of your engine is assembled using chemical locking, have you had any stuff fall off?

 

Does your Zephyr have a ring mount? If so, have you drilled and lockwired the engine attachment bolts?

 

My engine mount bolts are lockwired, but I have a bed mount.

 

 

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Edited...

 

Ah...wrong comment if no nut used.....(was going to say nyloc nut)

 

I'd guess with loctite/spring washer if in a blind hole......

 

Of course use mfg specs...

 

 

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What is your problem with drilling the bolt head (hex, allen, torx) to accept safety wire

 

I agree that this is a possible solution in theory, but in practice it is hard to successfully drill through the head unless you have a bench press drill and some very high grade twist drills. You would have to use a Numbered Drill in the 60 to 67 range.

 

since when did you have to have a designated anchor point for the wire - any suitable non moving point will do, including the engine mounting frame itself.

 

Again, quite correct. Wrap the wire around the tubing of the frame and secure the  bolt. But in this case, the design of the mount permits it

 

 912914suspensionframe.jpg

 

 

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I agree that this is a possible solution in theory, but in practice it is hard to successfully drill through the head unless you have a bench press drill and some very high grade twist drills. You would have to use a Numbered Drill in the 60 to 67 range.

 

Again, quite correct. Wrap the wire around the tubing of the frame and secure the  bolt. But in this case, the design of the mount permits it

 

 912914suspensionframe.jpg

 

I usually use a 1/16" cobalt drill and 'rocol' in a drill press (for the lock wire holes.  Tip - Nip up first to assess were the hole is best placed.) and I wrap tape around the engine mount frame where the lock wire will be wrapped to protect the paint coating against abrasion.  Cheers

 

 

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I suggest having a look at a Rotax ring mount. I have nothing against drilling and lockwiring, but have a look at how the allen head bolt sits deep inside a welded tube that completely restricts access for a useful lockwire. Maybe that's why checking the security of the engine mount bolts is part of the Rotax 100 hr engine servicing. Most of your engine is assembled using chemical locking, have you had any stuff fall off?

 

Does your Zephyr have a ring mount? If so, have you drilled and lockwired the engine attachment bolts?

 

My engine mount bolts are lockwired, but I have a bed mount.

 

Hi M6 - As already stated my 912 is not mounted on a Rotax Ring Mount but an ATEC design, somewhere between a ring & a bed, however I was not satisfied with the "security" of my engine bolts, so drilled the heads and safety wired them to the closes accessible fixed point - most often the engine frame - its doable !. Cant be sure of the bit size but a 2mm sounds familiar.

 

 

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Download the Heavy Maintenance manual. Have a look at Section 71  6.1.3.

 

It gives torque of 40NM with lockwashers and grade 10.9 spec. as well other interesting stuff.

 

I like Loctite 243. It's a medium strength locker that will also help keep out moisture, is not too difficult to remove and is good for temps up to 200°C.

 

https://tdsna.henkel.com/NA/UT/HNAUTTDS.nsf/web/96FA02BC2AE06C5E85257E49004D92EA/$File/243-EN.pdf

 

Thanks for that M61.

 

I've downloaded the heavy maintenance manual and happy to follow Rotax's instructions.

 

They don't even specify a chemical bond but Locktite 243 sounds good.

 

Cheers, Marty

 

 

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I usually use a 1/16" cobalt drill and 'rocol' in a drill press (for the lock wire holes.  Tip - Nip up first to assess were the hole is best placed.) and I wrap tape around the engine mount frame where the lock wire will be wrapped to protect the paint coating against abrasion.  Cheers

 

There’s no trouble drilling the bolts. The Allen head bolts that hold the ring mount to the engine are seated deep in those sockets shown in the picture. 

 

 

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Oaky - I see your problem - bit fiddly to "work" the safety wire down into and back out of a deep recess.

 

So how about purchasing some aluminium round bar stock , having it milled into 4 nice thick  snug custom spacers , purchase 4 allen key bolts of the appropriate diameter/ tensile strength but a bit longer than what you have now (dont forget to include a quality flat washer in your measurements) -  bolt heads are now just "proud" enough to easily use safety wire - a solution???

 

 

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