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OS 52 Surpass engine mounting.


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Afternoon All, I hope we are all looking  forward to the weekend!

A quick question on mounting my OS 52:

The manual suggest using a 'beam type' arrangement of hardwood bearers or an OS aluminium mount - I have one of the plasticky type mounts that I believe can be screwed into with self tappers or drilled through and used with bolts and nuts. 

The manual specifies a 3.5mm Allen screw for mounting - after checking what I had, I inevitably found only 3mm and 4mm screws. The 4mm screws do not fit through the mounting holes on the engine but the 3mm screws obviously do with a little slack to spare.

Is it a terrible idea to use the 3mm screws? Will the engine inevitably shake itself loose if the exact fit bolts are not used? Any experience in this would be very helpful. 

On a related note, what is the best method for my type of engine mount? Screw  directly into it or drill through  and use bolts with washers and lock nuts? 

Many thanks in advance,

Rob

 

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If you can find 3.5 mm bolt that would be good then drill and tap the mount . Failing that just drill clearance and fit nuts . 

Justin at rapid RC stock 3.5mm nuts and bolts . If you use self tapper then drill a pilot hole before attempting to screw into bearer as they have been known to snap . 3mm bolts would allow some movement  if they are loose although that will also allow for any inaccuracies  in the drilling of the holes.  I have used them in the past with nyloc nuts and washers  without any issues .

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I just drill the engine mount holes out to 4mm and use 4mm cap head allen screws (or occasionally self tappers into the plastic mounts).  There's more than sufficient 'meat' in the beam mount flanges.  Well, that's what I did when I used glow engines and what I did with my OS52 Surpass.

 

Geoff

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On 19/02/2021 at 16:19, Geoff S said:

I just drill the engine mount holes out to 4mm and use 4mm cap head allen screws (or occasionally self tappers into the plastic mounts).  There's more than sufficient 'meat' in the beam mount flanges.  Well, that's what I did when I used glow engines and what I did with my OS52 Surpass.

 

Geoff

One drawback of drilling engine bearers is it reduces the resale price of the engine if you ever want to sell it . I disagree ,JMO about " sufficient meat in the beam mount flanges" and have seen many drilled mounting lugs snapped off. A drilled engine is only worth spares or repair mo ey even if it's a good runner . Again I stress JMO  and don't want to start a bun fight but many of the IC brigade will probably agree that drilling engine cases/ mounts is not recommended.

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On another thread, you can read that manufacturers widely recommend that their engines be run on fuel with 18%+ oil content and this need is increasingly disputed, so I wouldn't park my brain just yet.

 

Personally, I wouldn't drill a brand new 'quality' engine and I wouldn't buy a second-hand engine that had been drilled, but I would drill an undrilled second-hand engine.

 

Alternatively, you can file out the mounting holes, concentrating on the sides opposite the corners of the lugs.  This will alter your centres, obviously, but it will also keep you away from the lug edges, thus enhancing meat preservation...

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I wouldn't dream of drilling or filing or in any other way interferring with the engine's mounting holes. Just use 3mm fixings. Half a mm of slack allows for any inaccuracies in the drilling of the engine mount.

Use washers and nyloc nuts.

If the engine moves in the mount then the fixings aren't tight enough!

GDB

 

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Absolutely -  use the correct fixings.  I'm not overly concerned with devaluing engines which are second-hand to me.  I'm more likely to gift them to friends than try and screw the last penny out of them in resale value - it's a hobby.

 

But I wouldn't advocate using undersized fixings either.  If you follow the logic that the manufacturers hole sizing is carefully considered and sacrosanct, then you should apply the same logic to the fixing hardware was well.

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On 19/02/2021 at 16:19, Geoff S said:

I just drill the engine mount holes out to 4mm and use 4mm cap head allen screws (or occasionally self tappers into the plastic mounts).  There's more than sufficient 'meat' in the beam mount flanges.  Well, that's what I did when I used glow engines and what I did with my OS52 Surpass.

 

Geoff

I was about to add that I fitted my OS 52 Surpass to the nylon engine mounts of my Sig 4 Star yesterday and that 4mm bolts were a good fit...

 

I used nuts, bolts & washers, though I have used self tappers into nylon mounts in the past without any problems. I have also drilled and tapped nylon mounts and just used standard machine screws, also without problem, though there is a limit to how many times you can remove and replace the engine using this method.

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On 22/02/2021 at 13:18, Dave S. said:

 

... it is held in place with 3mm until they get some more in!

 

Are you sure you want to do that?  As a wise man once said:

 

On 21/02/2021 at 20:52, Mike T said:

... If you follow the logic that the manufacturers hole sizing is carefully considered and sacrosanct, then you should apply the same logic to the fixing hardware was well.

 

?

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2 hours ago, Mike T said:

 

Are you sure you want to do that?  As a wise man once said:

 

 

?

It's just to hold the engine in place, it hasn't been run yet and is unlikely to be until the bolts are replaced. Prefer to stick with one system- metric, unfortunately, as I ended up with a good selection of metric fastener while living abroad - sadly not including 3.5mm!. If I start buying UK & US fasteners I'll need more storage space.

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If the bolt size is so  critical, where do you stand on MS v HT bolts?  Another wise man once warned against using HT (ie most cap head screws) as a crash can result in the mounting lugs giving way before the bolts, whereas common mild steel bolts will bend, stretch or break leaving the lugs intact.  Me, I'd be happy going down a half size to 3mm on a 52 4 stroke or cooking 40 2 stroke.

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Don't crash! ?

 

TBH I think once torqued up, it will matter little whether the bolt is 3mm or 3.5mm. If using 3mm you could always sleeve the smaller bolt (I say sleeve, I mean wrap with PTFE) to make sure the engine is aligned / located correctly, before torqueing it all up.

 

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