Engine mount - wood - best way to attach engine?

[EGB 953]

Finishing a Ben buckle style 25-30 size plane with a wooden engine mount. Unsure on two things:

1. Should I use wood screws and attach directly to the mount or bolts?

2. Should I use those brackets/plates (not sure what they are called) as opposed to attaching engine directly to the wood? I like the idea of the brackets as you gun make small adjustments to engine alignment. 

 

Any advice much appreciated, I haven’t used a wooden mount before. 

[Robin Colbourne]

Wood screws into wooden bearers don't stay secure for long.  The engine vibrates, which vibrates the screws, which opens out the holes and before you know it the engine is flapping all over the place.
If you can easily get at the underside of the bearers, then machine screws, washers and nyloc nuts are an option.  My prefrerred method is captive 'T' nuts epoxied into the underside of the wooden bearers and machine screws, passing through washers on top of the engine's mounting lugs going into the T nuts with a drop of nut lock on the screw thread.
If you use non-high tensile screws there is the possibility of shearing the screws and not the engine's lugs in the event of an 'arrival'.

With regard to a separate engine mounting plate, Using fairly widely spaced mounting lugs gives you the option to change to a different make or size of engine without making a mess of the wooden bearers, as it seems no two engines have exactly the same mounting hole spacing.  Use either a 1/8" aluminium or 3/16" or 1/4" tufnol or paxolin if you can get it.  They are fabric or paper reinforced phenolic resin.

 

Edited February 4 by Robin Colbourne

[EGB 953]

Thanks very much that’s very helpful. 

[Sam Longley]

I have Iroko bearers encased in west epoxy along with the rest of the engine bay. The engine is an OS 55AX. I have epoxied a piece of brass under each bearer.

Each piece is about 5 mm longer than the bearer of the engine & about the same width. The thickness is 6mm & I have tapped it for 3m SS cap headed bolts. When I applied the epoxy I put short, well greased bolts, in place to hold the brass pieces in place (The wood had been pre drilled) The bolts formed holes right through the epoxy for the future- see below.

Then when finished I was able to remove the bolts without the brass falling free. Unlike single nuts they will not suddenly rotate. They do not need access below & the brass will prevent a degree of vibration releasing the bolts. In the event of problems longer bolts will allow locking nuts under if required; but only after many flights.

Sam Longley