David Davis Posted July 6, 2019 Share Posted July 6, 2019 I found this mount among my souvenirs. It has obviously been driiled for an engine but I don't ever recall having used it and it looks brand new and unused. I must have picked it up at a bring and buy. I am thinking of using this mount in a model. As you can see in the pictures the front is an adjustable structure made from aluminium. Four set screws go through the firewall then there are four hard-rubber washers, four "threaded donuts" which I assume compress to absorb the vibration, and four nuts with washers to hold the mount in place. Do the hard-rubber washers fit in front or behind the firewall? When drilling holes in the firewall for the mount, I assume that I drill 4.5mm holes to match the set-screws rather than 10mm holes to match the donuts. Then I assume that you tighten up the donuts as tight as you can by hand, then tighten the nuts against them, in order to compress them. Any advice gratefully received. Quote Link to comment Share on other sites More sharing options...
Wingman Posted July 6, 2019 Share Posted July 6, 2019 They look rather like Rawlnuts so the mounting hole would be the diameter of the rubber sleeve so the rubber sleeve would compress on the inboard side of the firewall and the rigidity can be adjusted by tightening the bolt. If you dont do that and just drill a hole the diameter of the bolt you will have the metal bolt touching the wood which will produce noise - at least that's my way of looking at it Edited By Wingman on 06/07/2019 12:43:14 Edited By Wingman on 06/07/2019 12:44:30 Quote Link to comment Share on other sites More sharing options...
Steven S Posted July 6, 2019 Share Posted July 6, 2019 Yes - you want to completely isolate the firewall from the engine mounting screw. Quote Link to comment Share on other sites More sharing options...
Steven S Posted July 6, 2019 Share Posted July 6, 2019 In a LORD engine mount system there would also be a metal tube inside the mount so that you can torque the bolt properly. Edited By Steven Shaw on 06/07/2019 13:29:49 Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted July 6, 2019 Share Posted July 6, 2019 I don't know that type of rubber mount but many years ago I used to use shorter rubber mounts with a threaed piece coming out of each end. You then used a nut on each behind F-1 and another nut on each pillar tyo hold the mount on. They worked really well and made the model much quieter Quote Link to comment Share on other sites More sharing options...
Jon H Posted July 6, 2019 Share Posted July 6, 2019 Personally i wouldnt touch one of those things with a 10 foot pole. Invariably they cause the engine to thrash about wildly (more so with 4 stroke it has to be said) and this can cause considerable problems. Before i even started work there Laser observed a pretty stark correlation between rubber mounts and carb/exhaust failures. The loads on the engine were extreme as it thrashed about an quite often bashed into something, which made the problem worse. To be fair, they can work successfully, but they require considerably more attention and maintenance than a standard nylon mount. Although not the same type, this chap has a vibration damped test stand. The poor thing is falling about laughing Quote Link to comment Share on other sites More sharing options...
Bob Cotsford Posted July 6, 2019 Share Posted July 6, 2019 Sorry Jon but the ones in my Jungmeister never needed any attention at all! Admittedly the engine is an OS61FX two stroke so the Pitts exhaust doesn't flap about wearing or fracturing it's mounting. I used Rawlnuts from the hardware shop with tap washers as buffers between the mount and firewall. It certainly helped in getting the engine below 80 dBa, I can't remember the exact figure but I think it was something like 78, it was tested about 10 years ago! Quote Link to comment Share on other sites More sharing options...
Former Member Posted July 6, 2019 Share Posted July 6, 2019 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Jon H Posted July 6, 2019 Share Posted July 6, 2019 Bob, as i said before, with 2 strokes there is much less of an issue. I still wouldnt use them myself, but there is less of a problem Percy, the video shows an extreme example for sure, but due to the way the camera shutter works it captures the true movement of the engine. Our eyes do not work this way so what we see is not always what is actually happening. Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted July 6, 2019 Share Posted July 6, 2019 I used to use them on up to .40two strokes. They did tend to wobble a bit at low rpm but once upto reasonable rpm they were steady and didn't allow vibration to get to the fuselage. Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted July 6, 2019 Share Posted July 6, 2019 I used to use Rawlings to mount my engines and they worked very well cutting some vibes transmitted to the airframe but still holding the engine firmly. The mount in John's video doesn't seem fit for purpose as it allows a very variable thrust line and doesn't look at all safe ! I used a similar mount in a pattern model in the nineties with a smaller YS four-stroke with no problems. Quote Link to comment Share on other sites More sharing options...
Former Member Posted July 6, 2019 Share Posted July 6, 2019 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted July 7, 2019 Share Posted July 7, 2019 Where? Quote Link to comment Share on other sites More sharing options...
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