OS LA hints

We know these are lovely engines, however the nasty plastic backplate is a concern. Not to worry. For the 40/46LA, the backplate (cover plate) from the cult favorite OS40FP (OS pn 23307000) fits just fine, as does the OS 40FP screw set. Find the p/n yourself, this is a test. Find the NVA p/n also for extra credit. For the OS 25LA, the cover plate is OS p/n 2330700. The head bolts on the 25LA are 3x12mm, not quite the same as the scew set for the OS FP20, but hey, close enough. The cover plate screws are the same as the FP20. "A foolish consistency is the hobgoblin of little minds" (Ralph Waldo Emerson). In any event, believe me or don't, if your rut works it must be a groove.

Screw set 35,40 FP #23313000 20-40 FP-S NVA #22311000

Other than getting rid of the remote needle valve assembly and its mounting boss on the .25LA, what exactly about the plastic backplate is a concern?
From a performance standpoint, i've used a .25LA extensively for sport racing and can find no issue whatsoever with the backplate, or any other part of engine for that matter.

Les

I too, at first, thought this was a cheap way of manufacturing this engine. However, the hard plastic backplate makes a big difference on a non-ball bearing crankshaft engine when an elecric starter is used! You don't get that metal-to-metal friction between the con-rod and the backplate. The remote NVA can be criticised, but does make sense from the manufacture's stand-point as far as safety is concerned. (keeping the fingers out of the prop arc!) For the price, it's a great engine.

The remote NVA can be criticised, but does make
>sense from the manufacture's stand-point as far as safety is
>concerned. (keeping the fingers out of the prop arc!) For
>the price, it's a great engine.

Progress is our most important problem

Methinks, from the manufacture's point of view, the remote NVA is another way to minimize change from the standard (throttled) version and thus minimize cost.

>Methinks, from the manufacture's point of view, the remote NVA is another way to minimize change from the standard (throttled) version and thus minimize cost

Me thinks it was lawyer engineered. Who cares if it sucks as long as it might avoid a lawsuit.
Jim

>Other than getting rid of the remote needle valve assembly
>and its mounting boss on the .25LA, what exactly about the
>plastic backplate is a concern?
>From a performance standpoint, i've used a .25LA extensively
>for sport racing and can find no issue whatsoever with the
>backplate, or any other part of engine for that matter.
>
>Les

From a performance standpoint you are right--until...

The big problem with the plastic back plate is that if you tighten the screws too much they eat into the plastic. Through continued running they will also eat into it further, causing the screw to become loose. Then as the screw works its way out, a leak occurs which will cause erratic running or the engine to quit altogether.

A number of people have said they had no problem with this. And then a few reported back later that they did. You can wait and see if you are going to be one of them, or you can fix it with the aluminum back plate and be done with it.

Again, the voice of sweet reason. This is exactly what happened to my 46LA and was d***ed if it would occur with the 25LA. I'm sorry if you are unable to risk your precious fingers on a real needle valve, mine are whacked, beaten, CA'd and otherwise suited to reaching through the propellor arc. If it's a worry, I can still pick my nose.

....or use small washers on the backplate screws, a little Lock Tite and forget about it! I've never had one leek. Used a Dremel and carefully cut the remote needle off.