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Poorly OS40 repair

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Jon - Laser Engines20/04/2020 21:28:26
5510 forum posts
268 photos

Cheers guys.

I should have done a thread on the SC radial really as there is quite a lot to that one but i didnt think about it until i had already dismantled the engine. Its about half way back to being reassembled now so the moment has more or less gone.

The 90 and 160 only needed a bearing swap so nothing too interesting there.

If anything looks like it might be interesting i will post it but i dont think i have anything else that is especially interesting.

One thing i might do is dig out each of my models and fire up the engines as most have not run in months. I could run some other interesting engines on the bench too and take some more videos. The snag is that i have a dozen airworthy models and loads of engines i could bench run. I dont think my various neighbours would be too impressed with me running an engine each evening for the next 3 weeks.

Ron Gray20/04/2020 22:12:25
2173 forum posts
941 photos

Run them on Thursday evening at 8 in support of the NHS, the more noise the better!

Jon - Laser Engines21/04/2020 08:27:33
5510 forum posts
268 photos
Posted by Ron Gray on 20/04/2020 22:12:25:

Run them on Thursday evening at 8 in support of the NHS, the more noise the better!

I wasnt aware you could use 60cc V twins instead of your hands but fair enough!

Ron Gray21/04/2020 09:17:09
2173 forum posts
941 photos

It's a much nicer sound than saucepan banging.

Jon - Laser Engines26/05/2020 09:15:18
5510 forum posts
268 photos

Probably the final update on this little saga as the project has now been completed.

Firstly, i was sent a new cam cover stolen from an ASP 52 as i thought it would fit, alas, it didnt. So, out with the tools to make it fit. Long story short i reamed it out so the bearing would sit further into the housing. I then had to shorten the overall length and repair the hole i made in the outer cover during my various drilling and reaming adventures. Once repaired, i doubt most would ever even know it had a hole through it.

Thanks to the very kind donation of a seagull challenger from a forum member i now have a suitable test model for the little 40. Lucky for me the engine used in the model previously was an OS62v which just so happens to have the same bolt pattern. I lowered the engine a bit to help with tank placement, threw some old 35meg gear at it and it was ready to go.

Not having the instructions and being too lazy to look it up i guessed at control throws and c/g. Both turned out to be more or less spot on And the little 40fs is more than enough power for this model. It must go like a missile on a 46 2stroke. I wouldnt recommend anything more than a hot 25 or something like an old 35fp.

Anyway, the model flew extremely well and was able to do everything i would want it to do. No its not got infinite vertical, but loops were plenty big enough and it will bunt ok as well. I will change the prop as the 10x6 is too small, but other than that all was well...until some tell tale radio glitches told me all was not well. I landed, taxied back to my feet and as i went to cut the engine there was no response. The radio had completely died, which was quite alarming. Examination revealed a broken wire from the battery to the switch. no idea why it broke, the battery was almost new and it failed just as it left the heat shrink on the pack. Bloomin lucky i landed when i did!

So, a few photos of the model and the repaired cam cover. I will get a video next time if i can.



Edited By Jon - Laser Engines on 26/05/2020 09:17:30

cymaz26/05/2020 09:18:59
9253 forum posts
1195 photos

Sometimes, Jon, the flying Gods just smile upon you......lucky beggar

Jon - Laser Engines26/05/2020 09:32:08
5510 forum posts
268 photos
Posted by cymaz on 26/05/2020 09:18:59:

Sometimes, Jon, the flying Gods just smile upon you......lucky beggar

it was my old 35meg radio that saved me. I suspect 2.4 would have either browned out due to erratic voltage, or hung on until the wire broke completely. Trusty 35meg twitched and wibbled at me to tell me there was a problem and suggest i land!

Denis Watkins26/05/2020 09:48:01
4448 forum posts
113 photos

35mhz always gave you a little warning, going softer and slightly mushy

My guru at the time taught me plan C, stay calm and use one servo at a time as you got back

It just left enough in the pack to get down, but I had no plan for a broken wire!I

Brilliant to see the motor useful again


Edited By Denis Watkins on 26/05/2020 09:49:49

Nigel R26/05/2020 10:01:37
3916 forum posts
678 photos
Posted by Jon - Laser Engines on 26/05/2020 09:15:18:

the engine used in the model previously was an OS62v which just so happens to have the same bolt pattern

I'm still wrapping my head around that.

I guess many of the current generation four strokes have moved to a very short stroke pattern? I suppose a benefit of that is to keep the crankcase bulk down (and overall weight) and allow good valve area?

IIRC Lasers are using only two different bores for the current models so you have a fair mix of long and short strokes?

Jon - Laser Engines26/05/2020 11:09:17
5510 forum posts
268 photos

I just checked the specs of the two engines and apparently the 62 is 2mm wider in the case. Clearly there was enough wiggle room in the mount for it all to work out.

Both engines have similar bore/stroke ratio's with the 62 being slightly shorter in ratio terms.

And yes, only 2 bore sizes for Laser. 70, 80 and 100 share a bore, as do 120, 150, 155 and 180

Frank Skilbeck26/05/2020 12:14:42
4730 forum posts
101 photos

Used to run my OS 40FS on either an 11x6 or 12x5, depending on the aircraft, ran well on either.

Jon - Laser Engines26/05/2020 13:15:10
5510 forum posts
268 photos

yea 11x6 was my target but all my props are 18 or bigger these days!

Paul Marsh26/05/2020 21:51:11
4028 forum posts
1217 photos

I flew my old Magnatilla today, and it still has one of these Mk1 OS 40 four strokes in it.
It's been in the model since day one, and was 2nd hand when I bought it, and still runs well, and the bearings are still ok,

Paul Marsh27/05/2020 13:16:58
4028 forum posts
1217 photos

Most engines can be fixed. Next door's weed wacker wouldn't start, and he was flicking over for an hour. I looked at it, and found that it wasn't drawing fuel, even though ran with "start you ...." for a few seconds. Was the pipes broken inside the tank, as the bulb wasn't priming. 10 mins later, ticking over sweet, with a new fuel filter added...

Steve Hargreaves - Moderator27/05/2020 16:58:57
6763 forum posts
197 photos

"As we are off down the rabbit hole on this i might ask one of the mods to start a new thread on the subject and move our posts given that its clearly a subject worth discussing."

As requested by Jon a new thread on Engine Care & storage is here **LINK** & all relevant posts moved there.

As the poorly OS40 is now mended & back where it belongs, in the air, I'll close this thread.

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