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Author Topic: OS max s 35 r/c  (Read 442 times)
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whiskers
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« on: January 18, 2020, 04:50:42 AM »

Just took a risk on one of these motors as I couldn't resist at £15. From the photos it looks unabused and clean complete with muffler. Even the Phillips screws on the head and back-plate look fresh (usually the first sign of a bad 'un in my experience).


Anyway, I was thinking I might put it in a control line model if it proves a decent runner. With this in mind does anybody know of an easily available suitable venturi/nva I may be able to fit. Is it feasible to just lock open the r/c carb and use it that way? Also, I know this is not going to be a powerhouse so are there any thoughts on the sort of size model this engine would be happy with? Any other hints and tips will be accepted!
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Konrad
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« Reply #1 on: January 18, 2020, 12:14:15 PM »

OS had a C/L version, so you should be able to find parts. I think even the newer LA and FP parts will fit.
The fix venturi will give you more power and more importantly better fuel draw.

This will be an upgrade to any of the classic Fox Stunt 35 ships.

As I recall this is a lapped iron piston and steel liner engine, as such use castor oil fuels with more than 20% oil content. As I recall the great Fox Super Fuel had 28% castor oil for his lapped iron P&Ls.

Modern fuel mixes with oil content down around 17% won't cut it for these old tech engines. Well, not for long!

All the best,
Konrad
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greggles47
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« Reply #2 on: January 19, 2020, 03:16:13 AM »

Well mate I recon you've got a real bargain. I have a 35S (cL version) in a Thunderstreak (54" Aeroflyte stunter)

It flies that with complete authority. 10X4 prop 10%nitro 20% Castor. It's an absolute gem of an engine, easy starting and tuning. Leave the RC carb on until you source a venturi and NVA.

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whiskers
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« Reply #3 on: January 20, 2020, 02:42:34 AM »

Thanks guys...that's good info.
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Konrad
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« Reply #4 on: January 20, 2020, 10:13:06 AM »

Good point about the prop. I don't know why so many kits and engines said to use the 10x6 for the 35 cid engine. I found that everything was much better with the 10x5. Can't say as I ever went as far down as the 10x4 for stunt CL flying.

All the best,
Konrad
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whiskers
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« Reply #5 on: January 26, 2020, 06:05:26 AM »

Got the engine and it was stuck solid! I gently freed it up (bit of heat) and it turned over.

The piston looked a mess. Dark brown and thick, guncky jelly all over. Removed the back plate and it looked worse. Really gummed up. I decided a strip down and clean up was in order before start-up.


So, off with the head. I was going to mark the liner prior to removal but this had a machined mark at the front so I did not bother.

Anyway it all came to bits easily and on cleaning the liner I discovered a second mark on the rear face of the liner...Bother!

I summised the exhaust port was the one that centralised in the exhaust port casting in the case, the higher of the two ports , if I remember. I have slung it back together like this.

It was a real mess inside . The crankshaft was half full of that hard jelly too. However, it all cleaned up lovely.

There is no detectable play in the rod big end and little end or the gudgeon pin/piston. The crank bushing is likewise. Bore and piston look fine and un-scored.

The compression is snappy and has that lovely honed piston 'spring' to it. I must say, I'm very impressed with the quality of the fits/machining in this thing.

Now ready to run it up. I need to try to find a C/L venturi NVA from somwhere now.


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mick66
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« Reply #6 on: January 26, 2020, 07:05:08 AM »

Hello

I've just got one back end of last year for use in a Mercury Cobra.  I need a Venturi/NVA also.  If you find a supply let me know Smiley.  I also need to sort CL venturi/NVA for a couple of OS 25 and 45 LA I bought.  Wish I knew how to use my ancient  lathe I was given Sad

Cheers

Mike
Attached files Thumbnail(s):
Re: OS max s 35 r/c
Re: OS max s 35 r/c
Re: OS max s 35 r/c
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whiskers
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« Reply #7 on: January 26, 2020, 08:44:16 AM »

Mick66 - if I find a supply I'll let you know. If you learn how to use your lathe let me know!!
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Konrad
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« Reply #8 on: January 26, 2020, 01:06:16 PM »

Without seeing a photo, that Gunk (mess) you found is a vey good sign. It is dried castor oil. Without it most of the ferrous parts would be rusted beyond recognition. I like to get my old engines moving by heating up the engine and adding methanol to the warm case in which the heat has allowed some motion. This will dissolve the gunk without damaging the varnish that might be helping seal the engine. (I don't like to over clean an engine). The only concern I then have is for the wrist pin. If I can't see (with the back cover off)the wrist pin moving I will then tear down the engine to get to the wrist pin, and manually clean the wrist pin and associated journals.

As to needle valve assemblies there a few CL dedicated suppliers that should be able to supply you with something. I like the very fine Super Tigre valve for its very fine threads and shallow (sharp) needle. (Stuka Stunt might still be around)

As a recall (I never liked OS, so I'm a bit foggy here) I think the RC spray bar and needle are the same as that used on the CL engine. It would take the place of one of the carb retention screw.(This is with the old air bleed R/C carb such as that found on the OS S 35, see photo above).

All the best,
Konrad
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whiskers
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« Reply #9 on: January 31, 2020, 09:23:42 AM »

 Heads up for Mick66 and anybody else interested. Just Engines in UK seems to be selling C/L venturis and matching NVA in various sizes. I thought they are a bit pricy. But...if your engine's a belter might be worth a look. Cost together more than two of my OS 35s!!

Get that lathe fired-up.
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Big G
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« Reply #10 on: January 31, 2020, 10:05:48 AM »

Re: NVA and venturis for OS engines. If it's any help to you, I always found ST spray-bar/needles ideal for OS LA engines of all sizes, and more precise than the OS units. Problem is, I'm not sure if they're still manufactured. Re: venturis and metal backplates, I think Stunthanger in the USA can give you a contact address or two, but beware - not cheap by the time they're delivered to the UK. You could also try Alberto Parra in Spain - I know he used to stock ST NVA's and spares for other makes. The only other suggestion is to contact Ed Needham via the UK Barton CL Forum - he may be able to help with both NVA's and venturis. Other than that, find someone with a lathe.

What is NOT a good idea is to try to fly CL stunt with the rear-mounted NVA that comes as standard with OS LA engines. It'll work up to a point, but is very imprecise.

G
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mick66
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« Reply #11 on: February 22, 2020, 12:57:32 PM »

Hahah ... I fired up the lathe after talking to a local model engineering expert ... TomOliver

Anyway ... took me ALL day but I've got a Venturi.  Copy of a RandySmith venturi he sells in the US but ... sadly ... not the same quality.  10mm down to 7mm at NVA.

Not my NVA ... that's the next thing to learn!

Attached files Thumbnail(s):
Re: OS max s 35 r/c
Re: OS max s 35 r/c
Re: OS max s 35 r/c
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Konrad
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« Reply #12 on: February 25, 2020, 07:41:49 PM »

You had a lathe at your disposal all a long!  Grin

Looks like a nice piece of work.  With a lathe you can make a lot of nice fitting round parts, bushing, spacers, spinners etc..

All the best,
Konrad
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mick66
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« Reply #13 on: February 28, 2020, 01:20:11 AM »

Haha ... it looks better than it is.  The lip is a good few thou thicker at the top than the bottom.  Off centre. 

I must be a good workman as I blame me and not the tool.

Cheers

Mike
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Konrad
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« Reply #14 on: February 28, 2020, 10:57:35 AM »

Tolerance man, tolerance! As there are no other parts moving or fitting up close a milimeter off
would be fine.

All the best,
Konrad
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TimWescott
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« Reply #15 on: February 29, 2020, 06:18:03 PM »

A venturi has to be the easiest thing to turn out on a lathe that's actually functional.  Needle valves -- not so much.  I've made some semi-good ones, but they're not something I'd want to hand out to unsuspecting victims.

IMHO the OS FP needle valve is OK -- but I'm pretty sure that the 35S has a smaller hole for the NV than the FP.  I know the FP is a 3.5mm unit (and the ST is 4mm, so you have to drill out the case; I don't like non-stock parts unless it's really necessary).

You might scrounge around on eBay.

And finally -- wiring the carburetor open can be done; I've had pretty good success.  If the barrel leaks then you may get inconsistent runs, but it's worth a try.
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