1971 OS PET III 099

Rod, you may have a problem with finding screws for the OS. Some and I'm not saying this particular model used a special pitch metric screw. These are no longer used in production thus leaving many of us without. These screws were commonly used for the OS .15 steelfin. Even the MAX-S .35's from the 70's used those screws. If your screws are still good clean them up and reuse. These might come in handy, http://www.ebay.com/itm/OS-PET-099III-GASKET-SET-NIP-/221374800604?pt=Radio_Control_Parts_Accessories&hash=item338af762dc Ken

On this engine the screws, head and backplate, are M2.5 x 0.45.

Ken Cook wrote:Rod, you may have a problem with finding screws for the OS. Some and I'm not saying this particular model used a special pitch metric screw. These are no longer used in production thus leaving many of us without. These screws were commonly used for the OS .15 steelfin. Even the MAX-S .35's from the 70's used those screws. If your screws are still good clean them up and reuse. These might come in handy, http://www.ebay.com/itm/OS-PET-099III-GASKET-SET-NIP-/221374800604?pt=Radio_Control_Parts_Accessories&hash=item338af762dc Ken

Ken, I'm curious now to know if this engine may have utilized those odd-pitch metric screws? When you mentioned the "steel-fin" OS .15 having them.

Roddie, I believe that is the combat version which is somewhat a rarity. Quite popular in Australlia and probably easier to find parts in the UK or there. My knowledge in regards of these engines is limited due to I wouldn't loose or strip the screws. You just knew that SAE was always easier to obtain due to the lack of parts support and availability of metric screws back then. Nine out of ten times if the material allowed for it, you tapped the holes out for SAE. It's much easier to obtain metric hardware that's small today in small quantities especially in the r/c car market. This wasn't the situation in the 70's. That OS is a 60's vintage engine. Ken

I have an OS 15 - think it is a Max III - it is in the beauty parlour at the moment. I will measure the screws on that and test the pitch.

AND NOW - A THREAD ABOUT THREADS!

I will warn everyone that one of the most common mistakes in engine restoration is, through assumption, that you have selected the right screw with the correct thread.

IF IT ENTERS THE HOLE, TURNS FREELY AND THEN STARTS TO RESIST ------- STOP!!!!! ---------

A nice chap PMd me the other day with a query about the screws on the Frog 100. He is trying to rebuild an engine owned by his father and so it has sentimental value.

He asked me if the threads were 10 BA - a logical assumption for a 1947 British built engine. I thought more logically from the size of the head that they would be 8BA.

I removed one of the screws and immediately realised that 10 BA was too small - 8 BA too large. AH! 9 BA methinks! Wrong it would fit but I immediately knew when trying a 9 BA screw was that all was not well.

Then came the trail and error. Fortunately for me , I have a collection of nuts, bolts, and screws - I throw nothing away. I have every small set of taps and dies - this one was soon identified as UNC 1 64.
An american thread in a 1947 British built diesel!!!! Not surprising as just after the war they would have used anything they could lay their hands on. But it did make me wonder whether engines would have a consistant use of the same screw thread - all the reason to be more careful.

Just like there is UNC and UNF - the metric has coarse and fine. It is easy to become confused and ruin a thread.

9 BA, UNC 1 64, M2.5 coarse and fine - all fit!!! Pick the wrong one and the thread will be ruined!

M2.5 coarse is .45 pitch and fine is .35 pitch.
UNC 1 64 is approximately .40
9BA is .39

All close but slightly different with slightly different diameters but NOT EQUIVALENT.

Ken Cook wrote:Roddie, I believe that is the combat version which is somewhat a rarity. Quite popular in Australlia and probably easier to find parts in the UK or there. My knowledge in regards of these engines is limited due to I wouldn't loose or strip  the screws. You just knew that SAE was always easier to obtain due to the lack of parts support and availability of metric screws back then. Nine out of ten times if the material allowed for it, you tapped the holes out for SAE. It's much easier to obtain metric hardware that's small today in small quantities especially in the r/c car market. This wasn't the situation in the 70's. That OS is a 60's vintage engine. Ken

That OS Max III .29 was given to me by my Uncle, who was in the USAF during the late 60's early 70's. He could quite possibly have purchased it while Overseas. He was stationed in Thailand for a bit back then.

One of the neat things about this Pet is that to switch between CL and RC just remove the needle valve assembly and either add or remove the throttle, then reinstall the needle valve.

George

Here are my Pets.  How about the venturi choke on the second version! Early throttles fascinate me.  No one actually knew what would work best and tried everything.  Having only a rubber band's torque to actuate things only added to the challenge.


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Beautiful collection of engines there, Ian and GWILLIEFOX. I gather that the throttle barrel mounted above the venturi is very similar to Bernie's choke throttle used on the Cox Sure Start choke tube type engines.

The OS Pet series seemed to be decent engines for the day, continuing as late as they did into the 1970's.

I may have wound up being a proud owner of one, the OS Pet .06 CL/FF engine. I wanted something with a little more power than the Cox .049 Golden Bee I had on my GB Junior Falcon back in 1973. I placed a mail order with Hobby Shack, Fountain Valley, CA. To my pleasant surprise, they were out of stock on the Pet and substituted an OS Max .10R/C with exhaust baffle (no muffler) at no additional cost.

I put that engine on a 39" span TF Schoolmaster, turned it from trainer to a decent sport plane. Nice thing was without muffler, it only weiged 3 oz and put out considerably more thrust than a reedie.

Yes, the Cox surestart construction certainly has borrowed ideas from the 50-ties.
I think they knew very well though that it was only acting as an intake choke, as the larger engines had proper carbs in the late 50-ties. On the smaller engines it was also abandoned in the early 60-ties I think, so they only ran that for a few years.

OS shows a proper carb on the .10 engine in 1964 on their history pages; http://www.osengines.com/history/ostimeline03.html

Surfer_kris wrote: OS shows a proper carb on the .10 engine in 1964 on their history pages; http://www.osengines.com/history/ostimeline03.html

Whereas the Pet was an entry level engine the MAX-10 was a step up. It ran a bit better and cost al little more. If I remember correctly the MAX-10 had a drop-in liner from the beginning whereas only the last version of the Pet had a drop-in liner.

OS paid attention to details back then. I believe all except the Pet back then had brass glow plug threads.

They were (and still are) a great engine. My first MAX was a MAX-I .15 which was a very good engine. Of the Pets shown above, I had the first two when they came out and still have the last two. Unfortunately my Pet-2 is just a parts engine with the beam mounting lugs removed.

George

So good they are, I have two of the mid 1960's .10's and one .15 still NOS in the box. I believe you are correct, George, I'm away so can't check physically but the .10 IIRC has a brass insert for the plug. This engine is unbelievable, has a reliable tick over idle even though it doesn't have an idle mixture bleed screw. I can extend its idle and it will still power up without faltering. Half throttle or less without muffler and only the exhaust baffle sounds muffled. At half throttle a plane will fly like it has an .049 reedie. Wide open throttle its noise is very .049 like, no louder.

With flight characteristics and user friendliness as such, no wonder why OS became a favorite among many a modeler in the 1960's and beyond.

Yes, they don't have any adjustable airbleed screw but they do have a fixed airbleed function in the carb. The hole above the throttle is larger than below, hence leaning out the low end just like an airbleed hole does.

Here are two of my PETs;


And the instructions, recommending 28% all castor oil in the fuel;

Hello Friends , I am PET stupid and was the Pet OS engines a series of engines or the os before it was ? Eric

getback wrote:Hello Friends , I am PET stupid and was the Pet OS engines a series of engines or the os before it was ?  Eric

Certainly no expert on it, but I remember seeing the ads for the OS Pet engines in America's Hobby Center AHC catalog and in Hobby Shack's catalog back in the late 1960's and early 1970's. In the series were the smaller engines, a .06, .099 and I think may be a .049. Their 1950's heritage is quite evident with the 3 bolt back, exposed steel cylinder cooling fins on the earlier ones, etc. Peter Chinn writes favorably of them, seemed to be user friendly with no vices.

I like the simplicity of the choke tube styled throttles for RC use. Seems that back then, RC for smaller planes was escapement driven as these were the lightest actuators of the time. Receiving equipment had to be light weight, thus most were simpler super regenerative receivers with lower parts counts. It must have really been something to have to subsist on short lived 22.5 Volt photo flash batteries the size of modern 9 Volt ones ganged in series to provide enough plate voltage to provide tube (valve amplification) along with carbon zinc pen cells for valve filament power and another set for escapement power. The details in Hal DeBolt's 34" span Livewire Kitten plans are very telling:

Outerzone: DeBolt Livewire Kitten



Throttle controls mostly by escapement were quick blip (full on or idle), which didn't require true proportional throttling. Thus I gather the choke type throttles were reasonably effective. The later mid 1960's OS with true carburetor came about when Galloping Ghost proportional was in vogue.

getback wrote:Hello Friends , I am PET stupid and was the Pet OS engines a series of engines or the os before it was ?  Eric

OS made engines many years before it released the "Pet". AFAIK that was the first OS engine with a pet (pun intended) name but I only started following OS engines with the MAX-I so there may have been others.

George

Edit: As far as I can remember I bought my MAX-I .15 in early 1957 and my first Pet in late 1957.

An airplane design showing the OS Pet .099 in its plans is the 46" (1168mm) wingspan 1962 RC Aero Star by John Zaic, kit produced by Aero Models. It is an odd swept wing cabin. I purchased the kit on clearance from AHC back in the early 1990's, while they still maintained a mail order sales newspaper flyer.

http://outerzone.co.uk/plan_details.asp?ID=5612





That will be a real hoot to fly, albeit on rudder only with OS Max .15R/C on throttle.

Thanks Guys , Man I am glad its not that hard to set up today . I eally like the OS engines they are mostly user friendly witch can take the fun out of modeling pretty quick ! Eric

Hi Guys,

Sorry to resurrect an old thread, but I have been searching for information about replacing a needle valve assembly on an OS PET III 099 engine.

I've finally realised that I needed to register on some forums and ask some questions.

When in comes to machining metals, I'm not set up for it, neither do I have the skills. Unlike many collectors, I like to have my engines operational and preferably in planes. (I also don't have that many engines.)

Does anyone know of a source of replacement needle valve assemblies for an OS PET III 099?

I know it's an old motor, however, last time I asked online for parts, I had two different people respond with new-in-packet gasket sets for my OS Max III 35.

Thanks,
Mike

I fully understand the frustration in having an engine without a needle valve assembly. It is unfortunate that the NVA is so delicate and easily broken.

It has to be a very special engine for me to make one and it takes some time to get a replica and needs quite a bit of tooling.

In the UK, I am lucky because NVAs for DC engines appear regularly on Fleabay and I snap them up for the repairs I do. It is almost one size fits all.

Finding NVAs as spares, even for current engines is not easy. Hardly any model shops stock spares anyway and certainly not for control line engines.

It is easy to find needles for the larger .35 + engines but smaller engines are difficult. RSM supply some.

https://www.rsmdistribution.com/index-2.htm

In the UK - Progress Aero Works, stock and sell NVAs for their range of engines - FOR PAW 55, 049, 06, 09, 15, 19 - all at £6.50 + vat + postage. These can be fitted to quite a range of engines.

http://www.eifflaender.com/

A bit of modification is often necessary to get them centered (washers), sometimes the hole in the venturi may needs modifying, but if you want a runner rather than a looker then it will be worth he effort.

Just engines sell venturis for modifying engines that accept an OS NVA.

http://www.justengines.co.uk/acatalog/Venturi.html.

I am convinced that there must be a business opportunity for manufacturing a range of NVAs.

Thanks for your very informative response Ian.

I understand the effort required to make NVAs. In the past I haven't been afraid to replace standard items with alternatives, however, I was usually informed by someone who knew that they were compatible. One of my biggest problems is knowing what is compatible.

In the past I have probably broken some cardinal rule by drilling out an engine spray bar hole so that I can fit a much more readily available Enya needle valve assembly. Like I say, I just want to be able to use my engines in planes.

Knowing the correct sizes of the various NVAs is not easy, as they are rarely stated in the advertising, so unless you are using them for the intended platform, you're not even sure that they will fit.

You are correct when you say getting smaller NVAs is a problem...there are many replacements for the larger engines.

Cheers,
Mike.