O.S PET 1.6cc info needed

I think one of these, enlarged a bit, would be good: http://www.rcgroups.com/forums/showthread.php?t=1807526 Scroll down to post #6.

Okay...Some people might like that look. Is that plane indicative of the era that these engines were popular? I was thinking...cooler-looking... See my scratch-built Comanche, for instance.

GUS THE I.A. wrote:Okay...Some people might like that look. Is that plane indicative of the era that these engines were popular? I was thinking...cooler-looking... See my scratch-built Comanche, for instance.

I looked at the picture. You're right, Gus, it ain't near cool enough.
Uh oh, I hope I didn't offend Geoff. Sorry, just a spontaneous reaction.

Hello world there's a song that we're singing c'mon get happy!!!!

It's a neat design the color scheme is not for everyone. How quick is it?

cribbs74 wrote:Hello world there's a song that we're singing c'mon get happy!!!!

I got Chinese eyes just looking at it.

It's from the fifties, so very much a contemporary of the OS Pet. As for not being cool enough, to each his own. I like Dil-Bod's scale midget racer look. As for the psychedelic paint job - uhhhh..., wellllllll... I much prefer the more scale-like paint job of the original.

Geoff the non-hippie

Hello
I have 3 of these motors, all of the screws are in pretty bad state . I measured OD 2.7 mm , and a pitch of 0.6 mm . At first , I believed they were 4 x 40  , but no .. The threads looks like the old SI european system ..
Do you know where to get such screws ?  
Thank you ..
Nobody knows ?

I think you'll find at least 1 test report for the PET on this fantastic site:

sceptreflight.net/Model%20Engine%20Tests/Index.html

You'll need to add the www or something to the link as I am still on probation and am not allowed to post an actual link. Spend the time to get to Sceptre; it is worth it.

gcb wrote:

Jason_WI wrote: Need to turn the carb around yet and give it a bath in my crock pot.

Interestingly, to convert the RC version to CL you remove the needle valve, remove the carb, reinstall the needle valve.

Of course to convert CL to RC you remove the needle valve, position the carb in place, reinstall the needle valve.

Conservative on parts!

George

It is not really any carburator though. It is just an intake choke, just like you would normally have for cold-starts. Using the choke will reduce the rpm by making the engine run overly rich, but that's about it....

The engines are a cross flow design but there is no baffle on the piston, instead there is a machined step on the piston;

frenchomebuilder wrote:Hello
I have 3 of these motors, all of the screws are in pretty bad state . I measured OD 2.7 mm , and a pitch of 0.6 mm . At first , I believed they were 4 x 40  , but no .. The threads looks like the old SI european system ..
Do you know where to get such screws ?  
Thank you ..
Nobody knows ?

The screws are all M2.5 and finding matching screws will be difficult unless you come across spares for this engine.

However, I would replace them with M2.5 cap head screws. See picture - the ones shown are M2.5 x 10mm and would require trimming to match.



I don't know where you are based but try a search on Ebay for M2.5 x 10 screws bolts.

ian1954 wrote:

frenchomebuilder wrote:Hello
I have 3 of these motors, all of the screws are in pretty bad state . I measured OD 2.7 mm , and a pitch of 0.6 mm . At first , I believed they were 4 x 40  , but no .. The threads looks like the old SI european system ..
Do you know where to get such screws ?  
Thank you ..
Nobody knows ?

The screws are all M2.5 and finding matching screws will be difficult unless you come across spares for this engine.

However, I would replace them with M2.5 cap head screws. See picture - the ones shown are M2.5 x 10mm and would require trimming to match.



I don't know where you are based but try a search on Ebay for M2.5 x 10 screws bolts.

I' m based in France, so here are tons of M2.5 screws .. They fitted the latest versions of OS PET, not the old, which are, as I measured, 2.7 mm dia, and 0.6 mm pitch .. On an other forum, I asked to a japanese man, he said that these screws are not a japanese standard. For some unknown reason, OS made these screws on the first PET production time . Never mind, I will let the old screws with damaged heads. If one day I have really the need to change, I will rethread 3 SI, as the pitch is the same, 0.6 mm. 3 SI screws are pretty hard to find now, as the SI has been gave up in the sixties , but however possible to find on fleamarts there .

I hadn't realised that the older PET had a different thread - I don't have one to try as I have a variety of screws.

Is it possibly 6 or 7 BA? BA screws were quite popular on some early engines.

ian1954 wrote:I hadn't realised that the older PET had a different thread - I don't have one to try as I have a variety of screws.

Is it possibly 6 or 7 BA? BA screws were quite popular on some early engines.

Thank you , no more they are BA or other brit standard . I studied and tried , anyway, nothing works ..
My screws, actually , are in good condition. It is these damned phillips heads that do not withstand the onslaught of unsuit screwdrivers ..
Have a nice 2015 !

Yes, the phillips heads do tend to suffer more than the threads. I also have an early 3-bolt backplate type Pet. There's a lot of speculation around, but if anyone can positively identify the head screws and possibly a source that would be really helpful.
I haven't heard of an "SI" screw thread as someone suggested and it didn't come up on a Google search.

Rod.

Oldenginerod wrote:Yes, the phillips heads do tend to suffer more than the threads.  I also have an early 3-bolt backplate type Pet.  There's a lot of speculation around, but if anyone can positively identify the head screws and possibly a source that would be really helpful.
I haven't heard of an "SI" screw thread as someone suggested and it didn't come up on a Google search.

Rod.

Someone knows
When in high technology school, the norms system was changing. The former SI system became ISO. Here we find the foundations of the SI:
http://physics.nist.gov/Pubs/SP330/sp330.pdf
and to get some guidelines SI threads, just google " filetages si" .

There are quite a few differences between M and SI, they are mainly located at the threads truncation , and only for some small diameters, in the pitch . Example 3 SI is 0.6, while M3 is 0.5 pitch.
That said, at the end of a  professional life in mechanical studies, I can say that sometimes, does any manufacturer would be required to design special screws, depending on many parameters, which sometimes  completely escapes to our subsequent reasoning.
What is sure is that Japanese mainly used metric system .
In relation to the subject of this post, maybe M Shigeo Ogawa decided that the choice of 2.7 mm screws  was the good relation between strength and weight.
Maybe his steel supplier , when Japan was still terribly short of raw materials, suggested him to save a bit, offering  2.7 instead of 3 steel wire.
These are only considerations , 60 years after the facts ..
So we will ever know more I think ..
That said, it is still possible to make specially manufacture such screws, it is only about price.
Personally, I'm repeating myself, if I really needed, I'll retap  3 SI, so as not to destroy the threads using another pitch than 0.6.
The best . André

The thread is indeed a 0.6mm pitch, and there is also an M3x0.6 thread that you could "convert to". I have both a tap and a die for it, which came with a cheap chinese set. Screws might be hard to find though as the regular M3 thread is a 0.5 pitch.

The reason for the easy damage to the "Philips"-heads is because they are not actually Philips heads. They are instead a Japanese standard that is close to a Philips head screw in appearance. Sometimes there is a dot on the screw to separate them from the regular Philips heads. The only way to safely handle these screws is to get a set of Japanese screwdrivers...

Surfer_kris wrote:The thread is indeed a 0.6mm pitch, and there is also an M3x0.6 thread that you could "convert to". I have both a tap and a die for it, which came with a cheap chinese set. Screws might be hard to find though as the regular M3 thread is a 0.5 pitch.

The reason for the easy damage to the "Philips"-heads is because they are not actually Philips heads. They are instead a Japanese standard that is close to a Philips head screw in appearance. Sometimes there is a dot on the screw to separate them from the regular Philips heads. The only way to safely handle these screws is to get a set of Japanese screwdrivers...

Yes, I know these different  Phillips heads, I have a Japanese screwdriver set, I do not had when I was a bad brat ..
In France it is quite easy to find  3 SI screws; personally, I have a small stock. We can recover someones in old tube radios, what I done for other applications, and even 3.5 mm SI pressure screws if needed, in the knobs.
What is difficult is to find SI screws in a good quality steel .. It is better to have them from a  M3 screw, re threaded with a good 3SI die, I do not think that a Chinese one could cut in such a steel. These tools work well for restoring a damaged thread, but no more. SI dies are sometimes available on fleamarts, ebay ....

Surfer_kris wrote:
The reason for the easy damage to the "Philips"-heads is because they are not actually Philips heads. They are instead a Japanese standard that is close to a Philips head screw in appearance. Sometimes there is a dot on the screw to separate them from the regular Philips heads. The only way to safely handle these screws is to get a set of Japanese screwdrivers...

The correct name for the "Japanese Phillips" is JIS (I'm guessing it stands for Japanese Industrial Standard). Surprisingly hard to find tools that fit, at least in Finland.

My old Honda has those screws, the originals are a mess, I already have new ones but I haven't bought the correct driver yet. It is not only the shape that is different, the JIS screw heads are also smaller than ones on "regular" metric screws of the same thread size. That's why I haven't converted to Phillips on my engine case screws.