OS Max-S 35 Engine

[Steve Dwyer]

Anyone know where I can find a Max-S 35  Venturi and needle valve, also need a OS-703 strap on muffler.

Appreciate your help.

Steve

[Robert Zambelli]

Hi, Steve.
You can use either an OS or ENYA NVA.
If you can't find one, get one from Randy Smith.

If you can't find a venturi, let me know and I'll make one for you.

Bob Z.

[Robert Zambelli]

Also, I might have the muffler you need.

[Dan McEntee]

  I think Jim Lee can help you on the venturi, maybe the OS needle valve. Bob Brooks, known as shtterman on eBay, had Enya make him some OS spec NVA that should work also. His email is shtterman@aol.com The 703 with strap will be the hard part, to get one that is complete. I just messed with one, and drilled out those bosses just inside the exhaust on from and back and discovered that OS FP/LA 25 mufflers are the same dimension. I have not tried those as of yet but it's on my list. They are similar in size to the 703, might be about the same restriction. The to3 had a big diameter at the end of the "stinger" but the hole inside the muffler is much smaller. Flight testing is the answer. It looks like the LA/FP muffler will center up well enough. The difficult part is drilling out the bosses but if I can do it with the drill press I have, anyone with a drill press ought to be able to. Just get yourself a good center punch mark so the drill picks up clean without walking.
  Type at you later,
   Dan McEntee

[Motorman]

Are those the engines that had the soft con rods? Might want to pull the backplate and check the big end before you put time/money into it. At one time Len Newman had good aftermarket rods for sale if that's the engine I'm thinking of.

Motorman

[Robert Zambelli]

Yes, the early Max S engines had connecting rod issues.
I know, I had one that I bought in 1968 - still have it. Sent it back to World Engines and they reconditioned it - never a problem since.
Also, I have been told that the rod from a plain-bearing Super Tiger 35 will fit but I've never tried it.

Bob Z.

[Steve Dwyer]

  I think Jim Lee can help you on the venturi, maybe the OS needle valve. Bob Brooks, known as shtterman on eBay, had Enya make him some OS spec NVA that should work also. His email is shtterman@aol.com The 703 with strap will be the hard part, to get one that is complete. I just messed with one, and drilled out those bosses just inside the exhaust on from and back and discovered that OS FP/LA 25 mufflers are the same dimension. I have not tried those as of yet but it's on my list. They are similar in size to the 703, might be about the same restriction. The to3 had a big diameter at the end of the "stinger" but the hole inside the muffler is much smaller. Flight testing is the answer. It looks like the LA/FP muffler will center up well enough. The difficult part is drilling out the bosses but if I can do it with the drill press I have, anyone with a drill press ought to be able to. Just get yourself a good center punch mark so the drill picks up clean without walking.
  Type at you later,
   Dan McEntee

Dan, I see where the bosses you are referring to could be drilled out. I lined up a LA/FP muffler and it would work. Before I try this I'd prefer locating a OS 703 muffler. We'll see how that goes.

Thanks,
Steve

[Steve Dwyer]

Are those the engines that had the soft con rods? Might want to pull the backplate and check the big end before you put time/money into it. At one time Len Newman had good aftermarket rods for sale if that's the engine I'm thinking of.

Motorman

MM,

This looks to be a low time engine, it's clean but has run. I don't feel any play in the crankshaft pin to connecting rod nor do I have any idea if this is an early engine. Any thoughts how I can determine if this may be a problem or was it a crap shoot back then?

Steve

[Steve Dwyer]

Also, I might have the muffler you need.

Bob that's great, hold on that I've reached out to Bob Brooks - Shtterman as well and he responding but I'm waiting on clarification of what he has.

Steve

[Trostle]

I ran the OS 35s in competition for a number of years with various commercial fuels from the mid 60's through the early 70's.  My experience that excessive rod wear started to impact the performance of the engine after 200 flights or more.  The replacement rods that Len Newman made available worked well.  I also had heard that the bushed rods from the Super Tiger .35 also fit, though I never tried one.

Keith

[Dick Tyndall]

  The Super Tigre .35 rods will work but you have to ream the bottom bushing with a .250 reamer. I made a fixture years ago to do this in my milling machine to get the proper alignment.

                   Dick Tyndall

[Dan McEntee]

MM,

This looks to be a low time engine, it's clean but has run. I don't feel any play in the crankshaft pin to connecting rod nor do I have any idea if this is an early engine. Any thoughts how I can determine if this may be a problem or was it a crap shoot back then?

Steve

   If you have the engine that far apart, I would take the rod out and chamfer the pin holes just a bit, as a way to help oil find it's way to where it will do some good. If there are no oil holes in either end of the rod, I would drill some oil holes about6  .030" and chamfer those holes also with a bigger drill bit. Won't hurt a thing, and if the extra oiling helps, you may double the life of the rod while you look into options for replacing it. Might be a lot of Len's rods out there not being used, and may be some other option we don't know about. Meanwhile, just run the engine with at least 25% total oil with at least half castor and enjoy it. I like the run they have.  You could also drill the muffler holes at this time, just because you can. If you find a 703 and strap, fine. They are just kind of a pain in the butt on a full fuselage airplane. Not much of a problem on a profile. I don't know if you can convert the 703 to bolts or not. Not very much meat to drill and tap.

 Good luck with it,
   Dan McEntee

   

[Steve Dwyer]

Dan,

There is a hole at the bottom of the rod see photo. I wonder if this is a factory add brought on because of early problems with wear out? 

I do use about 24% oil 50/50 castor/synthetic in all my engines except the old Foxes and McCoys where I use straight 29% castor.
I'm still on the hunt for the 703 muffler and correct venturi.

Steve

[frank williams]

There is one NIP right now on Ebay.

https://www.ebay.com/itm/223453536441?hash=item3406de60b9:g:KaIAAOSwuiNZuZ5y&amdata=enc%3AAQAHAAAAoGtKTxPIZioQ8peTtYL5ToqS2HngD9FjHZ7zwZgxEdGV6E0Ko1h27VMKFt%2B3SrIqvgrxzqvDC8TZMUA6XalhITLRHjuV9rRFSFoZiKYyAEHYcDOg6Co4oG%2FNwmqiViep8YAD3YSvpgqmRx4ap%2FNLrAeOmKQRHVQfU%2FLwvYZSCoYq%2FdVPvD9zEhmKSbRC2nAtpnezgUt2RC7yB1UgJuPeHp8%3D%7Ctkp%3ABk9SR7qF7dTZYA

[Dan McEntee]

Dan,

There is a hole at the bottom of the rod see photo. I wonder if this is a factory add brought on because of early problems with wear out? 

I do use about 24% oil 50/50 castor/synthetic in all my engines except the old Foxes and McCoys where I use straight 29% castor.
I'm still on the hunt for the 703 muffler and correct venturi.

Steve

      It very well could be. I think they made this version for quite a while, as just casually looking at my examples over the years shows some differences, such as those bosses. Some are deeper than others, some already have holes. I think the later versions of the engine came with the "Jet Stream" muffler? or something like that? It was a lightweight, cannister type muffler that bolted together similar to the British Merco mufflers and these were popular with stunt fliers at the time. I may be mixing memories a bit but I think I'm in the ball park. I think you have a handle on everything, just need to find the missing pieces of your puzzle.
  Type at you later,
   Dan McEntee

[Dick Pacini]

Anyone know where I can find a Max-S 35  Venturi and needle valve, also need a OS-703 strap on muffler.

Appreciate your help.

Steve

I have a complete OS Max 35-S with the .281 venturi, strap on muffler and needle valve.  PM me your address and I will send it to you.  It hasn't been run since the 1975 NATS.

[Air Ministry .]

Velly Good .

Theres little ' T ' Nylon suckers , that plug into the big end , by JIM LEE /thisis to stop the conrod walking back & going CLANG .

Theres some O S 35 info , Randy / Aerosports - Big Art , etc etc . Ifin you were getting serious , youd use a tall nylon intake , to size .
Look on SEARCH in Engine Page . " OS MAX 35S " .

That Threres a lateish ( post 1970 maybe post 73 , as its NOT got drilled & tapped Jetstream bolt holes in the zorst .Pos. as late as 80 ish . ?

Some Hardened ( 3 seperate hours at 300 Deg . ) the Piston & liner - Then lapped em with toothpaste . To last longer . Bit of a fuss in that .

Good as they are , but maybe 30 % oil for the first 1/2 hour or hour . Tech Info . http://sceptreflight.com/Model%20Engine%20Tests/OS%20Max%20S-35%20and%20S-30RC.html

[Air Ministry .]

Er . . .

The strap on mufflers are a bit vulnerable if the engines side mounted - muffler down . Unless the undercarrage legs protect it well . Itll tear a lug off the muffler in a mild hit , Notching
the bolts so theyll break in a hit if the ground habitually shifts might help . but a few mm clear so theres something to grip removing the broke screw . How do we know this . . . 



Often tears the back one out , if the grounds hard .
sometimes tears the front one out .
A nick say 1/3 across the bolt might save it . ?

[Trostle]

I think the later versions of the engine came with the "Jet Stream" muffler? or something like that? It was a lightweight, cannister type muffler that bolted together similar to the British Merco mufflers and these were popular with stunt fliers at the time. I may be mixing memories a bit but I think I'm in the ball park. I think you have a handle on everything, just need to find the missing pieces of your puzzle.

  Type at you later,
   Dan McEntee

Hi Dan,

As I mentioned earlier, I flew the OS 35s in competition when it first appeared in the mid 60's through the mid 70's.  The first early versions were for the "Jet Stream" muffler.  As you mentioned this muffler was a canister (or more like a clam shell thing) where the outer shell bolted on to the inner shell where this inner shell was bolted onto the engine with a single bolt in a boss in the middle of the exhaust stack.  I used this muffler exclusively during those years which included the 66 Nats (5th place), 68 Nats (5th place), and the 70 Nats (1st place).  I do not think it was the first to win the Nats with a muffler, but it was one of the first.  I think Bob Gialdini used a muffler on his Sting Ray when he won in 63.

The Jet Stream muffler had an internal baffle and rings could be inserted in that baffle as well as the outlet to muffle the engine more with the attendant power loss.

Those Jet Stream mufflers are hard to find.

Keith

[Steve Dwyer]

Randy posted this years back regarding mufflers and venturi sizes.

Steve

[Steve Helmick]

Proper sized screws for these engines aren't easy to get. Most of the tuners tapped out the metric threads to 5-40. I did several cases for PTG. The OEM screws were 3mm x .6mm pitch. For some reason, the standard for 3mm screws has been changed to .5mm pitch. The 5-40 is very close to 3mm x .6mm pitch, but not exact. Some just oiled up the holes and screwed 5-40 SHMS in and called it done. Be careful and check that the counterbores in the head will clear the screw heads. You can either open up the counterbore or grind the OD of the screw head for some clearance. Note that 5-40 and 4-40 socket head screws both use a 3/32 hex ("Allen") wrench.

The first picture of the rod looks a bit more like a ST rod to me, because of the machining marks. So I went into the dungeon and looked at one .35S that I got at a swapmeet. The rod in mine looks the same, but there are no machining marks on it.  The one I looked inside looks to have 4-40 socket head screws, but they're only finger tight, so I think the case threads are ok. I'll probably take them out to 5-40. DO NOT substitute 4-40 screws in these engines!!! Steve   

[Steve Dwyer]

This engine came from an estate sale on ebay, it's anybody's guess where it came from or its history. I don't think it has much run time on it and I doubt I'll be running it a great deal, it'll be added to the fleet for occasional use. I'm waiting for parts from Brooks at Shhterman. I did discover the mounting pattern matches a OS FP 40 which is a good thing.

Steve

[Motorman]

Not a SuperTigre rod wrong shape and color. Estate sale, probably OEM rod. I would suggest you don't drill muffler holes in the exhaust casting. There is a possibility when you bolt on the muffler that way the piston and sleeve will distort badly. Happened to me on a very similar Enya. Later OS designs, that have bolt on mufflers, are more robust in the exhaust flange area.

Motorman

[Dan McEntee]

Not a SuperTigre rod wrong shape and color. Estate sale, probably OEM rod. I would suggest you don't drill muffler holes in the exhaust casting. There is a possibility when you bolt on the muffler that way the piston and sleeve will distort badly. Happened to me on a very similar Enya. Later OS designs, that have bolt on mufflers, are more robust in the exhaust flange area.

Motorman

     I have a Randy Smith set up MAX-S .35 and two Tom Lay T&L MAX-S specials ( like the ones Bob Whitely used on his LA Heat), and guess how the mufflers are held on? This was a common modification back when the engines were being produced and in daily use. I have done a few myself, no problems. As I said, the strap on muffler is OK if you have the engine on a profile model with all sorts of room to install it. On a full fuselage, they are a pain in the butt, so guys started to drill the cases for several different style mufflers. I have some engines that have the case drilled and tapped, and some with a clear bore hole all the way through so a socket head screw can reach the threaded  bosses on a muffler. If drilled down the center line of the boss in the casing, no matter what style of muffler, the sides of the exhaust stack take the pressure and it's not much.
    Type at you later,
     Dan McEntee

[Robert Zambelli]

I've tried a number of different mufflers on my Max-S 35 and this one works best.
It's mounted on the Argus.
As seen in the photo, I opened up the discharge hole and attached a piece of aluminum tubing, .454" ID.
It's attached to the engine side of the clamshell type muffler with JB weld and a small screw.
The downward/outward angle helps keep the plane a bit cleaner.
It works extremely well without any running issues. It's not as quiet as the strap-on muffler but satisfies any muffler requirement so far.
The only (minor) issue is that it leaks around the mating surface - a bead of high temperature RTV cured that.

Bob Z.

[Dan McEntee]

I've tried a number of different mufflers on my Max-S 35 and this one works best.
It's mounted on the Argus.
As seen in the photo, I opened up the discharge hole and attached a piece of aluminum tubing, .454" ID.
It's attached to the engine side of the clamshell type muffler with JB weld and a small screw.
The downward/outward angle helps keep the plane a bit cleaner.
It works extremely well without any running issues. It's not as quiet as the strap-on muffler but satisfies any muffler requirement so far.
The only (minor) issue is that it leaks around the mating surface - a bead of high temperature RTV cured that.

Bob Z.

   That's an OS Jet Stream muffler. Not sure if it's one word or two. Still a desirable item on eVilBay. I haven't been able to win one yet at a decent price. I just want to try one. The Merco unit is very similar. I may have to try using that.
   Type at you later,
   Dan McEntee

[Steve Dwyer]

Here's a shot of the Max-S 35 Dick Pacini was kind enough to send me. Dick used this engine was in the 74 and 75 Nats. and hadn't run it since. After dismantling and giving it a hot antifreeze bath it came back to life. Now it runs like new with that coveted 4-2-4 break and ready to go into my Jamison special.

Thanks Dick,

Steve

[Dick Pacini]

Glad to see it coming back to life.  We used K&B 100 fuel exclusively back when I was involved in contest flying.  Muffler pressure will help stabilize the run.