Those OS Max H 40s

Hi Guys,
Like a lot of other retreds,there is a gap in my modelling career(in
this case,from about 1964-75)when I lost touch with developments. I
think I read somewhere that the OS Max H 40 made a fine stunt motor.
Could someone tell me if this is true,also which particular version
(I believe OS made a lapped AND a ring version)? Did they make a
dedicated C/L model,and if so,was the timing the same as the R/C one?
Any information you can supply,plus tips on tuning would be much
appreciated. Thanks.

As our host would probably say - Why don't you register so we can email you and you can be a part of the group.
The OS40H's are almost always available on Ebay. I usually pay about $30 - $35 max for a used one and around $50 for a new in box. If they go for more I pass as they come up often. When I remove the carb, I put it up for sale to the R/C guys and they grab them at $12 - $15. The older version has a bushing front and bearing rear while the newer one has dual bearings. You can tell which is which by the front of the motor. The newer one has a sort of deep groove around it just behind where the prop rests. Newer ones were made in more than one version and you want to look on the side of the motor to see a raised "40". Do not get the one with the "P" in this area as it is a pylon engine. They did come as a C/L engine with venturi as well as R/C. The R/C version can be used easily by swapping out the carb. They do a 4-2-4 break and I use a 11X5 prop. I like them for use in planes that origionally used the Fox 35. Engine choice is a personal thing so try one and if you like them as I do you may also end up with a dozen.

This is the one that does not give the run we want:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3141646625&category=34055

Wish I could post a picture instead of giving a location.

>As our host would probably say - Why don't you register so
>we can email you and you can be a part of the group.
>The OS40H's are almost always available on Ebay. I usually
>pay about $30 - $35 max for a used one and around $50 for a
>new in box. If they go for more I pass as they come up
>often. When I remove the carb, I put it up for sale to the
>R/C guys and they grab them at $12 - $15. The older version
>has a bushing front and bearing rear while the newer one has
>dual bearings. You can tell which is which by the front of
>the motor. The newer one has a sort of deep groove around it
>just behind where the prop rests. Newer ones were made in
>more than one version and you want to look on the side of
>the motor to see a raised "40". Do not get the one with the
>"P" in this area as it is a pylon engine. They did come as a
>C/L engine with venturi as well as R/C. The R/C version can
>be used easily by swapping out the carb. They do a 4-2-4
>break and I use a 11X5 prop. I like them for use in planes
>that origionally used the Fox 35. Engine choice is a
>personal thing so try one and if you like them as I do you
>may also end up with a dozen.

LAST EDITED ON Aug-10-03 AT 08:53 PM (CDT)
 
I've been very happy with the performance of a couple of these oldies; mine have just a single (rear) ball bearing, but both (that I've used) came with their RC throttle still attached (I paid around $40 or so for another backup at eBay, I think). There are also some H's with twin shaft BB's, and some that were retimed for Pylon Racing. The hot ones are reportedly not as useful for CL aerobatics. Those will have a "P" in the displacement circle along with the "40".

When I first was testing a Max-H 40 about ten to 15 years ago, I still had some fairly recent memories of what I considered bad behavior from a couple of ST G21-40's, and an early mark of the OS FP 40, all of which would "run away" on the props I had easy access to. The way a Max-H "sounds" when it breaks from a 4 cycle to a 2 cycle has a sharp note that gives the illusion of being too strong, too much change from four to two.

I flew that first one in a straight, very rich four cycle only, for quite a long time - then when I was running a muffler on it (not usually required anywhere I go to fly), the break sounded far less of a problem, and I found it was fine in a 4-2-4, with or without a muffler. For a BB-equipped engine of its displacement, it is compact and light. It fits in the same mounts as the Max-S 35 and the FP 40 and its power is between those two (and of course the Brodak 40 now fits that pattern as well). It has the OS trait of being easy to start and to needle, but it is a steel cylinder engine with an iron ring on the piston, so use enough oil (22% minimum, by volume, half castor, half synthetic).

I have no experience with any lapped version, never have held one of the Pylon Specials in my hand. Maybe those had a lapped piston. My own use of the Max-H's (I do have several now) hasn't been continuous in the sense that I've seen a loss of compression from ring wear. Perhaps the rings in the H's offer longer service than some ringed engines, but I don't know for certain. None of those I have, as best I recall, have any bypass shape other than straight - no flares.

Added P.S., via Edit -- Will this show up for right now (all such URL's are temporary ones and expire rather quickly)?

[photo not recovered: os40h_1_a.jpg]

That's the picture that Bill Sawyer mentions - Pylon Special up for auction at eBay. Sometimes, with some browser software, you can capture the image location - URL - but most of the places used by eBay sellers will block that copying attempt, though. It worked here, so far!

.
Kiwi

The early version came out in 1965, and were produced in 4 versions. One article where this engine was used is Dave Rees and his futuristic stunter using the early version in the early 1970s in Flying Models. The by-pass on the exterior is staight and the later early 1970 version is Y shaped. I have personally used both engines and don't recomend the later version for stunt. It runs at a hundred mile an hour. The lapped version is hard to find and a NIB can go for about $100. The FP-40 uses almost exact mounting but the the screws in the back plate stick out an 1/8" further. If you are new to stunt or coming back a dedicated stunt engine will save many headaches. The FP-40 by Randy Smith and one by Tom Dixon have given me excellent service. I love the OS .35S and have used them in several planes. They do tend to wear out if not run correctlly. I have also seen the Tower 40 used with great success in stock configuration flying with the low pitch high rpm method. I have used Sig and Powermaster fuels with great success, Sig 10-25 all cator and Powermaster 10-29 all castor are recommended. The OS Max 40H can use a little less castor down to 22% and synthetic mix wont hurt them. I flew one in an RC plane and it had more power than a K&B 40. They are as reliable as any any engine can be. Jim Johnson

i have one for sale in the adds. I will take 35 for it if that is the going price. It is real nice, ringed. MM

> i have one for sale in the adds. I will take 35 for it if
>that is the going price. It is real nice, ringed. MM

I cant seem to find it in the classifieds
but I'll take it if it's in really good shape

call me 252-637-5704 or email me at address below

I've got an H40S which has the S stamped under the 40 in the same manner as that 40P but I don't know if they were retimed from the normal H40 or if it was just to denote it was a CL engine. It's got a single ring, single rear ball race and has what I'd call a straight bypass.

The "S" usually indicates that it was made from the factory as a control line engine and is the engine of choice for stunt. It should have been equipped with a venturi and needle assembly. Both the older version and the newer ones had a venturi/needle equipped version that we can use. I have replaced the bearings in one I have and they were then available from Boca Bearings. ( the man I talked to there knew the number off the top of his head when I called ). Frank Bowman is a source of rings in either the dykes ring or the standard. I also didn't mention that I prefer to use a tongue muffler and by selling the factory one and the carb to the R/C guys, I can about make them an equal swap for the tongue.

This thread really peaked my attention, as I have a 40H I plan on using in the profile I am building right now.

It came to me with the tongue muffler, but it also had an RC carb. I found a new old stock venturi at a local hobby shop and got an original OS needle valve to complete the transformation. I have not yet bench run it, but it has strong compression and good bearings......

I hope this is the one that runs well for our purposes...

(I know the spinner is not on all the way.... It was just there for sanding the curve of the nose....)

To the best of my knowledge as well as in my experience, the later Max H-40's like yours shown above (with the double ball bearing and the raised "40" on the bypass), will run just fine for our purposes by merely changing the carburetor for a venturi and NVA.

The earlier single ball bearing version with the stamped "40" with the "S" under it runs well for stunt as well. It was timed to do so from the factory and came with the venturi and NVA installed.

I have examples of both and they all run well. Bill's right. If one gets a good one or two in his hands, acquiring more for back-ups and parts sources becomes addictive. One blinks and he has a dozen or so and is still bidding on them!!

Jeremy,

Let me know when you are ready and we will get that motor 4-2-4 in no time. I will also show you how to lighten up that tounge muffler. It is an old Dubro multiple baffle style. Remove all the baffles and install the cover plate only. Drill about eight 1/8 inch holes toward the tip of the muffler and you will be set. Had one of these on an old Fox 40 Stunt.

Make sure you seal the backplate and venturi with RTV. Check the head gasket and make sure you are getting no leaks. Torque the head screws as tight as you dare. Control motors have to seal tightly to perform a decent stunt run. Air will get in through the slightest gaps. I will try to pass on a few tricks when we put your plane in the air.

> ... The by-pass on the exterior is straight and the later early 1970 version
>is Y shaped.

My own terminology is to refer to that as a "flared" bypass shape, but I have yet to handle any H's with that type, myself.

>I have personally used both engines and don't reccommend the later version
>for stunt. It runs at a hundred mile an hour. The lapped version is hard
>to find and a NIB can go for about $100.

>I love the OS .35S and have used them in several planes. They do tend to
>wear out if not run correctly.

Bu this, it's my translation that the well-known soft con rod is what is meant that wears out quickly. And it's true, that part is typically short-lived, with whatever fuel is used.

> ... The OS Max 40H can use a little less castor down to 22% and synthetic
>mix won't hurt them.

Not only does it "not hurt" a Max-H, I would say it's pretty much a mandatory addition for this engine. Straight castor fuels will gum up the ring and the bearings - no matter that it's a steel cylinder, any engine of any age with a ringed piston and/or a ball bearing shaft is going to provide better service with "some" synthetic oil in the fuel!

>I flew one in an RC plane and it had more power than a K&B 40. They are
>as reliable as any any engine can be.

My own Max-H's run stronger (CL comparisons only) than my Brodak ABC Torp 40, but I also have a GMA Custom version of the older engine that size & type from K&B, and it runs like a John Deere (very strongly).

.
Kiwi

I bought one new in 1970. It has been one of my favorite engines
for stunt. Great engine, (mines ringed)2-4s really well, plenty of
power and well made.

Trying to post a picture of my OS MAX-H .35 Stunt

Looks like you did more than try, Dan!

Hi Paul,

I've been trying to post pictures here but could never get past the review stage. Now that I submitted the picture it showed up.

I'm a happy camper now, time to go take a picture of my NIB Veco .35 Combat with the big Maroon painted "C" on the case.