I have an OS  Max-H that I bought in 1969. I want to fly it again but don't know what fuel mix to use. I have on hand some 12% nitro,18% synthetic. I have checked the mixing formula elsewhere on this forum and have come up with 1.6 oz. to bring it up to 22% oil. (per quart) Does this sound right? Would this engine require castor and how much? Also how does this engine compare to modern engines? It is a 40 size RC, factory converted to CL. I know that there has been aquantum leap in engine design since ' 69. Could it be eqivelent to a modern 35 or even a 25?                                                                                                                                                                                           Thanks in advance   Bruce Grosser "The Northeast Kingdom's only (and lonely) control line flyer."

HiBruce
A good fuel for it would be 22 to 24 % oil part castor, start with 10 nitro, The motor is a good strong one, not quite up to modern but will do well.
What type size plane will it use?

Randy

Basically there are 2 types of Max-H engines. Early ones had a straight bypass while later ones had more of a "V" shape. All of the later type were RC with twin ball races but may have been offered as a CL version with a venturi. Early versions included a 35 which had an iron piston so definitely needed lots of castor. The early 40's were all ringed but used a single rear ball race except for the P (Pylon) version which had twin ball races. The RC engine was just marked 40 on the transfer port but other versions had a letter underneath the 40 with either S (stunt), P (pylon) or RR (rat race).

The later version didn't come out until '72 so yours must be one of the earlier type. Personally I'd use ~25% all castor or the same oil content with a bit of synthetic mixed in. I have a couple of the H-35's and an H-40S but I must admit I've never used them.

attached are photos of the OS 40 H engines, One of these should be yours unless it was a converted RC engine.

Peter     Thank you for taking the time to research this and for posting the photos. My engine is clearly the 1965 version with the venturi from the 1970 version. I do not know the history of this thing as I bought it used from a base hobby shop whe I was stationed in So. Korea. It came in the original box with a spare head and nothing else. I tried the spare and determined it was way too fast.   Again many thanks    Bruce

Hi
Depends on the plane, I used a 11 x 5W  and a 12 x6 cut to 11.5, they worked very well on the OS

Randy

Thanks to all who replied. Sorry for the delay in responding. Kelley, your info explains a lot. Every plane I've used it on was way too fast ,being .19 to .35 size.           Bruce