OS Max-H .40

[dennyleo]

A few published designs used this engine.  Is it a good choice for stunt, and are venturis/tongue mufflers available?

TIA!

Dennis

[Bob Hunt]

I used the H40S in two of my original designs back in the early 1970s, the Avanti and to F-105 Thunderchief. They were extremely friendly, powerful, and easy to tune engines. Too bad they were discontinued.

Bob Hunt

[Brian Gardner]

Are there many out there?

Would people want replacement ABC sets for them? I've never been asked to do them - but could if I were to get enough orders.

Brian

[Steve Lotz]

I have several and would be interested. I don't like piston rings.

[M Spencer]

Ho Hum ,

Theres the EARLY 20.6x 19.5 , S , SP , P , & R.C. all of whts got the forer STAMPED in the litle round wotsit .


by the prop driver , this could be a later revised ' P ' . the early ball race prop drivers differant , if similar .
AND theres a V Similar C 35 & 35 RC , Same Case . Liners Dia's other than 35 S , but piston matches ,

BELOW is the for 1974 40 R C , which has the CAST IN ' 40 ' protrudeing from the little round ' boss ' thing .
And'll never have Jetstream screw tappings . BORE & STROKES the LATER 21,2 x 18.4 that was USED FROM THEN ON . FP & LA etc .

So a Early Liner dont go into a late case or late into early .  1964 to 1973 .revised totally 1974 onward . Cotton Reel prop drivers the giveawy on the late ones , too.

S & SP are Single Ball Race . R R & P Dual . ALL late are dual ball race .  Ya wanna lookat all the versions , on sceptre flight . quite Simple . For 74 the RC isnt as it was .

[Brian Hampton]

OS also made a stunt version as the 40FSR-S (late model crankcase)with a lower timing for the crankshaft port.
https://sceptreflight.com/Model%20Engine%20Tests/OS%2040%20FSR-S.html

[M Spencer]

OS also made a stunt version as the 40FSR-S (late model crankcase)with a lower timing for the crankshaft port.
https://sceptreflight.com/Model%20Engine%20Tests/OS%2040%20FSR-S.html

Zillions of themabout . Brians FP 40 liner goes straight in it . BUt ya gotta take a nanomilimeter off the backplate , where it goes into the case , to clear the skirt .
AND mine , the head needs dropping . Will deepen the gasket rebate in the head , one day . A FSR 45 P/L , with full skirt & maybe 128 / 136 timing ( Rojett Timing )
might be real good . as the 45 runs way better than the 40 , as init'll switch & back off , a little . Wants 4 inch pitch maybe , whereas the FSR 40 likes 5 inch .

Dem 40 S , the early version , pretty sure the 35 & 40 liner interchange - outer diameter wise . Maikis ran a SP & somebody tried a P , there pretty conservative .
Like a ols 30 S is 110 / 130 sleeve timing . so will go slow with plenty of tourque . THE POINT BEING a ' Early ' fit would go in the 40 S , SP , RC , & RR as well as
single ball race 35 RC , C, etc . Pretty rare . ive got two & a junk one , seen six or so , in pictures , anyway . ( ebay & RC groups .)

RIGHT , these ' Flat ' prop driver's , are on the SINGLE BALL RACE versions . The front is broze plain bearing . recessed  prop driver . std OS ' Flat ' on shaft & driver .



So , this here is a plain straight " H - 35 " , where mine are " C " and plenty are " RC in little letters Under the ' 35 ' . The 40 S looks identical . C is wedge head . 35 S head ( hemi ) interchages . ! 





you can see where its tapped for the Jetstream muffler . The 40 S is pretty much identical , externally . 

[M Spencer]

THIS SUCKER is the post 1973 REDESIGN . No Major Parts INTERCHANGE . Beware !  . so its one or the other . It wouldnt fit both pre & post 73 motors .


The chaps had better tell you which one they got .

all the early ones are 20 . 6 bore . The Stroke 19.5 on the 40 , 17.5 on the .35 . ( H 35 dosnt have the big end clearance machined in the case . the 40s do . )

THIS https://sceptreflight.com/Model%20Engine%20Tests/OS%20Max-H40S%20%282%29.html gives a bit of a un down , on the then available .40's .Most introduced around 64 . & the H 29 R .

H being the Ball race case . single or dual .

[dennyleo]

That F-105 is a personal favorite, Bob.  Thanks for all the great info, guys!

Dennis

[Steve Lotz]

Brian... how many orders would you need?

[Brian Gardner]

30 to justify a production run

Brian... how many orders would you need?

[Mark Romanowitz]

Folks, you need to be aware that there were *several* different OS Max H 40s.. Note that Bob said he used OS Max H40S engines.. There are others.. The H-40P is a Pylon engine.. There are also R/C versions which may have been converted (as one of mine was).

Not knowing all this a few years back I bought a couple of OS Max H 40s on eBay.. I ended up with two different versions.. One ran pretty well as a stunt engine, the other did not. I let go of them because it was getting too complicated to try to find ones like the one that ran well.

Take a look at Peter Chinn's engine tests:

https://sceptreflight.com/Model%20Engine%20Tests/OS%20Max-H%2040P.html

https://sceptreflight.com/Model%20Engine%20Tests/OS%20Max-H%2040S.html

https://sceptreflight.com/Model%20Engine%20Tests/OS%20Max-H40S%20%282%29.html

https://sceptreflight.com/Model%20Engine%20Tests/OS%20Max-H%2040%20RC%20%281%29.html

https://sceptreflight.com/Model%20Engine%20Tests/OS%20Max-H%2040%20RC%20%282%29.html

https://sceptreflight.com/Model%20Engine%20Tests/OS%20Max-H%2040%20RC%20%283%29.html

https://sceptreflight.com/Model%20Engine%20Tests/OS%20Max-H%2040%20RC%20%28final%20version%29.html

https://sceptreflight.com/Model%20Engine%20Tests/OS%20Max-H%2040%20RC.html

There is also this series from 2007 here on Stunt Hangar:

https://stunthanger.com/smf/engine-set-up-tips/os-max-h/

[M Spencer]

State Champs blown out after one round . Didnt get to run the 40 - S's .