OS MAX-H 40s

LAST EDITED ON Apr-28-04 AT 08:54 PM (CDT)
 
I've recently obtained two OS MAX 40s One has an S in the same circle as the 40 and has SV under the engines right mounting lug. It also has a raised portion in the backplate to drill and tap for a pressure fitting. The other engine has a raised 40 in the circle, instead of stamped, a more rounded head, a flat backplate with a number 4207 stamped in it. The bypass side of the engine is more rounded and wider at the top of the bypass. The second engine has RV stamped in the bottom of the right mounting lug and the thrust washer is different and about twice as thick as the other engine. The second engine is without venturi or carburator. The first engine was swapped for a Max 40 RR (rat race) and I understand it is a great stunt engine. My question is what is the difference in the engines other than looks? The "s" engine has a venturi that measures about .29" inside diam. Would the same venturi be a good match to the other engine? The "s" engine has a bronze front bushing the second may have a ball bearing.

Thanks for any help,

My own experience with several H-40's has been excellent. Whether two BB's or just one, all I've tested ran the same. It has more power in a solid, unbreaking 4-cycle than just about any 4-2-4 type 35 I ever used regularly; one of mine just about matched my G21-46 Tigres when both were operated that way. The rings seem to hold a seal longer than most any ringed engine I've used regularly. It's a relatively compact and light engine for its displacement, and for its decent power output.

They do have a deceptive exhaust note when unmuffled. I had the idea it was "breaking too hard" at first, just because of the sound. That was why I started running my first one below its natural break point. However, there was a "Pylon" special version that did have an over- strong break, and a tendency to runaway, and to not break back out of a two cycle when set to run the 4-2-4. That one will have an engraved or stamped "P" in the circle with the numeral 40.

Another point in their favor is that the ones turning up on the used engine market don't tend to be either worn out or to be priced too high to be able to acquire several. Last, I regret that if I did write down the bore sizes of the venturis I've used, I have managed to forget where I recorded that number, so if that 0.29 is too large of a venturi, I can't be sure (although I "think" it should be more like 0.275 when the stock 0.145 Max NVA is used).
.

Kiwi

Kiwi,

I don't remember if it was you that clued me in on using the hardware store nylon spacers for my fox .36 or not. These spacers come in two inside diameter sizes, .25 and 5/16" the outside diameter is a perfect fit for the MAX 40's and I have a tapered reamer that works great to shave a little out and they are cheap at 19 cents apiece.