And if you use neither starter nor chicken stick, you have to get used to flipping the prop with the top of your fingers. [8D]

George

i dont think those last 2 replys were very nice but kids will be kids? i didnt mean u pipe father ty for the great ideas people

Bill, as you say the Fox used it at least on their 29/35's but I'm not sure about other Fox's. All Merco's had DeSaxe from the 29 to the 61. The strange thing between the Fox and Merco is that they offset the liner in different directions. In a 2 stroke it does two things. One is that it can reduce the thrust load on the piston during the power stroke but the other is it gives a very slight assymetric timing to the transfer and exhaust ports. I measured a 1.5 degree difference in a Merco 61 I just got hold of but I haven't got around to doing the Merco 49 yet.

Reverse thrust on a ball raced engine is no problem, after all it's only a few pounds load on the bearing, but it's bad news with a plain bearing engine. The steel shim isn't designed for continuous use but only for the starter loads.

Motorboy is right, if it's got a removeable front end then turn it 90 degrees to the exhaust side. The old OS Max 60H and 80H with the drum valve has an extra drive slot in the drum marked R for reverse.

I has ETA 15 and ED Mark IV , they has an extra hole in rear dish valve to reverse the engine..

Jens Eirik

I recently bought a reversing cam for an OS FS-61 four stroke. That means I now have a pair of them, one left and one right hand running. Rather than try to find a L/H prop I thought it might be fun to build a Dornier 18? Push/pull waterplane. The other possibility is the German twin push /pull fighter.

I have spent some time wondering just how difficult it would be to make a copy mill to make L/H and R/H props. I quite enjoy building and making things NOTIONALLY.






old git aka JOHN L.

rear induction is more expensive to manufacture as tolerances are much more restrictive. It's easier and cheaper to just buy a pusher prop or a reverse rotation cam or crankshaft.

The Fox 59 was a Desaxe engine

That got me curious Jens so I've just ripped off the backplate from my ETA Elite...it's only got the one drive hole so maybe they changed that. BTW, it's the only diesel I've ever had that'll give a "bump" when turning it over slowly like a glow engine with the ignitor on

I just came across this thread when looking for a source of OS MAX 61 Four Stroke instructions. I have a pair of these engines and a reverse cam so that one will run in the opposite direction, need a L/H prop next. There is currently a reverse cam for these motors on eBay at the moment.

I worked with British motorcycle two stroke engines in the 1950s, pretty poor performance. I believe the term is Des Axe, probably Italian origin. It refers to the fact that the cylinder axis is not in line with the axis of the crankshaft. It purported to reduce sidethrust of piston on cylinder wall during the Power? stroke, cannot remember exactly if that was so.

I have no experience of operating a twin engined model but have often wondered if the outward sidethrust on a number of full size aircraft was to help single engine operation. Which raises the question, does an asymetric fin angle on twin fin models, where the fin is in the propwash, help to avoid asymetric thrust problems. Maybe I should have posted this in the aerodynamic section but it was all part of one concept.




old git aka John L.

Yes, to reduce sidethrust on cylinder wall during the power and reduce friction between piston and cylinder wall, less oval cylinder of wearing.

There are 2 difference to reduce sidethrust

1. The cylinder axis is not in line with the axis of the crankshaft.

2. The wristpin not in center in the piston, connecting rod less in angle during the power. (To example in Volvo automobil car during 1970-80 model)

Jens Eirik

I have an OS FS-61 reverse camshaft (and a couple of engines). I wanted to be able to run a twin without the problems of BOTH engines rotating in the same direction. I am now having a look at milling/routing a pusher prop using a tractor prop as a template.

Swapping a cam is easy (I have the timing gen) but have not progressed with reversing the template following mechanism. I bought a book on making a CNC mill, decided life was too short to attempt to learn so many new things.

I guess I just love these thought experiments.



old git - - - - aka John L.

Seeing this thread has been resurrected I found something surprising a little while ago. I was checking the timing on an SC 1.08 and found it's a Desaxe arrangement. There's about a 2 degree assymetry in the exhaust and transfer ports in that the exhaust (for instance) opens at 82 degrees BBDC but closes at 80 ABDC. That got me to check that the degree wheel was set correctly, it was. It seems that maybe the Desaxe is still around with a few engines but it's not something that most engine tests will reveal.

Using a pusher prop will not hurt the engine because the thrust is in the wrong direction. The bearing can handle the load. ALL prop driven boats are "pushers" and boat engines take a lot more abuse than airplane engines.