os40LA

Leonard, what gives? The OS 40 LA is supposed to be a schnurle with boost port, Or am I mistaken. At any rate i have one of the silver LA40's no boost port. If thats the case then it should make a much better candidate fo a controlline engine. Is this new or am i wrong

Interesting, because the 40 LA I have here (one that self destructed in the hands of another modeler and wasn't worth rebuilding--the LA's fault, not his) does have the boost port cut out just like on the FP. It is an FP clone made cheaper. I had heard that the 46 did not have the boost port cut out and thought this was unique to the 46. But...if, as you say, the new 40 LA engines do not have the boost port cut out, I can only imagine it is one more step in making the engine cheaper. If you don't cut the boost port, it is one less operation. And it makes no sense at all, since this is an RC engine. Not cutting the boost port means it is going to be more of a lugger. But the RC guys put small props on them and try to wind them up for as high an rpm as they can get. If it doesn't wind up as much as some other engine, they will downgrade it. Of course, one other explaination is, if it doesn't wind up as much, it has a better chance of staying together. At any rate, you are right. Except for the quality factor and extra weight it carries around, without the boost port cut it should be a fairly good CL engine--assuming they didn't also mess with the timing or deck height or some such.

So far, the only LA's I've seen were the blue ones that looked so odd that I overlooked the number of head bolts. Today, there was an eBay auction listing for an "OS 40," not otherwise identified; it ended quickly with a Buy It Now response and only has one photo.

That one was taken looking downward on the top of the engine's head. There were only 4 head bolts. I don't think I've seen an engine that size that has been produced in the last 25-30 years that had less than six head bolts (discounting a few larger size engines with threaded heads and cylinders that screw together).

The photo angle also seemed to show the head's front to back shape was strange; sort of a fat teardrop sort of thing . .

I've seen a variety of criticisms of recent OS design choices, but no one ever mentioned that they were saving money on head bolts also! This seems like a particularly goofy option to me . .

Kiwi

Recently produced larger engines with 4 head bolts? I've got a Thunder Tiger 42 with only 4 head bolts. I was a little suprised when I got it.

My MVVS .49 (8cc) stunt motor has only 4 head bolts. However, under the head are 4 cyliner retaining screws. (This engine has the option to rotate the cylinder before use.)

Also, I believe that the Super Tigre .51 has only 4 head screws.

I'm running a couple of 4 bolt Fox "sandcasts" right now (in fact, flew a Yak with a 29 sandcast on it just last weekend), and have never had any trouble associated with the relative paucity of head fasteners. They hold compression just as well as their 6 bolt cousins.

All things being equal (like, the ability for an engine to basically shrug off one loose head bolt and keep running pretty much as if nothing happened), sure, the 6 bolt head would be preferable.

The light case ST 51's all had 6 headbolts but the newer square head engine has only 4. Sure doesnt impair it ability to produce a fine stunt run!