I have acquired an older Sachs 3.2 engine that is updated with a CH electronic ignition.
It starts right up and runs fine, the only problem is that it heats up and runs very hot. I am using a 40:1 fuel mixture and am wondering if the is too lean on the the oil side and should be mixing something like 32:1 or even 24:1.

Any advice would be appreciated. Thanks.

Regards,
doubledee

Hot is relative...More oil won't make it run much cooler, if at all...
How hot is it ? You can't check it after idling around after landing, only way to tell is with an in flight temp sensor mounted under the spark plug, and a way to read it out...
300F is not too hot when running at WOT...
TOO hot is when the piston sticks in the cylinder
My engines routinely run at over 300F on the test stand, drop almost instantly when idled down...

I have had several Sachs 3.2s including a couple of A&Ms. I have always used Amsoil Sabre at 100:1. I never worried that they were too hot, and never even checked them. You want to make sure your timing is set correctly. You can find the timing instructions on C&H's website: http://www.ch-ignitions.com/CHinst.html

Running the engine with needle settings too lean will make it run hot, and like RCIGN said, sieze up. Over propping (running to large a prop) will help it do the same thing.

Exactly.

I don't where or when this idea surfaced that a 50 should turn a 24-8, but thats too much prop IMO. DA claims their 50 will turn a 24-8 AFTER break in. And then I read about guys using the 24-8 after 2 tanks and wondering why the engine is running hot.

You should be using a 20-10 or a 21-8 on that Sachs 3.2 Maybe a 22-8. Anything more than that is over propping it and will lead to excessive heat--no matter how much oil you run.

These old Sachs engines are industrial cylinders. Originally designed and ported to run upwards of 10,000RPM in a chainsaw. Prop it to run at least 7000RPM or better on the bench. I wouldn't go over about 7500--7800RPM on the bench.

So, you buy props and you experiment untill you find the one that makes the most thrust at those RPM and then you live with it. That's all the work that the engine is capable of doing.

Propping one of these industrial cylinders for 6500RPM is just going to make it hot and your cheating yourself out of the HP that it can produce with 1000 more RPM.

A 22-8 is actually a pretty good prop size for a 3.2, depending on what type of flying a person wants to do. Excellent for 3D work. For more speed, a 20" prop with a higher pitch would be better.

A reasonably good 3.2 should be able to turn an efficient 22-8 in the 6,900 to 7,400 rpm range at sea level. Perhaps more depending on the type of prop.

Above 22inch diameters on a 50cc engine is placing a lot of load on the engine, creating a lot of residual heat at the top of the piston, possibly contributing to detonation and later damage. Some will argue that they successfully run 24" props all the time, but the melt down just hasn't happened yet. The front bearings usually go first, though.

I'm going to start out with a 20-8 on my Fox 3.2 and tach it real quick.

Keep in mind that I'm at almost 5000'.

I just got an NX 21-8. I also have APC 22-8, 3W 22-8, 3W 21-10. Menz S 20-10, Menz S 21-8, Menz S 22-8, Menz Ultra 21-10, and MSC in 22-8 and 20-10.

It's just a matter of finding the prop that will let it unload too the proper RPM range and then find the one that pulls the way you want.

I'm shooting for MINIMUM 7000RPM on this engine. Plane is a 1/3 Pitts, so I'm not looking for a lot of speed--which is why I don't have any 12" pitch props in my shop. I'm looking for normal speed and good vertical. Probably end up with a 21" prop with either an 8 or 10 pitch.

Ya just gotta experiment.

I have a pretty strong hunch you'll settle in the end on the MSC 22-8. The final call will probably NOT be based solely on max rpm performance, but the low speed/rpm performance as well.

If the decision is to be based solely on rpm, then you will end up with the Menz. That would be to your loss, tho. I'm waaay ahead of you on this one with the same plane and engine displacement a couple of years ago.

The Menz Ultra spins a lot, but I've got better pull from an APC.[X(]

I have to admit, I haven't done much experimenting with props in this size. I've just recently started buying lots of different props in this size.

While a specific size and pitch from Menz or 3W may work well on 1 model--it may not be the best for another model.

I was surprised to see the blade width on the NX and MSC props. Much wider than I expected. The Menz Ultra and the APC look like toothpicks compared to those others.

We're gonna find out in a couple weeks. The engine needs more time on it. It hasn't been run much, so I'll be propping for closer to +/- 7300RPM at first. Run it like that for 6 or 8 gallons and then change the size or pitch. I'm really eager to put that NX 21-8 on it. I think thats gonna be the one that gets the RPM up where I want them--but only the fish scale will determine the thrust.

Run it the way you're going to want to fly it from day one. Just like you would a chain saw you just bought and plan to use for work today. I don't know how all this "break in" stuff for gassers started, but it's a bunch of useless crock. We're not dealing with abc technology, tapered cylinders, or cylinder liners here.

FYI, with that Pitts plan on going through a lot more props than you anticipated. Don't ask[]

There's going to be some heat for this one. I feel it comin' already

You saying the LG is bouncy? Been thinkin' about the TNT set for it. At $25--$28 per prop--I can't afford to break one every other landing.

Alright, I will slap the MSC 22-8 on it and see how it flies.[sm=thumbup.gif]

Agree with Silversurfer...Only thing you're breaking in is the surface of the piston rings, ball and roller bearings need no breaking in...Seals will get looser, nothing else in the engine touche....After many hours running time you may see slight wear on the bottom of the piston skirt, it rocks very slightly in the bore....When it gets about 500 hours on it you might see slight wear on the top of the piston above the top ring, that's from the bottom of the piston getting looser and the piston rocking in the bore, depends on how tight the clearance was in the first place..