Kepp us posted and please put some pictures up when you get them back. What did the guy do to your cranks for the small twin? When I get this DVIII finished I am going to get back into the machine work on mine.

Tim

He didn't pin them and just welded them on the end of the crank throws.

We went through 2 cranks, The first one ran almost 2 hours the 2nd one about 5 minutes.

It's really disheartning when you believe everything was done correctly and it fails.

Pictures and data to follow.

Hey Tim

Well I just got the email.
Ralph will run the Partner saw motor tomorrow to do some testing and recommend a prop.
Any guesses on the prop size and RPM? He tests all of his engines with out mufflers.
My G-62 turns a 22x10w APC pretty good and this engine is about 15% bigger.

The Piston on the Echo twin had a "couple of scratches in it and the cylinder is okay".
It should ship soon also but at least I can finnish the 540 now.

Great news Ralph. I would bet a 24/8 or 10 will be the ticket. I would try the 22/10 also as a base line gage. Can't wait to see a picture of it when you get it. Are you going to use a Pitts or a side muffler?

Do you have any idea of the RPM range of the partner saw motor ot the Echo twin?
I don't believe it would be the 10 to 12,000rpm like some modern chainsaws.

I have set myself up to start making mufflers.
I purchased a band saw and have found someone to weld them up at reasonable cost.
A good tig welder is about $1000.00 so buying one would not be cost effective, at least not yet.
I already have most everything I need.

As you know, I purchased the mufflers for the Echo twin and saw how they were made and looking at other
mufflers I have some good ideas.
I was looking at Toni Clark's site and he has good ideas also.
No use in re-inventing the wheel.

I have several of BME's Echo twins that need mufflers.
All together I need about 10 gas engine mufflers and this should be the cheap way out.

I would try to shoot for the 7000 range on RPM. All the saw is doing is running the chain, far less load than a big prop will have. I think making your mufflers is the way to go and reverse engineering them is smart. Now if I only had a welder...

Do you have a torch. If you do you can go to a welding shop and get a wire for aumenam. You can weld it with that. It does work. When I get done with the one I am doing. I will put up how to pics

Pau

I've been practicing with Aluma-Weld.

It's not great with my propane torch but it's a lot better with my oxy-Acetalyn torch.
But still not near that of a TIG machine.

It looks like it will cost me $50.00 to have 4 or 5 welded if I get everything ready and they just sit down and weld.
And at that price I'd just as soon have it done perfect that pretty good.

7000rpm with a 24x10 prop ... Thats a lot of wind.

According to ThrustHP, which is over rated thats 48 thrust pounds at 8 horsepower.

If I had to guess 8hp would be a low estamate for that engine.

I'm sure that a 24" prop is to long for my 540 with the landing gear that's on it now.

How about a 3 or 4 blade prop?
The plane weighs in at about 16 pounds ... I need to get a scale.

Aluma-Weld? What is that? If I may ask

Paul

Sticks of some sort of aluminum compound. I got mine at Harbor Freight. Do a search and the distributor is in Florida IIRC. I have used it and it works well. Never did a whole muffler with it though. Just header pipe flanges and repairs on cracked mufflers.

That's where I bought mine from, I was thinking it was Aluma-Weld.

Does it holds up to the heat on a flange on a gas engine?

That is the same thing I get. I just did not look at the name. I just ask for some rod that I can use on my torch. lol

Yes it will hold up to the head. it needs 800F and up to melt

I am making a mufler now. ask soon as I am done I will post some pics and some how to stuff.

Paul

Mine has held up. However I have not made a whole muffler out of it. Some have claimed it is brittle but we will be finding out soon.

Well I got her running.

http://www.rcuvideos.com/item/BMV2KV388GZSF0NZ

I have 3 pints of fuel through her and it doesn't quite have the top rpm yet.

A little more fuel and I'm sure she will come around.
I'm running a 22x10w APC prop and it spools up real nice, just not quite the rpm I know it's capable of.

I made and designed the muffler. It has 2, 1/2 inch outlets and the Carb. seems to be louder than the muffler.

I'll give an update ASAP.

Did you notice the throttle linkage came off at the end of the video.

You should see how the fence wiggles and shakes with this engine on it.

I think 2 1/2" pipes are a bit small for a 70cc engine.

So do you think I need 3 pipes?

And do you think that may be the reason it's not reaching full RPM?

I would say so. I use two 1/2" outlet tubes on my 25cc engines, and larger for bigger engines. That is not enough outlet for an engine that size.

AV8TOR

In retrospect I'd say you are right.

When I made the flange I drilled 2, 1/2" holes in a piece of 3/8 bar and cut between the 2 holes.
That was about 3/8 of an inch.
The actual I.D. of the tubing is .630. I cut the ends at a 45 degree angle so they would scavage better
and put them in about 3/4" from the top of the muffler, faceing the muffler walls.

At the time I believed that the rings had not seated yet.
But listening to the video a few times I can see where the exhaust could be choking the engine down.

Anyone know where there is a flow chart for tubing?

The muffler I have on a 70 has 1/2 holes in it.

What did you use to weld it with?

Paul

Wont make your neighbors happy, but give it a short run without a muffler and see what rpm you get.
If you need the quite effect from 2 1/2" pipes then you need a bigger canister.

I don't think a flow chart will help you. You can't just figure the volume of air the engine consumes, because the exhaust is super heated and expanding as it leaves the engine.

Do you have the old muffler? Maybe you could use that for some trial and error to come up with a good exit volume.

AV8TOR

I didn't get the muffler with the engine.

I think what I'll do is .... see what others have done and copy it.

I'll be back ...

I would do like Terry said then; run it open exhaust just enough to peak out the needle and get an rpm reading. (Or until the neighbors start throwing rocks!) Then you know where you stand...

AV8TOR

Basic rule for least power loss and most quiet is 10x the engine displacement... In you case that means a 700cc chamber

700cc chamber is right. but the exit has to be right. It looks as the one I have is what tkg said. 700cc chamber but the exit ports are 3% smoller then the port on the engine.

I not sure, I hope some one know more about it. but, If your port on the engine is 100cc then your exit prot out of the chamber should be 3% less then that. If I can find the page the said all of then and what the testing was that they did to come up with this I will put it on here.

That is what I did on my 77cc engine. It seems to work good. Ugly but workeds good lol

Paul