Test Bench Break in DA 100 Big Problem

[vernonf]

Well , I found out today why the engine is hard to start. I have zero compression on the rear most cylinder. It has a melted 3/8in hole in it after the first 15 minutes on the test bench. I am feeling sick.
I ran the proper breakin oil mix and recommended prop. I warmed the engine up a couple minutes and mid range for 1 minute cool down 1 minute then ran it up to Tached 6100 to 6200 rpm for breakin. It started slowing down , so I thought it was overheating, then when it went to idle, it blew out a white puff of smoke out the left exhaust. I pulled the plugs , the right plug looked great, brown and a little fuel/oil residue, but the left plug showed signs of being Lean, clean . I put the fat finger over the plug hole , no compression. The right side great compression. I pulled the exhaust off and the right piston shows oil / fuel residue on the piston and sleeve. The left piston is dry as a bone. The carb setting were verified . Low was 1 3/8 and High was 1 1/2.
I am shipping it to DA tomorrow.

What could cause the rear cylinder only to run Lean enough to melt the piston?

[Judge]

Why on earth were you running it on the bench?? That may well have caused the overheating due to improper cooling. These big gas engines like LOTS of air and the prop blast alone is usually not enough.

Now you may have had some sort of failure and DA will tell you for sure, but when you get it back (and it will be as good as new) DO NOT RUN IT ON THE BENCH!!!

Put it in a plane and fly it. It is NOT an OS .40 that needs breaking in before you can fly it.

[BuzzardChaser]

OK, I'm getting ready to fire up for the first time my new BME 115 on a brand new comp arf 2.6m. I got easy 5K in this this. There is no way I'm going to flip the prop for the first time gun the throttle and hope for the best! If I can't run the thing on the ground even for short times I'm returning my engine and buying another brand!

[airriley]

Its not a brand thing. And its not like you can't advance throttle to check for response, readjust needles etc. I think what judge was saying is that there is no need to run a gas engine sitting on the ground for any extended amount of time. One manufacturer I talked to told me not to go full throttle for more than 20 seconds.

[Kiwi]

airriley,

Too true. You can of course run them up to set transitions, mixture etc etc on the ground but any more than 20 to 30 seconds at wide open throttle is courting disaster in my books.
That prop blast is just not going to cut it cooling the engine, especially if it brand spanking new. It needs to be treated like a new puppy for the first tank or two until you knock all the rough edges of it. And of course thats just when its at it hottest during those first few flights. I like to leave them a smidgen rich and lay off the full throttle for a bit. Even over do the oil mix a little in that first tank if your really wanting to be kind to it. 30:1 or so never hurts that first ten minutes.

The better you treat thm in those first few hours the better they treat you back for years to come.

Kiwi

[bryan01601]

HMMM, two threads started in one day about DA engines that we know run very well (along with other gas engines). One started from a guy with 3 posts ?? and another from a guy with 2 posts ??? Somebody smells a troll.

[vernonf]

This is my first big engine. I set it up on a bench the same way 3W setup their 4 cylinder engine in their How to Start the engine video. I thought this was a proper way to start the initial breakin. However, Why one cylinder only ran lean and not the other kind of baffles me.
I am sure DA can help figure out if I did something wrong. I am not looking for a handout.

[GremlinX]

Either a troll or a new guy way way over his head in an otherwise fun hobby....

[Imac Kiwi]

Moderators, Posting about being new to gas engines and mentioning same problem

Beginner ? DA 100 . Proper position of Prop

Would like to give the benefit of doubt.

May I suggest he sends it back to DA as he mentioned in his first post and they will look after him with help and advise from the experts.

This thread serves no further purpose from then on.

[Toro]

Agree.... We can speculate all day long on what caused it. One cylinder lean.... AIRLEAK ? and so on. Bottom line is it has to be sent in, and I think you'll be able to see DA's service first hand. I believe you wont be dissapointed. Thanks for the post, and keep fighting the good fight. Send it in tomorrow, I imagine it will be back on your door with in 10 days. fixed and ready to go.

I just read your from Phoenix.... Uh.... Make it 5 days. Dave and his crew work quick !

[vernonf]

Thanks to all for the help. I am sure most of you have researched long and hard on this great website before you posted any questions or had anything to positive contribute. I bet I am not the first one to make 1st Post and need a fire extinguisher handy for the flamethrowers.
I will keep you updated on the diagnoses. Hope to be flying soon.
If the winds diedown around Phoenix, flying the Byron F 15 tomorrow.
Cheers,
Vern

[GremlinX]

Good point Vern. You just looked a little suspicious. No flaming gonna happen here. Please post what you find. It is always a learning experience for somebody!!! Oh, and welcome to the FG!