Does anyone have any idea what might cause this level of damage to a piston in normal use? Its from a DZ160 engine I sold to a chap 6 months ago and he's just sent me this picture claiming that its been like this since I sold it him. Yet the engine ran fine last time I used in in Argentina 2007; it had to 'cos of the howling winds there. I can't believe the engine would have run if the piston was like this.

Keith

wow! looks like extreme heat or contact with a extra long plug[X(]. no way i warranty that after 6 mos AND it was running fine when you sold it.

david

it is a well known case on dz's. Caused by either violent backfire or use of a very powerfull starter with too much fuel in the cylinder. Look at the carbon- builds around the edges....It is a relative old mishap and the motor can run for some time before the power fails. The piston, by the way, shows signs of excessive wear on the lower parts indicating that piston as well as liner and ring needs replacemant.
And I'm not with YS :-)

David / Eggert,

Thanks for your replies. I myself have never seen this kind of damage on a DZ and I've been running them since the Dingo appeared in 2002. So from what you say the mechanical damage appears to be the result of hydraulic locking or very significant backfire. I cannot say what has happened to the engine since I saw it six months ago, but the guy who bought it reckons it was like that when he tried it for the first time recently. Its hard to imagine the engine running normally in this condition. My problem is that I sold it to him in good faith, it having not run after November last year at the W/C in Argentina. I had many practise flights there in front of team members from Norway, Sweden, Ecuador, Brazil and Ireland and no one commented on it running badly, and I thought it was running well at the time; it had to due to the winds there.

Keith

Your best bet is to send this picture in an email to Richard Verano. I'm sure this is something he's seen before.
Greg Grigsby

Funny, the same thing happend to me.I sold my 160 and he never could get it to run.
The pic shows what the piston looked like
I am just glad the repair was not expensive

Maybe too lean run?

I love the YS160 and 170

There is a reason for those delay glow igniters...

That looks like if it was running very lean and probably being backfiring in the air, this happens if the engine is too lean, ask how many dead sticks the person you sold it to had, I think you'll know then.

This engines can break due to missuse, and depends on how it is run and the fuel,etc. But if you fly YS you know all that already.

Regards

Thanks for your input guys, I really appreciate it. The person who bought it has never run DZ's before and I suppose he could have started / run it lean based on how he used to fly his 120AC's. However I was suprised to see all the wear at the bottom of the piston and maybe thats down to the very dusty conditions in Argentina when we flew there. So I expect I'll have to compromise and go halves on the repair bill.

Thanks once again

Keith

In one reply to this thread it says "there is a reason for the delay glow starters".

I would argue that a delayed glow starter may be the reason for this piston failure. I believe that YS users use delay glow igniters to stop the knock or backfire which will accompany trying to start an engine with too much fuel in the cylinder. A powerful starter combined with too much fuel will stress the engine. The crankshaft will twist and eventfully break, probably in the air some flights later. The same with the connecting rod.

When an engine backfires or knocks on starting all the energy is fed back through the starter to your wrist, if it is allowed to backfire in this way most of the energy will be dissipated with less stress on the internal parts of the engine. If the starter is held in place through 'the knock' the stresses inside the engine will be enormous.

The delayed glow drivers have been referred to as 'soft starts' and I would suggest just the opposite happens. Instead of letting the engine dissipate its energy through the backfire (due to too much fuel) you are forcing the engine to turn by building up inertia generated before the glow is switched on which gives the impression that you are avoiding the knock when starting. Not so! The knock will still occur but because of the inertia before igniting the glow plug it will force the engine through TDC putting huge amounts of stress on the connecting rod and crankshaft. The nearer that knock occurs to TDC the more likely the piston will fail as the connecting rod at TDC is at its least vulnerable, but something has to give, in this case the piston.

The only way to 'soft start' or be kind to an engine is to start the process with the glowplug ignited and less than enough fuel in the cylinder to fire, and allow the engine to gradually start as sufficient fuel is made available.

Your thoughts would be appreciated.

If the soft start was obligatory, Yamada would have recommended the usage of such devices in the user's manual. Kickback is not common only for the DZ series but on the pressurized ones.

Troy Newman has recommended the usage of a very powerfull starter to avoid kickback, practice shows that he is correct. Also in warm days kickback is more possible as pressure is developed in the tank and engines is flooded. The usage of a heli tank clip may be useful here. Another way of avoiding this is hand start, by turning the engine clockwise.

The piston degradation is a long term process it does not happen at once, here is a piston failure of a YS-140 FZ I used to run in the past. The initial symptoms were loss of power, and not as stable idle. This lasted for a few gallons till the engine died in a upline. I replaced only the piston and engine ran like a pro.

I have seen a similar DZ piston failure in a Japanese F3A web site with cracks on top. These kinds of failure may be random and rare, I can not believe that the Japanese are unaware of running YS DZ engines.

That's my 2 cents...

Regards,
Nikos

Uhhh....go right ahead, I'll watch......LOL

Seriously, knowing how this beast CAN kick, I am not going to stick my hand in that prop....ever.

-Mike

Mike,

This is the way my team mate starts his DZ seriously, he rotates the engine from the spnner not the blade and engine starts at once, not reccommended of course as it is dangerous. The safest way to start YS engines is by using a starter

Here is a relevant thread:

[link]http://www.rcuniverse.com/forum/m_7830399/anchors_7833528/mpage_1/key_/anchor/tm.htm#7833528[/link]

I finally found the pictures at Masahiro's web site. You can see that the Japanese modellers face similar problems with the rest of the world. Here we can see only one crack on the piston which probably would expand as the one illustrated previously.

Regards,
Nikos

I'm just saying I wouldn't do it myself

-Mike

Oh boy, look what I have to look forward to! LOL
I've been thinking about the "soft start" glow drivers lately. It's a good idea unless the engine is flooded. Then it's a really BAD idea. We used to start circle track engines this way: hit the starter, get the engine turning, then turn on the ignition. Works great. The idea here was to the flywheel to store energy - this helped the starter a lot. A high compression race engine puts a severe load on the starter. We ran those things with a lot of advance too so if you didn't start this way sometimes you'd make the starter VERY unhappy when the engine kicked back. Sounds like that's what happens when you start a YS. The last thing you want to do is force a flooded engine to turn and then light the fire. I can see this as a cause for piston failure over time. I agree that you should make absolutely sure that the engine isn't flooded no matter what type of starter / glow igniter you're using. A little rich is OK - slobbering with fuel is not.

John Pavlick
Team Black Magic, Tech-Aero Designs

John,

The soft start is the only way to go with the DZ. As you spin the engine up it clears the fuel charge out of the cylinder before the plug is energized and you don't get the kick-back. If you have tried it both ways (With and without the delay) you won't be without a delayed glow driver.

Joe Dunnaway

Joe

I think you have missed the point completely. By turning the engine before igniting the plug you are charging the cylinder with new fuel and in effect flooding it.

When an engine is stopped by closing the throttle (cutting off the air) once the carburettor is returned to the idle position from closed, the engine is in perfect condition to start again, so cut off the fuel immediately after the engine stops, and only open again seconds before the restart, connect the glow and turn the engine, it will start. Every time without any kick.

Regards

Ashley

The only thing the delayed start does is to have inertia builded up on the cranckshaft so it can only kick on the right direction, nothing more, it does not have anything to do with flooding etc.

Sounds to me as if the problem is flooding, and not the starting method. Using the delayed start drivers will push the excess fuel out of the cylinder with out having an ignition event. However, as the engine is turning it is drawing more fuel into the cylinder. A better method would be to pull the prop through by hand several revolutions before applying any sort of glow or starter. Once the engine feels clear, you can start as normal.
Back to the flooding..this has to be stopped to prevent engine damage. This is why full scale pilots pull their engine through on their walk-arounds to clear out the cylinders(oil in their case). A pair of hemostats on the feed line would prevent any fuel from entering the engine while at rest, regardless of the conditions. Pull the engine through, remove clamp, apply heat, start...Everything else is a band-aid masking the flooding problem. No flooding= no damage.