Hi..

I have a NIB ZDZ60, and are wondering about this: With piston at TDC and looking down the exhaust port I can See below the piston skirt. The gap is small, about 1/2 millimeter. Is this normal.?

Sandman

It is called "sub piston induction". I remember some of the older engine wizards discussing this back in the sixties in the model mags. Allegedly, it is bad for a stable idle on glow engines and most designers tried to avoid it later on.

However, I doubt that it happened accidentally in your engine, so perhaps there is an advantage of which we are not aware? I can see how the crankcase charge could be partially diluted by residual exhaust gasses. I can also see how it could lend toward relieving the vaccum in the crankcase when the piston reaches top-dead-center, thus providing more gas for the piston to use to push the fuel/air charge up toward the top of the cylinder during the down stroke.

Maybe we will get lucky and one of the engine gurus on the group will give us a clue or two.

None of the ZDZ engines in our stock here at RC Showcase have this feature! I would check with the distributor you bought the ZDZ 60 from to see if the rest of his have this feature. I have forwarded a copy of the reporting email to ZDZ for their comment.

David Garrison
RC Showcase
ZDZ and RCS GAs engines

www.rcshowcase.com

Hi.

Thanks for the info David. I was hoping that this small gap would be normal, as I was to break in the engine this weekend.

Would be interesting to hear what ZDZ says about this. Btw, my engine is of the new type of 60`s.

Thanks

Sandman

Worked OK on unmuffled engines but I doubt it would work with the muffler backpressure but that remains to be seen. Comparative tests need to be made.

1/2 mm- can you actually run a tiny piece of wire into this "gap'?
Sounds very odd - never seen it on the 60's --You may be looking at the edge of the piston skirt.

Dick H.: Yes I can put a piece of wire under the piston. I have talked to the Norwegian reseller, and he did a check on his remaining engines and found another with this "problem" It seams that the one with a gap has a thinner cylinder base gasket, than the others. He is waiting for a reply from the manufacturer.

Sandman

have not seen that - but I understand how it could happen

OK this is the answer from the factory regarding my little "problem" :

>this has no influence on engine. We have made this on one series of 60RV but it has no effect to the engine.

>It is not caused by gasket but by shorter piston. It is not a problem for perfect run but if your customer wish we can ship you new piston.


So I`ll guess I just fire it up and then put it to good use..(In a GP Pitts)

This is a very interesting post because last spring I bought a zdz60 and set it up on the bench put about a gallon of fuel through it and could not come up with rpm numbers that other users were getting,not even close.I think ok Maybe more run in is required,different gas or something like that.Unfortunately I did not get to fly the motor this fall and did not give it much more thought.Until I came across this post!Low and behold mine is the same way but there are gaps in the corners too that no base gasket would take up.Low rpm means only 6400 on a 22/10 zinger but the motor starts good and has good transition.
Every thing checks out but that.
Pennzoil 40:1 91octane
uncowled
check and recheck timing
So I guess its time to get a hold of rcshowcase and see what they think about this.Maybe we could see some rpm numbers from other engines with this problem.
Terry.

Rock 114
which zinger 22x10 are you using?

It is the standard wide blade square tipped zinger

rock 114
My 60 won't do any better with a sqaure tipped zinger either.
You would't think an inexpensive prop would load the engine down that much.

2lo
Did you try any other props on your 60 pro zinger or menz somthing like that and if so what did you get with these.
Thanks Terry

ROCK 114

No I haven't tryed any othe props other than an APC 22x10 which the rpm's came up a little, but I sure diidn't like the way it spooled up. real slow.
I've been mainly sorting out the props on my BME 2.7, with a 20x8 ZINGER PRO is the only one I can achieve a stable 7200 rpm and not overheat the engine. All the other inexpensive props keep the engine loaded at or around 6200 to 6400 except for the master air screw scmitar wooden props which give pretty close to the same rpm's. I just haven't flown with one yet.
The first chance I get to buy some other props for my 60 though, that fre@#$# sqaure thing is coming off!
It's real ffrusting trying to learn new stuff and you don't have much response after half throttle.

2lo that is the only prop I have tried other than an old 22/8 fiber prop I had laying around that I was using for break in trying not to load the motor too much.About 7000 was all I could get out of that one.I know it is not broken in yet but I can't see 7300 even with the skinny menz or zinger pro.

I'm not familiar with the ZDZ's at all, but my broke in G-62 is turning a Mejzlik 22 x 10 at 7700, and it was turning a square tipped Zinger 22 x 6-10 at 7400. I would guess it would turn the Zinger 22 x 10 at 6900 or 7000. I thought the ZDZ's were supposed to be real strong?