Frequently Asked Questions

Why are ZDZ®Engines so light weight?

Simple answer; by design. The  ZDZ® cylinders and crankcases use  investment castings designed with both strength and lightness in mind. The cylinders walls are plated with Nikasil, a space age concoction of microscopic Silicon Carbide granules  held together by a matrix  of Nickel. Silicon Carbide provides the harness and Nickel the slipperiness.

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What is a Rotary Disc Valve?

All two cycle gas engines require a mechanism to close off the carburetor from the crankcase during part of the cycle. A number of methods have been developed by two cycle engine designers. The most popular, only because it is inexpensive to make, is the use of a metal reed that closes the opening to the carburetor when the pressure in the crankcase increases. This method works well at low engine RPM, but has problems  permitting enough fuel to enter at the higher RPM ranges. The Rotary Disc Valve is a thin steel disc that is attached to the crankshaft and by the means of slots cut in the disc alternately opens and closes the opening to the carburetor. The opening is designed to produce an even idle, instant throttle response AND a wide throttle power band. ZDZ® began using reed valves but has since modified or designed their newer engines to use Rotary Disc valves. A significant increase in engine performance was thus achieved. The inline ZDZ® engines and the quad 160 cc still use reed valves, as there is no practical method to incorporate a Rotary Disc Valve in these engines.

Why do these engines require premium gasoline?

ZDZ®Gas Engines have a higher than usual compression ratio; 10:1! Most other engines have a compression ratio of around 7:1. Strangely enough regular gas burns faster than premium and thus will cause detonation ,"ping", if used in ZDZ® engines. A minimum of 93 octane gasoline should be used.

RCS Gas Engines are rated for Regular gasoline.

I've heard that engines with rear mounted carburetors are hard to mount!

Not so! Take a look at our user gallery to see how our customers have mounted the ZDZ® engines. Very simple and straight forward. In fact putting the carb in the rear has the advantage that you can adjust the needles while the engine is running. Your hands are far from the spinning prop!!.  An added advantage is that the carb is placed  in relatively quite air and performs more consistently than those carbs mounted so the cooling air is rushing across them.

Carburetor Primer: Which way does the throttle rotate and how does one install the ball and swivel linakage?

The carburetors that are supplied with model airplane gas engines are of a generic nature and are not custom made for use on a model airplane engine. There are as many ways to connect the throttle lever to a servo as there are modelers! We present some general thoughts to aid the installation of your engine in your model.

The carburetors generally have a method for setting the idle speed that would prevent using a servo to "kill" the engine (completely closing the throttle) So the first item to do is to remove the mechanism that provides for the idle setting. Please note that removing the idle setting device sometimes allows the throttle butterfly to freely rotate 360 degrees (depending on the carburetor design. So prior to modifying the idle stop it is best to mark the shaft and car body so it is clear where the closed position is. It is also important to note, that the butterfly can be positioned 180 degrees out from where it should be, the engine will run with the throttle butterfly in position like this but not very well with a very fast idle and no full speed operation. . The throttle shaft OPENS the throttle butterfly by turning CCW (while looking down at the shaft).

When you set up your throttle servo, adjust the servo/linkage so that  low idle is at mid trim. This way you can stop the engine by moving the throttle trim to completely close the throttle buttlerfly.

Ball and swivel link arms are provided for those that want to use them on either or both the choke and throttle. Generally the throttle lever on the carb has to be removed from the shaft by grinding or filing off the swaged end of the shaft. Be sure to tape up the openings in the carb and exhaust port of the engine to keep metal filings from entering. If you loose the original closed setting, you can look into the rear of the carb (with the choke opened) and set it so the butterfly mounting screw is facing the front of the carb.

Throttle Linkage Setup - Select any image for a larger view

ZDZ® 80 BING carburetor- unmodified

Throttle butterfly valve in closed position

Butterfly partially opened. Note small hole on the front of the carb. This is the vacuum pulse hole and MUST be correctly aligned w/ the pulse hole on the carb mounting block. The carb must NOT be rotated from its original mounting position

Ball And swivel installed on a typical Bing and Walbro Carb. Some carbs allow the link to be installed without removing the original throttle arm. If the carb on the engine you have is like this then do not remove the return spring, just clip the end that is hooked around throttle arm and leave it in place.  Make sure that the throttle butterfly is set so that the screw is towards the engine body. If it is positioned 180 degrees out it will not close completely and the engine will not idle... and can not be stopped by closing the throttle. Some users use small steering arms as throttle control arms. Up to you and your set up.

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What about the Warranty and replacement parts?

RCS and Roto engines are warranted against defects in workmanship for a period 24 months from the original date of sale from RC Showcase, Inc.

RCS and Roto ignition units are warranted against defects in workmanship for a period 12 months from the original date of sale from RC Showcase, Inc.

ZDZ® engines are warranted against defects in workmanship for a period of 42 months from the original date of sale from RC Showcase, Inc.  

ZDZ® ignition units are warranted against defects in workmanship for a period 36 months from the original date of sale from RC Showcase, Inc.

We have a full compliment of parts and all necessary tools to repair the engines. Our goal is to repair the engine and get it back to you as fast as possible to minimize your aircraft downtime and get you back in the air as soon as possible! See our Warranty Policy Page for full details.

I'm new to gas engines, how does one go about adjusting the carburetor?

Single Carburetor Gas Engine Tuning Introduction:

  • Do not use the largest recommended prop. We recommend using a prop one size smaller for proper break-in. Break the engine in with petroleum based oil (6 hours of operation minimum) then switch to synthetic oil. Use good quality (92-93 octane for ZDZ® and 87 for RCS engines) gasoline. Use 32:1 for break in and 40:1 thereafter.
  • Set the timing first (factory setting recommended), then low needle and finally high needle. Fly the plane and check the engine response in the air. Adjust as necessary. Remember to adjust the high needle after adjusting the low needle as the low needle setting affects the gas supply throughout the entire throttle range.
  • Tune the engine with the tank 1/2 full.
  • All readings should be taken when the engine is hot. The needles should be adjusted with the cowl on. Stop the engine when adjusting the needles and then start it again. Allow it to run for at least one minute before taking a RPM reading.
  • Above all be patient. Don't take any short cuts and don't try to adjust the engine while it is running. This is good general advice, but the carburetor placement on the ZDZ® and RCS engines does permit this to be done with great caution. BEFORE MAKING ANY ADJUSTMENTS THE MODEL MUST BE PROPERLY RESTRAINED!
Definitions:
Running rough Popping, spitting, spluttering, burbling.
Goosing Opening the throttle from idle to full very quickly.
Lean The term lean means that there is less fuel being delivered to the engine from the carburetor for a given throttle setting. The engine will run faster, smoother and hotter as the mixture is leaned, provided that it is not leaned too much.
Rich The term rich means that there is more fuel being delivered to the engine from the carburetor for a given throttle setting. The engine will run slower, cooler and less smoothly and will probably foul the spark plugs if it is too rich.

Low Needle
Process Keep in mind the low needle affects the high one but not the other way round.

The low needle should be set as lean as possible without displaying any of the bad symptoms mentioned below. First get it to run smoothly at idle, then try goosing it to about 1/3 throttle. Adjust until the transition is smooth.
Symptoms Too Rich: Runs rough and shakes badly (may hop from wheel to wheel) Burbles in midrange and smoothes out at full throttle Engine will transition slowly May die after idling for a long period
Too Lean: Hard to start Won't decelerate (hangs at higher revs for a while) Dies when 'goosed' to full throttle
Warnings Setting too lean may cause a dead stick when opening throttle after a long downline.

High Needle
Process Keep in mind the low needle affects the high one but not the other way round.

Bring the throttle up to high and back the high needle out till it runs rough / rich. If you can not get the needle to produce an over rich condition then you have insufficient fuel flow (example: tubing may be too thin). Fix it and then restart the tuning process.

The high needle should be set to gain maximum RPM without overheating. When running in it should be set slightly rich.

Measure the RPM and slowly close the needle as long as RPMs continue to climb. If RPMs flatten out or fall then back off about 1/16 of a turn.

Test the high needle setting in the air by pulling vertical and flying some loops. If it loses RPM it is probably set too lean. Open it about 1/16 of a turn and try again.
Symptoms Too Rich: Full throttle blubbers, cleans up only on uplines Will not develop full power
Too Lean: Runs hot Sags on uplines May die in flight Will not run at full throttle
Warnings Setting too rich may cause the engine to generate carbon deposits and foul the spark plugs.

Conclusion/Confusion - Mixed Symptoms
Runs hot May be caused by high needle being too lean and/or by timing being too retarded.
Hard to Start Could be timing, needles or any of a host of other causes. Check low needle too lean and/or timing too advanced.
Runs rich May be caused by low ignition battery; make sure it is fully charged when setting up engine.
And finally Bad or stale fuel and/or a bad or leaky plug can cause a host of problems that would be difficult to diagnose.

 

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How Important is cooling?

In a nut shell: VERY! The longevity* and performance of your   gasoline fueled engine depends on adequate cooling. Simply providing an air intake and an air exit is not sufficient. The air MUST be directed so that it flows through the cooling fins on the cylinder. Air isn't stupid, it wants to follow the easy path to get out of the cowling, and that is not the path through the cooling fins. You will have to make the air flow the way you want it to...through the cylinder fins!. The way to this is with a system of baffles that offers the cooling air no choice, but to flow over the cylinder fins.  Next time you open the hood of your car take a few minutes to examine the air dams and baffles that force the air that piles up in front of the moving car to pass through the radiator. We need to use this same concept to keep our gas engines cool. For more information on baffles and engine cooling try doing a search on "Cowling baffles" on www.google.com... there is truly a wealth of information available on cooling aircraft engines of all sizes from radials to simple air cooled opposed engines. A point to remember is that ALL full scale airplanes with air cooled engines use baffles to control the engine temperature.

 

If you want to know what happens to the insides of an overheated model airplane engine look at this sad photo! The piston was firmly welded to the cylinder wall. It took an 8 lb. hand sledge hammer and a wide punch to dislodge it! What a shame!

*The RC Showcase warranty on engines does NOT cover abuse, and operating an engine that is not cooled properly is abuse!

Baffling baffles? Here's a great mini-article from Ken Spears of Arlington, Texas
The best cooling comes about when you can force most of the air that comes in the front to go through the fins on the cylinder and the head. The engine remains very cool because of the baffling and ample cooling air outlet. I made the baffle from 1/32" ply with a few stiffeners thrown in. Notice the small turned down aluminum piece on the cowl. It serves to create a low pressure area at the outlet to improve flow.

When using the ZDZ®80, 60 or 40 single in an Extra, CAP, Edge, Cub, or Decathlon there can be dead air space, depending on the design of the cowl, right in front of the cylinder. If you don't use baffling, then most of the cooling air bypasses the cylinder. By using a baffle that semi pressurizes the front end of the cowl, then you are able to allow the cooling air to flow where you want it, by the cylinder and head.

To make a pattern for the baffle, you actually have to make two patterns and join them. To make the first pattern, I use a piece of cardboard like poster board. Cut a hole in the cardboard to fit over the prop hub. While sliding the cardboard on the engine, trace the area that you want to remove and cut it out. I allowed 1/8" clearance around the crank case area and the muffler exhaust box.

With the engine installed, mount the cowl. Looking through the front air intakes, take a felt tip marker and make a few marks on the inside of the cowl where you want the baffle. These don't have to be exact but are used to give you a reference for trimming the second pattern that you are going to make.

Take another piece of cardboard and trim it to fit inside the cowl near the marks. Cut the center out of the cardboard to clear the engine and muffler box or side mounted muffler. Tape the pattern in the cowl and trial fit. Adjust as necessary. Make final marks on the inside of the cowl where the baffle goes. Use Goop or Zap-A-Dap-A-Goo to glue 1/4 square balsa or bass wood sticks in front of the marks. Shape the sticks so the baffle will have a flat surface to seat against. Tape the pattern in place. Slide the first pattern in place on the engine and tape it to the engine. Slide the cowl on and mark where the first pattern touches the second pattern. Remove the cowl and the second pattern. Tape the two patterns together and trial fit. When you are satisfied with the fit, cut the baffle out of 1/32" plywood or material of your choice. Paint the front side flat black for looks and glue or screw it to the sticks.

Ken Spears
Arlington, Texas
rcflyer@ev1.net

What is included with ZDZ® engines?


Small twin engine hardware kit shown
 All engines are supplied with an ignition system and a complete hardware kit, including a spark plug and wrench. Very handy ball and socket adapters are supplied for the throttle and choke servo connections.

Shown here is the hardware kit that ships with  the smaller ZDZ® twin engines. Similar kits ship with every ZDZ® engine.

How is the Ignition Sensor adjusted on a ZDZ® engine?



It is a good idea when setting up a new engine to make sure the timing is set correctly. After installing the Hall sensor, adjust its position by following this setup procedure:

  • Position the piston exactly TDC
  • Measure the distance from the center of the magnet to the center of the sensor (see image above).
  • Set this distance to: 5mm for the 40RV-L and 50NG engines
  • Set this distance to: 6 mm for 60/80/80B2/100B2 engines
  • Set this distance to: 7 mm for 120B2 and 160 Champion engines
  • Set this distance to: 9 mm for the 210B2 engine


Should my engine need service, how do I go about it?

In the unlikely event that your engine would need service, there are three simple steps to follow:

1) Call RCS at (301)374-2197 and request a Return Merchandise Authorization (RMA) number

2) Download the Service Request Form available to the left and fill it out neatly and completely.

3) Pack your engine well, include the Service Request Form and ship insured to:

RC Showcase Service
Attn: RMA (your RMA # here)
3442 Gough Drive
Waldorf, MD 20602



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ZDZ® is a registered Trademark of RC Showcase, Inc.