Manufacturer C.M.B. Country Italy Type 21 RALLY LSi DD

* factory supplied numbers

An Italian buggy engine from one of the famous world champion manufacturers of 3.5 cc boat engines.
With the knowledge of these boat engines C.M.B has manufactured a nice looking and good performing buggy engine.

When we received the engine from the German C.M.B distributor HS Micro Motor Service the box with the engine it was factory sealed with a label. When you buy an engine be sure that label is intact. If not, ask the shop owner to check the contents before buying it.

I broke the seal and looked into the box. The engine is nicely packed in two plastic airtight bags so no debris can enter. One is with bubbles. Further the user guide with instructions to maintain and break-inn the engine (all in German language!).
*Also an explanation with drawings are there for the proper pipe length.
*A conical type 6 glowplug
*A boost bottle with tube and ty-wraps.
*The black carburator.
*And some stickers.

I first took all the papers out and read them carefully. (who isn't?!)
One paper is dedicated to:
*the engine break-inn and maintenance.
*how many head shims are required.
*which glowplug to use in which condition.
*which fuel to use and most important the amount of oil required! In this case even the maximum and mixture between synthetic and risinus oil is provided.
*the correct length of the pipe.
*the warranty regulations.
Paper two is dedicated to the flat slide carburator only.
Paper three is the parts/price list of the engine.

After reading all papers (I understand the German language) I opened the engine and took all parts apart.
The factory claims that the engine does not need extra cleaning as this is done in the factory already before assembling. And they were right. The engine parts inside were covered with a film of oil and no metal debris parts were found.  

 A full ABC piston-liner is naturally used in this race engine. But a patented system of the piston design makes it different from all other known buggy engines.
The piston is a so called "intelligent piston". 

CMB has a patented system to manufacture the piston sleeve called "intelligent piston" in such a manner that the thermal specifications make it less critical for break-inn and expands the lifetime of the piston sleeve.
Break-inn is reduced to a period of one tank of fuel running the car in rich setting on the track.
After this one tank of fuel the engine is ready for use the manual claims!!! The second tank of fuel you can set the engine for the correct setting without abusing the engine and its lifetime.
When the engine is just started it might sound a little crunchy. But when it is warm (take the time a few laps will do fine) it will sound OK. Also when finished running, let the engine idle stationary for 30 seconds and then cut the engine. Place the piston in its lowest position. This will make starting an other time easier.
Also a cut out (ditch) in the top of the piston is there to provide better performance.

More features are the  C.M.B Multi Exhaust System "MES". The system speeds up the gasses leaving the exhaust and fills it with fresh fuel mixture. Beside the 5+3 ports in the liner there are two extra ports in the piston. They are working together with the "MES" ports to provide more power and better fuel economy.

The engine is a long stroke one and the cranckshaft measures 13 m/m. It has three carved TURBO cutouts at the end near the cranck pin (bigend). This is to better the fuel flow to the combustion chamber.

The crankcase of this engine is nicely finished. Two extra ribs at the bottom are making it stronger.

A green tapered cooling head makes it looks nice and also efficient for the right amount of cooling without making it too heavy. The cooling head is constructed with a head insert that accepts only conical glowplug the so called "TURBO" plugs.

A boost nipple is located at the right side of the engine. This means normally that there is not much space to prevent the silicone line get in contact with the central drive shaft. So it would have been better if this nipple was located at the opposite side of the engine like all other manufacturers do. You can replace it with an 90 degree angled nipple but this should come as a factory standard! 

The flat barrel slide carburator is nicely black colored (anodized) and is fully made out of aluminum and is a story of its own. There were already flat barrel slide carburators made by Picco for car engines but they were made out of composite plastic. As producing and maintaining the right specification over a period of time the composite material could give problems in settings and reliability. Instead of plastic this carburator is completely manufactured with a CNC machine out of aluminum. This means that the tolerance of the carburator will stay the same. Around the throat of the carburetor that goes into the crankcase there is nice nylon isolation bushing. This is to prevent the full metal carburator to get warm by transporting the heat from the crankcase and causing "vapor lock" in the fuel system. Manufacturing this carburator is a costly process, but it looks very nice and stable.
Three needles in total for adjusting high speed, bottom speed and idle speed at one side of the carburator. The angle of the idle needle is horizontal and can easily be accessed from the left side of the car.
The airflow of the intake and the part that fits into the crankcase is nicely tapered to give better airflow and so performance of the engine.
The carburator is large. Then I mean with in all areas. Fitting this one in for example a MUGEN MBX-4 needs rework over the throttle linkage. The total width differs 12 m/m compared with a Nova Rossi based 8 m/m carburator. Also due to the larger height the airfilter is touching the inside of the body more. This all shouldn't be a big problem. But when you are used to swap Nova based engines (training/competition engine) this could provide a little more work. BTW a Nova Rossi 15 m/m throat diameter based carburator fits without rework on it. Only add the o-ring that comes with the original CMB carburator on the throat of the Nova based carburator. The throat is a 1.5 m/m longer and will not fit airtight against the crankcase if the extra o-ring is not placed.
An other small disadvantage is the throttle connection ball that moves the flat slide barrel. This one can rotate freely. So no fixed angle can be obtained. In the test set up of this engine in a MUGEN MBX-4 the ball was changing position every time and no constant push-pull motion could be achieved.

A rubber shielded NMB bearing is sealing the front. A large main bearing does its job inside.

The purple boost bottle that comes standard with this engine is not build inside the rear cover plate but is an external one. This is to prevent the bottle to become the same temperature as the hot engine. The bottle needs to be placed somewhere on the rear stiffener bar. If boost bottles are useful in all cases is to be discussed. But it is standard so try and error will prove if it works on different tracks.

The claim of the working of boost bottles is to enhance the idling and pick up from low speed.
Also better fuel economy is an advantage that is described to the use of boost bottles.
Boost bottles do not boost the maximum power of the engine itself!

The first impression of this engine out of the box is OK. 
Parts and engine are nicely machined and assembled!
Although the manual is completely in German language it is crisp and clear. (an English version will be available soon)
The specs tell us it is a bottom power engine.
No horsepower or torque rating stated in the data.
The real engine performance and fuel economy can not be judged by looking at it. So we will track test this engine and compare it with others and if possible dyno test it.

TWF8 rating **** stars

Paco Raap

	The box with the engine with a sealed label!
	The right side of the engine with the boost nipple
	The left side of the engine
	All mechanical parts of the engine
	The three slots "TURBO" cranckshaft and bigend
	The exhaust port with the two MES booster channels
	One of the booster ports and channel clearly visible
	The other side with the second extra booster port and channel
	The other of the 5 normal ports
	The nice chromed layer inside the bronze sleeve
	The ditch in the top of the piston
	The connecting rod mounted inside the piston. The top piston pin has no bronze bushing in the connecting rod!
	The piston and the connecting rod with a bronze bushing and the two extra ports in the piston itself.
	Watch the small cut out for easy removal of the piston pin retainer spring (good job)
	The cranckshaft
	The crankcase inlet for the carburator and the old straight nipple for the boost bottle connection
	The piston in the sleeve. Watch the ditch in the piston
	Those two screws need a little silicone sealing to prevent possible air leaks
	The high performance 8 m/m flat barrel slide carburator
	The type 6 conical "TURBO" plug
	The complete engine equipped with the angled nipple and boost bottle

Comment by Dieter Suchan from HS Micro Motor Service the CMB car engine distributor for Germany dated 18-12-2000:

Regarding the carburetor, CMB claims that a flat slide ( they had already one in the early 80 ths)
provides always the same vacuum because the air-stream is always forced to pass the needle directly in all stages of the slide. This leads to more power of the engine. 
We tested this and found that the claim  is correct !

We have already discussed why the carburator is that big. 
Mauro Braghieri of CMB argues that he wanted to make it in the same way he builds his engines: stable and of high quality. We have made some suggestion how to alter the carburator in the height, but Mauro claims then the air-intake will be badly influenced what will cost power.

The rotating lever is also a point we claimed. It is easy to solve the problem and CMB will do this
also. (You open the carburator and cut away the piece of the of the lever with the carving around (which holds the slide). Then you grind a groove right and left of the lever and fit the slide in this grooves=the lever cannot rotate any more!)
You must however watch these two grooves are uniform in depth and measurements otherwise the slide may stick in some positions. 
However the carburator as it is now, is different from all the other buggy carburators for the 3,5 cc engines and this causes doubt about the performance. But according to our experience it does not cause problems when installing it in off-road cars, as this is the case in the on-road cars.
CMB thinks about that and will surely bring a solution in the near future.

Now to the nipple for the "pressure-hose" at the engine. We have no problems with those. If the engine is properly installed the hose will not touch the driving shaft! If you mount this nipple on the reverse side (left), than those can touch the hot pipe!
On the Mugen MBX4-RR we used in Las Vegas the stiffener was vertical and not
horizontal. I have sent you the 90 degree nipples and shall pack those into
every box of new engines until CMB uses those. (That is called super service and customer voices response, Paco)

Regarding the performance of the new patented "tapered piston" I only can refer to the experience of the Marine -users (Where it was introduced first) and they are enthusiastic about the performance and to our Las Vegas World Championship experience with the 21 Rally LSi DD -you probably watched yourself - as well as the comment of some "Expert -visitors" see "www. mamo-modellbau.de" = "The CMB engine in Matz Sönkes Mugen was one of the best of the whole engines participating."

When no original C.M.B muffler is used the best options are Picco mufflers. Nova Rossi based mufflers do not give good performance in combination with C.M.B engines!

Dieter Suchan, former C.M.B Germany.

Comment by Paco Raap 28-12-2000:

As promised I received the angled nipples and mounted them. This makes the fuel line running beside the engine instead of away from the engine where is might get tangled with the center drive shaft. Good point CMB Germany will put an angled nipple in all boxes with no extra charge. The top picture with the original straight nipple. The bottom picture with angled nipple.

Comment by Paco Raap 30-12-2000:

The manual was already warning for this and take care of it! If you mount the engine on the engine mounting blocks be sure that the bottom surface of the engine mounting blocks is flat. The engine mountings blocks of the Mugen (MBX serie) and Kyosho will have no problem. How ever the engine mountings blocks from Thunder Tiger are not straight at the inside and they conflict with the two extra ribs that are on the bottom of the crankcase, so flat mounting is not possible. Therefor remove some material (the marked triangle) at the marked spot of the engine mounting blocks. If the engine is mounted check if the ribs are not touching the inside of the mounting blocks anymore.

Comment by Dieter Suchan from HS Micro Motor Service the CMB car engine distributor for Germany:
We have discussed the dimensions of the CMB flat-slide carb and the fact it brings some trouble due to this mainly in on-road cars, but also in sometimes in off-road cars. However this carb is very expensive in production. 
Mauro Braghieri has tried to solve those problems; he used a injection-molded Aluminum for the body, at the same time trying to reduce the dimensions. 
The result was not to his satisfaction, because the accuracy and the function was not to his standards.
Though he decided to make use of a composite barrel-slide carb, he was able to get
from the market.
This carburetor corresponds mainly to those Picco introduced in Sept.1999 which you show on Picco page .But the main needle corresponds to those of the CMB flat-slide. 
Those carb will be standard with all CMB engines ( Buggy 7mm / Rallye and Car 9mm) from
February 2001 supply.
The CMB flat-slide will remain available as an "Extra". 
With this, we will be able to keep the price low as well as solving the space problems with some cars.

18-02-2001 comment by Paco Raap

With a outside temperature of 6 degrees Celius it was not warm. Glowplug was a number 6 from CMB. Pipe the CMB 9904. Ok the car was ready and so the engine. I use my standard Modell Technics Dynaglo with 16% Nitro. As described in the manual I first ran it stationary for a tank of fuel.
Had to higher the stationary as the engine would not start from itself!
Ok the manual states that because this is an INTELLIGENT piston engine only one tank of fuel for  break-inn was needed. To be honest I did two of them :-) and then let the engine run at 95% performance setting. Due to a defective plug, as these engine use Turbo (coned) plugs which I do not have in my sparebox, I had to wait. So today the real first try. After fitting a new CMB 6 plug I hit the track to obtain a good setting. It might be the problem of the flat-slide carburator or the characteristics of the engine but the 95% performance point was hard to find. Critical on every little turn of all screws that are there.
I finally managed to get it almost right.
You want to know how it performs. If you need bottom power this is your engine. Warning for novice drivers! DO NOT USE THIS ENGINE. On the Mickey Mouse track (compared with the WORLDS track from Las Vegas) I ran it, it worked like an ON/OFF switch, it was all or nothing. Some one said that my throttle punch on my Sanwa M8 was selected. But I do not even know how to program that!!! :-)))  so took an other model and programmed it from standard. Same problem! This engine delivers almost all his power in the low rev range. As the car ran on astro turf there is almost no resistance when the car is at speed. So after 13 minutes of racing the tank was empty!
Do not think this engine is fuel economic. But as I could not lay the power down I was running it economically! On tracks with more rolling resistance like dirt or grass the fuel economy will go down dramatically. The engine ran further 1 liter of fuel without a problem. 
Next test is to use the engine with 8 m/m Nova based carburator and normal glowpugs.
Maybe we can tame this power horse to suite our home track.

Two other minor things to mention:
When the engine starts. You have to rev it very high to get the crankcase clean of fuel.
When the engine is upside down it has the famous flatslide trouble that it rev's higher. As soon as it is turned in normal position it is normal again. In a few cases the engine stalled after 5 seconds. We will test if this problem also happens when a Nova based carb is fitted.

25-02-2001 Comment by Paco Raap

The outside temperature was 3 degrees Celsius and we ran Mcoy MC9 plug. Same Model Technics Dynaglo 16% and the original CMB 9904 pipe.
As said the carb was swapped for R&B 8 m/m version. Also the head insert was swapped for one that accepts normal glowplugs. As the setting from the R&B S7 does not corresponded with the settings required for the LSi I had to do some adjustments. Again the right setting was not easy to find. I ran some laps to check for the engine temp but that staid below 75 degrees Celsius.

The bottom power was reduced to reasonable figures. The track conditions were comparable with last time. Not much grip! Run time was reduced to 11 minutes. But this time I could trigger the throttle 30% more then the first time tried. Last time the 10% was the limit. This mend a more controllable car. The upside down high revving was gone too! Only problem I had was that after a pit stop for refueling the engine stalled at the first corner. I had to readjust the stationary needle a little higher to prevent this from happening.

10-03-2001 Comment by Paco Raap

The outside temperature today was 11 degrees Celsius and we ran again the same Mcoy MC9 plug. Also same Modell Technics Dynaglo 16% and the original CMB 9904 pipe. I received a comment from a German CMB team driver Paul Eckman that the upside down high revving could be caused by airleaks in and on the carburator and he advised to seal it with silicone. So we remounted the flatslide but this time we sealed the carburator neck that goes into the crankcase and we sealed the top base of the carburator with silicone sealant.
The upside down high revving was gone! Also the carb was a little easier to adjust. His comment on the long runtime was that the engine was running to lean. But resetting the carb fat and later to 95% setting of maximum performance it was never running to lean at all. Beware that these extremely long runtimes could only be achieved because of the surface of the track and the fact the power could not be put on the track. Now the flatslide was mounted again also the snappy throttle response was there again. So this flatsilde adds a certain amount of bottompower. As rain was predicted and again driving this engine on this track is not easy I opted not to put it in for the race next day.
During the time I ran the engine this day there were no problems. The engine temp did not exceeded the 84 degrees Celsius. Runtime in race trim was 9 and half minutes with boost bottle and FUEL ECONOMIZER. Still running on that same artificial grass track at our club.

CMB FUEL ECONOMIZER I also mounted the rear engine cover that normally comes standard on the ON-ROAD version and that can be purchased as option for the other CMB engines. In theory this design would help the fuel economy and a minimum 1 minute gain should be possible. As I had not enough time to swap for the normal rear engine cover, I could not see if this rear cover had any effect on the fuel economy in the same conditions. I will test it next time out on this same track again. Also when the engine dyno is ready better figures about fuel economy and these gadgets can be tested without guessing if it works.

The new style CMB carburator is an OEM product and is made by Picco. There are two things to take care of! * first is when you want to rotate the fuel nipple on the high speed needle housing for better alignment. Take a 7 m/m wrench and turn it anti clockwise gently!! * when the high speed needle housing is removed check for thread blur on the aluminum body part. If it is there (see red arrow) take a 8 m/m drill bit and slowly rotate it one turn to remove the blur. Do this with the carb upside down so no metal debris will fall into the carb housing!! This blur can cause a fuel leak as the washer that will be on top of it is not sealing perfectly between the aluminum body and the high speed needle housing.

11-04-2001 comment by Stipna Skropil
I have participated in the Czech National Indoor Championship for the year 2001.The engine was more than perfect for the whole race. Is has got an excellent idle thrust and its temperature differed from 85 to 95 degrees  centigrade. There was only a problem with a balancing  pot which loosen up, but it was promptly solved. I unfortunately participated in the final race with damaged rear muffle-just after the start a collision appeared so I finished the race on the fourth place. Due to the injured front muffler in the next race I fell down from the first place to the fifth place, but I managed to finish the race. Many thanks again for all and please find enclosed photograph of my car and a cup for my total third place in the Indoor Championship of the Czech Republic.
Yours sincerely Stipna Skropil
!Used with the new composite carburator!

15-04-2001 comment by H.Hugo h.hugo@ndh.net
Today I have ran the engine(21Rallye LSi DD) 2 liters with only refueling. After the running-in procedure I
started to go to full power. I must say the engine has beaten one Nova Rossi 21SBK and an OS RZV 99 very easy. This thing goes really good! The only problem is the setting of the carburetor what is not easy. Beside this I am highly pleased with this engine and can recommend those very much!! Does this engine get warm sometimes? I could drive as much as I could but never reached more than 90 degrees !How many liters will this engine stand? 

11-06-2001 comment by H. Hugo " 27 liters has the 21 Rallye LSi consumed up to now and it looks like
the conrod has a little play .Shall I replace those or at the same time also the complete cylinder/piston ?"> h.hugo@ndh.net< (Answer from hs: As long as the idling is O.K. and the engine runs with a "healthy"-
sound , nothing has to be done)

Paco Raap

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