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Old 03-25-2008, 06:22 PM
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RCGF 100cc Rear Induction Twin

RCGF 100cc Rear Induction Twin Review

(Author's note, 4/1/08)

After making the original assessment of this engine the manufacturer, either due to this review or through the efforts of AussieSteve and Dreisbabe, has provided parts that indicate their willingness to make design changes that will make this engine worth a closer look. I have not yet had the time to change out the old parts for the new crank, pistons, bearings, and ignition but the changes incorporated in the replacement parts, and more, will be incorporated in the next release of this engine. Don't rule this engine out based upon what you read below. They had problems, but they reacted with the necessary upgrades to correct the problems. We may well finally have a big twin manufacturer that makes an acceptable product for the price structure. Next up will be a solid distributor network close to home that will service the product as needed in a reasonable time line. The dealers are here, all they need is the new, upgraded product to get the ball rolling.

Pat



Some of you are aware that early in February, 2008, I elected to purchase one of the new RCGF engines from either Aussie Steve in Australia or Dreisbabe (Andreas) in South Africa. Both were initially quite helpful is making the purchase happen. Andreas and I had some fax issues, mostly on my end, but after a brief delay an engine was shipped from South Africa. Here again Andreas went to some extra effort to help the product cross all the borders and make the trip. The price I paid for the engine was likely discounted to some extent, but was several hundred dollars below the leading U.S. 100cc twin. I’m not going to disclose the precise amount due to any pricing structures currently in effect with any existing U.S. dealers.

Disclosure:

To eliminate some arguments before they are presented some background information is required. Many of you are aware that on a personal level I’m not fond of exporting dollars or jobs from the U.S. to other countries, with special emphasis against exporting more dollars than we already do to China. My feeling is we have some very good and well established engine manufacturers here at home and in Germany that have been providing us with high quality, reliable products for a long, long time and there’s no reason to pull the carpet out from underneath them simply because we think we might save a buck. If better engines were made available at a lower price that view would change significantly.

The above was not meant for discussion, debate, or argument. It’s simply my personal position; it won’t change, and clears the air for what follows and inform all that my personal attitude bears no influence on this review. What I do with an engine is pertinent to the machinery, not its place of origin.

The review will not be further muddied with my personal political opinion about world financials or other matters, but will concentrate only on what matters. An engine, its quality level, customer support, and customer service. These are things that matter to everyone regardless of where they are. So let’s get to it.

Engine and Conditions:

The engine arrives in a cardboard box containing the engine, an RC Xcl v-2 ignition, two NGK BMR7A spark plugs, and four 1” aluminum stand offs. The engine was disassembled and inspected with a few photos taken, which will be uploaded in another post. It was them mounted on the firewall of the Giles. Gas used was Shell premium, about 97 octane (+/-), with whatever level of ethanol and other additives California was requiring that day. Oil used was Pennzoil Air Cooled mixed at 32-1. The mufflers provided with the engine were used for the run tests. Spark plugs were the provided 14mm, NGK BMR7A. DO NOT use a plug longer than the BMR7A. Piston damage with longer reach plugs would be very probable due to the short distance between the edge of the piston and the plug electrode. If you elect to later install reducers in order to use a CM-6 type of plug be very sure of the plug reach before running the engine. Test elevation was 400msl, with temperatures between 65 and 72f. Relative humidity averaged between 35 and 45%.

Description and Testing:

The RCGF 100 used for this test is an opposed twin, staggered cylinder, rear induction engine. It’s externally similar to a mix between a DA-100 and a 3w-100b2i. The heads would be almost identical to a 3w if the exhaust flanges had not been ground flat 90 degrees to the head. The actual exhaust flange castings are the same as 3w until the flange was ground away. The induction system and the front housing are very similar to DA. The spark plugs are angled to the high side of the heads.

The dimensions of the engine are as follows:

With the plugs and ignition installed the cap to cap spread is 11-3/4”
Head to head: 9-3/4”
Face of prop hub to rear face of mounting lugs: 5-3/8”
Face of prop hub to end of carb: 9-1/2”
Weight: I have to obtain it again later. It was posted in another RCGF thread and I’ve slept since then. The only lighter 100cc twin is the BME 115.

I ran this engine a total of 4 times for review. The runs were kept relatively short using approximately 8-12 ounces of fuel per run. About 10-12 minutes per. The rpm levels were varied to properly heat cycle the engine, with extended cool down periods between runs. The engine was mounted on a W/H 40% Giles 202 to best approximate what others would experience. Good clearance was provided between the firewall and the rear cylinder for adequate air flow and cooling.

An Eagle Tree engine telemetry unit was used to monitor cylinder head temps, using thermocouples placed between the top and second fin of the cylinders. This location is very close to the top of the combustion chambers. The type of thermocouple used for this unit is of the “wrap around” variety. Unfortunately this places the resistance sensor at the front of the cylinder, not the rear, as I would normally prefer.

I had some issues with my Hanger 9 tachometer. I could not obtain a good reading from behind the prop. I went so far as to place a white sheet of drywall in front of the engine and paint a flat black stripe on the back of the prop to provide a better “target” for the tach, to no avail.

Initial tach readings indicated a peak of 6,200 rpm for this engine. Those readings were taken from the rear of the prop and were very erratic. Later readings were taken from the front, obtaining stable rpm readings, and peak rpm levels never exceeded 5,700 rpm. The lowest I was able to idle the engine was 1,200 rpm, which is quite low. At the lowest rpm level engine spool up was still very smooth as the throttle was advanced and there was no threat of the engine stopping. In fairness, there have been reports from Driesbabe (Andreas) of obtaining 6,300 rpm at an elevation of 4,000msl using a Menz 27-10, similar gas, and similar oil at the same 32-1 ratio. His reported low idle with the Menz was 1,500 rpm.

Throttle response was quite good, with smooth and consistent transitions from low to high throttle. Never was there a “burbal” after the carb was tuned. Prior to first starting the engine I closed the needles of the carb and reset both to 1-3/4 open and tuned the needles accordingly from there. There should be no problems for anyone tuning the engine. The carb responds nicely to changes in needle settings. If anyone asks what the “factory settings” were I don’t know and don’t care because the engine was not tuned for where it was run until I tuned it. All engines are this way.

Points of Interest:

1) The engine arrived damaged. A broken fin on one cylinder and a bent crank. This should be attributed to poor packaging and shipping damage. The engine is not well packaged prior to leaving the factory, and the trip from China, to South Africa, to the U.S. can be a little rough at times. The manufacturer should package the product anticipating that rough handling will occur. The crank was straightened to barely serviceable specs prior to running.

2) The prop washer pilot hole is over 1mm larger than crank pilot shaft. This contributes to off center prop drilling and makes drilling the prop considerably more difficult to perform. You must be extremely careful when position the prop washer as a drill jig. Incorrect positioning when drilling will leave you with a ruined propeller.

3) The prop washer itself is the factory intended drill jig. Currently there is no drill jig available. The aluminum used for the prop washer is much too soft to permit drilling without also damaging the original holes in the prop washer. This could be easily fixed by making the prop washer from a much harder metal. The user should consider taking the engine to a machine shop and having a thick drill jig washer made of a hard material for accurate prop drilling. Aussie Steve already provides a harder prop washer for his customers.

4) The prop washer has engine specific bolt pattern. It ensures that large props currently owned and used by BME 115, 3w-106, and DA-100 owners cannot be used for this engine. Due to this I elected to use only one prop for the engine test, a Xoar 27-10 that had been previously used on a Brison 105 with good performance levels. Many owners of this engine would use the same size prop from the same maker due to lower pricing.

5) Included 1" stand offs are both good and bad. Bad because they are generally too short and useless for practical engine spacing. Good because people will not be encouraged to use factory provided long metal stand offs.

6) RC Xcl ignition apparently defective on one side at lower rpm/current levels. One cylinder drops out below roughly 2,000 rpm. CH Ignitions is the U.S. factory authorized RC Xcl repair station. Only the external plug wire cap is repairable with RC Xcl ignitions. Internal module issues require complete ignition replacement.

7) Max rpm levels between 5,700 and 6,200 rpm. Idles down to 1,200 with Xoar 27-10. Last runs on engine produced a max of 5,700 rpm.

8) The carb used is a foreign version of a Walbro SDC-80, but parts will not be interchangeable between the two models. If an option was presented where a true SDC-80 could be substituted that option should be exercised. Doing so would greatly facilitate carb servicing in the U.S.

9) The top of pistons are not finished smooth. The best visual description I can come up with is that they resemble a “steel drum” musical instrument. If I recall correctly it’s called a “shango”. This will contribute to extremely fast carbon development. Higher oil content fuel and keeping the engine cool will assist in preventing carbon build up at the pistons. Better attention by the factory in parts manufacturing would eliminate the issue.

10) The piston rods have bushings at both ends, not bearings. This requires very close attention to engine temperature and oil ratios. Going completely opposite to what I normally suggest for engines, I suggest a maximum oil ratio of 32-1 with a very high quality mineral oil for the best oil cycling through the engine.

11) The induction pulse is provided through the reed block. Carb needle access is at the bottom of the fuselage with the carb in the stock position. The carb can be easily rotated but the reed block cannot due to asymmetrical mounting holes on reed block. Rotating the carb requires that a longer pulse tube from stock be used and that may slightly change the induction pulse timing. There’s no physical reason for the reed block mounting holes to have been drilled asymmetrically.

12) I noted quite a bit of fuel blow back through the carb. Not good. The reeds may not be correctly seating. If you go with the rear induction version of this engine you should seal the inside of the engine box with epoxy to protect the wood and provide a drain hole for accumulated fuel residue.

13) CHT for both cylinders rises appreciably at low rpm levels. This is exactly opposite what it should do and I have not yet found the reason for this. Because of this it is advisable to let the engine run for about a minute or so after landing at mid throttle settings to cool it down. The engine will cool to about 150 to 170f after a short cool down run and heat soak up to about 327f after shut down. I don’t like the idea of shutting down an engine at a high temperature where it could heat soak to even higher levels. Cooling from the heat soak starts roughly 1 minute after the post shut down peak temp is attained.

14) The case mounting lugs are quite stout, which I am pleased to see. The holes in the mounting lugs are drilled to accept a maximum bolt diameter of 5mm. Due to engine spacing requirements it’s quite likely that stand offs be used that require bolt lengths longer that can be obtained in 5mm diameters, which seem to be limited to 95 or 100mm lengths. If you’re careful you can re-drill the holes to 6mm and obtain bolts long enough to mount the engine. This is something that can be changed on later version of the engine at the factory.

15) The mufflers are a little on the “cheesy” side. The can volume is rather small. They are essentially the same design of mufflers used with the 3mm-53, if not the same. The construction is of thin sheet metal with a spark arrestor installed inside at the top of the exhaust tube. The muffler port flange did not match the cylinder ports. The muffler ports required grinding more than 1/8” away from one end to better match the cylinder exhaust ports. The muffler mounting holes were just over 1mm short of aligning with the mounting holes in the cylinder heads.

It has been reported that the muffler can size has been increased and the muffler flanges have been corrected by the factory since the time of this engine test.

16) The cylinder exhaust flanges were been ground extremely thin. This could cause an easy failure point, and promote rapidly loosening mufflers. It has been reported that this has been addressed by the factory and corrected.

17) External machine work is pretty rough. If the case machining was performed on a CNC machine it must have been done at extremely high speeds. The cylinders have a rather large amount of casting flash between the fins but that can easily be cleaned up by the customer.

18) E-mail communications sent to the factory bring slow or no response. Weeks pass before you obtain a response to e-mail communications. A request for replacement parts has taken an extremely long time to obtain a response, and the response could be best described as non committal. This engine is still awaiting the parts that were damaged in transit and will now be removed from the airframe without being flown.

Conclusion:

The engine has potential but at the moment it’s not ready for prime time. More effort needs to be expended in true engineering. Consideration at the factory needs to be given to increasing power output and long term reliability, with less effort in reducing manufacturing costs to the bare minimum while eliminating bearings and other components which provide a longer lasting, high power engine.

Communications with the engine dealers in Australia and South Africa were quite good and generally open. Andreas offered to remove the crank from another engine and send it to me to replace the bent one. I declined the offer to see how well the factory would respond to service requests since I had initially contemplated becoming a dealer for this engine line. The response came up lacking. Poor response and lack of communications from the factory finalized in my decision not to support this engine or become a dealer. Had the factory been prompt and open with communications the decision could have gone the other way. I have been told that newer engines will be incorporating some design changes to correct some of what was noted above. Until I personally see one I cannot verify.

Customer support from the RCGF factory is woefully lacking. If the factory is not talking, the customer knows not what is going on. The original owner of BME well illustrated this fact. The customer must be kept informed, and in a timely manner. If a manufacturer has any desire to retain the customer they need to communicate with them. The internet is an extremely rapid and wide reaching method of communication and there’s no reason not to make use of it if you have a computer. Customers are the ones that sell product, and that should always be kept in mind. Ignore the customer only if you want to significantly reduce your bottom line.

This engine does not provide the power that a 100cc engine should. At least not the power of any other 100cc class engine I’ve used or had experience with to date. It roughly equals the output of a 70 to 80cc engine, but without rod bearings cannot be run as hard as most engines in that size currently available. The fuel mixture must be mixed rich with oil. Engine temperatures will need to be closely monitored to avoid damaging the rod bushings. Fortunately I have a large Cub that was looking for an 80cc twin. The Cub will not require high rpm throttle use so this engine might suffice for this purpose. Given a little more time and attention to detail this engine could have the potential to be a good product.



Pat
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Old 03-25-2008, 07:51 PM
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Re: RCGF 100cc Rear Induction Twin

Thanks Pat for the report and opinions, guys like me trying to get back on little funding need this kind of thing. I'm hoping the next purchased bird will be in this class. I personally can't bring myself to send cash over seas. Need a local importer.
I'll not consider this one.

Ive already decided to buy used or go with Brillelli if it's a 33% at this point but I wanted to let you know your report is appreciated.

I tried buying direct about 12 years ago but the language barrier killed it forever !
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Old 03-25-2008, 11:15 PM
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Re: RCGF 100cc Rear Induction Twin

You could have posted a shot of the crank, NO ONE wants a 100cc gasser with bushings on both ends of the rods...Net even another Chinese compahy...Someone will run 100-1 Amsoil in it...
with predictable results....You might get by with 1/2 pint oil to a gallon of gas, like the OLD bushing rod outboards...But they never ran 6000 rpm.....
Only twin I ever saw with bushing rods was the old Chinese 2.4 Twin Star...The rod material IS the bushing..The rods have caps held on with small allen screws...I still have one here NIB...Single carb piston port.....Comes with a rope and pulley for starting...Really...
If the Chinese twin cranks I have here are any indication, they have some work to do....The center piece is flat steel, too thin for a good tight press fit, so all the parts are welded...But they need welding lessons, and the center piece is so soft that it bends..Little or no penetration on the welds...I have a 50 and and 2 100s, both the same....The 50 was a replacement, was too large and long for the case...I turned the OD down slightly and bored the rear bearing deeper in the case...Haven't run it yet...
I could tell ya who made the cranks but I'd have to kill ya
The German 275 Limbach ultralight twin has rod caps but roller bearings..One piece forged crank...It works VERY well....
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Old 03-26-2008, 02:24 AM
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Re: RCGF 100cc Rear Induction Twin

Good Morning Guys,

Pat, thank you for the review and the findings concerning the product.
I would like to add a couple of things that I have found in the running of a new 100cc twin rear induction RCGF engine. The engine that Pat has run, is of a previous production run, and as he has mentioned some of the issues have actually been addressed by the Factory on the batch of engines that I have currently in stock and testing on a stand.

As Pat has mentioned, the Mufflers have received a reworking and now A. fit better (no more bolt offset) and B. have a slightly larger capacity. They are also now welded with separate end caps that actually reach around the Muffler drum and are made of thicker material.

The ground down muffler flange on the Cylinder head is still present although it is now at least 3 mm thicker and I have been promised by the factory that the issue will disappear in future.

The carb insulation block has been changed, and is now rotated at 90 degrees, meaning that the needles are now accessible from the side of the carb and not at the bottom. This makes mounting the engine allot easier. The reed cage has work done to it, and the reeds have been stiffened by an additional tiny piece of stainless steel.

The 1” Standoffs have disappeared from the package, I have not approached the Factory about this, but I will report on the issue.

The engine that I have on the stand, is performing very well, turning a Menz S 27X10 at 6300 at full bore and idling at 1500rpm, all this at about 10oz of 32/1 fuel.

My engine is not spitting back fuel from the carb as stated by Pat, I attribute this to the stiffer reeds, that are actually closing or seating well now. I do however have the same sort of heat buildup at idle, I have not checked, but I think this is due to a retarded timing.
I will check and report back.

As for communication with the Factory, I have been in constant communication with Cathrine over the past couple of days. I have to admit, that this is not via e-mail, but via Skype. The attached pictures she has send me yesterday of the new 50cc engine design, and it was added that this engine dose actually incorporate needle bearings at both ends of the crank. I am hoping this will lead to the same changes to the 100cc engine.

Regards
Andreas
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Old 03-26-2008, 10:16 AM
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Re: RCGF 100cc Rear Induction Twin

Looks nice...Why is everyone going with those @#$%^ 6 bolt hubs ? A 3/8-24 grade 8 is all anyone needs on ANY engine...If you want 2 anti rotation pins, fine, but a single bolt will never shear and can be TIGHTENED enough to keep the prop from ever slipping...Especially on a small engine...Our 30+ hp racing twin has one 3/8 grade bolt in the middle, with two anti rotation pins..Never slips, 31 pitch, 9400 rpm....I TIGHTEN it with an 8 inch socket wrench....Never measured the torque, but it's considerable...I read somewhere lately
the bolts on a REAL airplane prop never touch the sides of the holes, they keep the prop tight enough against the hub so it can't slip...Can't confirm that, but it makes sense....
40 inch lbs on a 8mm prop bolt seems too little, maybe not....
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Old 03-26-2008, 01:53 PM
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Re: RCGF 100cc Rear Induction Twin

Ralph,

If and when I get the parts to correct the 100 would you be interested in doing the repair work and noting what you see with the engine? I can do it myself but I would like to obtain an independant view.

You're quite right about the bolt/nut torque on an 8mm or 3/8" size. 40 in.lbs. is much too little. Closer to 100 or more.
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Old 03-26-2008, 02:46 PM
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Re: RCGF 100cc Rear Induction Twin

Yup, like to put the crank in my jig and see how close to concentric it is from the factory...
Don't even know what the torque is on the 3/8, it's as tight as it can get with an 8 inch long socket driver....It stops moving at the end....If I can't do 75 lbs feet I must be getting old..My props don't slip...
My 2024 hubs can only be stripped with a 3 foot long extension on the end of the wrench...Tried it..3/8-24 threads 5/8 deep in the aluminum...Took lots of force...Tried it with 6061, no problem, way less torque needed.....
I can't imagine twisting off a good 5mm by bottoming it out, not with 40 inch lbs..3w must use low grade bolts....
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Old 03-26-2008, 03:07 PM
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Re: RCGF 100cc Rear Induction Twin

Soft bolts is an understatement for the stock 3W's. But you'll never strip out a hub using them. Maybe that's the idea
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Old 03-26-2008, 03:10 PM
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Re: RCGF 100cc Rear Induction Twin

Be prepared for the onlsaught of 3W fanatics who just LOVE 6 bolt hubs and NEVER sheared prop bolts.....They ARE out there...
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Old 03-26-2008, 06:26 PM
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Re: RCGF 100cc Rear Induction Twin

I've always wondered why so many bolts. If I had a center bolt I would use two of them as pins and skip the rest. Seems like so many would weaken the hub and promote splitting. But obviously it works. I'm afraid I will strip the hub with the small bolts though.
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Old 03-26-2008, 06:41 PM
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Re: RCGF 100cc Rear Induction Twin

That's the way BME set up the 115 originally. A center 3/8 for primary prop retention, with a hub that permitted using six outers for those that had props for DA's and 3w's. You tightened the center nut and just snugged the outers to prevent any potential prop sliding. There's no need for more than two outers but some feel they need a slew of bolts to hold the prop.

Ralph,

It's a deal then. If the parts get here I'll send you the engine. If they don't I'll still send you the engine for a complete tear down and inspection. You know my money's good. All I ask is an accurate and honest assessment of the engine.

3w provides some pretty soft bolts. Don't know what they are but they frequently cannot be removed without stripping the hex head after torqueing to 40 inch pounds. I've had to cut a boat load of them away from the prop washer....
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Old 03-26-2008, 07:59 PM
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Re: RCGF 100cc Rear Induction Twin

Quote:
Originally Posted by rcign View Post
Be prepared for the onlsaught of 3W fanatics who just LOVE 6 bolt hubs and NEVER sheared prop bolts.....They ARE out there...
Knock on wood I've never sherded bolts before on any of my 3w's. Then again I call MC masters Carr and always order replacement bolts and check there tightness regularly.
6 bolt hubs are a pain in the A$$, my other large gassers only have the center nut and two indexing bolts. All those bolts look nice, but when testing multiple props it gets old quick.
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Old 03-26-2008, 10:03 PM
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Re: RCGF 100cc Rear Induction Twin

Interesting ...
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Old 03-26-2008, 10:22 PM
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Re: RCGF 100cc Rear Induction Twin

If there are only 2 bearings on the crank, there's a whole lot of unsupported shaft out there..If the bearing is at the crank web there's a lot of crankshaft between it and the hub....
If the bearing is behind the hub it's too long from the crank web to the bearing...If the bearing is at the counterweight I betcha you can move the hub up and down, all that movement is transferring to the center joints of the crank....Not good......
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Old 03-26-2008, 11:43 PM
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Re: RCGF 100cc Rear Induction Twin

Ralph,
This think about two bearings gets me. I have an engine here that is from the latest batch I received, and that most certaintly has three bearings. I hope my wife brings my camera, I will then tear it down an let you have a look.
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