doxilia

My Feedback: (3)

I recently bought what I believe to be an early MVVS 3.5 (.21 cu in) GFS/R ABC RC engine. It has a finned crankcase (see pics) and a slanted square bodied bleed type carburetor. I bought this engine as I was looking for a .21 cu in rear exhaust (RE) setup. Another alternative would have been a K&B 3.5 but I've been having a hard time getting a hold of one.

Although this engine is discontinued, I was hoping there might be some answers to questions I have. Here they are:
[ul][*] The engine came setup with the cylinder in the GFS (SE) configuration. Since I wanted a RE engine, I disassembled the engine and re-assembled it by rotating the cylinder and sleeve leaving everything else as is. The engine, while probably manufactured and bought during the '80's, appears un-run so I understand the trick of rotating to the GFR configuration is allowed. My question is regarding the ports in the crankcase and cylinder which appear designed to mate in the GFS configuration but not in the GFR configuration. There are two intake ports on the front and rear of the crankcase and cylinder and a boost port on the left side (viewed from behind) with the exhaust sleeve port on the right. Is there (or was there) a crankcase designed with ports on the sides and front so that the cylinder and crankcase ports match in the GFR configuration?
[*] If the engine is designed to be operated in the GFR configuration as is (i.e., no mating of intake ports), can I expect the engine to perform less in the RE than SE configuration?
[*] While this engine can be seen to not have been run, what harm is there is rotating the engine cylinder and sleeve to a different setup after the engine has been run? Is the issue with the sleeve and piston mating?
[*] I understand this engine should be run on FAI fuel, 20% castor, an 8x5 prop and a medium to hot glow plug. Is this correct?
[*] What is the RPM range I can expect on an APC 8x5 using the above setup?
[*] There is a wire that is bent into what appears to be a header/mousse can muffler (3243 GFS/3244 GFR) support that attaches to the exhaust adapter. Should this be installed as shown in the pictures below?
[*] What is the ideal AUW of a sport/pattern model for this engine?
[/ul]
Thanks in advance for any insight or suggestions.

David

doxilia

My Feedback: (3)

Here's the instruction manual that came with the engine.

pe reivers

If the engine has run, it is better not to change exhaust port orientation. If you do, running in starts again and some extra wear is to be expected.
Performance should be better in RE configuration, but I found little difference.
an APC 8x5 should run between 17500 and 17800 rpm using the 3243 muffler. The 3241 has more power in these upper rpm regions and runs a MA8x5 at 19000 rpm.
MVVS has mufflers that use the wire, but also has mufflers that bolt to the cylinder.
A plane of 1.2 - 1.5 kilo will be fast and aerobatic. a 9x4 or 9x5 prop would be better then.

Do not use synthetic oil in these engines. The first runs will have extra power. After that they will run worse and worse and become untunable, until they get Castor again.

doxilia

My Feedback: (3)

Pe,

thanks for your reply. If I understand correctly, you are the designer of these engines?

As shown in the pictures, there doesn't appear to be any sign of this engine ever having been run. The glow head is as shiny and clean as it would be when new. Given that, I trust it won't be a problem to run it in RE configuration?

I'm still somewhat puzzled about the case and sleeve porting re-configuration when the cylinder is rotated to the RE setup. Is it normal and a non-issue for the ports not to be aligned? I somehow wondered if perhaps a different crankcase was needed when using the engine with a RE cylinder and sleeve setup. If you could shed some light on that topic, it would be much appreciated.

One further concern is with the piston skirts being oriented in the sides. When the piston comes up to TDC, one can see the conrod between the skirts. Am I doing something incorrectly or is this how it's supposed to be?

I know that the side/rear option on MVVS engines has been there for a long time but I just wanted to make sure that I got it right and am not somehow missing something.

I'll plan to break the engine in with a APC 8x5 and switch to a 9x4 or 9x5 for sport/pattern flight per your recommendations. The AUW of the suggested model is within the range I expected - 40-50 oz, thanks for the info.

As far as fuel, I'll go with FAI 80/20 with 100% castor. The only issue is where to source such fuel in Canada. If I could source the methanol, it would be easy enough to self blend it I suppose be methanol is a banned substance of sorts here. I am actually able to buy it in small quantities (1L) so I should be ok if I need to blend it myself.

Thanks again, David.

doxilia

My Feedback: (3)

I am starting to like these MVVS engines and had the opportunity to pick up another older but new 6.5 (40). Pe, if you have recommendations regarding fuel, plug and props on this one they'd again be much appreciated. I plan to run this one like the 21 in RE configuration with a tuned pipe; probably a MACS 6.5 cc muffled pipe.

The support forum concept is great - first time I have the need to use it!

Pictures attached.

Thanks, David.

P.S. Are these the model numbers of the engine: 3066 GFS mode and 3067 GFR mode? (I don't have it in hand yet)

pe reivers

The current 3.5cc pistons do not have any cutout that would create skirts. Cylinder rotation as such will not cause the lower piston edge uncover the lower exhaust port edge in TDC. If your piston does have a cut-out in the lower skirt, then that should go over the bearing. The rear crankcase cover has a flat (if needed)  to allow the full length piston to travel all the way down. The skirt should not raise so high as to open the port lower edge causing piston sub-induction.

BTW, I am MVVS dealer! No other MVVS relationship apart from being a big MVVS fan.
Like stated before, the slight port mismatch in side configuration does not seem to hurt performance. Cleaning it up did brin nil extra rpm.

GFS is glow - front intake - side exhaust
GRR is glow - rear intake - rear exhaust
As for fuel: some fuels with castor blends work out as well. I use Tornado fuel in my small engines. So far the only synth/castor blend that worked on engines 6.5cc and smaller. Larger engines can be run on any glow fuel of max 5% nitro. No nitro is better.
 Maybe someone else can chime in.

doxilia

My Feedback: (3)

Pe,

before responding to your comments, let me ask, did MVVS ever produce engines with rotating cylinders that were not meant to run in either side or rear exhaust configuration - if you know?

Somehow I have the feeling that this 21 size engine I have may not be designed to run in GFR (RE) configuration - possible? Here's why...

I should have taken better (or more) pictures when I had the engine disassembled. The piston in my 21 engine has two skirts on opposite sides of the piston. Otherwise said, the piston has two inverted "U" shaped cutouts that are oriented fore/aft in the cylinder when the piston is connected to the crankpin. Rotating the piston 180 degrees doesn't change the symmetry - the engine would still have skirts on the sides and cutouts front and aft. This engine also has no flat part to the backplate and is circular. The two cutouts in the piston prevent it from hitting both the crankshaft in the front and the backplate top in the rear. The cutouts also align with the intake ports in the cylinder and sleeve in the SE configuration. But, as I mentioned above, when the piston comes up to TDC in the RE configuration, the cutouts result in the conrod being exposed to the exhaust port in the cylinder as well as the front intake port.

You mention that the piston should not allow exposure of the conrod to the exhaust as this causes sub-induction. This is what I was concerned with. Also, the crankcase (but not the cylinder in the RE setup) now has an intake port which is aligned with the exhaust port of the sleeve. However, since the cylinder and sleeve stay aligned with each other (they both are rotated 90 degrees clockwise for the RE config), maybe this does not matter and the rearward intake port on the crankcase remains unused.

I took some other pictures of the exhaust outlet showing the piston at TDC. One can see the conrod exposed to the exhaust outlet. This doesn't strike me as viable but I'm no engine designer or engineer. One of the pictures was taken with flash which shows the conrod as the shiny object.

If it turns out that this engine can't be run in RE configuration, so be it. I just don't want to assume that all MVVS 21's can and I end up wrecking it when I run it.

That's good to know Pe. Are there any pros and cons from obtaining parts/accessories from mvvs.cz versus from your site (mvvs.nl)? Shipping time? Warrantees?

I see. In my engine the port mismatch does not happen in the SE configuration - it is matched in the case, cylinder and sleeve. It's in the RE configuration when mismatch happens between the case and cylinder. Not only is there mismatch but the intake port on the rear of the case ends up being "blocked" by the cylinder which only has the opening for the exhaust outlet (i.e., no intake port cutout). This essentially leaves the engine with one intake port on the front, a boost port on the left side, no intake port on the right side and a covered intake port on the rear by the cylinder.

I think photos #2, 3 & 4 in my first post depict the above reasonably well - I believe.

By extension, GFR would be glow - front intake - rear exhaust I take it. For the 40 (6.5) I was wondering what model number I might have bought (3066?).

So for 40 and below I'll plan on using FAI fuel (0% nitro) or a max of 5% nitro. I'll see if I can source some Tornado fuel for mixed oil types but otherwise will plan on using 100% castor and 20% by volume.

David

P.S. For some reason the photo I took with a flash wouldn't want to rotate so it shows the engine on its side.

pe reivers

I must admit I have never seen a 3.5 like this. I would not try to run it, it seems that this particular engine is meant to run in side exhaust configuration only. Just to be sure, maybe Josef Svajda can shed more light on it. ( [email protected], ask for Mr Svajda).
He will need the numbers on the engine mounting flanges.

doxilia

My Feedback: (3)

Pe,

thanks for the info. I suspect you are right and this engine might not be able to run in RE configuration. I'll drop Josef a line asking for his take on things.

I appreciate your help,

David

Diesel Fan

The older 'Modela' marked series of engines do not have the 4th port cast into the lower crank case and were a precursor to the later engines that had that mark deleted.
I have an older MVVS 'Modela' 40 that has the same construction, it has 4 ports in the barrel and only three in lower case.

It can only ever run as a side exhaust.

(Even stranger were the engines before this that had ringed pistons!)

doxilia

My Feedback: (3)

Diesel Fan,

thanks for your comments.

My 3.5 cc engine doesn't have any "Modela" markings on it but as you mention, it is missing the right hand port in the case. This prevents fuel from being delivered from left and right hand ports. However, even if the port was cast into the case, the issue with the piston conrod being exposed to the exhaust port (due to the piston being "slotted" front and back) would remain. As Pe suggested, this would cause sub-induction which would damage the engine.

As for the 6.5 cc, I have not received it yet but the photos show a case with castings on all four sides. I wrote to Josef at MVVS per Pe's suggestions and he confirmed that the 3.5 cannot be run in RE mode but the 6.5 could. I'll have to see the design of the piston, backplate and crankshaft when it arrives to confirm this.

I hope it does allow RE use as otherwise I will have ended up with two MVVS engines that I bought for RE use that won't allow that...

David

Recycled Flyer

Um, yes it does.

The large 'M' on the case stands for "Modela.'

My only hint of advice with these engines is to perhaps watch the bearings, they weren't the best from new and that news comes from Josef Svadja himself.

Cheers.

pe reivers

On these older engines, Josef knows his stuff. So back off from RE use. The engine is a GFS , not a GFS/R

Recycled Flyer

This seems to have slipped through the cracks, the wire hoop that holds the pipe on is upside down as shown in your picture.

It is easier to lever off the pipe when placed 'hoop away from the bearers' since it is more accessable.

At least that is how I have mine installed! (Pe´to confim please.)

pe reivers

It does not matter much. Either way will keep the muffler attached, so it boils down to personal preference.

doxilia

My Feedback: (3)

I received the MVVS 6.5 GFS last week and found a moment to re-orient the engine for rear exhaust use (GFR). The quality of the machining of this engine is considerably superior to the older "Modela" 21 I purchased. I assume the engines are now being produced with CNC machining.

I've seen several different head colours on the 6.5's (40) ranging from black (mine), blue, yellow to red. I was wondering if this was simply an anodizing "preference of the year" when manufacturing or whether they referred to some particular trait of the engine. I believe the yellow heads are for the pylon version (GRRT) but not sure.

Here are some snaps of the RE re-configuration for those interested.

David

doxilia

My Feedback: (3)

Pe,

would you be able to send me a PM with a price on the MVVS 4.6 (28) - engine and low cost shipping to Canada?

I would also be interested in a header that has a slight rise to it. The standard 3257 header appears to be a straight (0 degree) solution. Would MVVS or someone else be able to supply the engine with a 1/2" rise (so called fuse-top)?

I believe that Macs may have one appropriate for this engine (model #3372) as well but it is a 1" rise fuse top header. They also specify a dimension for a ".20R" engine of center to center = 24.94mm = .982". I suspect this may apply to the 28 as well but please let me know if the lug hole distance is different than this. I think this is the correct distance of the 3.5 (21) that I have but the 4.6 might be different.

The engine would be used with a tuned pipe (e.g., Hatori 300 or Macs 1020) and I'd be looking to ideally turn an APC 9x5 or 9x6 prop, or whichever brand you recommend.

I particularly like the way that MVVS goes about the exhaust much like Rossi does with an adapter flange and, presumably, a softer header pipe itself.

David

Recycled Flyer

David, you will always have an unused cavity in the lower crank case directly under the exhaust outlet and in some instances there is an advantage in plugging this up with a small piece if wood.

With the front intake design it serves no purpose other than design flexibility, or if you are using the rear intake it will be part of that inlet tract, so you can decrease your lower crankcase volume here if you wish.

This is of benefit with either diesel conversions or control line stunt use where neither applications use a tuned exhaust system.

pe reivers

For prices and shipping cost, use my web page www.mvvs.nl which has all information you need. There is no low cost shipping of parcels.

The 3.5 - 4.6cc series have no such header, However, the 3257 allows to be slanted a little in any direction. The material is soft, so you can also bend the tube.

BTW, the carb on your 6.5 has the old spray bar construction. This will have a very rich midrange. The modern spraybar set cures that. It will fit in the old carb.

doxilia

My Feedback: (3)

Pe,

I'm picking up this thread from last April. Thanks for your latest reply regarding the spray bar on my 6.5. In addition to the new spray bar which you recommend, I'm also in need of an R/C carb for a new MVVS 4.6 (28) that I recently bought. As can be seen from the pics below, the engine comes with a C/L venturi as well as a "tongue" type muffler. I will be rotating this engine too for a GFR configuration. Am I correct in assuming that the 28 and 40 both use the same carburetor?

I looked for the carburetor part for the 28 (3216) on your web site but was unable to find a listing for it. If you have both the carburetor and the spray bar you mentioned for the 6.5, I'd like to purchase them. I will also need the locking pin which retains the carburetor in place. Please advise on how to proceed.

As an aside, I noticed the current 28's have blue anodized heads and thrust washers while the engine I bought has a red head and silver washer. Was this just a color preference at the time of manufacture or were the colors used to denote C/L and R/C for example? Another detail I noticed is that the engine I bought has an instruction sheet which mentions a spec of 0.7 kW@17K while the specs on your web site mention 0.8 kW@17K. Is this power spec difference due to when the engine was manufactured (if there is indeed a power difference) or is it a matter of whether the engine is running with a muffler or a tuned exhaust?

Thanks in advance.

David

pe reivers

The 3216 fits all 3.5 to 8cc engines and will have the new spray bar. The locking pin is item #3216-401 (page accessories)
Power is what you make of it, and how you set up your engine.
I measured 0.84hp on my 3.5cc using a 8x5 Master airscrew and a 3241 muffler @ 19500 rpm in side exhaust configuration, 20% aerosynth oil. Your results may differ, depending on how you run in your engine.
Advice: use 20/80/5 castor mix only . Pls no more than 5% nitro. Less is better
After extended running in, your engine may run well on all synthetic oil. If running gets worse after each tank, switch back to castor!

doxilia

My Feedback: (3)

Pe,

Thanks. How do I go about ordering a carburetor and locking pin? Can I also order a new design spray bar alone for older 40 carb?

David

pe reivers

go to my web page  mvvs.nl