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UMS Gas Radial Engine Enthusiasts Rabbit Hole

Old 03-17-2024, 06:01 AM
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Default Evolution 7-35 vs UMS 5-55

Maxam , I've been reading through the thread you started in 2011 "UMS Evolution Radial Care and Operation" and with you having experience with both 7-35 & 5-55 are they similar in build?

Are the carbs similar/same in venturi size . Could the 5-55 be converted to glow with spark ignition with the supplied carb and run as good as the UMS Seidel engines you speak of in the forementioned thread?

I know warranty will be null & void if I were to use glow fuel in my 7-50 as it states not to use even gas mix with ethanol but internally if they are the same and having a glow based carb wouldn't it meter glow fuel better than gas?

I wouldn't mind running a methanol mix (no nitro) with 6% oil if it meant reliability , even with a little more maintenance at the end of the day. In theory it should produce more power too right?

Of course , I will run-in the 7-50 per the manual first and see how it responds but if it doesn't run reliable enough to confidently install in a plane , other avenues will need to be tested . Adrian at CH Ignitions has something in the works . Morris at Morris Mini Motors has a conversion that has not been a proven cure yet and the cost of the fix is/will be expensive.

If the 7-50 & 5-55 can run reliably by just changing fuel , plumbing and tank , it seems the least expensive option. Not to mention the potential power gains possible.





Chris
Old 03-17-2024, 12:40 PM
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Originally Posted by Robert Dochterman
And so for my 5th post to allow me responder privileges.
I want a radial in a 5-cylinder configuration running gasoline.
My first choice was the Saito FG73r5. What worried me was the weekly posts on Facebook of the Saito gas radials with photos of the bent-up rods.
Next in the hunt is the UMS 55-5 which is the perfect size for my application but appears it will need a Walbro carb and a pump. I'm willing to do that but i can't find good comments on its operation in either configuration.
Next leads me to the UMS 75-5 stock with a Walbro carb. Seems to have happy owners.
So a question comes back to my first engine. Is there a reason the Saito radials are bending rods, is this really that common, or a user operational error?
Hi Robert........ I have a UMS 5-cylinder 55cc radial and I am going to install a Walbro carburetor I recently received in the mail from Morris Mini Motor as well as the pump kit. When I first got this engine (I purchased it from Adrian) I had lots of problems trying to get it to run properly. Eventually, it got to the point where it wouldn't even start. I was upset and finally sent it back to Adrian to see what he could do with it. I guess he got it to run again and sent it back to me but never did say what he did to get it to run. Frustrated....... I'm here in Alaska and do not have proper weather conditions to do a test run yet outdoors but am working on a method where I might be able to run it inside my garage with the exhaust going out underneath my overhead door. We'll see about that. I was thinking that the problems with getting it to run correctly might be related to the inferior carburetor that comes from UMS on this engine. I think it is nothing more than a glow carb. So.....why I am going to try the Walbro carb on it soon. When I have some results I will post them up here for everybody to check out and comment on.
Old 03-17-2024, 12:50 PM
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Default UMS radial engine evaluations

Originally Posted by dodgers72
I recently bought a 7-50 from Adrian @ CH Ignitions. Even after reading about it's problems I purchased due to size restrictions. This is my first radial and will be testing it on the stand this week. I spoke with Adrian a couple days ago and he is well aware of its shortcomings and is working on the solution. In the mean time I will get some run it in some and see what happens .

The carb body is very robust with a small venturi compared to my 2 stroke glow engines. I do understand multi cylinder engines sometimes share a carb that is equivalent to an individual cylinder but other than the f-90 r3 15cc Saito carb has anyone tried any others?

After reading through this thread on the 50 & 55 no one has mentioned the exhaust pressure tap for the fuel tank. Has anyone used this as it was included in the hardware pack and the exhaust ring has accommodations for it?
Chris

Hello Chris....... I have a UMS 55cc 5-cylinder radial that I'm working on to try and get it to run correctly. I would be very interested in any kind of results you have had with some of the testing you've done with your UMS 7-50cc. Have you been able to do any testing so far? Please post anything you have discovered or had good results (or bad results) up here on this forum. It would be most appreciated. Thanks.........
Old 03-17-2024, 03:09 PM
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Chris. I have three UMS7-35's (glow) The stock carb is decent. I have flown them extensively. Yes I had the 5-55 and it ran OK on gas but when I tried glow one of the bottom cylinders would flood out almost immediately. Stay with gas on that one. My issue with the 7-50 is the size and weight of the ignition unit and all those wires on such a small engine makes it impractical, let alone the carb issue, -Tom
Old 03-18-2024, 04:45 PM
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Speaking with Adrian at CH ignitions last week he said I could run an exhaust pressure line to the fuel tank for the 7-50. Has anyone done this as it doesn't state this in the manual?

Most of my glow engines are set up this way but I didn't know you could do this with a gas engine.
Old 03-18-2024, 04:57 PM
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You can try this but I bet the needle adjustments will become rather sensitive.
Old 03-21-2024, 02:42 PM
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Default First Run 7-50cc Success!!

Got the 7-50 set up on the stand today and was able to run about 14oz through it.

Turnigy 18-10
Echo Power Blend Gold Semi Synthetic 25:1
Turnigy 7.4 3600mAh 2S lipo
HS needle 1-3/4 open
LS factory
No muffler pressure

1st run- took a prime well with the choke on and 3-4 rotations. Ignition on , 1/3 throttle and and she fired right up with the starter. First run was at 1/2 to 3/4 throttle for 3 mins and then a cool down.
2nd - Didn't go as well. Started but just barely and wouldn't throttle up, ran rough for approx. 1 min, needle the same as the 1st run then I shut it down. Weird , it ran well 10 mins before. Decided to reset the needle to the factory setting 1 turn open , I shouldn't have touched this but the manual stated 1-3/4 to 2 turns open and I didn't want a lean run.
3rd- Fired up with the starter and cleared itself out. At this setting it ran well idled as low 1200 for 10+ sec and topped out at 6300. Mostly ran between 4000 to 5000 rpm. 3 mins.
4th- Same setting. The #5 cyl dropped out , top rpm 5700 2mins
5th- HS needle leaned 2 clicks. Rpms back up to 6300 at the top transitioning good for the low run time. 3 min run.
6th- Same setting. 6300 top 1200 to 1500 idle . Thrust 10lb at 6300rpm 3mins.

Conclusion: My expectations were very low going into this and I was pleasantly surprised at how well it ran once I put the HS back to factory!
Tomorrow I will clean the plugs and get some more runs in. I'll also try and get some video of it too.

Chris
Old 03-22-2024, 05:22 AM
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Originally Posted by dodgers72
Got the 7-50 set up on the stand today and was able to run about 14oz through it.

Turnigy 18-10
Echo Power Blend Gold Semi Synthetic 25:1
Turnigy 7.4 3600mAh 2S lipo
HS needle 1-3/4 open
LS factory
No muffler pressure

1st run- took a prime well with the choke on and 3-4 rotations. Ignition on , 1/3 throttle and and she fired right up with the starter. First run was at 1/2 to 3/4 throttle for 3 mins and then a cool down.
2nd - Didn't go as well. Started but just barely and wouldn't throttle up, ran rough for approx. 1 min, needle the same as the 1st run then I shut it down. Weird , it ran well 10 mins before. Decided to reset the needle to the factory setting 1 turn open , I shouldn't have touched this but the manual stated 1-3/4 to 2 turns open and I didn't want a lean run.
3rd- Fired up with the starter and cleared itself out. At this setting it ran well idled as low 1200 for 10+ sec and topped out at 6300. Mostly ran between 4000 to 5000 rpm. 3 mins.
4th- Same setting. The #5 cyl dropped out , top rpm 5700 2mins
5th- HS needle leaned 2 clicks. Rpms back up to 6300 at the top transitioning good for the low run time. 3 min run.
6th- Same setting. 6300 top 1200 to 1500 idle . Thrust 10lb at 6300rpm 3mins.

Conclusion: My expectations were very low going into this and I was pleasantly surprised at how well it ran once I put the HS back to factory!
Tomorrow I will clean the plugs and get some more runs in. I'll also try and get some video of it too.

Chris
Good to hear Chris.
I've been reluctant to run mine from all the previous posts. That gives me more confidence to try mine.
Incidently, the carb Tom adapted to the 5-55 I believe is the Saito SAI90R3821 for the FA-90 or FA120. He had an extra carb and adapter that he sold me to install on my 5-55.
I have not run that engine either, but the time will come. Tom was concerned about the o-rings holding up to gas. I suppose an auto parts store would have o-rings and they surely
would handle gas.
Old 03-22-2024, 12:55 PM
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Got 3 more runs in today and the only way I could be happier is if it had the roar of it's bigger siblings. The 18-10 is not enough prop so I switched to a MA Classic 20x10. It can idle down to 1200rpm and it topped out at 5700rpm. Thrust maxed out at 11.37lbs which UMS claims 11lbs with a 20x8 Menz. I'm sure these numbers will increase once fully broken in. I got some video of it with the 18x10 Turnigy but I must not have hit record with the 20x10 MA. I'll try and get it uploaded this weekend. There is a lot black sludge coming out for now but hopefully after break-in and lowering the oil content this will be minimal.

Last edited by dodgers72; 03-22-2024 at 06:37 PM. Reason: spelling
Old 03-22-2024, 01:01 PM
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Originally Posted by GIJon
Good to hear Chris.
I've been reluctant to run mine from all the previous posts. That gives me more confidence to try mine.
Incidently, the carb Tom adapted to the 5-55 I believe is the Saito SAI90R3821 for the FA-90 or FA120. He had an extra carb and adapter that he sold me to install on my 5-55.
I have not run that engine either, but the time will come. Tom was concerned about the o-rings holding up to gas. I suppose an auto parts store would have o-rings and they surely
would handle gas.
I'm not sure what kind of problems the other guys were having with theirs but for now mine shows no signs of any problems after 20+ozs of fuel.



Regards,
Chris
Old 03-22-2024, 02:02 PM
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Glad to hear this Chris!! Maybe UMS improved the carb???? -Tom
Old 03-22-2024, 02:43 PM
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Originally Posted by Maxam
Glad to hear this Chris!! Maybe UMS improved the carb???? -Tom
Did the carb barrel on your 55 have 100% travel at full throttle? Mine only opens to about 80%.


Chris
Old 03-22-2024, 03:20 PM
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Default Prior to very first run UMS7-50

Before the very first run I oiled the valve train liberally inside & out. I also checked the valve lash with the included .05mm gauge included, there is no .1mm. During this check ,on two cylinders the exhaust valve was below specs (tight) so I adjusted those. It seemed like all of the others were pretty loose but I couldn't confirm that as all of my feeler gauges were at home and I run my engines at my (construction) shop . I also cleaned the spark plugs and they were coated heavily with black oil.

Fuel Tank Set Up:
12oz DuBro tank with gas stopper
Fuel line to the clunk=Sullivan ProFlex (Large) I had to solder a barb
Fuel line Tank-Carb= DuBro 1/8 Tygon

Also I have not needed to use exhaust pressure so far.

I pulled the #1 plug today (after 6 runs) figuring using 25:1 they would be loaded with oil & the same sludge coming out of the exhaust BUT it was much cleaner then after the factory did their initial run of 20 min , according to the test sheet.

I also checked the #1 cylinder valve lash with the .1mm gauge and it slid right in. It's running so good that I decided to leave them alone for now.

Last edited by dodgers72; 03-22-2024 at 06:38 PM. Reason: spelling
Old 03-22-2024, 04:03 PM
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Yes the carb could open all the way. Valves better too loose than too tight!
Old 03-23-2024, 12:36 PM
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Default Ums 5-100

After reading all the comments and especially Maxam i received my UMS 100 today. Absolutely beautiful and an easy transaction thru CH Ignition. I've been in the hobby and fullscale for 30+ years but this is my first radial, so I'm being cautious and have questions.1 Instructions say to always use a starter. Ok to start by hand?2 Instructions say to always shut down by cutting off the fuel supply. Is it also ok to shut off by killing the ignition?3 The crankshaft thread has an E clip 3mm from the end. Is it ok to leave off to use a solid hub type spinner?​4 Instructions says to use WD 4/ liquid moly additive, high quality gear oil. Is this something you mix, WD 40 seems like a thin viscosity for this application? 5 Best 2 stroke oil to use in the fuel mix?6 The valve lash is a little loose at all positons out of the box. Is this checked cold or warm?I plan to put it in a Black Horse Gilmore.
Old 03-23-2024, 04:38 PM
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OK Robert, here we go;
1. Easy to start by hand but do wear a glove.
2. shut down by either ignition shut off or complete closure of the carb
3. I have never used the E-clip, six bolts!! Prop will not come off.
4. I use 3 in 1 oil
5. Amsoil Dominator 2 stroke oil
6. 2 oz to the gallon Sea Foam additive to keep the plugs, pistons cleaner and prevent stuck valves.
-Tom
I use a 25x12 Xoar prop

Last edited by Maxam; 03-23-2024 at 04:39 PM. Reason: additional info
Old 03-23-2024, 04:56 PM
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Originally Posted by Maxam
OK Robert, here we go;
1. Easy to start by hand but do wear a glove.
2. shut down by either ignition shut off or complete closure of the carb
3. I have never used the E-clip, six bolts!! Prop will not come off.
4. I use 3 in 1 oil
5. Amsoil Dominator 2 stroke oil
6. 2 oz to the gallon Sea Foam additive to keep the plugs, pistons cleaner and prevent stuck valves.
-Tom
I use a 25x12 Xoar prop
All clear except my engine does not have a provision for six bolts, just a 10mm nut. I guess just locktite the prop spinner hub would be the best i could do?
Valve clearances set warm or cold?
And which Seafoam product, SF16, SF22, ?
Thanks a bunch.
Old 03-23-2024, 05:11 PM
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Brain fart. right just one bolt but I have never had a prop come off, Tighten with a real high quality wrench. Do not loc-tite. Tighten every so often especially when new. Set valves cold. better slightly loose than tight. Too tight you will burn the valves. SF16..
Old 03-23-2024, 06:08 PM
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Originally Posted by Maxam
Brain fart. right just one bolt but I have never had a prop come off, Tighten with a real high quality wrench. Do not loc-tite. Tighten every so often especially when new. Set valves cold. better slightly loose than tight. Too tight you will burn the valves. SF16..
All sounds good. I'll keep everyone informed how it does.
Old 04-09-2024, 02:54 PM
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My UMS 5-100 has a gallon of fuel thru it and runs beautifully. Now I'm ready to increase from the breakin maximum rpm 4000 to 5500. At 4000 the cylinder temp is 225F. I know increasing the rpm will put me 250F or more, maybe 300F. What is the maximum temperature?
i use a telemetry sensor looped around the #1 cylinder and i use an infrared gun which agree.
Old 04-09-2024, 03:26 PM
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Robert, Not good. I would not allow my 5-100 to run on the ground above 4500. RPM increases greatly in a dive. I use a 25x12 prop (Xoar) or a 26x12 Fiala. both have similar RPMs around 4000. 225F is close to the upper limit of permissible temps. I have spent several days making an efficient baffle to keep the engine temps down in the cowl.
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Old 04-09-2024, 03:34 PM
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Originally Posted by Maxam
Robert, Not good. I would not allow my 5-100 to run on the ground above 4500. RPM increases greatly in a dive. I use a 25x12 prop (Xoar) or a 26x12 Fiala. both have similar RPMs around 4000. 225F is close to the upper limit of permissible temps. I have spent several days making an efficient baffle to keep the engine temps down in the cowl.
Interesting about the rpm. Factory test took it to 5500 as is the max listed in the instructions. Not an issue for me as I'm a fullscale pilot and always pull some power if the nose is down. I'm working on a sample cowl and baffles. I like to work out all the issues before mounting in the airframe.
Thank again for your expertise.

Last edited by Robert Dochterman; 04-09-2024 at 03:42 PM.
Old 04-09-2024, 03:39 PM
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Over propping will also raise the Temps. To get lower temps drop down in Diameter
Old 04-09-2024, 04:37 PM
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I stated 225 is close to the upper limit of temps. Unfortunately some of the UMS engines run on the hot side. My Moki's run in the 180-190 F range. Moki states 220 is the upper limit of their engines running temps. There was no mention of rpm vs temps. My concern is longevity of the engine. Most larger radials, (Moki's for instance) run efficiently at lower RPM . Saito's however thrive at very high RPM's 6500 to 7500 rpm due to valve timing and short stroke to a degree. The greatest advantage of a radial is the scale sound! Running them fast makes that sound go out the window. All of my radial engined planes rarely see full throttle even at takeoff. Just stuff to ponder.....Tom
Old 04-09-2024, 04:39 PM
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Robert, you are wise to ask these questions. The rewards of proper running radials in models is great.
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