HEILEMANN STERNMOTOREN
Feinmechanik in Perfektion - handmade in Germany
  • 180ccm SM
  • 350ccm SM
  • 700ccm SM
  • 1. Generation | 9-Zylinder 180 ccm
  • 2. Generation | 9-Zylinder 350 ccm
  • 3. Generation | 18-Zylinder Doppelstern 700 ccm
 

Seidel-UMS ST 7-250B - Remodeling

The history

At our second radial engine meeting Klaus Uhl (radial engine fanatic) showed me his latest achievement, a Seidel-UMS ST 7-250B, bought at Seidel Triebwerke in Malsch near Karlsruhe. An engine of the second series with countersunk cylinder heads.

bild2037

 

After a few months, Klaus called and told me, he had gotten a call from Wolfgang Seidel telling him the valves in this series of UMS ST 7-250B broke easily, the needle bearings were defective, and that the push rods were made of too soft aluminum and would therefore need to be replaced. He could not take care of the repair work even though the warranty time wasn’t over yet. He could guarantee the supply of parts though.

Klaus asked me to do the repair as well as further modification. I gladly agreed. He is after all a faithful participant and helper at our radial engine meetings.

bild1925

 

First I reconstructed the engine support plate. The holes for the screw connection to the engine frame remained untouched. I decided to make a two-parted plate so the ignition has a secure fit.

bild1926

 

bild1927

 

The ignition was originally fastened with only three screws. After checking closer I also found out that the original plate was crooked and bent.

bild1928

 

bild1929

Plate is measured ...

bild1930

... and drawn

bild1931

Newly made engine support plate ...

bild1932

The ignition sits in the ring groove.

bild1933

Ring groove for ignition

bild1934

Bayonet catch

bild1935

 

Now the ignition system is mounted as a test and the bayonet catch is put to the endurance test. It worked straightaway and fit exactly into the countersunk part.

bild1936

 

bild1937

 

The rusted cam case screws bothered me right from the beginning. Unfortunately the rusty parts had already eaten deep into the aluminum and had to be downright polished out.

bild1938

 

 

bild1939

 

On further inspection I noticed that the tubes to the carburetor, that give the impulse to the membrane, was slightly ripped. So the engine could only run difficultly, if at all.

bild1940

 

bild1941

 

Before taking apart the engine I had measured the ignition, how the sensor is oriented to the dead ignition stroke. For that I had asked Company Becker to make me an electronic little helper.

bild1942

 

So the ignition was adjusted to 15° prior OT. Usually it should be 0° at OT so the engine doesn’t kick back while starting. The ignition then adjusts every 1000 rpm to about 3,9° advanced ignition (i.e. at 5.000 rpm = about 19,5°).

bild1943

 

Dismantling rear plate with carburetor and mounting engine carrier

bild1944

 

bild1945

 

At the front the cam case is unscrewed.

bild1946

 

bild1947

 

While looking into the crankpins I had to find that metal shavings from production were still there. I carefully removed them.

bild1948

 

bild1949

 

Pressed out crankshaft with cam disc, and ignition magnets. It is astounding how little grease was in the case. Even though the engine was new and had only run at the factory. Luckily the grease had not made it to the weight-reducing holes on the lid.

bild1950

 

bild1951

 

Good to see here: The aluminum disc that takes up the magnets. 21+3 negatively polarized to recognize the first cylinder. As the cam has three cam pairs and is underpinned 1:6.

bild1952

 

bild1953

 

The cam disc seems to be in good shape. All teeth are luckily there :-)

bild1954

 

bild1955

 

The crankshaft gearing also looks good. The crank arm is screwed to the crankshaft. The only thing surprising is that the Indian doesn’t use the whole thread depth.

bild1956

 

bild1957

 

All connecting rod bolts are pulled and the individual cylinders are dismantled. Sadly only one piston ring is built in. For a good and lasting compression two seal rings are actually needed.

bild1958

 

bild1959

 

At the factory the connecting rod bolt was pressed in at an angle. I had to adjust it.

bild1960

 

bild1961

 

All parts are taken apart and neatly stored away. It is very important to make sure all parts remain paired up.

bild1962

 

bild1963

 

The valves are now disassembled from the cylinder head.

bild1964

 

bild1965

 

It is not so easy to disassemble the little wedges without losing one. If you don’t pay attention for a second, the wedges fly all around the workshop.

bild1966

 

bild1969

 

All parts are cleaned and now ready for assembly.

bild1967

 

bild1968

 

Now it is time to check the cylinder heads’ tightness. As the old parts (valves) go into the trash, we make a breakage test.

bild1970

 

bild1971

 

A shocking result. The old valves break like glass even though I had only tapped them lightly with a hammer.

bild1972

 

bild1973

 

I exchanged the Indian needle bearings of the main connecting rod for German INA needle bearings with wide needles. For this building size that is essential for the tilting moment on the crank pin.

bild1974

 

bild1975

 

The new needle bearing is now pressed in. The result looks very good. Next we check if the bearing clearance of the new bearing has changed on the crankshaft’s crank pin.

bild1976

 

bild1977

 

Everything fits. The tolerances are unchanged. I also swapped the little needle bearing in the connecting rod head. According to Wolfgang Seidel the needle cages break open here and the needles fly around the engine total --> wreckage :-(

bild1978

 

bild1979

 

What I personally dislike completely are milled lanes on the main connecting rod. It is a highly strained building component, that mustn’t have any notch effect from machining. So, we had to rework and polish completely.

bild1980

 

bild1981

 

I didn’t bother as much with the other connecting rods and pushed the needle bearings out. I threw them all away and exchanged them with new connecting rods.

bild1982

 

The transition from connecting rod to connecting rod eye was completely gnawed away (as if finished mechanically with a file) and the aluminum itself was soft as butter. That does not mean that it’s not working; however it doesn’t meet my technical understanding to remount these again.

bild1983

 

This is what a new and freshly polished connecting rod looks like. I also glued and pressed German INA needle bearings into this one.

bild1984

 

bild1985

 

The thread for the cylinder barrel screws in the engine case wasn’t cut deep enough. So I made the drillings deeper and recut the thread. The cylinder was sealed anew to the engine case with surface sealing agent.

bild1986

 

The rule of thumb is: The depth of the screw drilling hole should always be twice the diameter of the screw (for M4 = at least 8 mm deep). Also, the right cylinder sealing is very important. The tighter the engine is, the easier it starts up and keeps a low and safe stationary throttle.

bild1987

 

I only use screws with a strength of 8.8 and galvanized surface. The assembly quickly proceeds.

bild1988

 

bild1989

 

The pistons with the connecting rods are now pushed into the cylinder and the individual cylinders are screwed together one after the other.

bild1990

 

bild1991

 

The connecting rods now have to be hung and secured into the main connecting rod with a connecting rod bolt.

bild1992

 

bild1993

 

I threw out the original rear plate’s o-ring and exchanged it with surface sealing agent. O-rings settle after a while and become brittle = no sealing. Engine pulls false air.

bild1994

 

bild1995

 

New tubes for the carburetor impulse are pulled in with a new Y-piece as distributor. The tubes are gas resistant and don’t harden, in comparison to the originals.

bild1996

 

bild1997

 

Mounting the engine carrier

bild1998

 

bild1999

 

The Becker ignition is fixated neatly into the engine carrier with an adapter plate.

bild2000

 

bild2001

 

The ring muffler wasn’t mounted ex works but only enclosed. For good reason: It doesn’t fit at all! Over the years I have assembled quite a few RSD and experienced a lot, but I have never seen anything bent so carelessly.

bild2002

 

bild2003

 

As the ring muffler has to be mounted more or less stressless and in the middle of the engine carrier plate, I rebend all the aluminum manifolds in meticulous rework. I also adjusted the welding sockets with heat treatment.

bild2004

 

After endless swearing and hours later the muffler is finally where it should be and looking very good.

bild2005

 

And now to the cam case. It was unscrewed to remove the name and logo of the Seidel Company as well as hammer blows and scratches (new engine?)

bild2006

 

bild2007

 

On request of Klaus Uhl his name, the Bavarian seal and the engine details were engraved by our engraver in meticulous handwork and polished by me.

bild2008

 

bild2009

 

The Indian bearings were quickly exchanged for European bearings.

bild2011

 

bild2010

 

The same also for the main bearing disc that takes on the crankshaft.

bild2012

 

bild2013

 

And the same for the cam disc. I also glued in the bearing as it is not fastened at all (with a band or safety ring).

bild2014

 

bild2015

 

The cam is built into the cam case with enough fat filled in to last for a year.

bild2016

 

bild2017

 

I also greased the crank shaft gearing with fat and, after adjusting the steering times, pressed it into the cam case with a degree wheel (360°) and ignition box (for checking purposes).

bild2018

 

bild2019

 

Checking with the degree wheel and pressing in the crankshaft.

bild2020

 

bild2021

 

So the engraving on the cam case can be seen even better, I filled it in with black and repolished it.

bild2022

 

bild2023

 

The cam case is now screwed together with the engine case and the engine is almost finished.

bild2024

 

bild2025

 

In the original push rods an obvious compression can be seen. That is why I pressed out the inserted parts ...

bild2026

 

bild2027

 

... and inserted them into the new pipes. After that greased well and assembled.

bild2028

 

bild2029

 

Now the valves are adjusted, i.e. figuring out the slight out-of-round of the cam, in this case 0,15mm and adjusting the valves to 0,1mm.

bild2030

 

bild2031

 

I checked the glow plugs for a clearance of 0,4mm and rebent some of them.

bild2032

 

bild2033

 

Laying the ignition cable neatly and assembling it for the test bench.

bild2034

 

IT IS DONE

bild2035

 

The engine starts up very well, runs smooth and has a low and stable stationary throttle.

bild2036

 

bild2037

 

Now Klaus Uhl can receive his engine again after four months of remodeling.

We are already looking forward to seeing the engine fly in his GeeBee, hopefully at the next radial engine meeting.

As always special thanks go to the helping hands in the background: Peter Haag, Florian Karpf, Carmen Kugler and my wife Elke.
Without you it would not be possible to realize such projects.

unterschrift



This website uses cookies. If you continue to use the website, we assume your consent.