ESE's works engine tuner

[husaberg]

The 258 drawing is only 23 kB and very difficult to read?

See how this goes.

I don't have access to any decent picture programes at the moment.
I can't find the source for the origional on the net but it appears to be from a official Rotax parts list.

[seattle smitty]

Mr. Thiel, over the course of your career, did you ever have any contact with the outboard hydroplane racing community in Europe, or ever have any personal interest in that sport? Not to dismiss motorcycles, karts, sleds, ATVs, etc, but outboard racing (the classes in Europe include 125cc (singles-only), 175cc, 250cc, and 500cc)(in the USA we have those plus 700cc and 1100cc) has some attributes which might appeal to an engine man:

First, since you have a whole lake or river full of (relatively cold) water available, designing provisions for cooling is considerably simplified.

Second, the engine burns methanol, which has several advantages over gasoline which I don't need to describe for you (and in the USA we're free to go beyond methanol to any liquid fuel, though few do so). One real advantage of this at the races is that we don't have our fuel inspected and approved by anyone!

Third, there are no problems of cornering traction as with motorcycles that require an engine designer to compromise his designs; with a propeller hooked up to the lake, a driver can use all the power the engine designer can provide.

Fourth, the racing outboard engine designer is barely constrained by such factors, found in motorcycling, as cornering clearance, fitting the engine into the frame, joining the engine to the transmission, etc.. in recent outboard racing practice with multi-cylinder engines, opposed-twins (and fours) using a common crankcase have been popular, being lightweight, relatively simple, with good balance and reduced rocking moment.

Fifth, as for pipes, an advantage in fabrication time when testing expansion chambers is that they are easy to build, being straight-line downstream of what our Kiwi buddies call "the spigot."

Finally, with those straight-line pipes hung out back of the engine and supported by brackets, we are able to add an extra element of "tunability" by making the pipes slide in and out over a range of about 10cm. For temporariy lowering the powerband even further, as when getting the boat on-plane, with our lake-full of water we can also spray a little water into the pipe, slowing the acoustic waves. These two features help us live without the necessity of a transmission.

I would think, given your toils over the decades, you would regard our situation as almost laughably easy by comparison! Anyway, most eager to hear your comments.

(EDIT) Three fellows you might have encountered, previously involved in GP motorcycling in the 2-stroke years and more recently building outboards, are Giuseppe Rossi, Carlo Verona, and Holger Arens, and also the late Dieter Konig.

[jamathi]

No, I never had anything to do with outboard engines.

[trevor amos]

Hello Jan, let me first say how much all viewers of this site are enjoying your anecdotes from the many years your racing past.
I notice from details released by Frits that the Aprilia piston crown had a radius of 190mm, giving a crown height of 1.9mm. Most other 125 race engines use a piston crown height with a smaller radius and therefore a taller crown height. Are there specific reasons for using this lower crown height, if so could you perhaps explain the reasoning behind this strategy?
Regards, Trevor

[jamathi]

No specific reason at al, it just went well as it was designed many years ago.
Probably at ROTAX by someone who had no idea why he did it!

[husaberg]

No specific reason at al, it just went well!

Jan, Frits has mentioned the results you obtained from a Reed valve derbi before you started on the Derbi engine with the rear disk that became the RSA.
Do you recall What changes you made.

A technical explanation? Nah, too much to do today. But since you were kind enough to post that picture of your sex six sisters, I will show some curves of my own.
When Jan Thiel went to Derbi to design the bike we now know as the Aprilia RSA125, he encountered the 125 cc reed valve Derbi ridden by Lorenzo the previous season. Jan played around with the reed valver as well, because he wanted to find out the differences between reed valve and disk valve power. He managed to extract 2 HP more from the reed valver than anyone else had ever done before (never mind the fairy tales of reed valve 125s producing over 50 HP; those Horses must have been Shetland ponies, probably measured at the piston ring).
My graph shows the power curve for the Aprilia RSA, the Aprilia RSW and that best-ever reed valve Derbi. It's not quite in the same league as the rotaries, hmm?

EDIT: Shame on me; I discovered that I posted a wrong graph (and I do not have the correct one at hand here in Holland). Power curve DERBILOR shows the reed valve Derbi as Lorenzo rode it. After Jan finished playing with it, it had 49 HP. Still, the best-ever disk valver produced 10 % more power than the best-ever reed valver.

Attachment 321334

I looked it up Chris: you joined the KiwiBiker forum three months before I did, so you may already have seen everything I could contribute, including these powercurves from the Aprilia RSW, the RSA and the reed-valve Derbi ridden by Jorge Lorenzo in 2004, I think it was.
Honda had already abandoned development of their 125 cc racers but Derbi-tuner Harald Bartol had carried on with his Honda-clones (the Derbi cylinders and pipes were exact Honda-copies). Bartols best result was 47,6 hp.
When Jan Thiel joined Derbi, he played a little with Bartol's inheritance and he managed to extract 49 hp out of the reed-valver before concentrating again on his own disc-valve engine.

[jamathi]

Mainly working on the crankcase.
Improved water cooling passages, which were far too small
And some work on the inlet with good effect.
We made some cylinders with a different exhaust duct, with auxiliary's.
They were cast, machined, and plated.
Then Derbi was closed and I had to go back to Aprilia without trying them....
Still sorry!
The central bridges in the exhaust keeped cracking.
And I really came to hate reed valves!!!!
Being used to rotary valves that never gave any trouble......

[husaberg]

Mainly working on the crankcase.
Improved water cooling passages, which were far too small
And some work on the inlet with good effect.
We made some cylinders with a different exhaust duct, with auxiliary's.
They were cast, machined, and plated.
Then Derbi was closed and I had to go back to Aprilia without trying them....
Still sorry!
The central bridges in the exhaust keeped cracking.
And I really came to hate reed valves!!!!
Being used to rotary valves that never gave any trouble......

Thanks Jan
Speaking of rotary valves did the CF ones at Aprilia give any trouble or have any measurable gains. From the material rather than the shape.
I have seen the pimple finish casings which i asume is for retaining oil fuel for lubrication and decreaded friction surface.

Were they coated with anything slipery?

[jamathi]

We never had any trouble with the rotary valve!
With the reed valve we had trouble every day....

[shnaggs]

We never had any trouble with the rotary valve!
With the reed valve we had trouble every day....

When you say you had trouble with the reed valve, do you mean you had trouble with it repeating on the dyno? Or trouble trying to get power out of it?

[RomeuPT]

Hello.

Long time since I posted on this thread. Being watching this weekly has it one of the best 2 stroke threads ever, keep going guys

There was an engine, that had several people making stuff for it here in Portugal, and the small end top part of the rod blown up in the first miles of running in (claimed by the owner). He also says that there wasnt any strange noise on the engine before the "tic-tack and blow". Squish clearance 1.2mm, with combustion chamber designed by me. Around 12:1 compression

I would say that is con rod fault 99% sure, but now each one blames each other works has the fault :/.

The rod is a wossner and the engine is a DT125 with athena big bore, 54mm stroke cranck etc

Cylinder/piston/cases, reeds etc goes to trash.

pics attached, what do you experts think

Cheers

[Norman]

Also to me that shiny circled area looks suspicious, and I believe there could be a bonding fault or a large pore in the casting/forging from the manufacturing. This must be detrimental in that area. Possibly it could even have been positioned just under the surface, not possible to detect without x-ray or ultrasound detection. There is a good chance that any metallurgist/lab with a microscope can check the cracked surfaces and conclude the root cause.

[tjbw]

I was thinking the circled area might contain a fatigue crack surface, in which case the matching part would have an identical pattern.

[Norman]

I was thinking the circled area might contain a fatigue crack surface, in which case the matching part would have an identical pattern.

Yes, hmm..you are right, could be that too. When the crack has propagated from a point (possibly a surface defect causing crack initiation) and by each cycle you get an additional half circle pattern (striation) that shape a large crack, and eventually it is large enough to cause a sudden failure/rupture. The crack propagated surface and the later ruptured surface will have different appearance, which you would look for in a microscope. Could be that you in worst case need a scanning electron microscope to sort things out.

[Grumph]

I'd do a simple hardness test on the surviving rod pieces. My suspicions lean toward faulty heat treatment leaving the small end brittle.

Any pic of the small end bearing - or what's left of it ?