Hirth or MZ engine experience?

[Soleair]

I plan to start my MiniMax build early this year, but I'm still researching engines.

 

Front runners at the moment are the Hirth F23 and the MZ-201

 

Both are in the 45 - 50 hp range, both fairly low revving for 2-strokes, with the MZ particularly impressive at a quoted 45hp at 4700 rpm, both offer dual ignition, & both are a similar weight when fully fitted (around 30 kg).

 

So pretty even on paper, though I have to say I love the look of the Hirth's boxer format, & I'm guessing this would be a lower vibration arrangement.

 

Hirth quote 1000 hours TBO, which is impressive to say the least. It must be true because it says so on their website:yikes: I'm enquiring about the MZ TBO, but at 625cc and 4700 rpm max, it would have to be a low stressed lump.

 

So - has anybody flown with either of these engines? Or even better, both? (Bit unlikely that last, but hey, worth an ask!)

 

Happy landings for 2014

 

Bruce

 

 

[Bob Llewellyn]

No; but I'll make a few comments anyway!

 

Hirth - back in 1917, Hirth were working on contra-rotating rotarys (from memory), with astonishing power to weight ratios etc - real innovators in the aero engine field. By 1987, Hirth were a quiet little shed across the valley from a huge outfit called Bombadier (Rotax), and had not much of a reputation in ultralight use. In the '90s, Hirth retooled with a bunch of CNC machines, and redesigned everything. From the few I have scraped acquaintance with, the new millenium ENGINES seem very sound, provided you treat them like two strokes... but the PSRU (prop gearboxes) appear designed with no consideration of propellor gyroscopic loads. I was privy to the basic details of a Hirth gearbox, mounted on a motorglider, the prop of which decided to take up a solo career - after about 27 engine hours (or was it 37? less than 40, anyway...).

 

I'd be willing to consider flying behind a Hirth engine, but unless the gearbox design has mutated drastically in the last few years, I'd roll my own PSRU.

 

MZ used to have a good rep in the noisy small motorbike field - ~40 years ago. From your hotlink, it looks believeable, but that output shaft & redrive mount don't look fit for more than about a 50cm balsa prop to me....

 

Bear in mind that the gyroscopic design loads from a 54" Jabiru prop on a Corby Starlet contribute something like half a ton to the most critical engine mount loads...

 

 

[winsor68]

Good luck on your search Bruce...there is a serious need for an economical Rotax 2 stroke replacement... Hirth(pronounced "hurt" apparently in German) don't seem to have a good reputation in Oz...which is a shame in my opinion.

 

 

[Gnarly Gnu]

No direct experience but yeah, like others have heard of issues with the Hirth. Apparently the Japanese HKS is a tough little beast though, being a four stroke is sweet too.

 

 

[winsor68]

Nikasil heads and sound construction... They tick all the boxes on paper...I would be curious to know why they have the bad rep. They are certainly rare Down Under so the experience gained couldn't be from a large user base..

 

 

[Soleair]

Apparently Hirth had a cooling related problem a few years ago which did a lot of harm to their reputation. But they seem to have learnt from this, and our Merkan cousins now rate the F23 quite highly. I guess it's a case of "give a dog a bad name. . ."

 

However, Hirth are evidently not keen to do business over here. I have written to them twice asking for price & shipping information , and they have chosen not to reply. So if I do go this route, I will have to import from the States. Crazy - from Germany to USA to Oz!

 

MZ on the other hand are very helpful.

 

So there are alternatives to the ludicrously overpriced Rotax range.

 

 

[turboplanner]

As it is hard to get new product assistance, so it is usually harder to get parts and service assistance.

 

 

[Downunder]

Not sure how "experimental" you want to be but here's a new design... http://www.quicksilveraircraft.com.au/QUICKSILVER/AVIATOR_HFA.html

 

And I was just thinking that people use the half-VW engines, so why has no-one made a half Rotax 912? Got to have potential?

 

 

[Soleair]

Thanks for that Aviator engine link. In fact, I spoke to a guy from that company at the Narromine show.

 

I'm sure the engine has great potential, but I was disappointed to be told the price would be in the order of $10,000. So no advantage over Rotax there :(

 

And of course it is still very early in its development. Does look very well made. Maybe one for my next project - assuming the costs can be kept in hand.

 

 

[Bob Llewellyn]

Not sure how "experimental" you want to be but here's a new design... http://www.quicksilveraircraft.com.au/QUICKSILVER/AVIATOR_HFA.htmlAnd I was just thinking that people use the half-VW engines, so why has no-one made a half Rotax 912? Got to have potential?

A 912? but they're made out of gold and platinum, with rare jewells and exotic incense - or that's what the prices reflect.

Seriously, a horizontally opposed 4-stroke twin is a good way to shake the fillings out of your teeth, the cylinders out of the crackcase (it will be, trust me!), the nav lights off the wingtips... the halflingers work thanks to low powers, low stress levels, and short lives. Go and buy a 25hp Honda V-twin industrial engine; 42kg ready to rock your cement mixer, electric start, CDI, oil pump. Trash the "industrial' carby & fuel tank, and it'll make your Hummelbird zip!

 

 

[Downunder]

A 912? but they're made out of gold and platinum, with rare jewells and exotic incense - or that's what the prices reflect.Seriously, a horizontally opposed 4-stroke twin is a good way to shake the fillings out of your teeth, the cylinders out of the crackcase (it will be, trust me!), the nav lights off the wingtips... the halflingers work thanks to low powers, low stress levels, and short lives. Go and buy a 25hp Honda V-twin industrial engine; 42kg ready to rock your cement mixer, electric start, CDI, oil pump. Trash the "industrial' carby & fuel tank, and it'll make your Hummelbird zip!

Hmmm........ the Minisport SD 1 has used a commercial B&S engine (V-twin). These engines are popular in the US in "swamp" boats so there are companys producing stronger parts and even complete high performance engines.

 

 

[Nick Evison]

there is a bloke called Kev Armstrong here in the UK that has been upspecing a B&S twin with excellant results. ideal affordable candidate for a minimax i believe.

 

heres a copy paste from a uk microlight site post:

 

Briggs & Stratton V-Twin tuning parts and reduction drive now available in UK

 

For anyone wishing to build their own tuned briggs vanguard we can supply the tuning parts and reduction drive. Listed below are the prices for both a low power application and the full power as per Kevin's build:

 

28-30HP build requirements (all in stock)

 

HC head Gaskets - £30 pair

 

High flow filter, billet manifold & throttle linkage - £135

 

Rev kit incl ignition advance key - £85

 

Stainless Steel Exhaust Valves - £66 pair

 

Roller rockers - £345

 

Total: - £661

 

Reduction drive (1.8:1). - £600 (complete with all hardware and belt ready to fit in either orientation, prop high or prop low)… (stock expected next few days)

 

Total £1261

 

Some people have opted not to use the roller rockers for the low power build hence saving £345. They are however required for the high power build.

 

Additional requirements for 38-40HP build including the roller rockers:

 

High lift Camshaft (40hp) & followers - £185

 

10:1 piston and rod set - £420

 

High torque solenoid shift starter - £150

 

30mm twin choke Carburettor upgrade - £220

 

Total cost as per Kev Armstrong build: £2236

 

Other optional extras can also be supplied:

 

Re-usable Copper head gaskets W/sealing rings - £80 full set (available in different thicknesses 0.6mm – 1.0mm – 1.2mm)

 

Stainless steel inlet valves - £66 pair

 

Billet aluminium adjustable flywheel - £325 (no charging facilty)

 

Billet finned rocker covers - £160 set (special order)

 

Titanium big valve ported heads - £950 (special order)

 

All the above prices are applicable to retail sales and are inclusive of VAT, we keep many popular items in stock, any out of stock and special order parts have a minimum lead time of two weeks.

 

CAD drawings and DXF file for flywheel machining will be supplied free with kits as will any relevant advice, if required we should soon be able to offer a flywheel lightening service on an exchange basis but costs for this service have yet to be established. Exhaust manufacture has so far been on an experimental by application basis but we hope to standardise a design and offer a kit as soon as possible. We do however already have CAD files for general design and cad/ dxf files to simplify exhaust manifold plate manufacture.

 

For orders please contact Brian at Fallows Motors 07925 027138.