Hirth F33

Greetings,
I am researching UL's, planning to purchase one, have considered three or four so far. My problem is, the BYf (probably my favorite so far), has a waiting period of a year or more, plus the cost is more than i like. It has the 4 stroke which i would really prefer. Second is the Belite, however if you choose the 4 stroke, it jumps the price up to around 32k, up from around 17 with a 2 stroke.. A Challenger is another choice, however there we go with the 2 stroke. My question, does anyone have first hand experience with a F33? I read that TBO is around a 1000 hours, compared to 300 on a Rotax 447, plus i've read that all 2 strokes are prone to stop running, especially during idle. So far the F33 would be my 1st choice in a 2 stroke, should i go that way (2 stroke), just would like any and all information on these engines, the good and bad of them.

Thanks in advance,
Jim

Jim, if you go in with the expectation that the Hirth engine will last 1000h, you sure to be disappointed. Unless they offer some kind of unlimited warranty for that time, it's just a number.

Sad that installing a 1/2 VW engine increases the price on an ultralight by $15k.

Hey Jim. Are you talking about a true ultralight or lightsport? If you meant ultralight, Challenger's are far too fast and heavy. There are very few 254 pound or less true ultralights. The lightest Challenger will weigh well past 300 pounds. Don't count out 2 strokes. I had a Rotax 503 powered CGS Hawk for 15 years. It never let me down. It was overhauled by an authorized Rotax facility with over 600 hours at 15 years old. The mechanic said it looked like a 150 hour engine inside. The crankshaft was in perfect shape so it was reused. He only did a top end and replaced the seals. At 600 hours it still had good compression and ran as good as new. The new owner wanted to have it rebuilt for his peace of mind, not because of any problems. In my opinion, a Rotax 447, 503 or 582 blue head is as reliable as anything out there if it's maintained properly. They don't just stop running any more any other engine stops running. I'd personally stay with Rotax. They're well proven to be very reliable. I haven't had any personal experience with Hirth but what I've heard and read was not good, long term. Don't let the advertised TBO fool you. Something to think about, if you're going lightsport, think about going with one of the old classics. Taylorcraft's can be bought all day long in the $15,000 to $20,000 range. Those old Continental's are super-reliable and you can train in your own airplane which will save you a bunch. You could get your sport pilot ticket and still spend a lot less than buying a new 2 stroke powered ultralight. Good luck, James Thomas

challenger can make part 103...they always have been able to. sure, buy an old taylorscrap and and have a mechanic digging in your pocket on a regular basis. try to find a crank or bearings for an antique 65hp... good luck with that.

To say a two stroke runs or won't run any better then any other engine is wrong. IMHO. I have owned a handful of two strokes. All being new. Not like new but new. All of them had engine issue's within the first 10 hrs. I have owned one 4 stroke. Put over 200 hrs on it now and it has never let me down.

Before you say I maintained the two strokes wrong. let me tell you I do nothing different from what my buddy does with his two strokes. I do the same exact things. But I have had issues. he has not. So now you want to blame the operator.

I have a 447. It has a weak stator. When hot it would loose spark. I replace the stator with a brand new one from Rotax. Install it. Do my run ups, taxi her around. Go to take off and guess what. The new stator went bad. Just as the tires leave the ground she shuts down.

I call Rotax. I am told one in a thousand will do this. I parked the airplane and never flew behind a two stroke again.

My buddy I hangar with uses or flies in front of a two stroke. never has a problem. What works for one may not work for the next. Remember 1 in a 1000. You could be that 1000. I was. But myself after 8 engines out in under 100 hrs I had enough. Went to a 4 stroke and the engine out days are behind me. At least so far anyway.

Tony

As to TBO. Hummel engines say 1000 hrs on the VW. But we all know at 500 hrs the heads come off. They get some attention. But before you need to rebuild the complete engine is around 1000 hr depending on how you use it. Keep the MP under 24 on the MP gauge and from what Scott Casler told me I will have no problem seeing 1000 hrs on this engine. I hope so, I put 150hrs on her last summer. Run it over 25 on the MP gauge and it will not make it this long. Scott told me the engines he see's that come back to him for over haul before 1000 hrs are ran above 25 on the MP gauge.

But my point the two stroke is the same. No matter what they say for a TBO we all know they must be decarboned around 150 - 200 hrs. But if you watch how you use it, it can last longer then 300 hrs or 500.

A couple issues with two strokes though. I loved the comment...The crank looked good. Really. How does one know a good looking crank on a two stroke. If you understand how one is built you will understand looking at it tells you nothing. These cranks are put together by force. That is it. They are two cranks joined together by a huge press. They are press fit. In service this press fit can work loose. or if you have the slightest hit on a moving prop you can get one cylinder out of time just a little. No way to fix it either, not without this huge and I mean huge press. Then you need to make sure both are in time. This is work left to the factory.

There is also a seal between the two rods that seal each cylinder from the other on this crank. Really a two stroke is two engines in one. This seal can only be replaced by taking the two crank halves apart then pressing them back together. Something not easily done. If this seal leaks you will seize one cylinder from a over lean condition. It needs replaced when the engine is taken apart. Only way to replace. Replace the crank with new. How many do this? Then they fool themselves in saying, I have a rebuilt engine. Well no you do not. You have an engine with some fresh parts but nothing about it is rebuilt 100% what we call zero time. It can not be zero timed unless every seal and every part is replaced. You just have an engine that has been worked on. That is it. Not a rebuild. If that center or crank seal was not replaced, you did not get a rebuilt engine. Yes one seal makes all the difference.

So I laugh when someone tells me they rebuilt their two stroke but did nothing to the crank. You rebuilt nothing. You added some new parts to your engine. Leave one part old or do not replace it and its not a rebuild. Never will be. I myself would not fly behind and engine with such a rebuild. When that seal fails and it will make sure you are above a landing spot.

Aeroschmitz, I'll try to remember your advice-while I'm flying my Taylorcraft- which will still be flying faster, farther and, less expensively than a two cycle snowmobile engined lawnchair ever will.