I have been looking at the Hirth F-33 for my 1100 build. I have seen it pictured with the re-drive in two different configurations. The prop center line is either below the bottom of the engine or up near the center of the cylinder. I was wondering if it can be mounted either way or if it has to be ordered one way or the other. I can't find any info on it anywhere. I was hoping to find some dimensions somewhere so I can get the mounting height correct in the fuse as I won't buy the motor until the end. I am hoping to mount the motor with the head facing up instead of inverted. anyone have any info or insight on this? Thanks, Doug
I've run engines with the cylinder(s) down & up I prefer up. When inverted, it's sometimes possible to flood the spark plugs with fuel, making for hard starting. This is less likely with dual ignition as the plugs are not right at the bottom. But cooling might be better with the cylinder in free air & propwash, when the engine is 'upright'.
After looking at this some more I wonder if the re-drive has to be mounted down so it is not blocking the cylinder. The re-drive up would be fine for a pusher configuration but not sure on a Max.
If you mount the engine with the cylinder "up" the re-drive should probably be under the crankshaft to properly locate the thrust line. I had a similar question after I bought a 277 and wasn't paying attention. It had a "up" box and the conversion to the "down" gearbox required a part that seems nearly impossible to find. If I recall correctly, I talked with David at TEAM who suggested that the thrust line "up high" would present problems with climb because of the higher thrust line. That was several years ago so maybe time has affected my memory.
It had a "up" box and the conversion to the "down" gearbox required a part that seems nearly impossible to find.
What part was that? I suppose a 277 would use the early B gearbox, and that can be mounted up or down - you just reverse the breather / oil drain bolts. There are two oil level marks - up and down.
I too found the mounting of the F33 one of the reasons why I am reluctant to go with that engine. I had assumed it requires to be mounted inverted on the MiniMax. The other reason is I heard it vibrates a little too much.
On the plus side, it is a more modern engine, and is very light.
What part was that? I suppose a 277 would use the early B gearbox, and that can be mounted up or down - you just reverse the breather / oil drain bolts. There are two oil level marks - up and down.
The hard part to find was a short crankshaft gear. The "up" box requires a spacer plate to clear the cylinder and that dictates a long crank gear. The box cannot merely be flipped 180 degrees since the top and bottom gearbox holes are not spaced the same. I had the mis-conception that it was a simple unbolt, flip and re-install operation until I went to flip my engine from being an "up" box to a "down" box. You're right on the breather/drain holes and the oil level holes. It's the bolt spacing that creates the need for the spacer with mounting studs (or deleting it) and the appropriate length crank gear to align the bolts for mounting the gearbox.
I couldn't stand it so I did a search on Google to find a photo of a 447 with the gearbox up and one with it down. As best as I can tell from the photos the 447 crankcase appears to have 8 gearbox mounting holes. One set of 4 allows for the bolt spacing to mount the gearbox up, and the other set of 4 are positioned so the gearbox can mount down. I have read reference to a "provision 8" engine, so maybe that's what it refers to.
Perhaps there are 277 cases with both bolt patterns but mine was certainly not one of them. Maybe one with just the one set of 4 is called a "provision 4" crankcase?
* More added below before posting. Some of the info is duplicated but I didn't want to re-type it all *
Here are links to info on A & B gearboxes and Provision 4 & 8 crankcases.
In the last link, 3rd from last paragraph it says "Type A and B gear boxes are not interchangeable. "A" fits provision 4 and "B" fits provision 8." So-o-o-o, it would seem that my 277 crankcase was a provision 4, and perhaps all of them were? It would also seem that I had a Type A gearbox too, but I sold the whole engine years ago.
So, I maintain that I still retain some level of sanity. The debate on that continues.....
Every bolt I touched with a tourqe wrench on my used f33 stripped out. The belt redrive I had to order was fine. I ran my gearbox in the up position. This may have been because of a early engine, I don't know. The cylinder head bolts stripped out when I tried to replace the cylinder heads. The threads that hold the nut for the small belt drive pulley stripped out too. This may have been just a issue with early hirths but it put a sour taste in my mouth.
Logged
The debate on that continues.....
