I just seen a video on youtube of a twin HP VT 49. I just got a couple of those engines and want to know how hard it is to make the twin. I have never rebuilt an engine and dont have very much experience but some of the club members are really good with engines and wouldnt mind helping. If anyone has experience with this please let me know...thanks[link]http://www.youtube.com/watch?v=euUP4MpIzYY[/link]

That is pretty impressive and really neat.
OK I think you need to make a special connecting rod set for it, to share the same crankpin on the engine. Probably a split rod setup like the Harley Davidsons use. You could also make a master and slave rod like they do on radial engines, but only for two cylinders. A master slave rod would have more bearing surface on the big end to support the combustion process better than a split rod like the HD's use as the crankpin is only so long. Then you have to machine the two crankcases so they can bolt together into a unit, One case has threaded holes and the other has the screws that go through to the one with the threaded holes. That is probably about it, except for setting the timing of course, but each engine would set its cam timing like normal for each half.

Here is the inside of the HP VT-21 twin

Reggy,


Here is a much better, larger photo; from which one can see the details.


This is a wrong crankshaft! If anything, Hirtenberger should have used a 180° crankshaft, to achieve even 360° firing intervals and a much, much better balance.
The con-rods would also be more conventional; instead of the 'knife and fork' arrangement.

This engine, as designed, has 180°/540° firing intervals and a single counterweight...

This pic shows a different way of how they did the connecting rods if you look close. I dont like how they did this one tho. Looks as if they just machined them thinner and offset them. It would be more balanced than the other pic.

Squirrel,


The difference in balance would be minuscule at most, as long as the single-throw crankshaft is used...

If a 180° crankshaft is used, like the one in the OS Gemini, the pistons will be moving in opposite directions, primary vibration would be quelled and only low amplitude secondary and tertiary level vibration would make the engine very smooth.



The cylinders would need a bit more offset than your photo shows (hence tertiary vibrations).

Granted using separate throws for the rods would have been best for more of a ideal firing sequence and balance, but if you use the original crankcases then you are constrained to keep the original crankshaft with its finite length of crankpin. So the rods would have to be more thin for both to fit. In this case using the knife and fork rod setup is a reasonable way to do it. But I think that using a master slave rod design would offer stronger rod strength and less wear at the critical crankpin end. I have seen flat twin engines and V-twin engines using the master slave rod design before, but I don't remember where at the moment.

These engines were not built by HP but by Dietmar Kolb from Germany
Here is the engine from my collection

Reginald have you built one of these?...


I think ive figured out the crank and rod setup. I dont know anything about 4 stroke engines. How do the valves or pushrod things work on a 4 stroke?



Would this engine be reliable enough to fly a plane? As cool as the engine is I dont see a reason to build a engine to set on the shelf. And I dont even know what kind of power the twin would put out.

The HP VT series of engines were a rotary valve 4 stroke engine. There is a gear drive and a driveshaft to the overhead rotary valve. As the rotary valve rotates it opens the intake and the exhaust ports respectively. It does not use poppet valves like the conventional 4 stroke engines use. The rotary valve design doesn't have problems with over-revving the engine as there are no poppet valves, no camshaft, rocker arms, nor valvesprings in it to cause the valves to float. They call the rotary valve in the HP VT engine a Aspin Valve. It is a gear driven conical valve with a opening that as it rotates it exposes the intake port, then the glow plug, and then the exhaust port.
They were talking about it in this thread too http://www.rcgroups.com/forums/showt...413&page=3