This weekend I finally pulled the engine and transmission from the bus – each time I’ve done this I’m amazed at how few connections there are and how relatively quickly it goes. The goals for this effort are to figure out what happened that caused the breakdown last year as well as fix the problems that had been occurring since the original ‘rebuild’ (more of a clean and reseal). These problems included:
- Immediate pop out of 1st gear and inability to hold in gear. This effectively meant no 1st gear, requiring always starting in 2nd gear.
- 4th gear popped out under load, but could be held in place by a bungee cord. This worked, but is a really inconvenient way to drive and would eventually cause excess wear on the shift forks and slide gears.
- Gear oil leaking from center. This should be an easy fix, I didn’t originally realize the paper gaskets used for the reseal were not treated; using gasket sealer this time should solve this problem.
- Too slow. Currently the bus red-lines in 4th gear somewhere in the low-to-mid 60MPH range, which mostly rules out interstate travel. More flexibility to do longer trips and even to more easily run errands locally would be nice to have. The engine is a little bigger than stock and should be able to handle the higher load, but gearing changes will be needed to get the RPM’s down.
I started disassembly and found that the internals seem to be in incredibly good shape, the teeth show little or no wear even looking under a microscope. All the gear ratios match what would be expected for a ’67 bus except 4th – for some reason it has a 0.88 ratio rather than the 0.82 ratio that would be expected. The 0.88 4th gear would be consistent with a beetle transmission, so I think this information combined with the amazing internal condition tells me that the transmission was replaced with a new or re-manufactured beetle transmission (while keeping the bus axles and reduction boxes) at some point very late in the bus’s history. The top speed would have dropped dramatically after this change and perhaps this contributed to it being parked semi-permanently in the early 80’s.
The jet engine combustor is now mostly complete, all that’s left for it is to #1 drill/tap for the spark plug and fuel injector(s) and #2 add an intake duct for compressor air. I’ve also mostly completed the 3D model – there aren’t many straight lines or surfaces on it, remembering all the 3D modeling tricks to make this was a lot of fun. I even went a bit overkill with the model – I may not actually build a bell mouth intake, screen, and/or jet tube.
The biggest looming challenge is deciding on a hole pattern for the flame tube. It’s critical that the flame tube holes are in the right places to correctly ‘hold’ the flame through various engine speeds, particularly while starting. If there are too many holes the air will mix too readily and the flame will be blown out, not enough holes and the engine will starve for air and not achieve self-sustaining operation. This is the biggest area for experimentation on the system and it’s why I made the flame tube easily removable from the combustor, modifications may need to be made.
- Finish 3D module including stand w/ various support systems
- Oil system (Oil tank, oil pump, electric motor)
- Fuel system (This will be propane at first for simplicity and safety, but provisions may be made for future use on Diesel/Kero/JetA)
- Starting system (Air jet strategically aimed at compressor wheel)
- Ignition system (old ignition coil excited by a power transistor pulsed by the control system)
- Electrical design, construction, and programming for instrumentation & control system (tachometer, temperature sensors, etc)
Today as I was backing the bus into a parking place, the clutch pedal suddenly became unusually light. It did not stall as I slowed down, so the clutch wasn’t stuck engaged – however once pulled out of gear it would not go back in while running, meaning the clutch was at least partially engaged.
I’ve always thought of the engine/transmission that are in the bus as temporary – I didn’t do much to these other than disassemble, clean, and reassemble. As such, there have been one or two roadside repairs needed, but I’ve always been able to MacGyver it well enough to avoid a tow. That wasn’t the case this time and I had to have it towed a few miles back home.
It’s not a problem with anything I can see on the outside (pedal/cable/fork), so instead something has occurred somewhere inside the transmission. I didn’t hear any pops or bangs, so likely it’s something along the lines of a bent clutch fork. I’ll pull the engine/trans over winter to both find out the problem and also rebuild for more speed, less noise, etc.
Before anyone gets excited, this is in reference to BUILDING a gas turbine (jet) engine rather than flying one, but it should be almost as much fun…
I’ve had a gas turbine (jet) engine on my ‘some day’ projects list for a long time. While cleaning the shop the other day I realized that I now have basically everything needed to complete this: a spare turbocharger, old oil pump, numerous microcontroller demo boards, various switches & sensors, scrap metal, and an assortment of plumbing fittings. All that’s needed to make it happen is to design and build it – a fun ‘free’ project.
I started on the combustor tonight. Fabrication should be generally easy compared to the CNC machine build, however without a lathe or mill there are some parts that I will have to fabricate creatively. I have jumped the gun a bit in not designing digitally first. In general the design will consist of wild guesses based on other similar projects online; so I haven’t lost out on anything by not having a digital model first, but I will create one as I go to make future changes easier to understand.
Christina and I went for a short cross-country flight today. This was the first flight that I wasn’t either solo or with a flight instructor. It was a bit bumpy, but extremely clear and Christina got a lot of pictures.
I haven’t updated in quite some time; summer was very busy with work, travel, and the occasional practice flight. I documented a number of these things with the intention to later post, however I failed logging into my phone one too many times and it deleted all photos.
Bus: Only minor work done on the bus, mainly more wet-sanding & polishing.
CNC: I created a homemade drag knife for cutting out vinyl/cardboard/paper. This is still a work in progress as are accuracy refinements and fine tuning.
Aviation: I passed the Private Pilot check ride! This generally means I can now fly any single engine land airplane (that does not require a Complex, Hi Performance, or tail-wheel endorsement) to/from any airport (besides the obvious: military/etc); and I can now carry passengers that aren’t flight instructors. I should be getting the official plastic certificate (There’s no such thing as a “Pilot’s License”) card in the next few weeks like the one below.
In practice, switching to something other than a Cessna 172 would require a little bit of transition training and there are time limitations to renting the trainer plane. So not sure what’s next with this hobby, but there’s a lot to learn and it’s still very interesting…