Homebuilt Mid-Engine Sports Racer

[Neil]

I was letting the rear of my car down from jack stands and inadvertently dropped it too fast and a pair of wood blocks that I was using as spacers to raise the jack travel higher slipped and the car fell about 6 inches. Wouldn't you know it- the jack stand hit the rearmost shift rod (actually a 3/4" OD tube) and bent it into a question mark. Arrggghhh.

I had planned to replace it and one other part of my shift linkage anyway so that wasn't a complete disaster. I bought some Thompson Case 60 ground & polished rod a while ago for that purpose since the linkage runs in ball bushings. The problem started when I tried to drill the shaft for universal joint retaining bolts. A high speed drill would not touch it and neither would a cobalt drill. Not having a carbide drill, the hard surface of the shaft was resisting my attempts to drill a hole through the rod. Thompson says their surface hardness is 60 Rockwell C minimum and typically 62 RC.

The solution was to grind off the hard outer surface on both sides of the rod, exposing the softer inner core. I used a Dremel tool with an abrasive and it worked very well. I was finally able to drill the through hole with an ordinary high speed #10 drill. Cutting the rod to length with a hacksaw was impossible but an abrasive cut-off disc worked just fine.

Regards, Neil Tucson, AZ

 

[Joel K]

Murphy’s law, ugh. Glad it wasn’t worse.

 

[Neil]

I removed my main power relay to check the condition of its contacts. This relay is able to be easily disassembled, unlike most others. I was surprised to find that the contacts looked virtually new, no wear, arcing, or pitting. Not bad for a relay that probably dates from the 1940s.

I can't find any reference to its part number on the internet but it is a style that is still in production (but modernized somewhat) by Cutler-Hammer & Eaton. This style was predominately used as an aircraft engine start contactor... but what aircraft? Most military planes had 24V electrical systems by then but this relay is 12V. Any guesses?

Regards, Neil Tucson, AZ

 

[Neil]

I re-designed my shift linkage. The gear change shaft on a Porsche G50 both rotates and moves in and out so I used a series of straight shafts running in Thompson ball bushings to accomplish the shift motion. The rinky-dink way that I had to reverse the shaft rotation was not really very satisfactory so I came up with the approach shown in the photo. I used Ruland shaft collars to fasten the swing arms to the 3/4" shaft and 16mm trans shifter. I drilled holes to bolt everything together and used a surplus threaded link to couple them together.

The shaft collars are nice- they can be loosened to allow their positions to be adjusted.

Regards, Neil

 

[Terry Oxandale]

I've seen a previous post here describing a "reversed" pattern with the G50 vs the 930, yet no where on the internet does such a difference get noted or described. Lots of articles of folks transplanting the 915 or 930 with G50s, but no mention of shift pattern changes. What gives?

 

[Neil]

Terry, it's necessary to distinguish between the shift pattern that the driver sees and the shift pattern of the G50 shift rod. When installed in the "conventional" way, the G50 shift rod faces toward the front of the car but in a mid-engine layout, it faces the rear. Thus the left/right shift patterns are reversed. It does not matter if the transaxle is inverted.

 

[Terry Oxandale]

That's kind of my point. My 930 in a mid-engine config still maintains a standard H-pattern with the reverse top/left, with no need to reverse any of the movements. When viewed from the rear of the transaxle (in my project), fully rotating the transaxle stub CCW, while pushing inward, is reverse for the 930. This appears to be reversed for the G50.

 

[Neil]

Terry, according to this thread, the G50 and 930 transaxles are indeed “reversed”. https://www.gt40s.com/threads/porsche-930-4-speed-transaxles.26851/

 

[Howard Jones]

Well Neil, I looked for a few hours trying to find your contactor. Sorry no joy, If it was mine I'd throw it in the garbage and use a American made name brand old school ford starter solenoid. Here's appears to be a pretty tuff one rated at 700 amps momentary and 300 continuous.

https://www.ebay.com/itm/HD-12-VOLT...1134?_trksid=p2349526.m4383.l4275.c1#viTabs_0

If you must have airplane stuff then here is a FAA certified part rated at 300 amps.

Lamar Starter Solenoid FAA-PMA | Aircraft Spruce

Lamar Starter Solenoid FAA-PMA FAA-PMA Certified Aircraft - Starter Solenoids

www.aircraftspruce.com

Everything stays the same if you both flip AND reverse it.

 

[Scott Calabro]

6041H43C

www.krn.com

Probably an old twin like a Travel Air, Apache or C310?

I’d keep it since it’s “rebuildable”

Two are available via the link.

So Neil, I spy lots of aircraft specific (genuine) hardware / parts on your build, are you in aviation?

BTW, love the tri wing screws on your turnbuckle assy

 

[Neil]

Thanks, Howard. I just re-installed my original 6041H43C relay after checking it one last time. It is old but a good relay and it is made for motor starting. I did order a replacement when I wasn't sure if the original was toast or not. It is a Cole-Hersee 12V continuous duty contactor that looks like the one you referenced but this one has only one small terminal. When that terminal is connected to ground, the contactor pulls in.

https://www.elecdirect.com/media/specsheets/CHh1.pdf

A starter solenoid has high current ratings but its coil is only intended for intermittent duty. If it is operated continuously it will overheat and fail, maybe even catch fire. The Cole-Hersee contactors are popular with RV and golf cart manufacturers for battery relays.

Thanks for the links.

 

[Neil]

Scott, thanks for the information. The relay looks good so I'll reuse it.

Yeah, those Tri-wing fasteners are trick if you have the appropriate screwdriver! They are titanium so corrosion won't be a problem.

I'm a retired electronics engineer but at one time I did think about building an airplane so I took the Airframe & Power Plant Mechanics course at our local community college. Those skills are directly applicable to building race cars. I've collected a lot of surplus goodies over the years and some of it turns out to be very useful! In fact I just sold a 28VDC/115VAC 400Hz power inverter from an Apollo command module that I picked up in a salvage yard here in Tucson back in the early Eighties. It was from Apollo Boiler Plate #14. I bought all three inverters from the CMD; removing them was not an easy task.

 

[Neil]

The swing arms I made were a little too flexible so I cut some 1/2" square steel tubing and inserted two , one inside each edge, and riveted them in place. This stiffened the assembly considerably and the shift motion feels good now.

Regards, Neil Tucson, AZ

 

[Scott Calabro]

Scott, thanks for the information. The relay looks good so I'll reuse it.

Yeah, those Tri-wing fasteners are trick if you have the appropriate screwdriver! They are titanium so corrosion won't be a problem.

I'm a retired electronics engineer but at one time I did think about building an airplane so I took the Airframe & Power Plant Mechanics course at our local community college. Those skills are directly applicable to building race cars. I've collected a lot of surplus goodies over the years and some of it turns out to be very useful! In fact I just sold a 28VDC/115VAC 400Hz power inverter from an Apollo command module that I picked up in a salvage yard here in Tucson back in the early Eighties. It was from Apollo Boiler Plate #14. I bought all three inverters from the CMD; removing them was not an easy task.

After 36 years in aircraft maintenance the bottom drawer of my box is loaded with bits for specialty fasteners like those! Keep up the good work.

 

[Mesa]

The swing arms I made were a little too flexible so I cut some 1/2" square steel tubing and inserted two , one inside each edge, and riveted them in place. This stiffened the assembly considerably and the shift motion feels good now.

Looks like you were originally trying a little to hard to 'add lightness'
Is weight as critical on LSR cars as it is in other forms of motorsport?

 

[Neil]

No, Mesa, in LSR cars people actually add weight to help tire traction on the salt surface. I built this for a general-purpose fun car that I could run in many venues- albeit uncompetitively.

Part of the original approach on the shifter swing arm was to keep it simple and easy to build. It was that, but it also didn't work well enough.

 

[Ian Anderson]

On your shifter mechanism, have you thought about a rifle bolt action mechanism near the gearstick?

I believe Chris (Flatchat) on here used this method with a Poreshe box in his RCR T70, but I cannot locate the photos

Perhaps send him. Pm

Ian

 

[Neil]

I guess I don't understand what that would do, Ian.

 

[Ian Anderson]

Aussie RCR T70 capers

The thread title refers to 'caper(1)', your berries etc refer to 'caper(2)'... & Flatchat could be considered very frisky for his advancing years!!, but you probably already know that or should...:)

www.gt40s.com

Post 200 and 201

Though that is not the post to which I refer above. But Chris has done the job efficently so perhaps could shed light on the other end too.

Ian

 

[Neil]

Thank you for the link, Ian. That looks a bit complicated but nicely done. His post #199 shows an alternate way to couple the shift rod to the transaxle.