After seeing an Austin 7 special up close at the Sonoma Historics last year, Bob, I had major envy for folks who grew up where the requisite bits were plentiful and affordable. The level of relative sophistication of this particular model was surprising for a home-build budget-racer 'formula.' Best of all, it performed as good as it looked! Mike
After all this time... I just have to know... what the heck are those vertical blades extending from the front of so many of these cars? Bumper substitutes? Tag holders? Curb feelers? Varmit slicers? Gary
Such a great little beastie, one of my favorite cars that show up to the historics. Great to see it tearing around the track!
The sticky out the front things, they are timing struts , they are there to break the timing beam at the start and finish of hill climbs and sprint events , They always seem to be the last bit to be made on a car and the most often forgotten parts when packing for an event , so it's not uncommon to see them lashed up from items begged borrowed or stolen from around the paddock, I did see one made from a wooden spoon and card ,
That supercharged Austin 7 is a great example , but it is either a copy of a works single seated or an actual works car , so very few parts are from road going Austin 7 and way obove the normal STD of Austin 7 specials ,
i may have missed it, but has any photographed and or explained how a GN/Frazer nash transmission is built and works? I would really like to see a detailed bit of engineering on it. do the GN's have a differential or is it "locked" a diagram of the shift linkage would be great...does the one lever shift all gears, or are there 2 levers, such as 1 for one set of gears (reverse and first) and another for a second set (3rd and 4th) why is the rear track so narrow? (is it due to a locked diff)? anyone ever build one?
Gn and frazer Nash are similar , Basically there is a solid back axle with four chain and sprockets each of a different ratio to select the desired ratio this is done by dog clutches as one is engaged the last is disengaged so the is normally only one set engaged , Diagram here http://www.petergiddings.com/Cars/union_spcl.html When it is all set up it works well the frazer Nash I recently drove required a firm deliberate change using the outside gear lever
It shouldn't really be all that difficult to furnish a GN or Frazer Nash with a differential, by making the axle in two hollow pieces which bolt together in the middle at relatively large bell-mouth flanges, sandwiching between them a plate which carries a differential planet carrier. Left and right axle shafts run on bearings inside (plain bronze bushes might suffice as the differences in rotational speed between the inner and outer axles will normally be small.) There is even a perfect space for the resulting pumpkinlet, directly behind the right-angle box.
The drawing at the Giddings site shows a three and reverse arrangement, by the way. I have read that the arrangement of the two shifting bars ahead if the bevel box was referred to as the "wiggley monkey" by boffins in the day. I have often thought about creating an arrangement like this in one of my cars--but never did anything but think. I will say this for the arrangement--if you get a chance to drive a FN, you will realize the standard that all transmissions should be judged by for shifting. Herb
was thinking about the differential idea, as the shafts that come out of the "diff" are solid, drive chains are able to be driven off of both of the half shafts. This is where my mechanical ignorance gets the better of me: in a standard rear end, if you jack up one side of a car with out a LSD, that wheel will spin and the other will not. If you add a differential to a GN style transmission, would you only be able to drive through one of the half shafts? need an education on how power transmission through a differential works...I have built a few but really never thought about it in this situation where there is an attempt at achieving driving forces from both half shafts. thanks!
If you replace the right-angle bevel box with a conventional final-drive unit with a differential, you would get no drive at all! As only one chain transmits power at a time, that would merely get the sprockets on the other side spinning very fast. The differential would have to go on the actual axle with the rear wheels on it. I've heard about the legendary FN shift quality, but have sadly never experienced it for myself.
ok, my thoughts are correct. I understand that to compansate for the "locked" rear end the track of a GN/FN is narrow, as if to compensate for the inability for the outside wheel to turn faster than the inside wheel. How "bad" would this set up be, were it to be extrapolated to the width of a model T rear axle? obviously there would be tire wear, and possible sheared valve stems, but what else? you mention the that a dif would have to be installed on the drive axle, so if i think about this the bevel box would be the same, but there would be a diff installed on the drive axle, so literally one set of drive chains would provide power to one half shaft and another set to the other. drive then being transmitted to the powered half shaft like a normal car.
More ancient build your own cyclecar drawings from the archives. This one's German and all measurements are in millimeters.
Let me try some basic geometry here. Suppose we have a Model T negotiating a tight parking-lot turn, which would be a worst-case scenario. The wheels are at full lock, which we assume to be 45° for the inner front wheel. The radius of the curve described by the inner rear wheel would then be equal to the wheelbase, i.e. 100". The same for the outer rear wheel would be that plus the track, so 160". The ratio of radii gives the ratio of rotational speeds for the two rear wheels, i.e. 1.6:1. That's quite some difference. In less extreme situations the difference would obviously be less. I think the GN/FN represents the limit, just about. It works because of the narrow track, but also because the grip afforded by the rear tyres is limited, and the tendency for the rear axle to want to pull the car straight ahead in turns counteracts the rearward weight bias and the roll-steer induced by quarter-elliptics at both ends. Change any of that and you might have a far less happy concatenation of circumstances. I'd expect that grippy tyres on a 60" track would be asking for trouble. I wouldn't try duplicating the chains for the two rear wheels, as that would require synchronizing the shift action between the two sides very finely. One would go from an exemplary shift quality to a sub-standard one, as invariably some bits would lag behind others, which would increase as things wear. And imagine the effect of missing a shift on one side only! One wheel would be in fourth while the other has failed to disengage third. The diff gears would be spinning to keep the car from wanting to steer itself, which is exactly what it would do if there were any slip-limiting action. In the approach I proposed above, all the rear sprockets would be rotating at the same speed, because they'd all be attached to the same outer axle (likewise all the front sprockets' driving dogs would be rotating at the same speed). The axle itself would be shaped like two toilet plungers bolted together at the rubber-cup-shaped bits, with sprockets attached to the "handle" bits. It would obviously be made in steel, not rubber and wood: The lump formed by the two rubber-cup-shaped bits and the diff planet carrier plate sandwiched between them would sit directly behind the right-angle bevel box, where every GN and Frazer Nash has a convenient space.
Interestingly, the timber sizes, which presumably were standard at the time at least, reflect standard English Imperial sizes quite closely, even though they are expressed in millimetres. Something similar applies in South Africa, due to a rather authoritarian process of metrification in the early '70s, plumb spang in the middle of the Bad Old Days and driven at least in part to an aversion to all things English that went back to the Anglo-Boer wars, on top of every despot's natural desire to change everything, which has left a generation without any feeling for how big an inch is. I had to go out of my way to teach myself my 25.4-times table. Worse, it has left a generation without any feeling for how much a horsepower is, and therefore incapable of getting any perspective from imported magazines, none of which express power output in killerwhat?, now or then. Nevertheless we had every young lad worthy of snapping a whip boasting to his peers that his 50cc conveyance has more killerwhat? than theirs. I see the rails are given as 35x110. We have a standard size for unplaned timber, 38x114, which is the Imperial 1½"x4½". This is timber which is cut before curing, and it invariably shrinks a bit subsequently. What one finds at the local lumber merchant does most often actually measure 35x110.
My original choice for my jappic chassis was 40 x 100 , and after looking closely at the v8 jap and doing a mock up chassis rail I have decided to go for 30 x 100 which will laminated from three layers of 10 mm ash glued together , The 100 mm dimension was chosen as I need a 100 mm step up to clear the rear axle this wil allow a simple joint with steel flitch plates on either side of the joint, these plates also contain the front pickup for the rear suspension and mounting for external gear and hand brake The wood is now cut , and hope to start building the real chassis rails on Monday , drawings for most of the steel flitch plates are done , and will get mock up plates cut next week , from 3 mm mdf before committing to get the steel parts water jet cut I have a jap crankcase to use as a mockup and have a good drawing of the sturmey archer gearbox , It's all coming together
I'm looking forward to seeing how your Jappic comes together. Remember to post pictures coz we like pictures My own twenty pound cyclecar project is getting revised in light of these German plans I've found as the bits and bobs I've already got fit in better with the German design. So I suppose that means it will be a 20 Marks cyclecar now
Thanks for the great collection of drawings. I don't think in metric, but can do the math if needed. Have plans in my head for a "Early Morgan" style clone along the lines of this one, powered by a Yamaha 500cc single, somewhere in the future when I get all of my other projects together.
Some further comments on FN drive. The one that I had the opportunity to drive, had no tendency whatsoever to "push" the front end- this was on dry macadam however. Things might have been very different in the wet. The turning circle wasn't all that tight--but at full lock, there was no squalling from the rear wheels, starting out gradually--nor did I see any evidence of rubber left on the road. I fail to see how putting a diff in the middle of the FN rear axle is going to do anything but give you one wheel drive--which ever side the chain and sprocket that you selected was on. the diff gearing will ensure that the other wheel gets no power. UNLESS I'm overlooking something. My brainstorm adaptation would be to put the chains and sprockets directly behind the clutch (in place of the conventional transmission. This has one benefit- the torque that the chains transmit is reduced by (typically) one third. The bad side is that this would take up a lot of space right where your feet want to be--unless the package was moved back--after the driveshaft and U joints- to the rear. Perhaps with the smaller chain and sprockets that the diminished torque would allow, the unsprung weight wouldn't get too excessive. But worst of all--I think that one of the best features of the stock FN setup is that the dogs are basically claw couplings--very coarse, and the rotational speed difference is very slow between ratios. With my proposal this would increase by a factor of 3 -- or whatever the rear ratio is. Undoubtedly some of the great shifting would be compromised. Why, oh why didn't I buy JB1285--a '32 Nurburgring----- Not really cycle cars, and sorry for hacking a great topic. Herb
As to why I would want to go and use my brainless power on figuring out how to adapt a GN/FN style transmission to a more normal width axle, ala' model T: Been toying around with the usual idea of a large aero engine stuffed in a relatively small package, repleat with double chain drive. Why? because it is cool. Why the GN/FN package? potential design ability to execution with limited access to expensive machine work, and lots of off the shelf parts options, coupled with the ability to adjust gearing and so on. Other perks such as low unsprung weight, fast shifting, cool noises, and ability to handle "large" amounts of power just add to the benefits. Also, double chain drive transaxles are very expensive and not easy to come by, taking other ideas such as grafting a transmission to a rear axles has come to mind, though become a very large "package". But generally the design exercise of building a GN/FN transmission sounds like fun. Some where I have the article on this car (Classic and Sportscar January 2000), he built exactly what I am trying to figure out. All I have is this picture...of a wonderful aero engined special: Ox-5 powered leZebre converted to double chain drive.
The axle forms a single, solid unit from left to right, and all the driven sprockets are attached to it. The whole thing rotates together; all the driven sprockets rotate at the same speed. But the axle is hollow and there is a differential and two axle shafts inside it. Conceptually the drive path would be: Engine > clutch > prop shaft > right-angle bevel box > countershaft > one of several dog clutches > driving sprocket > chain > driven sprocket > hollow outer axle > differential inside axle > two axle shafts > rear wheels. That is why it doesn't matter on which side of the bevel box the chain that is in engagement is; it all goes through the hollow outer axle.
OK--that makes sense. The fact that there were a number of GN's and FN's built with solid rears, we may be making too much out of what really isn't a problem. Granted, there were many more unpaved roads back then--which may have been kinder to tires in the curves--but since that sort of car would be a fun project rather than a daily driver-would anyone care if a set of rear tires wore a little too quick? Does anyone who hill climbs, or drag races worry about rear tire life? Herb
check out the snowmocycle in the beginning of this video by the yoopers, I have to build one of these, half snowmobile, half three wheel motorcycle http://www.youtube.com/watch?v=t3q3x-vB_JE
The Jalopy Journal
