The real task for today was refurbishing the chassis. A chunk of fiberglass that started life as a peg-board circuit test fixture salvaged in a warehouse clearance give-away. A small router table, a Dremel tool, and some careful planning and fixturing brought this chassis into shape. Holes are tapped directly in the fiberglass. Some of the holes were not perfectly made, and some trackside chain repairs have allowed some desperate alterations to compromise the holes. Today, all the M2,5 holes were deepened and retapped. All were salvaged and the new screw of choice is a Schroff offering for their electronics racks. Their length and large head diameter is uniquely appropriate for this application. Here is a closeup of the screw:
Having limited access to real shop tools does have its advantages. The pilot holes and the tapping were done with much greater precision that the 1st time around. The other mod required, as eluded to yesterday, was to counterbore the holes for the steering linkage - pivots. This was done with a drill press and a 7,5mm mill bit. It was a bit touchy trying to keep the bit centered over the hole. But if you recall, the 1/4" hex shaft required a 3mm deep counterbore. As you can see, this was accomplished beautifully:
And a 2nd plus about this revised features; all the screws are the same:
...except these, which I had to nip the tops off of:
When I assembled the plastics, the tips of the front sideplate screws now protrude past the plastic. A quick nip of the front gearcase took care of that:
Here is a shot of the steering linkage installed:
...and the sideplates:
...and with the diff case:
...and this is a 1,000 words all put into technicolor!
A final word about this chassis: all these tapped holes are M2,5 with plenty of material for M3 tapping. Some custom undercut M3 screws [captured hardware] could be used. That simply means that there is an M3 hole tapped in the metal plate slots and drive the screws in [captured]. Once loosely fastened to the chassis, the slots would work as before to adjust the chain.
Of course, this level of progress only begs the other questions that must be answered... Which drivetrain?
I've wondered if I can belt-drive this setup. I have all fresh [new] parts to make this a sweet belt drive buggy: new ball diffs; hardened pinion; new cases; new spur gears and full bearing set... but alas, this chassis is a long chassis that requires a different belt length. And I don't know what that length would be. It also turns out that Kyosho took a standard belt type... the XL series, and ordered a special narrow version of it. So this makes industrial suppliers less likely to want to talk to us hobbyists. So, since this buggy has always been a chaindrive buggy... and chaindrives are ~very~ efficient [and rebuildable!], we will stick with chaindrive.
The front differential is in perfect shape. The bearing spin freely, dirt and dust is absolutely minimal and the bevel gears spin quite freely and smoothly. The washers at the bearings are a great way to avoid dirt in the bearings. It could go back in as is and it would be perfect... but then again, a rebuild demands inspection, and since I have dozens of unused chain gears, I could dedicate a new set of plastics to the rebuild. Even the dogbone drivers are in really good shape signifying the low hours on this car. This car has been run using stock class motors for the most part. Now my dilemma... 18T/19T or 18T/Blank?
This is only the beginning of difficult choices. I have every intention to make the rebuild on-road compatible. This means that I don't want the front wheels over/underdriven. This is a good reminder of this unique option provided on the original Optima. At one point, I obtained a belt drive gear with this function but it never went anywhere. The real difficult choice is still looming in the back of my mind... dual chain drive ball diff or conventional diff and conventional gearing for the gearbox. Stay tuned!
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