Need some tech advice re: Turbo Optima gear upgrading

[Coelacanth]

Since I'll be eventually upgrading to a brushless ESC & motor combination, I've been doing a lot of research on bulletproofing my T.Optima's drivetrain. Note that I'll be sticking with chain drive for now, as I can't either find or afford a belt drive conversion kit. Upon disassembling my old gearbox (replacing the gears & gearbox with brand new plastic I had lying around since the 80's), I saw that the final pinion gear was pretty worn out. I have an anodized one coming from pargu2000, that should take care of one weak link in the chain.

I subsequently talked to an eBay seller who was something of an Optima guru, and he informed me about spur & counter gear upgrades from Thorp, Dirt Burners, Robinson...these gears are correct 48-pitch, while the original Kyosho ones weren't (for some reason). The ones he has available for sale come in different numbers of teeth, 42T was one of them.

I also purchased a limiter gear assembly (#OT-74) to replace the stock original Optima one.

So here are my technical questions...

1) What is the stock number of teeth for these 2 upgradeable gears?

2) What is the result of going to a less/more toothed upgrade gear?

3) What gear recommendations do you have to strengthen the T.Optima drivetrain, excluding the diffs?

Thanks in advance.

[Coelacanth]

Nobody here is a "gearu?"

I've seen aftermarket center (cluster) gears from 54T all the way up to 66T. I believe 62T is stock, right?

I've also seen an overdrive counter gear that's 26T instead of the stock 28T.

Hopefully someone here has experience with the change you'd expect going to a lower-than-stock center gear or counter gear...

[Mr. ED]

The bigger the pinion, the higher the topspeed but the less power during acceleration
The smaller the spur, idem
The bigger the countergear, idem

changing the spur by 1 tooth creates a small change, changing the countergear by one tooth, or moterpinion, gives a larger change.

I have some Robinson gear sets towards 48 pitch but would not advise buying them to anyone. They have a bad reputation when it comes down to a nice even mesh. The smaller pitch also doesn't help strength.

[ROH73]

In my opinion, I think you shouldd leave the metric 0.8 module (just about the same as US 32p) gear set on there. The various US 48p gear sets that were offered made pinion gear selection easier, but they didn't strengthen the drive train; the original gears are pretty strong. I've run 12 and 10 turn brushed motors in my Turbo Optima without issues on the original gear set. The hard final pinion is a must, however, and Pargu2000's may not be hard enough as it's annodized aluminum; the vintage Kyosho Option House one is hard-annodized, which has significantly more wear resistance.

Also, in terms of strength, the original chain and sprockets are plenty tough; they're just noisy and not as efficient as the belt conversion.

Regards,

Robert

[RichieRich]

I echo Robert's comments. The main issue with those gearboxes is the final drive pinion. They're plenty strong but don't last long before they need to be replaced. Again, the hardened final pinion is a must. May the force be with you as you try to locate one.

[mugenbulldog]

I'm neither an expert nor have I tried this, but supposedly the plastic final pinion from the UM-1? gear set for the Ultima might be as good or better than the hardened steel ones. I am sure someone else on here knows more than me about this and can chime in one the specifics.

[RichieRich]

The plastic pinion requires a shaft with a crosspin. As far as I know, none of the Optimas have this setup.

[Coelacanth]

Thank you guys for some great information!

The bigger the pinion, the higher the topspeed but the less power during acceleration
The smaller the spur, idem
The bigger the countergear, idem

"idem"? No idea what that means...

I've been looking for a hardened final pinion for a while now, I have the part number burned into my memory: OT-76! Haven't found one yet, but I need something to replace the 2 that I have, one of which is about a 3/10, the other is about a 8/10. Pargu2000's unit should keep me running until I find a hardened F.P.

It's true that, in all these years, none of my gears or the diffs had almost any wear whatsoever, other than the final pinion gear, so it seems that the suggestion I've heard from a few people, that going to the "true 48-pitch hop-up gears" is more efficient, is perhaps not really the case. I'll hold off on that purchase.

Also, I'm glad someone brought up about the plastic UM-1 gear; someone else mentioned that to me as an option on eBay, but it doesn't appear that it really is an option.

ROH73, with those 10 & 12 turn motors, what motor pinions are you using? I have a hardened 9T, 11T, and several normal aluminum pinions of higher tooth count.

Thanks again guys, love the advice!

[ROH73]

ROH73, with those 10 & 12 turn motors, what motor pinions are you using? I have a hardened 9T, 11T, and several normal aluminum pinions of higher tooth count.

I use a 9T pinion.

Regards,

Robert

[highwayracer]

hello Marc,

Kyosho made 3 types of top shafts for the optima / ultima series:

1. Threaded on the end - This was used on the early optimas. It acted like a slipper clutch, by allowing the outside gear to spin. While this was a nice idea, the threaded part of the shaft was 3mm and it broke if it was tightened too much. The final pinion attached using a set screw.

2. Solid with a notch - This was the second version that was used on both cars. The thread was removed and the whole part was now 5mm. Because of this, the outside gear had to be redesigned to accept a pin. This is what you have on your car.

3. Solid with holes - This is the final version that's used on the ultima series (ultima 2, outrage, etc). There's no change to the outside gear, but it now uses a pin insetad of a set screw to hold the final pinion. The final pinion is now made of the same plastic as the gear set.

If you use the latest version of the top shaft, then you can use the plastic ultima final pinion.

With respect to the gearing, thorp and other companies made over-drive and under-drive gear sets. Both were made in 48 and 32 pitch. Companies like trinity re-packaged the thorp units with their label. The underdrive kits gave the same effect of using a smaller pinion. The problem with the original optima gearing is that if you ran 4wd modified, then you would have to use a really small pinion (in some situations).

The rule that I used (based on my motors) was, if I ran and 15 tooth pinion with a stock motor and the stock gear set, then I can run the same pinion with the under drive and a modified motor. This was a good starting place for me.

Fast forward to today...we can't go to the LHS for these parts anymore...and the set on ebay are $30 minimum. So the only really practical choice would be to use the stock gear set and cary a bunch of smaller 32 pitch pinions.

Hope this helps...

Regards,
Roger

[Coelacanth]

hello Marc,

Kyosho made 3 types of top shafts for the optima / ultima series:

1. Threaded on the end - This was used on the early optimas. It acted like a slipper clutch, by allowing the outside gear to spin. While this was a nice idea, the threaded part of the shaft was 3mm and it broke if it was tightened too much. The final pinion attached using a set screw.

2. Solid with a notch - This was the second version that was used on both cars. The thread was removed and the whole part was now 5mm. Because of this, the outside gear had to be redesigned to accept a pin. This is what you have on your car.

3. Solid with holes - This is the final version that's used on the ultima series (ultima 2, outrage, etc). There's no change to the outside gear, but it now uses a pin insetad of a set screw to hold the final pinion. The final pinion is now made of the same plastic as the gear set.

If you use the latest version of the top shaft, then you can use the plastic ultima final pinion.

Thanks Roger. I just received one of my hop-up parts today, the OT-74 Limiter Gear Set, which replaces the stock original Optima counter gear. My existing counter gear was a one-piece unit on the shaft. The OT-74 was one of the things that changed between the Optima and Turbo Optima/Salute. I wanted it to give some drivetrain protection.

The guy I bought it from told me there were 2 versions of limiter gear, the original one was not-so-good, and the newer one is better. I've no idea which one I have, but he looked at the picture on eBay and said I had the better one. It has the notched shaft, the other end is threaded and the counter gear attached by a nut, and the other side of the gear has a beefy-looking spring that wraps around the shaft about 3 turns and is book-ended by 2 black washers. Which one do I have? I hope I gave enough detail, I can take a picture tonight if there's still any doubt.

The search continues for a hard final pinion gear...

[highwayracer]

Thanks Roger. I just received one of my hop-up parts today, the OT-74 Limiter Gear Set, which replaces the stock original Optima counter gear. My existing counter gear was a one-piece unit on the shaft. The OT-74 was one of the things that changed between the Optima and Turbo Optima/Salute. I wanted it to give some drivetrain protection.

The guy I bought it from told me there were 2 versions of limiter gear, the original one was not-so-good, and the newer one is better. I've no idea which one I have, but he looked at the picture on eBay and said I had the better one. It has the notched shaft, the other end is threaded and the counter gear attached by a nut, and the other side of the gear has a beefy-looking spring that wraps around the shaft about 3 turns and is book-ended by 2 black washers. Which one do I have? I hope I gave enough detail, I can take a picture tonight if there's still any doubt.

The search continues for a hard final pinion gear...

The one you have sounds like the type I broke...but I may have tightened it too much with the impact wrench

I've wanted to redesign the part (and have figured out how to do it), but I just haven't had the time to actually build it.

Regards,
Roger

[RichieRich]

There are two versions of the one with the limiter. There's one with a threaded end for use with a locknut. The other one has the shaft with tapped hole and the limiter is adjusted with a screw. I have no idea which one came first, but I have examples of both in my toolbox.

[Coelacanth]

You used an impact wrench on a 1/10 RC car?? Man, you wanted that sucker on GOOD, didn't you?

Here is what was originally on my Optima, and the version of OT-74 that I saw on eBay that I *don't* have. The one I bought has a much beefier, single spring instead of that strange springy-washer thing you see in the attached picture, held on with an e-clip. So, there appears to be at least 2 variants of the limiter gear assembly (the original Optima part isn't a limiter of any sort).

[Mr. ED]

idem or idem ditto in my case means : same as a above
so a bigger spur has the same effect as a smaller pinion or a bigger countergear.

A good upgrade are tufnol counter gears and spurs (with steel back gear) but they are as good as never available