belt conversion for chain driven optimas?

[Charlie don't surf]

Is there a way or list of parts required to use to convert a chain driven optima into a belt driven version, without replacing parts other than the chain, diff, tensioners etc?

[aip47-2008]

Actually quite simple until you get to the belt tensioner and cover!

[tamiyadan]

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[sgirouard]

What you're looking at is

1 new rear gear box (the belt drive has an extra idler gear)
1 new rear diff case (the internal gear diff is the same, just the case is different)
1 new front diff case (same as the rear, you don't need the actual gears, just the housing)
1 idler gear (this is the same gear found in the optima mid idler)
1 lexan cover to protect the idler gear

If my memory serves me right, that's the full set up, and of course the belt.

EDIT: There was no tensioner in the Optima belt conversion (aside from the actual chassis screws)

[ROH73]

Check out this thread: http://www.rc10talk.com/viewtopic.php?f=30&t=17279

[Bormac]

Reggie I have the majority of the parts needed to convert to belt drive which include the front and rear belt drive componants for the diffs + the drive belt.

Yours shipped for NIX if you want them.
Cheers-Jason

[tamiyadan]

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[Charlie don't surf]

Well what I had in mind was converting my Superior SRP-1 into belt configuration as a runner, but after considering making all new non magnesium bulkheads and suspension then changing the solid spools to diffs, then the driveline does not use the optima gearbox but rather a yokomo type 2 chain system and a slew of other handmade components (all due to the rubber tires that they are running) I think I will just restore the car instead.

[EvolutionRevolution]

well if you grab a Optima Mid parts car you can grab the driveline out of that.

when you get to the tensionar you will need to fabricate a replacement for the chain drive tensionar.

I would have to go through my parts to see if the mid version tensionar is close enough to drop into an old optima.

I thought the MID didn't have a belt tensioner? Are you talking about the idler gear that lifts the belt so it clears the motor properly?

[Coelacanth]

well if you grab a Optima Mid parts car you can grab the driveline out of that.

when you get to the tensionar you will need to fabricate a replacement for the chain drive tensionar.

I would have to go through my parts to see if the mid version tensionar is close enough to drop into an old optima.

I thought the MID didn't have a belt tensioner? Are you talking about the idler gear that lifts the belt so it clears the motor properly?

I thought the idler gear was to lift the belt so it doesn't rub on the upper chain guide...and as mentioned before, you don't need a different rear gearbox, you just need to drill the holes EvoRevo mentioned, but you also have to cut out a small section to allow for the idler gear.

[tamiyadan]

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[ROH73]

I thought the idler gear was to lift the belt so it doesn't rub on the upper chain guide.

It is. If the tension is set correctly, the Optima chain tends to rub along the top guide, the rear gearbox exit point and the front gearbox entry point. The idler ensures that this doesn't happen with the belt (which would cause a lot of friction and wear the belt out quite fast) by raising the belt level up to clear the gearbox and guides. If you set your belt tension correctly, get creative with a dremel on the gearboxes and set your guide a little lower, you actually don't need the idler. Back in the day, conversion kits were plentiful and reasonably priced (I think I paid $30 for mine), so it was easy to just get the kit. Today...well, it's probably easier (and definitely cheaper) to get creative with a dremel .

As a power transmission method, chains are technically more efficient (IIRC 98% vs. 95% for a belt), but in no way do they give better performance in an Optima. For example, my friends and I used to race our Optimas almost daily on a makeshift asphalt road course behind my house. My lap times dropped considerably after switching to the belt...I could finally keep up with my friend's brand new Optima Mid .

[ROH73]

The idler is not a tensioner; one is not required for a reinforced belt drive.

The Optima chain drive does not have an idler.

[sgirouard]

What you're looking at is

1 new rear gear box (the belt drive has an extra idler gear)
1 new rear diff case (the internal gear diff is the same, just the case is different)
1 new front diff case (same as the rear, you don't need the actual gears, just the housing)
1 idler gear (this is the same gear found in the optima mid idler)
1 lexan cover to protect the idler gear

If my memory serves me right, that's the full set up, and of course the belt.

EDIT: There was no tensioner in the Optima belt conversion (aside from the actual chassis screws)

1. You do not need a new rear gear box, 2 holes are drilled for the idler.
True, but you have to cut it a little otherwise your belt is going to rub and there are other parts you're going to need so you might as well get a spare box (hopefully the one for the conversion)

2. Rear Case is the same, the chain drive is simply upgraded to use a belt, changes to the Internal gears is changing the sprocket case to belt case internal ratio is the same no change.
I'm thinking we're describing different items. When I'm talking about the diff case, this is what I'm talking about


3. Front gear case is the same there is no difference between the belt and chain case, just the sprocket side of the gear diff is changed to a belt tooth. No other gears in the front case.
Yup, we're using the same words to describe different things. What you're calling the gear case is what I called the gear box, what you're calling the sprocket case so I think we're actually in agreement

4. You can make an idler, you can use this as a tensioner also by changing diameter, granted it's an over site from kyosho but after 20 years my car still doesnt need a tensioner.
The Optimas never had a tensioner. You'd adjust the screws of the chassis and literally "lengthen" the vehicle to establish the desired tension. The belt didn't stretch (as far as my experience). The idler was used to avoid the belt from rubbing against the chain guards

5. The lexan cover is more trouble then it is worth, especially is your running on a blue groove clay track.
Cant disagree, in this day and age, I wouldn't worry if I couldnt get one, but if I have one, it's being installed.

The idler tends to be a huge pain it can loosen up and basically jam the rear gearbox.
Just use Loctite 242 on the 2 small screws, never loosened on me ever

From a performance standpoint the chain is actually better.
Plus it has a cool sound LOL.

[Coelacanth]

Good post, Scott. I'd like to point out something potentially very important with this misleading image, I downloaded this same image long ago too.

The image makes the 2 idler gears appear the same, but they're NOT. Sure, they have the same number of teeth and are the same overall size. The problem is that the belt conversion idler gear is WIDER, with the teeth being longer as a result. You can remove one side of the yellow plastic rings from the Optima Mid idler gear, but the other side's ring is fused to the gear. I considered removing the excess of that ring down to the gear teeth, but you've already lost the advantage of a wider gear; i.e. the belt/gear mesh will be more forgiving of sideways motion with a wider gear. With the narrow gear, you'll have to:

-Remove one end ring;
-Trim down the other end ring that's fused to the gear;
-Use careful measurement with spacers to make sure the narrow part of the gear is directly in line with the belt.

I have both for comparison, that's why I'm critiquing this mod of using the Optima Mid stuff to complete a DIY belt conversion. It's entirely possible but it's NOT a drop-in mod and will have major functionality issues if not done VERY carefully.

Anyone have a spare idler gear (non-Mid)? I'd rather just have that gear and fabricate a shaft and be done with it, instead of farking around with that narrow Optima Mid gear and the fused-on ring.