An YR-4 chassis mystery

[EvolutionRevolution]

So some time ago I got myself a YR-4 II with glassfiber chassis, and some junkers consisting of two incomplete YR-4 II Pro's and one YR-4 Pro (I think...?). My idea was to rebuild the complete YR-4 II with the carbon fiber parts from the YR-4 II Pro's.

However, I've just discovered a small problem:
The fiberglass YR-4 II and the YR-4 Pro have a wheelbase of 26 cm, while both YR-4 II Pro carbon fiber chassis are 5 mm shorter! The chassis are not for the YR-4 II Compact, as they will fit a 6-cell pack with no problems whatsoever (they come with some foam because the battery compartment is too long for a 6-cell pack). This means that the front belts included with the other two chassis are too long to use with the carbon YR-4 II chassis (which both lacked belts).

The fiberglass YR-4 II came with a manual, which tells me I need a ZR-015 front belt. The belt it came with is a ZR-483 front belt (YZ-10). Can someone tell me whether there indeed is a belt length difference between these two belts (ZR-015 is shorter than ZR-483?)? If yes, does anyone know where I could find one?

Since what I wrote might seem confusing, here's a run down of the chassis:
a) YR-4 II Fiberglass: 26 cm wheelbase, ZR-483 front belt
b) YR-4 II Pro carbon chassis #1: 25,5 cm wheelbase, no front belt, dark grayish carbon fiber
c) YR-4 II Pro carbon chassis #2: 25,5 cm wheelbase, no front belt, blackish carbon fiber, extra hole next to battery pack
d) YR-4 Pro carbon chassis: 26 cm wheelbase, unknown manufacturer narrow belt that's the same length as ZR-483

a) was a pre-assembled (by Yokomo) almost ready to run car which originally included a F50 body and Futaba electronics.
I suspect b) is the optional chassis for the YR-4 II or an aftermarket chassis using the same shape.
c) likely comes from a YR-4 II Pro chassis kit and came with top deck and shock towers

[LTO_Dave]

If it's any help, the YR-4M2 drivetrain was a little different than the YR-4M2 J Pro. The diff gears were different and I think the belts were also different.

The YR-4M2 used the same ZC-656 rear belt as the YZ-10. The ZR-015M2 is listed as the front long belt for "M2".

[EvolutionRevolution]

Thanks, but...

The YR-4 II is the chassis that takes a stick pack along the right side of the chassis in two Associated-style battery buckets (YR-4 designations are confusing).

I guess I need a belt that is 3-5 teeth shorter than the YZ-10 front belt.

[Mr. ED]

Which motormount does the yr4-II (pro) use? Is it the same as the YZ-10, or is it a dark blue anodised unit? The later one requires a different length rear belt: about 1 or 2 teeth more.

How is the tension on the 483 belt on the fiberglass chassis? Did you count how many teeth it has?
Since the belt is M3 and the difference in wheelbase between the fiberglass and graphite chassis is 5mm I'd say you need 3 teeth less (9/2mm).
Tower hobbies have a very long list of belts in stock, and the toothcount is mentioned for quite a good part of them.
If in doubt , get a tooth extra and add a belt tensioner: just slide it forth and back till you get the right tension and fix it there.