Cause I don't have enough going on....YZ870 edition

[rccars4sal]

Ive got 1 car using stock chassis, with a really tight front belt. No top deck even installed yet. Its so tight that just belt tension causes a verrrry slight curve to the chassis deck. Everything is in there, both diffs, center shaft. Im wondering if some of the chassis were cut slightly long? This particular one is a new chassis plate, but its the same material as the used ones I also have, so assuming its just a NOS chassis, and not a repro. Anyway, Im figuring the lower deck is just slightly off. My planned fix is to elongate the front bulkhead mount holes just by about 1 or 1.5 mm to be able to slide the front end back just a hair. My cars, as far as I can tell are all yz870c type, which I think also includes early TA yz10 models? Anyway, Im pretty sure Im not mis matching any pieces causing the tight belt. Actually, that car has a machined front bulk head,, which is getting switched out for a stock mag piece,, so cant verify if its the bulkhead just yet.

These Yoks are funny arent they? Little issues, that point to perhaps slightly lower budget manufacturing than say,,, Kyosho of the same time. Makes me appreciate them even more.

[stickboy007]

Ive got 1 car using stock chassis, with a really tight front belt. No top deck even installed yet. Its so tight that just belt tension causes a verrrry slight curve to the chassis deck. Everything is in there, both diffs, center shaft. Im wondering if some of the chassis were cut slightly long? This particular one is a new chassis plate, but its the same material as the used ones I also have, so assuming its just a NOS chassis, and not a repro. Anyway, Im figuring the lower deck is just slightly off. My planned fix is to elongate the front bulkhead mount holes just by about 1 or 1.5 mm to be able to slide the front end back just a hair. My cars, as far as I can tell are all yz870c type, which I think also includes early TA yz10 models? Anyway, Im pretty sure Im not mis matching any pieces causing the tight belt. Actually, that car has a machined front bulk head,, which is getting switched out for a stock mag piece,, so cant verify if its the bulkhead just yet.

These Yoks are funny arent they? Little issues, that point to perhaps slightly lower budget manufacturing than say,,, Kyosho of the same time. Makes me appreciate them even more.

I have two of the Lazer ZX, and indeed they are quite nice in terms of build quality. But I cannot stand the drivetrain being so difficult to access. I guess it's a pick your poison thing. The Lazer drivetrain is better sealed from dirt, but maintenance is a pain. The YZ10 870, despite its sloppiness, is ridiculously easy to work on. I would say their build tolerance issues make them more charming

[rccars4sal]

Yes, my comment above,, makes me appreciate the yoks even more is what i meant. I have been a kyosho guy sinse about..... 1985 though.

[GoMachV]

The new chassis on mine is copied exactly from stock, the holes are in perfect alignment. I will however swap the drivetrain back to the stock chassis and play with the old belt a bit to see what's up. Anyone care to take a quick measurement from the rearmost front bulkhead screw centerline to the front most motor mount bulkhead screw centerline? I'll compare the measurement tonight

[DennisM]

app. 199,6mm
How about the new bulkhead/s?
I´ve seen YR4´s with magnesium bulkheads - don´t know if they are an exact match?

[GoMachV]

Front bulkhead came from a member with a yz10 that it was installed on...86.9% sure it's proper.

This is all very strange

[rccars4sal]

Im getting a reliable 7.9 inches on both cars pictured. The clean one is tight, the dirty one is loose. The difference is more dramatic in person. The clean one is slightly bent from tight belt, and the dirty one is soo loose it will require the standard belt tensioner to run without skipping. I havent torn into them yet to see if diffs or pullys are different. Using a 1/10 scale because Im doing alot of cad lately,, but a mm scale might be closer,, but like I said,, both cars chassis plates are giving me same numbers from screw center to screw center.





Upon closer inspection, I just noticed both of these cars have the machined aluminum front bulk head,, so I have to eliminate that factor from the equation.

[Alex B]

Is the belt the correct yokomo one?

There are three types YR4, 870c and works and YZ10 94.

[GoMachV]

I stopped off on my route to measure...I get 7.9" or 201.5mm from front most center bulkhead screw to left side rearmost bulkhead screw.

Dennis...your measurement is under mine by a good bit. We will have to see what's up!

[rccars4sal]

I measured mine by marking a center line between the 2 center mount screws, and going from the bottom view right side front(rearward) bulkhead screw. So, a straight line rather than a crooked line directly from screw to screw which would slightly skew the numbers.

[DennisM]

Okay After removing the undertray, I read app. 200,4mm
That´s about 1 mm difference to Your reading - perhaps a running change? I don´t think the dog´s burried here.
If I were to eliminate the slack on mine without the tensioner, I´d have to move the front bulkhead at least 3-5 mm forward.

[DennisM]

A new belt from bag meassures 248,5mm (loop length) streched over a steel ruler.
The belt is "ridgid" and I´m not able to "stretch it"

[rccars4sal]

Might be a difference of perhaps 4 or 5 teeth on a belt to make such a difference? Ive got no time to count mine!

[GoMachV]

I measure the new and old belts, my ruler had a dead spot before the numbers start so without doing the math there was a 1mm difference old to new ...x2 makes it about 2mm longer total from stretching. I installed the old belt and you could run the car without a tensioner if you wanted to. It isn't tight, but I wouldn't run it any looser either. This leaves me questioning everything.

I installed the new belt in the junker chassis and it's tight too- no real difference.

Oh. And I found out yr4 nitro pulleys are 33t. It would fit perfectly lol.

[rccars4sal]

Just a little bit more info regarding the tight front belts. I swapped the loose belt from the dirty car onto the clean car. It eliminated the bend in the chassis, but is still tight, like a new belt might be. Not at all slack as in the picture above. The 2 belts side by side were different lengths, but only by perhaps 3 or 4 mm when stretched over a couple pencils.