XRAY - Model racing cars

Hi Guys,

I recently bought a T4 upgrading from a T3 2012.

I am having the same issue I had on my T3 which is rear belt does not last more than 2 battery runs and cuts.

I solved my T3 problem by replacing gear diff with ball diff, but the ball diff does not fit the T4 (wider by around 0.5mm).

Help please, what do you think the issue is???

I run a gear diff on my T3 2012 and have never experienced your problem.

Do you think the belt tightness between using the gear and ball diffs is pretty much the same?

Are you sure there is not a damaged tooth on the gear diff - or indeed the layshaft?

Were you using the same gear diff on the T4 as you were on the T3, or was it new from the T4 kit?

What weight oil were you using on the gear diff(s)

What surface are you racing on?



A bit more info may help us deduce what is going on

The belt is tightened as stated on the manual, I even tried 1 point looser and one point tighter, it breaks.

No, no damaaged tooth on the gear diff or layshaft.

I am using a 4.5 turn motor (Team orion kit) with 84 Spur and 20 Pinion.

On both T3 and T4 I am using 350cs oil on my gear diff. on a dusty technical track with 1 long straight.

I hope i gve you enough info so we can brainstorm and hopefully find a soltution. You will be surprised to hear this, but I lost 4 belts in 2 days because of the above (on the gear diff).

Indeed it is the same gear diff. model but offcourse used the new one provided with the T4.

Last but not least, I emailed X-ray with my issue on my T3 6 months ago, and they claimed no issues are there. Though on the forum, one of the main topics was the rear belt issue.

350cst is extremely light. The diff isnt leaking oil onto the belt and softening it?

You say it's a dusty track so is this outdoors ? If so, you are most likely getting grit in between the belt/pully and it's just snapping it. I have the same problem when I run at my local outdoor which is very gritty. Since I bought my t4 I haven't worn out a single belt and I run twice a week indoor.

Have a very close look at the diff and layshaft pulley's and check that there isn't any dirt etc in the teeth.
Because the pulleys are black, it's very easy for some teeth to be clogged up but you can't see it easily.

If all else fails I would take the entire car apart and rebuild it in case there is something small you've missed, a rebuild with the manual should eliminate anything.

Skiddins

OK so this has happened on two different cars and two physically different XRAY gear diffs. You are also running a mod motor which will put more stress on the transmission than most of us do- but 4 breaks in two days is not acceptable!

So the chances are it is not build problem or a faulty diff. I do not understand why it would be OK with a ball diff and not a gear diff; does a ball diff slip on start-up reducing the strain on the belt? But how come people with gear diffs generally do not suffer from this.
Andrew makes a very good point; personally I would take it to at least 1000cst minimum for the moment as part of trying to sort out what is going on.

Are the four screws which hold the assembly together tight enough. It is easy to over-tighten these, as I found out!!, but equally they do need to be firm.

So what is different about you- well most of us race on carpet and/or asphalt. So what about this dirt. Skiddens suggestions are sound. Then again how come the people you race against are not suffering the same problem – are they running gear diffs?

If it runs OK with a ball diff then I do not see how it can be the dirt.
I assume you have not turned the layshaft 180 degrees by mistake.

So that sort of points to the diff oil as the first consideration

Just put a yokomo belt in.

I tried to replace the diff oil to 1,000 cst like reccomended by most of you. tried it and the belt cut again.

So i think i will try the yokomo belts, maybe the result will be positive. Defcone, why do you think the yokomo belt will not cut??

I also had the same problem. Ignore what the manual says about "initial middle position" and put the tightness much looser. The belt has to be loose, whatever some people say. Also, I find difference between the 189mm belts in older bags (with older Xray logo, made in Slovakia I believe) and the ones in new bags with new logos (which are made in Japan!)- the new ones require different settings to get the same tightness. I must admit I also use a Yokomo belt in my car, simply so I didnt have to open Xray bags- I am very satisfied with it

Make sure that the belt isn't too tight. Make sure that you arent using a too soft shock oil which may cause the oil to leak and soak the belt (not sure what it does, just an idea). With the last batch of belts the team have not had any problems. They should last 30+ batteries on carpet.