Catching/Knocking Noise

[Jammi3D 0]

I've got a TT-02B with a BZ motor, 68T Spur and currently a 19t pinion fitted. This has been working ok but noticed a catching/knocking noise on the last run.

Have taken apart the rear/front diff , everything looks ok (no plastic shavings ect) put back together and re-greased still have the noise. After dismantling most the buggy I thought I'd try the torque tuned motor it came with and no noise. I've tried the torque tuned motor again today and the noise has re-appeared so can rule out the motors.

Anyone any ideas what the noise could be?

Video shows approx 30-40% throttle.

https://drive.google.com/file/d/1TS5SOjCLLFUZYqkqg3PzP32nBXvqTrDd/view

[TurnipJF 9192]

The sound is quite rhythmical and at a relatively low tempo compared to the RPM of the motor. This suggests that it is somewhere further along the drivetrain where things are moving at a lower RPM having been geared down a bit.

It is hard to see in the video, but is it occurring once per wheel revolution maybe? If so, I would suggest working from the wheels inwards, looking for anything that might be catching or binding. There may be a small stone or piece of debris stuck somewhere obscure that is catching as the wheels, axles, dog bones or diff outdrives rotate?

If it is not occurring in sync with the wheels, might it be occurring in sync with the propshaft? Is this straight and centered in its drive cups, not knocking on the chassis or wiring anywhere? Is the spur gear free of debris and are all the teeth in good order?

[Willy iine 18805]

Small rock in the gear teeth..?

[one_hit 1046]

Check for vertical play in the diff bearings. Grab both diff cups and try to wiggle up and down. If there is any play, use some aluminum or electrical tape on the diff cover to tighten up the bearings. 

[Jammi3D 0]

cheers for the replies.

I have noticed there is damage to the prop joint which would say there is debris in there but I've taken it all apart/cleaned and put back together and still the noise. The damage which removed the blue was done on the 1st run, the faint marks are recent.

I have added shims to reduce any extra movement, do you think I've added too many causing extra pressure?

one_hit, I'll grab some aluminium tape as I need to order some different sized shims.

I have picked up a reinforced red chassis so may just do a rebuild.

[OnTheTrail 1152]

Can you duplicate the sound only when driving or is the sound still heard if the car is running while up on a stand?   

If it does it while on the stand, start taking things off one by one starting from the wheel on in.   

[Jammi3D 0]

Sound was heard both driving and while on stand (video above was on stand)

I found the problem, I bought replacement pinions (TAM 50355) and have been running the 19t pinion for a while with no issues.

I've installed the kit pinion which seems to be smaller in size and no noise. Both are .06 mod so should they not work?

Have a feeling I may be understanding the motor mount wrong? hole 19 for 19t ... have tried both mounting holes on the BZ motor with same results. It does look like when using the 19t hole the pinion & spur are too close together.

[one_hit 1046]

30 minutes ago, Jammi3D said:

Sound was heard both driving and while on stand (video above was on stand)

I found the problem, I bought replacement pinions (TAM 50355) and have been running the 19t pinion for a while with no issues.

I've installed the kit pinion which seems to be smaller in size and no noise. Both are .06 mod so should they not work?

Have a feeling I may be understanding the motor mount wrong? hole 19 for 19t ... have tried both mounting holes on the BZ motor with same results. It does look like when using the 19t hole the pinion & spur are too close together.

The kit pinion is 17t, did you use the 19 holes with the kit pinion? If so then that is your problem

EDIT - re-read your original post. You said you are using a 68t spur. I believe the smallest pinion you can use with the 68 spur is 18t in the A position. Since you are using 19t then you should be using the B holes

[Jammi3D 0]

I think I've not understood the motor mount correctly which would explain the spur/pinion been tight together.

The 17t was just a test today.

With the 19t I was using hole 19 (D) on the mount but as you explained I should be using hole 17 (B)

EDIT

thank you everyone for the suggestions, as one hit pointed out I was using the wrong mounting holes, just moved to hole B and working perfectly again thank you