XRAY - Model racing cars

Hi All,

During a maintenance session, I found that one of the balls on the thrust bearing fell out. This is the second time it happened. I believe this is probably caused incorrect gap settings which is caused the shoe to hit the bell with too much force. Also, i have some issues with the clutch where I have to rev a few times in order for the car to start moving. I assume the clutch spring is too tight. FYI: This is not a one-way bearing issue because the i can see the pinion is not moving until i rev it a few times. In either case, the settings i have are wrong.

I was hoping someone could verify if I am understanding things correctly:

Clutch gap is 0.7 mm
End Play is 0.05 to 0.15 mm
Clutch spring preload is 0.8 mm (distance between top of the clutch nut and top of the flywheel nut)

Clutch gap is the max distance between bell and shoe.
Endplay is the minimum distance between bell and show.

Is the above correct?

Also, the book stays to set the clutch gap to 0.7 mm before setting the endplay. Then if I set the endplay to 0.1, does that mean the clutch gap ends up being 0.6?

Any help would be appreciated!

Thanks for the info. The brass or ceramic ring looks like the way to go. Where do I get a brass or ceramic ring like that? I can't find any brass or ceramic shims, rings, etc on amainhobbies.

As for the gaps, in the manual, its says to set the clutch gap to 0.7 first and then the endplay to 0.1. When I do that I always seem to end up with a gap of 0.6. I guess i'm doing it wrong. So do I set the endplay first and then check to see how much the bell moves forward and aft to make sure it is only 0.7?

Also, if I use a brass ring and set the gap to 0.6, will i have issues?

How do you measure the 0.6mm gap when all is shimmed out?

With a gap of 0.7 and an endplay of 0.1 your gap will be 0.6-0.7. Probably when you have shimmed it al you will tighten the nut what can result in a tiny bit smaller gap but still within tolerances.
When mounting a new shoe it is OK to use a gap of 0.6, the first run will re-shape the shoe and start some surface wear it will create automaticly a gap of 0.7.

I have found these brass rings in the hardware store between the brass nuts and bolts, so far no issues with it than only they are about 0.5mm smaller. Ceramic you will not find but if you know someone with a lathe you can purchase a piece of real bearing bronze or ceramic and make some rings. For sure you will never have a failing thrust bearing again
When using a ring then do not use the zero endplay setup. The endplay with it is less critical, just be sure the clutchbell is not touching the shoe.

Hey Roelof, Thanks a bunch for helping me!

I check the gaps using one of two ways:
1. Using a digital caliper like shown in the serpent video on youtube.
2. Using the hudy tool shown in the manual.

In both methods I follow the direction of the manual where I remove the internal bearing and 5x7x0.5 shims that sit between the larger internal bearing and smaller internal bearing. I leave the smaller bearing and thrust bearing. Then put the bell back on. When I use the caliper, I will push the bell forward away from the shoe and then set the caliper to 0.00 mm. then move the bell back towards the shoe and then look at the caliper reading. This will tell me the current gap. Then I will take the shims I need and measure it with the caliper to make sure the reading will be 0.7. Then I will put the shims outside of the thrust bearing and then check the gap again until I get as close to 0.7 as possible.

When I use the Hudy tool, I will do it like the book says. But because the tool only measures between 0.4 and 0.7 mm and the gap is usually larger than 1 mm, i have to guess how many shims to put in there. There is a lot of trial and error using this tool. But it still gets the job done. After I put the shims in front of the thrust bearing I will check again. Once I get 0.7 or close to it, I will install the internal bearing and the 2 5x7x0.5 shims. Then install the bell with the smaller bearing and thrust bearing.

The biggest issue I have is once I install the internal bearing and the two 5x7x0.5 shims, the gap is no longer 0.7. It actually becomes between .5 and .6. According to the Hudy tool, the gap is larger than 0.5 but smaller than 0.6. It is definitely not 0.6 or 0.7.

I think I am following the direction correctly. What am I doing wrong?

Also, I went to Osh and Home Depot today but no luck finding the 10x5 brass ring/washer. I found some brass washers but one had the right size hole but wrong sized washer diameter. The other has a hole that was too small but the diameter was correct. In any case, no luck. I found brass washers for an HPI Savage 21 that were 5x10x3mm. I"m not sure if the 3mm is the thickness or hole size. Will this one work?

I'm going to go test out the car at the Rose Bowl to see if there is any difference in how the clutch engages. I will let you know how it goes later tonight.

I ran it at the bowl and it was much better this time. When the car was cold 118 degrees, it would take a few revs for it to move. This is the norm for me. In the past, it did this when it is cold. If i let it idle for a few seconds after it is warmed up, it still requires a few revs to move the car. Today, after it warmed up, the car would just move when I hit the gas. So it was definitely better. I'm still not sure if 0.55 mm gap is ok. I can't reduce the endplay further as I didn't put any shims between the flywheel nut and the internal bearing. I could remove some shims from the thrust bearing side but that would cause the gap to be greater than 0.7 when setting the gap initially. What do you think?

On a side note, my buddy had his XO-1 with him today. I couldn't resist doing a speed run with the xo-1. We ran 10 times and he beat me 10 times obviously. actually I won one time when he flipped his car. But in each race, i actually took him on the jump and stayed ahead until my second gear hit the top speed. then the xo-1 just pulled away after that and didn't look back.

The gap is no science. A larger gap will give a more agrassive clutch and a smaller gap a mild clutch. Within 0.1mm tolerance The spring tension will have a larger role in how the clutch reacts.

Got it! Thanks man. I'm going to try this new setting out on the new thrust bearing which should arrive Friday. We'll see how long this one last with these settings. The last 2 bearings only lasted 2 gallons of fuel combined.