Play in RCM Losi 8ight mount
 

Hey guys, I need some help. I bought the RCM motor mount to convert my new 8ight 2.0 Race roller but after install I noticed some play in the center diff, i.e. I can move it slightly back and forth (approx. 1.0~1.2mm of play), is this normal at all? what can I do to fix this?

I also noticed the center shafts angle up a bit and the "front center" shaft end dog-bone or whatever you call it sits nearly at the opening of the center diff drive cup, is this safe to drive? if not, whats the solution?

Anyone had done a conversion from a 8ight 2.0 race roller can help out? I'd appreciate it. Thanks

Shims should fix that.

As long as there is no binding I would say the angle is fine. I think Mike has some longer drive cups if the dogbone doesn't sit right.

Everything you are mentioning is probrably the same with the factory mount "other than the height wich is not a problem".If you do decide to shim it make sure to put the shims so they move the diff. forwards.

ok so what are shims? where can I get some that would fit on this diff? where to put the shims? does it go between the flange bearing and the diff?

Can you link me to the longer drive cup? i can't find it on there. thanks

Hello PTT81,

The driveshaft angle is fine, I have 2 8ights that have the same occurance. race them every weekend and never have thrown a front driveshaft. It will be alright.

Shim are more or less high precision spacers. very thin metal donuts that fill the space where the diff moves. They go in between the bearing and the differential mounts.

Your plastic front diff mount may be worn. My cars do not have any play in that department. I wouldnt worry about it to be honest

do you know where I can get the shims that would fit the 8ight diff? I found two in the bag that looks like shims to me, not sure if these are the ones. Also my buggy is brand new out of the box so there is no worn. I think the play is because of the RCM motor mount, the stock plastic mount has no play.

So I tried the two shims I mentioned above that came with the kit and put them between RCM mount and the diff. bearing, the play is gone now, is this the correct way to do this? is this what the guys mentioned above? i just wanted to be sure I don't want to run something wrongly setup.

This is the one:
http://www.amainhobbies.com/product_...Shims-8ight-20

Shims aren't going to hurt your setup unless it binds something. I can't think of many ways to mess that up so your probably fine. Just make sure to put the shims on the back side of the diff, that way it will push the slop towards the front where you say the dogbone is not close to the cup.

thats what I did, it helped a bit, i'll post some pics later when I get a chance

I just noticed this ratcheting sound coming from the rear diff, is this normal? I hope someone know about this before I take it apart and try to fix something that may not be a problem at all. There is no binding at all, everything is smooth apart from the sound.

Before you say anything, again this is a brand new buggy and I have not mess with anything from the front or rear. I can confirm this is not coming from the center diff because I already try taking it off and the sound is still there.

Here is a vid showing the ratchet sound.

http://www.youtube.com/watch?v=taAC8r-AnRc

That just sounds like the ring/pinion gears on the rear diff. Sounds normal to me as long as it doesn't bind. If it didn't make that sound, the shimming inside the diff could be too loose. The only setups I have that don't make that sound are the ones with helical cut gears.

Whew! thought I got a bad kit or something. It doesn't bind at all, I can roll it freely by pushing it on the ground and it rolls a couple fts. So I should be fine moving to the next step? mounting electronics, etc.

Also I want to use the stock 48T metal spur, what pinion should I use? for 4S setup and CC 2200kv motor. I was gonna use the 45T plastic spur but its too wide and rubs on either RCM mount or stock mount, so metal spur is my only option and since i got the stock one, i don't want to waste it.

2200 is wayy too much motor for a buggy, I have tried that setup lol

start with a 14t pinion and gear from there

well i bought the motor new a while back so I want to use it instead of buying another motor. I also heard that the smaller CC 2650kv run hotter than 2200kv, any thought on that? What's wrong with using the 2200kv in this buggy?

i've never heard of anyone having to shim the center diff on a new build, but if it works, it's not gonna cause any harm as long as the conversion was done right.

can you maybe take a close up video of the motor mount, the center diff and the rear drive shaft and demonstrate the issue? i'd like to see exactly where the play is coming from. i have a brand new 2.0 sitting next to me and mine dosen't do that.

as far as the front and rear diffs.....the 2.0 comes with extra diff shims. the 1.0 didn't that i could remember. some drivers like to run a tighter diff setup side to side.

some drivers say it seats things better in the longrun after the diff breakin. every diff is going to shim a little differently. it's really nothing to be concerned about.

also, your drive train sounds new and perfect. like BrianG said, it's absolutely normal.

as far as the 2200, it depends on the track. right now, our points leader is winning every damn race with a 2200 on 4S hyperions geared 48/14.

i run a 2650 on 4S and i'm right there with him, he's just a better driver some days.

some people say the systems tend to run hotter that way and you ought to run a lower kv motor with it, but my temps rarely see anything over about 165-170.

obviously,if you live in nevada, then i would recommend a lower kv motor.... as running a 2650 in 115 degree weather is gonna make it run hotter than 2650 in 80 degree weather, but i've had good results on the 2650 and the 2200.

well in that case I will stick with my 2200kv and 48/14 since thats what I already have and it sounds like it is a good setup as well. I'm just a basher, no racing on track so I think 2200Kv is better for me as far as temp goes, I live in TX so its also hot here during summer.

Ok here is a vid showing the play problem. The same problem remain on or off the chassis. This has nothing to do with the front or rear shaft, just the mount and center diff itself.

http://www.youtube.com/watch?v=6biZnoiiH9U

I found that the grove where the bearing goes into is cut a little too deep on the RCM, stock mount does not have any play. May be i got a defective mount? because no one that have RCM mount seems to have the same problem as me.

EDIT: all of mine have that play in the center diff. no biggie. i've been racing them like that for a year and 2 are brand new.

i'll video it. i misunderstood what you were saying...what you have is normal.

i guess i'll leave it like that then. but I still think for quality wise, they need to fix it for future customers so at least it is like the original mount and there would be no play at all.

here you go:

http://s247.photobucket.com/albums/g...=fghfgh002.flv

Ok thanks man, i guess i worry too much, i'll finish the build now.

The 2200kv is OK if you are just bashing, but it's too much on the track :( I have the 2200 too and you need to be very smooth with the throttle. I'm going for a Tekin 1900kv buggy motor this summer and maybe the tekin ESC too.
Friends are driving the 2050kv buggy motor and the temperature is ok, but it's more controlable then the castle neu 2200.

hey pt881,

you are fine to use that 2200kv motor on 4s in your buggy. it will be perfect. extremely fast and cool temps. i have had 3 losi 8ights and ran all of them on 2200kv on 5s and even tried 2700kv. the 2200kv on 4s is a great setup.

as for the ratcheting noise in the rear...that is "ok" if there is no binding but there is a way to minimize that sound or eliminate it. those shims you used for your center diff are actually able to be used in the rear diff bulkhead also to adjust the gearing mesh of the rear diff and pinion. you can use shims to adjust the mesh just right to eliminate that noise....and get smoother power transfer. but here is the most simple thing to do to eliminate that noise:

it will require you disassemble the car so you can access the rear bulkhead. once you have the rear bulkhead open take out the diff. then remove the rear cvd from the pinion gear. now, put fresh threadlock on your set screw that holds the cvd onto the pinion gear shaft. from inside the bulkhead push on the pinion gear as hard as you can. while doing this put on the cvd and lock down the set screw with the cvd as close to the bearing and bulkhead as possible. make sure there is absolutely no play in the pinion gear to move inward or outward. now put the rear diff back in and try the engagement. notice it any quieter? this should do the trick almost every time. does this make sense? let us know if you have questions.

I'm glad to hear the 2200kv on 4s works good. That's what I have, I plan to run the 2200kv with MMM, 4s 5000mah 30C, 14/48 gear. I hate to have to buy something when I already have something.

I appreciate your time for the write up but I'm not clear as to what you said about fixing the rear diff, may a video would help, but im not going to mess with it until I run it for a while, may be the sound will be gone once the gears are worn a bit.