Rear split sprocket fitting problems (Clubbie)

[dunc_sx]

Hi guys,

Hope everyone is starting to have fun playing in their cars in the nicer weather?

I'm having problems with tight spots on my clubsport, I previously used a single rear sprocket (not split) but moved onto split sprockets this year for easier swapping. With the split spockets I've had a tight spot around one half of the sprocket, what's the technique to tightening the two halfs of the sprocket in place? I have been tightening them with the chain in place to maintain the correct spacing between the teeth, any tips on a better way to prevent/minimise a tight spot?

I purchased a new sprocket from R to rule out the other sprocket but it has been the same. At the previous event I just had to back the tension off to prevent excessive tightness during the tight spot phase.

Massive thanks for any help,

Dunc.

[Josh Smith]

How much of a tight spot is it?

We always check our chain tension in 3 places, and it fluctuates between 0.5" to 0.75" play in the chain.

Josh

[dunc_sx]

Hi Josh,

Loads more than that, sprocket aligned.

[paulmj]

The bolts are actually academic for alignment. The alighnment (on the diff not the chain alignment) is as a result of the R sprocket fitting well on the R diff flange. Make sure that the chamfered edge is facing the correct way though. It can only really sit in one place and that will result in tooth alignment - I don't recall any gaps between the halfs when installed. Best to check the chamfering.

That said, the first time I had to fit the largest sprocket (for Lydden as I recall) I found that the diff wouldn't move forward far enough to allow the tension to be set correctly. In the end I filed the slots a little to give an extra mm or two.

Hope that helps....

[dunc_sx]

Cheers for that Paul, it's a fair point about the chamfer but I always mount the chamfer on the diff side, think they are just there to clear the rad on the diff flange?

Cheers,

Dunc.

[splitpin]

Given that the tight spot extends about 50% and you'd be unlucky to have bought two lots of duff splits, wonder whether the old non-split rear sprocket was set up for a different chain pitch? Obviously if you changed the chain when you changed the sprockets that would probably rule that out - so said, I'd still have a look at (and almost certainly replace) the front sprocket - obviously, the contact area length is much smaller on the front sprocket and I dare say it'd could initially drive more than one particular pitch, but slowly and surely beggaring it up for the later fitment of the correct pitch in the process?

[dunc_sx]

Hi Trev,

Appreciate the help, here's some more details. The single rear sprocket was bought by me and is std pitch as is the chain (also new). I don't think it's the front sproket and the reason for this is the tight spot develops once every revolution of the rear sprocket, in fact it seems to go slack for one half of the revolution and tighter on the other.

It was the same for both rear sprockets - the unknown and the Radical new one I have just fitted. It sounds like I'll have to spend a bit more time examining it to find out what is causing this. Radical recommended tightening the sprocket bolts with the chain up to tension, I could easily do this by backing of the bolts with it how it is just now and retighten them.

Thanks,

Dunc.

Edited by dunc_sx on Tuesday 10th May 14:28

[splitpin]

Just to see/because I was interested anyway, I've just opened up two new unused genuine Radical split rear sprockets.

It's clear that (as one might expect) they are machined as a single unit and then 'sawn' split at the end. That loses about 1mm of material and hopefully as a way of helping you get it right, I've figured out by fiddling that the design pitch can be corrected/replicated back to the original pre-split by inserting a credit card to each saw cut.

So said, I find it difficult to think the rear sprocket itself is your problem; the Radical items are well machined and the scope for it being that much out of kilter seem very small indeed - the only real scope I can see is that two of the holes (one in each half) are oversize compared to the others, presumably being the peg holes that they use to secure the single piece blank to machine it.

[BertBert]

It's a bit embarrasing to ask having had a clubbie for a few years, but when the two halves are bolted up, how is that "saw's width" gap maintained to make the sprocket round?
Bert

[splitpin]

I guess because the supreme accuracy of the holes and fit of the bolts is to Swiss Watch standards ............... which is why I'm minded to be using (perhaps a developed version of) a couple of credit cards .......... hopefully a couple belonging to SWMBO?

[Martin B]

I bought a new rear sprocket from the big R recently and fitted it to my clubbie with a new chain and a new front sprocket, also had a tight spot much more than normal. I ended up just making sure the tight spot wasn't too tight and used it like it expecting it to bed in a bit. Did 2 races at Combe (last meeting) like it no problem and will check it all before the next one as usual.

[BertBert]

splitpin said:

I guess because the supreme accuracy of the holes and fit of the bolts is to Swiss Watch standards ............... which is why I'm minded to be using (perhaps a developed version of) a couple of credit cards .......... hopefully a couple belonging to SWMBO?

So is it possible to measure the diameter of sprocket when attached to work out whether it is round or not?

[splitpin]

BertBert said:

So is it possible to measure the diameter of sprocket when attached to work out whether it is round or not?

Both the unused ones I checked out were very round and consistent in terms of what was missing as a result of the 'saw cutting': to make sure it stays that way 'of itself' (because I don't have every tool under the sun), I'd be using permanent marker alignment lines and those credit cards. Once it's on (still round and apparently right in the middle), if I had Dunc's problem (again because I don't have every tool under the sun), I'd then be 'string checking' for any difference in dim from the centreline of the front sprocket shaft to the rear sprocket chain seats on the same axis at various points around the rear sprocket's circumference.

I'd also check the 'quality' of the bolts and indeed the holes they go through relative to the rear sprocket and diff; with 500G forces involved in the area, I'd want to be sure a previous owner hadn't run it loose sometime, launched it hard and 'stretched and bent' stuff.

As I still think that it could be front rather than rear sprocket related, I'd also want to watch the front sprocket going round under gentle drive and without the chain to see whether there appears to be anything going amiss with that.

[dunc_sx]

BertBert said:

It's a bit embarrasing to ask having had a clubbie for a few years, but when the two halves are bolted up, how is that "saw's width" gap maintained to make the sprocket round?
Bert

I thought it might be to do with the hole in the middle of the sprocket, much like a wheel centre bore on a hub (the wheel bolts should only clamp the wheel in). The diameter should closely match the diff diameter. The R ones seem to match in this way well (better than non-R ones) but the reality is that it's not going to be perfect, I've heard of people using a couple of washers much like Trev's method with the credit card.

I've examined the car further tonight (for much longer than I would have liked) and my findings make little sense, the tight spot does not appear to be linked to the front or rear sprocket revolutions as I first thought. It appears to be more like every SECOND revolution of the chain the major tight spot comes round. I realise this isn't really possible, only thing I can think of for now is that the front sprocket isn't even and neither is the rear and on occasion they both meet at the worst case point. Every second rotation of the chain is strange though, on every other ration (of the chain) a lesser tight spot appears.

Martin, I ran two races like this as you did without any major problems but with 3 races due this coming weekend I'd like to fix it if possible, failing that it will just be set as before. It does seem to be more severe than what I'd expect to be the norm for this type of thing.

Thanks for all the advice keep it coming, don't cars drive you nuts sometimes?

Dunc.

Edit: The diff does not seem to run out in any way

Edited by dunc_sx on Tuesday 10th May 22:42

[SportsLibre]

The tight spots are usually due to the chain wearing unevenly (as they all do) however you said it is a new chain so it is unlikely but not completely out of the question that it is the chain. Check each individual link for tightness.

More likely given your descriptions is the alinement of the rear sprocket to the front.
This is both that the correct side shims are in place to ensure longitudinal directly behind the front and equal spacing on the length adjustment to ensure true running in line with the front sprocket, look for the chain "wandering" from side to side rather than running central on the sprocket teeth.

If you have really checked all the possible alinement then it can only be the chain.

Personally have not had any problems other than the chain getting a bit worn (eventually, after a couple of seasons), but then Douglas is very particular at getting the total alinement correct every time we change the sprocket.

Edited by SportsLibre on Tuesday 10th May 23:52

[dunc_sx]

Thanks, I'll recheck the alignment, the chain was new when the split sprocket was fitted at the start of the year but it has done a couple of hours now - I'm wondering if the chain might have stretched at a section(s) causing the tight spots like you say.

Appreciate all the suggestions I'll take them all into account and I'm sure I'll get to the bottom of it, or replace them with spares.

Rgds,

Dunc.

[stiglet]

Duncan

This may seem a silly question, but what chain are you using?

Cheers -JP

[dunc_sx]

Hi JP, it's a DID x-ring 530, few months old.

Dunc.

[splitpin]

dunc_sx said:

Hi JP, it's a DID x-ring 530, few months old.

Dunc.

Not a Made in China replica off the E is it?

(I hope I'm) Only Joking

[stiglet]

dunc_sx said:

Hi JP, it's a DID x-ring 530, few months old.

Dunc.

Is it the "super heavy duty version"? (ZVM2 from memory)

The one that was on your Clubbie when you got it was one Angus gave me when mine broke at Golspie. It's the kind he uses and certainly lasted the rest of the season in the Clubbie with no issues. I bought another exactly the same as a spare

When I got my Prosport I snapped the chain at one event and replaced it with abovementioned spare. It stretched beyond use within 2 events. I fitted another - it stretched at the first Hillclimb(and Douglas had checked my alignment!). Turns out that the original chain was not broken as such but the soft link had come apart. I put in a new softlink and used it for a full season.

The original chain was the super heavy duty one - the others weren't

Cheers
JP