Kids hotrock 20 - replacement parts

The Rookie

If you look at your races you'll see they are curved to match the balls, as are the cups, how would a cartridge bearing fit in that?

danlightbulb

Oh i see what you mean now. Ill have a look at the races later to see if they are curved. Not sure which part the 'cup' is?

Going for loose balls is going to be really fiddly isnt it? Dont know where to get loose balls from or what size i would need.

The Rookie

Loose balls are not fiddly at all, put grease in the cup (the erm, cup shaped bits pushed in the frame) and put in the balls (as many as will fit) stock size and available from your LBS for peanuts.

No point looking at the races and cups, they will be curved. the races and cups match the bearings, just fit new balls in a decent grease and assemble correctly.

Chunkers1980

loose balls are more fiddly than their caged counter parts whatever way you look at it. How much comes down to your skills and experience.

The Rookie

Agreed, but the cage is the weak point and its an inferior solution, its used for production for convenience and cost (less relatively expensive balls).

danlightbulb

Im getting a bit confused with terminology. Are you using cup and race interchangeably? I thought the bit pushed into the headtube top and bottom, what the bearings sit in, was the race.

I dont really have a local bike shop, tend to buy everything online. Will the loose balls be bigger than the ones currently in the caged bearing?

Chunkers1980

No same size, just you'll need more to fill that void of where the cage was

jimothy78

danlightbulb wrote:

Im getting a bit confused with terminology. Are you using cup and race interchangeably? I thought the bit pushed into the headtube top and bottom, what the bearings sit in, was the race.

no, those are the cups - the races are the outer pieces that run on the bearings. The lower one ("crown race") is pressed onto the forks' steerer, and presses upwards into the lower bearing when the fork is fitted. The upper race is usually one of the topmost pieces of the headset. Both will have a distinctive concave cross section (like a 1/4 circle) and should be smooth and polished unless the headset's been neglected.

If you're familiar with cup-and-cone wheel bearings, then the pattern is the same - cups on the inside, cones/races on the outside.

danlightbulb

There is a new potential problem. Although I haven't fitted it yet because im waiting for the crank puller to arrive, it looks like the new islabikes crank arms (both sides) will foul the chainstays. This is because the original hotrock crank arms 'splayed' out alot more than the new islabike crank arms, which are much flatter, if you know what I mean.

Obviously a critcial issue, what will be the solution for this please?

cooldad

danlightbulb wrote:

There is a new potential problem. Although I haven't fitted it yet because im waiting for the crank puller to arrive, it looks like the new islabikes crank arms (both sides) will foul the chainstays. This is because the original hotrock crank arms 'splayed' out alot more than the new islabike crank arms, which are much flatter, if you know what I mean.

Obviously a critcial issue, what will be the solution for this please?

Correct size BB.

See below

cooldad

cooldad wrote:

The sockets are thinner - my normal socket set won't fit. But generally the cranks won't come off easily, hence the need for a remover. You can whack them a bit, or ride with the bolts loose and they should come off. Stuffs up the taper but if you're chucking the cramk it shouldn't matter.

The Ilsa bike crank should fit, you might need to use the matching BB as well to get the right chainline.

danlightbulb

If i fit a wider BB then my chainline is being pushed out to get the crank clearance? From what I can see by offering up the parts I'm going to need at least 10mm more width if not more. This looks like its pushing the chainline to the smallest rear sprocket.

It looks like his feet are going to hit the chainstays too, if I only get marginal clearance, because the chainstays continue to splay out as they go rearwards.

cooldad

Looks like the cranks aren't compatible with the frame then.

danlightbulb

You guys said they would fit, Ive spent £35 on these.

Current cranks from above:



And showing the isla crank underneith:

The Rookie

I hate to state the bleedin' obvious, but if the chainwheel fouls the chainstay its further in, so pushing it out will mean the same chainline as before! Will have a slightly higher Q-factor though.

Giraffoto

The crank axle (on ours at least) is surprisingly long - it's what you'd expect with a triple. I'd not considered why it should be like that and just replaced like for like, but now I see this it's clear that the chain stays (tubes between the rear hub and bottom bracket) have to flare out as much as they do on an adult sized bike but over a considerably shorter length. This in turn means that the cranks have to be pushed outwards to clear them.

danlightbulb

The Rookie wrote:

I hate to state the bleedin' obvious, but if the chainwheel fouls the chainstay its further in, so pushing it out will mean the same chainline as before! Will have a slightly higher Q-factor though.

The chainring isnt the problem, i think that would end up in the same position with the current bb. The problem is the crank arms. Look how the hotrock crank arms flare out to clear the rollers and chainstays, where the isla cranks are very parallel to the chainring itself. Its the crankarms that are going to foul the chainstays.

The Rookie

Argh, understand now, looking at it the effect on the chainline will be very small though as the current arms have massive clearance?

danlightbulb

The Rookie wrote:

Argh, understand now, looking at it the effect on the chainline will be very small though as the current arms have massive clearance?

They have over an inch clearance from the chainstays at the ends of the arms, but the chainstays continue to flare out going towards the rear of the bike.

How much clearance do i need to allow for between the new crank arms and the chainstays whilst making sure his feet dont hit the chainstays either? Can i get the adjustment i need through a wider bb, given that the widest bb i can get will only be about 6mm wider on that side than the one currently fitted (113 vs 127)?

The Rookie

Too many variables to know how much you need, for example what is his foot positioning like on the pedals.

danlightbulb

Phew! Thankfully its not as bad as I thought it would be.

Here is the drive side crank and non drive side crank:


Now these have not been fully tightened yet, they are just pushed on. How much more will they move in once the crank bolts are fully tightened? If its a few mm then I'm going to need a wider BB.

jimothy78

They'll move 1-2mm at most, I'd have thought, if you've pushed them on 'til they stop already. To be honest, that's as much clearance as a lot of adult bikes have - a miss is as good as a mile.

danlightbulb

Its gonna be very tight. Should i just go for a size or two bigger on the bb anyway now? Its a 113 at the moment the next size up is 118 and 122.5 after that. The 118 will only give me 2.5mm extra each side and the 122.5 will give me 4.75mm extra each side.

its a caged ball bb with a bit of play so i was going to replace it anyway.

The Rookie

Tighten them up and see, one of my frames only has about 3mm clearance each side....if its less than that consider one size up!

dirkpitt74

Can I ask where you got the crank set from?

danlightbulb

Islabikes spare parts dept.

its not lighter though. The whole thing weighs almost exactly the same as the cranks, chainring and chainguide/ roller system that was originally on the hotrock.

but will still get the benefit of the lower gearing for my lad.


Are the VP brand of cartridge bottom brackets ok? Halfords have a 68x118 for £9.99.

The Rookie

VP are good, yes, but you can get Shimano for less that that, try CRC and ebay.

danlightbulb

Yeah i know i can get shimano for the same money but i want to finish the bike off tonight so the vp in halfords is a stock item.

The Rookie

I can't see a hotrock rider giving it a hard life, and VP are good anyway, go for it!

danlightbulb

Its completed! Really happy with how its worked out. Thanks for all the advice. I did get a bit worried about the cranks at first, and the chainline could be slightly better, but overall Im happy. Look forward to the lad seeing it on Friday.

It weighs in at exactly 10kg (22lb). 2.1kg heavier than an Islabike, probably mostly due to the fork, which does at least move nicely now.