NC21 cooling system

[spikenipple]

My NC21 doesn't have an expansion tank, is this normal?

[Neosophist]

My NC21 doesn't have an expansion tank, is this normal?

No it isnt.

Where are you looking for it? It should be on the rear of the bike under the rear plastics

[spikenipple]

This bike has been used and abused as a track bike before, and doesn't have the original rear subframe or plastics. The subframe is a total bodge job, so clearly room wasn't made for an expansion tank, or the reg/rec, indi relay and even the starter solenoid. There's no room for anything really so it's all sat above the rear cylinders currently.

I'll have to have a look at the routing of the cooling system and work out where I can fit a tank back in then!

[spikenipple]

Coolant route is pump>rear block>front block>thermostat>rad>pump
The rad has a small hose coming out from just below the cap, which is routed to the right hand side of the swingarm and left open ended, so any expansion is wasted basically.

[Neosophist]

Coolant route is pump>rear block>front block>thermostat>rad>pump
The rad has a small hose coming out from just below the cap, which is routed to the right hand side of the swingarm and left open ended, so any expansion is wasted basically.

thats bizzare.

i think youll find originally that open ended pipe went to a small bottle somewhere as all trackbikes need a catch tank.

if its an abused track bike its probably going to cost way more than its worth to put it back to half decent condition considering how cheap you can pick up a 21 for

[spikenipple]

I'm not trying to get it back to pristine condition; it's a fun little project bike to go alongside my VTR1000 road bike. I intend to get it roadworthy and reliable, then put a daytime MOT on it and use it as a weekend bike and track bike. I've got it running nicely now the carbs are set up (thanks again for your input on that) but there are still many things left to do.

Do you know where the expansion tank was originally plumbed in, with regards to the actual pipe routing? Will I get away with just fitting a small catch tank on the pipe coming from the rad?

[Neosophist]

I'm not trying to get it back to pristine condition; it's a fun little project bike to go alongside my VTR1000 road bike. I intend to get it roadworthy and reliable, then put a daytime MOT on it and use it as a weekend bike and track bike. I've got it running nicely now the carbs are set up (thanks again for your input on that) but there are still many things left to do.

Do you know where the expansion tank was originally plumbed in, with regards to the actual pipe routing? Will I get away with just fitting a small catch tank on the pipe coming from the rad?

Yes that will be fine, it will also be the cheapest.

The plumbing on your coolant system hasnt changed, they've just removed the rather large expansion tank and replaced it with a small bottle.. fruit shoot / ribena bottle / small size baby bottles are durable and work fine.

Coolant runs from water pump to rad to engine in a loop, theres a small spigot just under the cap that is the expension bottle, this just runs to the expansion bottle :) stick a little coolant in a fruitshoot bottle and tie it up somehwere, so long as you dont sit idlign for a long time it shouldnt over-heat.

if its a trackbike check it still has a fan and that it works..

[spikenipple]

Interesting. Every coolant system I've seen (usually cars, when they go wrong!) loops the coolant back into the system through the expansion tank rather than just catching it. By 'tie it up somewhere' do you mean have the bottle as the highest point of the system, so any coolant caught in it runs back into the system when it's cold?

[Neosophist]

nearly all bikes work this way.

the original coolant bottle has a minimum fill line on it. the expansion pipe enters from the bottom of the bottle so is always covered in fluid, this way when the bike cools down an sucks back in some coolant it can never suck air in.