Hi DJ, 

I would suggest that the only hope would be Bantam John who may have a few Trail Bronc parts knocking around. I spoke to him a few years back and he said that he had a stock of D7 Trail Bronc and D7 Trails parts but that there was little demand for them.  There are people out there who can make sprockets to order but I don't know who. 

If you do manage to locate a 80T rear sprocket then you will also need the stock D7 Trail Bronc chain tensioner that forms a part of your new rear brake bolt. The wearing part is simply an A65 primary chain tensioner pad, its the bolt that is special and just a bit trick.  If you do not fit this you will wear away your bottom frame fittings and it will sound like a bag of spanners.      

I have a genuine West Coast trail bronc (liberated from Washington State USA), here on std 14/80 final drive and it is definately out of gearing on tarmac.  The trouble with the std D7 engine is that it hits the top of its power band at about 5700rpm and after that there is not much left.  This gets you to about 35mph before you run out of gears and power.   I can vouch that a std trail bronc in good shape with 14/80 gearing will carry a pillion and a load of camping gear up a 1 in 4 slope (just) but it makes a lot of fuss.      

The Trail Bronc also has a modified gearbox oil seal holder to accommodate the smaller gearbox sprocket and the 14T sprox. So you need to think about that as well. 

My suggestion would be to consider running it at 15/58 which will give you a good on (or off) road compromise and avoids the need for the chain tensioner and the oil seal holder. 

If, however, you are determined to run it on 14/80 then let me know, I could be talked into getting a few copies of my spare original chain tensioner bolt made up for sale (at cost) to club members.  SpacedMarine said he might be able to run some up on his lathe. A few club members have expressed an interest in this part and have either not been able to obtain one or have given up. 

As an aside, I spotted a box of trail bronc parts at an autojumble in Garstang last year.  The vendor said he had been carrying them for years but nobody was interested as he and they didn't know what they were. I did though.  I offered him £12 for the box and its contents and he bit my hand off.  I came away with some folding footrests, a spare chain tensioner and a host of those little miscellaneous bits that make a Trail Bronc unique amongst Bantams.  As I was walking away I noticed that he also had a TB frame with the tell-tale D1 forks and a good rear mudguard, I had no more money so had to walk away but it shows that there are parts out there. You just have to look carefully.  If you are serious about this build then PM me your mobile phone number and I will keep an eye open for parts when the autojumble scene gets going once more.  If I spot something I will let you know.  

Otherwise good luck and sorry to have been so long winded. 

Sponge