Flat Tank Frame Repair

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tribonnie
Posts: 1
Joined: Sat Sep 06, 2014 6:30 pm

Flat Tank Frame Repair

Unread post by tribonnie » Sun Sep 07, 2014 10:38 am

Hello all, have recently purchased a reasonably complete 1927 flat tank Royal Enfield. Frame is complete but quite badly pitted. Anyone know of a UK based firm who can restore this type of frame, will need some new tubes fitted and some new parts made. Thanks .... Richard

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gautrek
Posts: 54
Joined: Mon Oct 22, 2012 11:19 pm

Re: Flat Tank Frame Repair

Unread post by gautrek » Sun Sep 14, 2014 11:19 pm

Try these mate.
I haven't used them but have seen a favourable write up in the panther owners club magazine

http://www.vintagechop.com
1937 350cc Red Panther trial bike
1975 650cc Ural outfit(http://www.russianbike.co.uk/)
1983 R80 BMW.

coming soon a 1938 model 85 350 cc Redwing Panther(when I get it rebuilt)

Rick Parkington
Posts: 511
Joined: Mon Feb 23, 2009 1:21 am

Re: Flat Tank Frame Repair

Unread post by Rick Parkington » Fri Dec 22, 2017 1:10 pm

Bit late to reply to this, but seeing as I'm here...
Bad pitting on a vintage frame is probably much less risky than having repair work done. My fist flat tanker was very badly corroded having been built up around a frame/forks found rotting outdoors (it cost me a tenner in 1984 so you can guess how good it was!) The only issue I ever had was the fork spring breaking while crashing over a field on a rally. The frame was decidedly on the piss (after riding behind it an American mate described it as 'looks like a dawg runnin' down the road'. When I came to straighten it (cold) it took an almighty amount of force (2 of s with prybar and scaffold poles) and it was obvious that although badly corroded and pitted, it certainly wasn't weak.
On the other hand... I have heard about re-tubed frames letting go, the whole front end coming off. The only way to remove an old tube is to saw it off and then bore the rest out of the lug, which usually means dismantling the whole frame and starting again. You can't simply melt the braze and pull out the affected tube because for one thing it is pinned in place and for another you can't get enough heat into the joint from the outside to melt the braze inside. There is a huge danger if you try, that the iron lug will have to be so hot that the braze will alloy to it creating what I believe is known as an 'admixture' and turns the iron lug into a brittle piece of scrap. Having bored out your lug you need a very wide flame that will heat the entire joint - my mate uses an oxy propane 'roofer's torch' which gets the whole thing glowing; remember these frames were made in a brazing hearth, the tube was covered in spelter (braze shavings) before insertion and the whole lot was heated red hot all over. Just the same as trying to solder with too small an iron, trying to move the heat around with a pencil flame is just not going to work. Although (and this is where it all goes badly wrong) you can end up with a lovely neat meniscus of braze around the joint that looks very professional, this is probably all that's holding it together and having the front of your bike fall off on a bumpy road is much worse than a broken frame tube which generally just results in rubbery steering. A mate of mine once had a Bantam that suddenly felt very odd and seemed to drooping, rising again when he put the brake on to stop; at which point he found the front downtube snapped through.
On a vintage bike you are unlikely to be travelling at 100mph and trying to bend the frame pulling down from high speeds with twin 4 pot calipers. If you leave the frame as it is but paint it, just inspect it regularly. The twin top rails are unlikely to give too much trouble, there being two of them, and I think the top one takes the most load. The front downtube does the most work so pay a bit of attention to that.
No disrespect to the guys recommended, they may well be able to undertake the work but just worth mentioning that it is not something to be taken lightly and in my experience at least may not be as necessary as it seems.
Cheers Rick

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