SUZUKI DR600
Paul Berryman and a cam-chain masterclass.
Can an in-frame cam-chain replacement help CMM’S DR finally flex its muscles?
This month the search for oomph from CMM’S mega-thumper deepens still further. Finding just five of the missing 13bhp we’d been looking for on our 1985-vintage DR600 after a major engine refresh was not a decent outcome. Although the new 1mm oversize piston into a fresh bore had seen power go up from 27 to 32bhp the bike had failed to produce what could reasonably be expected: I still coveted the idea that we’d get somewhere north of 35bhp. Suzuki’s claim of 45bhp when new meant using time-honoured ratios of claimed vs real-world bhp, even as high as 40 ponies might be possible. So, work to do. One important thing the top-end refresh had proved was I had inherited a bike with a significant cam-timing issue, and by the end of the top-end refresh I hadn’t done anything to cure it (this being in spite of fitting a new manual tensioner). My cam-chain had used up ALL of the OE tensioner’s travel, and used 99% of the replacement manual tensioner’s adjustment too – the manual adjuster was supposed to be the fix, but it didn’t change anything. All the clues were there for me to realise what I really needed more than new ways to put tension in the old baggy chain was a new tight chain. I should have changed it, I didn’t – the trade-off for that piece of frugality was sticking the bike back together with the cam-timing still nearly half a tooth off of the ideal. My reluctance to change it had only been because of an implied need to do a full engine strip; OE cam-chains are usually supplied endless and thus need to be looped around the crank and through the chain gallery with the crank-cases split asunder. That wasn’t going to happen to the DR, as it’s a repair that could have ended up being somewhat more expensive than the bike!
What I hadn’t realised at the time was that an ‘in-frame’ split link cam-chain replacement isn’t quite the dangerous and half-baked repair that many would have you believe. In fact, I found a man that made a living good enough across the last 30 years to raise six kids from doing just that very thing! Cue a visit to Tony Galea Cam-chain Services in Wickford, Essex. I had seen Tony’s name somewhere online recently, and had a moment of instant recall of his ‘Tony Galea in-frame cam-chain replacement’ adverts from the 1980s’ magazine small ads. I found an email address somewhere (he hasn’t got a website, good on him) pinged him a mail, and very quickly got a reply back. He cheerfully suggested an in-frame DR600 replacement cam-chain wasn’t going to stretch (ha!) his considerable experience very much, and that I could get it done for somewhere around £200 all in. The DR was packed into the rusty but trusty Visorvision T4 and rolled across to Tony’s basic but welcoming rural workshop in the Essex backlands. There are some things that give immediate comfort when you meet someone you don’t know and when it turned out pretty quickly that Tony not only loves motorbikes, but he loves the same kind of motorbikes that we do here at CMM, so I felt right at home. A nigh-on mint 1986 GSX-R1100 slabby, a GPZ750 Turbo in the same nick, a Z650, a well-used Kawasaki ZX-6R and proper ratty 1986 N1 YPVS made up just part of the metal menagerie on show. None were customer bikes, they were all his. He reckons if he didn’t have another customer turn up, he’s still got two years of work to do on restoring his own stuff. Cool! Coffee and chit-chat gave way to the day’s task of re-cam-chaining the old DR. It came apart easily enough as it’s only been together for about nine months since the top-end was completely refreshed. First off was looking at the condition of the old cam-chain. Even wrapped around the cam sprocket, Tony was quite clear it was ‘Donald Ducked’. It was as he explained the various ailments of my sloppy, twisty, slack cam-chain that the next pearl of wisdom about cam-chains slipped out: cam-chains don’t really stretch, they wear. Mmm. The difference is subtle but important. The modern cam-chain is a multi-plate item, with side plates holding the whole thing together and inner plates with ‘claws’ which grab onto the sprockets and do the work of transferring the force from crank to camshaft. Holding this little ensemble of plates together are the