SUZUKI DR600
Paul Berryman and a cam-chain masterclass.
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
pins, which naturally have peened ends. The side plates have an interference fit with the pins, and they never move in relation to each other, thus the side plate/ pin relationship never suffers from wear. However, where the inner plates rotate around these pins, wear occurs. When this happens, the claws, which engage with the sprocket, develop free play. The play in each pin is tiny (see pic) but when this slight difference in working pitch accumulates across the entire chain, the cam timing goes out and will stay out. Applying tension to the chain doesn’t rectify the cam-timing issue it just keeps the chain in contact with the sprockets/ gears and stops it jumping. Once Tony had split the old chain, he weaved a split pin in between the old and new cam-chains, carefully pulled it through and joined it (see series of pics showing this) Once we’d shared a period of marvelling at the fact that our fingers could no longer move/twist/rattle it off the cam sprocket, Tony set about looking at the cam-timing. It didn’t take long before something very new and exciting became completely apparent – the cam timing was now absolutely cock-on! The amount of tensioner adjustment that I didn’t need was also apparent – it had taken a full three minutes of delicate 1/6 turns to back my manual tensioner off fully before the chain swap, but it took seconds to wind it back to the right tension – it was incredible to see the difference (see pic). The valve clearances needed doing, which Tony always does when he puts a new cam-chain in, and then it was a case of buttoning up the motor. On the third kick from dead cold the engine came to life, and thumped away perfectly – Tony was surprised I didn’t think it was any less rattly than before, but oddly I wouldn’t ever have described the cam-chain as noisy, which is alarming given how bad it was! To quantify just how bad it had been, I asked Tony on a scale of 1-10 how bad the DR’S chain had been, 1 being brand-new, 10 being the worst he’d ever seen: I scored an 8 – wow! And yet I hadn’t heard a peep out of it – maybe that’s just my un-tuned ear, or maybe it’s a warning to all of us that cam-chains aren’t simply going to tell you they need replacing through audible cues, whatever any buyer’s guide may say. A long test ride was out of the question on the local rush hour roads but a quarter mile blast up the lane told me something very different was happening inside my engine – a twist of the throttle in first was finally yielding air under the front wheel – shouldn’t a 600 single always do this? Well, believe me, it hasn’t been. Even standing still the power pulses of the engine felt different as I sat on the bike – this was good! Tony’s bill was almost as pleasing – £199 for a job that would otherwise have needed the engine taking out and completely stripping, capped off a good day’s work on the old girl. He comes highly recommended on every front – thanks Tony! What next? Well, with great hopes for bags of new found power it’ll be back to the dyno for the next and hopefully final instalment of curing this DR’S ailments. I’ll try some re-jetting and a free-breathing silencer to cap off the hunt for extra bhp. Fingers crossed, we’re almost there. We think… cmm
Thanks to Tony Galea of Galea Camchain services based in Essex. Tony hasn’t got a website, but he has telephones (and answers them too). Call him on 07860 152188 or 01268 735355.