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|Bike Profile - Posted 28th December 2010|
The misfire is back, then it's gone again, and then the (valve seat) recession starts to bite. Martin Gelder attempts to fix one sick seventies BMW airhead by buying another sick seventies BMW airhead...
Has it really been over a year since my last update? That's the beauty of old airhead boxers, though; they just keep going. They're a bike for riding about, not writing about.
In the last episode - posted in August 2009 - I'd just fitted a Rooster Booster points assisted electronic ignition thingummy, to work around the problem of contact breaker points that were constantly pitting and going out of adjustment. It worked, keeping the bike in tune and on song between services.1977 BMW R80/7; new tyre proudly on show
Since then, I've transformed the handling of the bike by switching from very worn Continental tyres to a matched pair of Metzlelers - ME33 Lazer at the front, ME77 at the rear. Although nominally the same size at the Metzeler, the rear Continental was just wide enough to make removing the rear wheel a real chore. I ended up taking off the number plate, pannier brackets and one silencer before the wheel was finally freed from the bike's embrace by letting all the air out of it so that the tyre could be squeezed out through the gap between swinging arm and brake shoes.
In my somewhat hazy memory of previous BMWS, this had been a much easier job; undo the spindle clamp bolt, undo the spindle nut, remove the spindle, ease the wheel off the final drive splines, and then roll the wheel out. Simple. And sure enough, the new Metzeler shod wheel slotted in with no sign of the struggle I'd had getting it out while it was wearing the old Continental. A few millimetres can make all the difference, obviously.
At the same time I cleaned and greased all the wheel bearings; a tiny amount of play in them had prompted an 'advisory' at the last MOT but with fresh grease and all the crud cleaned off the various spacers and spindles they were back to their taper-roller best.1977 BMW R80/7; you can almost *hear* the improved handling.
And what a difference. The bike now rolls confidently into bends at low and high speed where before it was a bit reluctant at low speed and somewhat vague at high speed. It's also lost the 80mph waver that could threaten to become a weave if I clipped a cat's eye when changing lane. With soft and long-travel suspension, it would be hard to describe the bike's handling as precise, but at least it's now predictable and the bike can be flicked around its low centre of gravity with confidence. New tyres should be top of the shopping list for anyone with a bike that has questionable handling.
The BMW mostly gets used for bimbling, so I've fitted a set of higher handlebars from a K1100LT, bought via eBay. They give a bolt upright riding position which is perfect for chuffing along B-roads and fine up to 70mph or so. Above that it all gets a bit strained in the arm and neck department, but I still can't get on with the original equipment BMW "T" handlebar screen that was fitted to the bike when I bought it. I either need a massive tankbag, or to slow down a bit.1977 BMW R80/7, "LT" Bars
So; ignition sorted, handling sorted, riding position sorted. All smiles in boxer-land? Well, no.
Back in the spring, Mad Mike organised a gathering of the clans in a pub car park somewhere near Hinckley. The plan was for me to bimble over to meet up with Paul The Destroyer, collect A10 Newbie and Chilly at the Black Cat roundabout on the A1M, and then ride together to the pub. For the first time since I've had it, the BMW refused to start, needing a push from my girlfriend and her jockey son before it could be coaxed into life. The fact that the Destroyer's Honda CB750 also struggled to get beyond the end of his drive isn't really note worthy, but for my BMW to need a push was devastating. A bit of CSI work back at home showed that the exhaust valve clearance was 0.10mm instead of 0.15mm (4 thou instead of 6 thou, in old money). As 0.10mm is the right clearance for the inlet valve, I just assumed that I had set it wrongly when I'd serviced the bike a month or so back. Pillock.
Normal service was resumed for a month or so, until the bike developed a misfire. At low revs it was fine, but at higher revs or under load the bike would hiccup and stutter. My first thought - based purely on suspicion and prejudice - was that it must be the Rooser Booster playing up, but with that disconnected the misfire was still present. New points made no difference, new plugs made no difference, cleaning the carbs made no difference... Well, to be fair, all of these made a little difference, but ultimately the misfire was still there, and getting worse.
25 years back, my R100S had suffered similar problems when I first bought it, and these were eventually cured by the dealer grudgingly fitting new coils and HT leads. With new (pattern) HT leads from Motorworks and secondhand coils ("They never go wrong, don't buy new ones") from James Sherlock and freshly cleaned connections from points to coil, coil to ignition switch and all points in between... the misfire was still there. Which was impossible. I'd replaced virtually every component in the system.
Apart from the Rooster Booster. So I disconnected it again. Misfire, goodbye.1977 BMW R80/7 Engine. Not misfiring.
In the interests of science, I then started refitting all the old bits I'd replaced, just to see if they had been contributing to the hiccups. The old old coils were no different to the new old coils, but one of the old HT leads was definitely dodgy and the other was a bit hit and miss when the bike was fully warmed through. With the new HT leads fitted and the RoosterBooster removed, the bike was smooth perfection, so the Rooster Booster was sent back to its makers in disgrace.
Chris from ClassicGlory.com soon came back with the answer, and I quote, "After some prodding and poking your module burst into life and I found the fault. The primary switching transistor is suspended on the PCB by its own legs. We found out quite some time ago that due to vibration, this sometimes causes the legs to fracture and the module to fail. We therefore redesigned the PCB to hold this transistor flat against the board along with some other modifications to the LED circuits.
"On existing stocks of modules we flood filled the transistor in heat glue to protect it from vibration. Your board is prior to either of these developments and one transistor leg has fractured with the finest almost invisible crack I have seen. I will repair the transistor and modify the assembly to provide sufficient support. Hopefully the module will be back in the post to you on Wednesday."
It was, and it's now back on the bike and working fine. It would be easy to dismiss the RoosterBooster as having caused me hours of hassle chasing a mystery misfire, but this was compounded by a pair of failing HT leads and quite a few corroded coil connections. The electronic system was easy to disconnect, leaving me with the standard points still working, and it never left me stranded by the side of the road.1977 BMW R80/7
And with all the fiddling and fettling I've done, the bike now starts and ticks over faultlessly and pulls as smoothly as a boxer should from the tiniest throttle opening to Wound Fully Open. Well, most of the time. Ahem.
Remember the closed-up exhaust valve that gave me starting problems back in the spring? Well, it closed up again a couple of months back - causing more dodgy cold starting - and then again just before the cold snap set in. I had this theory that using unleaded fuel wouldn't cause valve-seat recession on my classics, because I do so few miles on them. I hadn't banked on the 100,000 miles my BMW had already clocked up, and my theory was wrong.
The obvious thing to do at this point would be to get the cylinder heads converted with "unleaded" valve seats, but I never like to do things by halves. Which is where my mate Chubby comes in.
I've known Chubby - through working in endurance racing - for more than ten years, and he's never struck me as the BMW sort. He's had LC Yamahas, XT Yamahas, and latterly various classic endurance racers. But not BMWs. Until he got in touch saying he'd accidentally bought an R80/7, a K100 and a trailer load of spares from a retired vicar, and "could I come over and listen to the R80 as he wanted to know if it was meant to sound *so* rattly?"
It wasn't. It sounded horrible. We dropped the sump and found some old bits of bearing shell shrapnel, which didn't bode well. Luckily, amongst the spares was what looked like a complete second engine, and as the R80 was so spotlessly clean the obvious answer for Chubby was to find the source of the rattle and replace whatever was causing the problem. The resulting bike would be a fine example of the breed, much better than my tatty old example. I was slightly envious, to be honest.
So I suppose it was inevitable that when Chubby suddenly had to find room - and cash - for a Peckett and McNab project, I ended up buying the rattly R80 and all the R80 bits in a deal which also involved message board regular JaySeaBea buying the K100.1977 BMW R80/7 on the left, 1979 BMW R80/7 on the right
Reader's voice: So let me get this straight; rather than spend £180 on an unleaded conversion of your existing cylinder heads, you've bought another non-functioning BMW and a vast but random collection of cardboard boxes full of greasy metal, at a cost of significantly more than £180?
Yes. So now I've got a shed full of sick R80s (one with a death rattle, the other eating its valve seats), a front room full (and I mean *full*) of boxes of BMW bits, and the whole winter to work out exactly what I've bought, and what I'm going to do with it...
Words and Photos: Martin Gelder
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