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|Bike Profile - Posted 7th March 2011|
What horrors can lurk in a box of boxer BMW bits, or in a boxer BMW engine? Martin Gelder is about to find out as he sets about his latest project with spanners flying...
At the end of last year I'd somehow ended up with one BMW R80/7 (a 1977 model) that was starting to suffer from exhaust valve seat recession, another BMW R80/7 (a 1979 model) with a death rattle, and a vast collection of cardboard boxes containing BMW parts that were either oily, greasy or rusty; or any combination of the three. The previous sorry tale is related here.
Plan A is to use some or all of the parts from the cardboard boxes to fix the bike with the knocking engine (henceforth known as "The Vicar's Bike" as it was previously owned by a retired Reverend) and then sell it to fund repairs to the bike with the failing valve seats (henceforth - and previously - known as "Roxanne" due to a red light incident some four and a half years ago).
Plan B - should The Vicar's Bike prove to be terminally ill - is to pinch the best bits of The Vicar's Bike and fit them to Roxanne, and then sell whatever is left to recoup the cost of its original purchase.1979 BMW R80/7 - The Vicar's Bike
But first, I need to find out just what I've bought.
The Vicar's Bike is, knackered-knocking engine apart, in very good condition. It's a 1979 R80/7, the model with the seat fairing/tailpiece and with the points ignition hidden in a 'bean can'. A year later the boxer range was revamped with electronic ignition, lighter flywheels and Brembo brakes so this is the last of the heavy flywheel, ATE calliper models. It's sprinkled with stainless steel, has perfect paintwork and has every extra known to man (or priest); SureFoot sidestand, auxiliary power socket, standard toolkit nestling under the seat, alongside it the original tyre pump. Oh, and it's got brand new tyres, a new battery and even a recent MOT. It's a beauty. Until you fire it up. Oh dear.
Perhaps it'd be better to begin by sorting out the stuff in cardboard boxes, starting with the clean stuff. There's a crate of consumables; oil and air filters still in their boxes, brand new cables still in their BMW labelled plastic bags, unused sparkplugs. There are tins of touch-up paint, tubes of BMW's own-label lubricants, special tools -unused - for removing exhaust nuts and swinging arm spindle nuts, and even a brand new, still in the box, fuel filler cap with keys. And there's a ring-binder full of parts receipts and service history, MOTs and tax discs, even some road tests copied from magazines, all in clear plastic document pockets.
1979 BMW R80/7 - Heads and barrels, bits and bobs
The boxes labelled "R100 cylinder heads and barrels" contain a set of very grimy barrels and pistons with a 94mm bore - so they're off an R100 of some sort -which look to be in very good condition. There's a pair of cylinder heads which are equally crusty, two head gaskets which seem to match the heads and barrels, four pushrods but only two (of four) cam followers, two little parcels of assorted rocker gear and a pair of scruffy rocker covers.1979 BMW R80/7 - Pistons and barrels are in good condition
Measuring the valve sizes to find out which model of R100 heads and barrels I have inherited (bigger valves for R100RS, smaller for R100/7, etc) reveals that while the cylinders are from a 1000cc engine, the heads are definitely from an 800. The heads have hardly any threads left on the exhaust pipe mounting stubs and there's a set of pushrod tubes which seem to have been stored in Davey Jones' locker at some point.1979 BMW R80/7 - Gearbox contains all five gears
The next box - a heavy one, this - contains a grubby gearbox, a scruffy starter motor and two indeterminate stands; one centre, one side, neither from an R80/7. All the gears seem to be present inside the gearbox, neutral is where you'd expect to find it, the return spring is nicely springy and everything seems to rotate smoothly. The starter motor looks serviceable but I've no idea where the stands belong; the previous owner also had a K100, so perhaps they're from that? Right at the bottom of the box are the eight studs that hold the barrels to the crankcases.Random side and centre stands. K100, perhaps?
Box number three contains round things. A complete clutch (pressure plates, friction plate, diaphragm spring) in a plastic bag. An alternator stator rolling around loosely and a rotor wrapped in a bit of soiled sheet. I can't believe that the same person who carefully packed the crate of consumables and who painstakingly filed every receipt and record in a folder was the same one who stripped these parts off a filthy engine and put them in their disordered boxes. There's a box of things with fins (heads and barrels), a box of heavy things (gearbox, starter, stands) and now a box of round things.
Time for the very big, very heavy box, labelled 'R100 Engine'. And that's almost what's inside. Almost. Cross-referencing the engine number reveals that it's a February 1984 engine of some sort, confirmed by the light flywheel that's still fitted to the end of the crankshaft. The camshaft is still in there, along with the other two cam followers. A connecting rod pokes out of each side of the crankcase, which - like the rest of the parts - wasn't cleaned before being dismantled.1984 BMW Motor
The good news is that one con-rod moves smoothly round its journal with no perceptible play. The bad news is that the other can be pulled backwards and forwards and from side to side slightly. Oh dear. That might explain why this engine ended up in a breaker's yard.
Comparing the muck and corrosion, in a 'CSI Cambridge' style, it seems quite likely that this was once a single, complete, running engine. Unless someone fitted a set of R80 heads onto an R100, it was probably an 800cc bike to which someone later fitted a set of R100 barrels and pistons. At some point a big end failed and the bike went to the scrapper, or was broken by its owner. Bits of the engine were flogged off separately - there's no bean-can ignition module, for instance, or clutch actuating mechanism, or oil pressure switch, or starter motor cover - before the remains were sold to The Unsuspecting Vicar.
We have to assume they were bought them with a view to fixing up The Vicar's Bike but then shelved when the sloppy big end was discovered. Did the seller know about the bearing wear when he sold the parts? Did he tell the buyer? We'll never know, as this collection of used pats is the only item for which there's no record or receipt in the big folder of receipts and records.
The only thing for it is to start dismantling The Vicar's Bike to find out exactly why it's knocking, and whether any of the grungy bits in cardboard boxes can be pressed into service as a means of repair.
The good thing about airhead BMWs is that removing the heads and barrels is an easy and quick job; everything is hanging out there in the breeze and 90 minutes of spanner twirling can get you within sight of the crankshaft. Well, in theory, anyway.
The furthest I got at the first attempt was removing one of the exhaust nuts. This is ideally done with a special tool that looks a bit like a spaghetti strainer, a special tool of which I own two; one lunking great big thing I bought in 1985 and one new, delicate and perfectly formed one inherited with The Vicar's Bike. It was in one of the clean boxes, and looks unused. The pasta strainer teeth engage with the exhaust nut fins and with a bit of a heave on the lunking old spanner, and possibly the gentlest tap from The Mighty Thor, the nut will undo leaving the cylinder head threads undamaged. And on one side, that's what happened.Removing exhaust nuts: Thus equipped, what could possibly go wrong?
The nut on the other side hadn't read the script, sadly. It remained unmoved despite the best efforts of my lunking old pasta strainer. So I decided it was time to try the new spanner, with its finer quality casting and more closely meshing teeth. Still no joy, so perhaps slipping an old fork-leg over the end of the spanner will provide sufficient leverage to get things started?
You can probably predict exactly what happened next. Nut 1, spanner 0. It was only later that I read the warning by MotoBins, supplier of said spanner, about not using excessive leverage. Harrumph.What indeed.
As penance, I trudged out to the shed at seven every evening of the following week to apply Plus-Gas penetrating oil to the threads of the seized nut. With the help of a kettle full of boiling water to heat the nut and a week's worth of Plus-Gassing, the recalcitrant nut finally admitted defeat and unscrewed to reveal another set of undamaged threads. Things were looking up.
Three nuts undo to remove the rocker cover, and then six more unfasten to allow the rocker gear to be detach and the cylinder heads popped off. The bore and piston seemed to be in good condition, none of the rings were broken, and sadly the little end was also sound. I say sadly because I'd been hoping that whatever was wrong would be a) easy to find and b) easy to fix.
There's nothing worse than dismantling a sickly engine to find... nothing wrong. No play where there shouldn't be play, no rough where there should be smooth, no tight where there should be loose. Do you just put it all back together and hope the sickness is cured? Do you replace parts anyway, hoping you'll strike lucky? Do you sell the whole lot to an unsuspecting mug, hoping for the best?
No such worries with The Vicar's Bike. The con-rod on the left hand side was rattlingly loose. It felt as though there was no bearing in there at all, it was that loose. This was a bike that started and ran, that ticked over quietly, and that only knocked on the overrun when revved. How it hadn't hammered itself into oblivion is beyond me. And here's me worrying about not being able to detect the tiniest amount of out-of-specification wear.Can you spot the problem?
Removing the rod (using the one special tool that hadn't come with The Vicar's Bike) revealed the extent of the damage. Big chunks of the bearing material have flaked or worn away; in the picture the black material is underneath the bronze material. The crank journal is also badly scored and both the rod and crank appear to have become 'blued' through excessive heat.The problem.
Measuring the crank journal shows it to be a couple of tenths of a millimetre bigger than it should be, presumably due to the scoring, and its surface is rough to the fingernail. If it was a priceless Brough or Vincent, a bike with a history or with some unusual provenance, it would be repairable. Adding the cost of that repair to the amount I've already put into this bike makes it an uneconomical option, sadly. It's just another high mileage airhead BMW, when all is said and done.
So I think my original Plan B will be the order of the day. Use the better parts of The Vicar's Bike to improve Roxanne; the cylinder heads, the twin disc front end, the newer battery, possibly the 1000cc barrels. And then sell the rest of the serviceable parts on eBay to recoup the costs.
It seems a shame to lay a bike to rest like this, but if it helps keep some of its brothers on the road then its passing won't be in vain. And I'm sure The Vicar would have some kind words to say...
Words and Photos: Martin Gelder
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