Dateline: 28/4/10. Cinderford, Gloucs. Freed from pounding out the novel I return to my roots. The comments will fall away but I took up blogging to fill in a techno-void. Rhyming couplets are OK but nuts and bolts hold things together.My four-year-old car is here at Winner’s Garage for only its second scheduled service which will cost at least £800 (actually £768.83). There’s nothing wrong but they’ll be replacing the cam-belt (the cogged strip that snakes round the gears in the pic) which means pulling the front of the engine to bits.
The belt drives the camshaft which opens and closes the valves to admit fuel and allow exhaust fumes to escape. In olden times (still the case with some large US engines) the shaft was buried in the engine and valve contact was by rackety push-rods. Now the shaft sits on top of the cylinder and is rotated via a plastic belt. Much more precise, greater engine efficiency, but at a price. Over time the belt stretches and the tensioners no longer tension. Left to its own devices the belt may slip a cog or break, a valve no longer synchronised touches the piston and excessive derangement ensues. A replacement engine for my car costs over £2000.
Nothing comes for nothing. An overhead cam engine is a great improvement on a push-rod engine but plastic belts don’t last for ever; similarly with chain drives. Sounds like a conspiracy, doesn’t it? Meanwhile the world waits for an eternal belt.
17 comments:
Rather than replacing cam belt material (rubber, so cheap to make, fairly durable, and designed to require low maintenance until its time comes), would it be easier for engine designers to adjust its position so that the belt is easier to replace? It would be truly interesting to know if car designers think in parts replacement terms when designing a car.
Ja, I am wondering the same ... what is the engineer's prime directive in designing an engine? What sort of input would a mechanic give?
Why should your comments fall off?
This commentator is delighted to see the blog in its orginal sharp focus. One of the big questions about design, and that goes for gear arrangements as much as for laptops or video recorders is the prospect of obsolescence and the long term profitabilty for manufacturers of spares and service, which is the unacceptable side of the forward march of technology.
Julia/RW (zS): By car design standards the cam-belt (I believe it is a mixture of rubber and plastic) is moderately easy to replace. But in these areas compromise is the name of the game. Car manufacturers can claim, justifiably, that modern cars need far less servicing and adjustment than they did twenty years ago. By using very expensive oil in my car I am able to stretch the service interval from 10,000 miles to 20,000. However the service when it comes is more expensive. The argument regarding the cam-belt is that a push-rod engine used to require many more valve clearance adjustments over the 40,000 miles that mark cam-belt replacements. And a push-rod engine was much less efficient. The short answer is that car designers are not inclined to make things easier for the mechanics these days. Mercedes has gone a stage further; with some of its models the owner cannot even open the hood (UK: bonnet) and must top up oil and windscreen washer fluid levels via a couple of capped tubes led to the outside of the body.
Plutarch: I'm pleased that you're pleased and in any case the comments from Julia and RW (zS) suggest I was over-pessimistic. I was merely going on past performance. Some subjects (possibly because they were badly written, I don't know) seem to be a turn-off. As to planned obsolescence it is a mixture of motives: if retro-compatibility were designed into some electronic kit it is conceivable the products would cost more and be bulkier. This has in fact already happened. Microsoft's Windows operating system was preceded by the very crude DOS system. In order not consign millions of computers to the dustbin MS promised to make Windows DOS-compatible and to make new versions of Windows compatible with those that went before. They maintained this policy for some years before it became a genuine wart on the arse of progress and it was necessary to condemn earlier Windows to the graveyard.
I was completely unaware of the presence never mind the role of the cam belt before moving here, when at some point it became necessary to find out what was this thing known as the 'courroie de distribution' which the garagist told us required replacing.
Then it seemed that everyone had had problems with them, and all knew that it should be translated as cam belt. Even the big garages all seemed to be running special promotions exhorting us all to 'pensez a votre courroie de distribution!'. Yet it seemed we had lived and driven many years Anglo-side with barely the least awareness of same.
Oddly, a similar thing seemed to occur with the miniscus of the knee joint, which Tom had trouble with in our first couple of years here, and suddenly everyone we met seemed to have had treatment for the same thing.
It's perhaps a similar thing to the Baader Meinhof phenomenon...
Sincere congratulations on the completion of the work. Looking forward to reading it!
I opened up your blog last night and pointed out the image to Alchemist.
'Who's blog, d'you think?' I asked.
'Bonden's, I reckon.'
I know nothing of cam belts, but am willing to learn, so thankyou.
Over on this side of the world we call this belt the timing belt. I once had a Plymouth Arrow (me and my Arrow!) that had a timing chain that stretched far enough. My mechanic was a creative sort who thought I was too short of cash for the actual replacement, so he wrapped it different somehow to take up the slack, changed the 4-cylinder firing sequence to make up for it and the net result was I lost a little power.
You can't do that these days.
Actually, the engines are laid out for ease of service as far as possible. The trouble is there are too many things to service in too little space. Something simply has to be difficult.
All: My apologies for pessimistically predicting this subject would draw no comment. The next post will deal with differential calculus - just to find out where the sticking point is.
Lucy: You travelled, you broadened your mind. One of the great pleasures about France (as with coussinettes at the dog parlour) is you do something new and your vocab expands.
HHB: I am delighted Alchemist sees me this way. I prefer to be known as a spannerman rather than a Hallmark Cards artisan.
Chris: Before I went to live in the US the stereotype was of a wasteful, throwaway economy. When I got there, things were entirely the opposite. This timing chain story is typical; however the trick is knowing how to do this cash saver in the first place.
As you say, modern cars carry very little wasted space. I had a VW Variant (ie, station wagon) in the US where the engine was crammed under the rear deck. I watched the mechanic work on it and complimented him on his ability to work under such cramped conditions. He grunted: "This is nothing. See this engine when an a/c is added."
Your image is very steampunkish, BB. I like it. I like gears and other Rube Goldberg-type things...you know - where something starts in one spot, goes indirectly up and down and around all sorts of other things before it gets to the end.
I still have my 1969 VW Beetle repair manual. It helped me repair my carburator. I even cut a new seal for it from a sheet of cork. However, when I blew a cam shaft, I took it to the garage.
I know my mechanic limitations.
Uh...threw a rod, not blew a camshaft. My bad.
The Crow: As a result of your former nomadic life across many of the states on the Union, you are able to come up with words that test my knowledge of US idiom to the full - this time steampunkish. Or perhaps you made it up. In which case my congratulations.
Perhaps this is also the time to to define Rube Goldberg and to compare it with its UK equivalent Heath Robinson. A Heath Robinson contraption would be be mechanical fantasy where amusing complexity has been brought to bear on some simple task (eg, a fifty foot high structure involving wind turbines and hydro-electric power to crack a nut). This definition seemed to fit Rube Goldberg but I was never sure. In any case it doesn't apply to the picture I have chosen. There are part numbers cast into the highly visible gear-wheels and they are preceded by the letters: LAMB. This may mean that the picture is part of a Lamborghini engine, used to power an impossibly quick Italian sports car and costing in the region of £120,000 which is an even larger figure in US dollars. I hope this doesn't sound as if I'm jumping on your toes; we appear to have crossed wires in a couple of our recent exchanges. No doubt due to careless expression on my part.
Crossed wires (not agreeing, necessarily, that you and I have experienced such) are probably to be expected, given that you are British and come from a different culture, and I am American and come from a country many folks would say lack a culture of any sort. Add to that the fact that you are male and well educated and I am female and not so much, and simple misunderstandings are likely to occur. Unless we come to blows, metaphorically speaking, I think it is our differences and any resultant misunderstandings that make our long-distance friendship so damned much fun and a real joy for me. Such discussions along those lines as we have had since the beginning have broadened my view of the world considerably, of you even more. I like the hell out of you, BB, and unless you start badmouthing my Mama, I always will.
Steampunk is a relatively recent art trend, and is a satire of the term cyberpunk, as it relates to artistic endeavors. While cyberpunk art uses modern technology as its inspiration, steampunk uses the technology of the steam-driven era for its inspiration. In fact, steampunk honors and glorifies the Victorian hero, the engineer. Instead of cy-borgs and computer-robotics found in some cyberpunk art, steampunkers use steam-powered machines and gears and springs in their art. The Tate mounted an exhibition of steampunk art, but I can't remember when it was. (I found it last year when I was Googling for a definition of steampunk, while researching mixed media art.)
It was the gears in your engine's image that reminded me of stempunk art, hence the comment.
Sounds like our Rube Goldberg and your Heath Robinson were cut from the same cloth. I used to love reading the one panel cartoons he drew. Did you know he was an engineer? I think that might be why my father, who was a mechanical engineer, loved his cartoons so much. Goldberg was the master of the over-engineered machine that went around its elbow to get to its thumb to accomplish simple tasks.
Although I understood the simplicity of what your engine image portrayed, in following the path of the gear belt around the gears and the stops, I was reminded of Goldberg's cartoons.
For better or worse, my brain sees connections that are related, however improbably those connections might seem to someone not privy to the inner mechanics of my thinking. I wrote the end result of that thinking in my previous post, when perhaps I should have shown a little more of the path it took.
I must have been channeling Rube Goldberg at the time.
Love,
Martha
I was trying to find that link from last year about Steampunk art at the Tate, but couldn't. However, there was a more recent exhibition at Oxford: http://steampunkmuseumexhibition.blogspot.com/
The Daleks (from Dr. Who) are a good example of steampunk, before steampunk was even a name.
The Crow: I'm astonished you know about Dr Who. I have never watched it - the technology never seemed persuasive.
The cam CHAINS (as opposed to belts) on SAABs are usually good for about 150,000 miles. I am up to 96,000 with mine and my SAAB specialist garage says it's as good as new.
However, I do miss my old Morris Minors (a Traveller "woodie" estate and a rag topped Tourer). The engines were so simple and small one could almost pick up an adjustable spanner and a hammer and go and sit in the space under the bonnet to work on them out of the elements!Sparking plug gaps were adjusted by eye alone and contact breaker points (what are they, today?)were spaced by the thickness of a cigarette packet.
Avus: I'm surprised about the durability of the SAAB's cam-belt. Even so it must surely require re-tensioning every so often. Unlike you I do not look back happily on the era of the repairable car. I acknowledge it existed but then it was just as well - lots of repairs and more frequent servicing marked that period. What's more I never knew how to get rid of the used oil.
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