Rubber pistons?
I'm told the camshaft is plastic in the Honda lawnmower I'm probably going to buy for the caravan in leafy North Yorkshire.
They don't give any bother, according to the lawnmower man.
The engine is 135cc and the plastic shaft is over the head of a single cylinder.
It only produces about 3bhp - the large capacity for the output is used to reduce noise.
Presumably, the engine is running at lowish revs with a low compression ratio and the camshaft is fairly short as it only has one cylinder to look after.
I can't imagine a plastic camshaft would work in a more stressed/highly tuned application such as a motorcycle - can it?
And has anyone come across engine - or other components - made of unusual materials?
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Discussed at length here
www.honestjohn.co.uk/forum/post/index.htm?t=5967
Plastic engines, plastic gearboxes, plastic inlet manifolds, bumpers, wings and self healing cars.
p
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Plastic in water pumps, plastic window lifters causing the windows to rattle on anything other than perfectly smooth road surfaces and the obvious chocolate camshafts used in some Vauxhall Corsa models.
With a motorbike you've gone to the other extreme. Stresses on a bike engine are greater than any road going car engine.
Edited by gmac on 14/06/2009 at 15:23
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...Discussed at length here
www.honestjohn.co.uk/forum/post/index.htm?t=5967...
Er, that was more than seven years ago and many of those who contributed are no longer with us.
Also, it was all a bit theoretical.
I was wondering about real world applications.
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With a slow running engine, and light valves, the valve momentum won't be great, and so, the valve springs may also be very light, meaning that cam loadings will be low, and so from a stress point of view, the shaft itself is probably OK. I would expect that the cams themselves, and the bearings would be cast iron with a splined inner bore which would key into the plastic during the moulding process.
Are the cams plastic, or of composite construction?
Is the engine liquid cooled?
The drive shafts which operate the flaps and slats on many Airbus planes have been made from carbon fibre composite with aluminium flanges for many years.
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I have one of these lawnmowers. The thing has been so reliable that I've never ever laid a spanner on the engine, but it certainly sports "OHC" on the valve cover!
Someone else told me that this engine had a belt driven OHC running in the engine oil - it's certainly not external. Apparently it's a test bed for future Honda engines with more meaningful outputs.
I'm overcome with curiosity. I'll take the lid off the engine and report back within a few days.
659.
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Its a Honda - they make mistakes but correct them with proper engineered solutions
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Edit function not working.
I meant to put that the OHC drive belt runs in the oil.
659.
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Edit function not working.
5 mins, or until someone replies to your post - whichever is the sooner.
PU replied to your post, and therefore no more edit key for that particular post.
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Years ago, you could buy nylon sprockets for motorcycles. It was said that they out-lasted steel ones. Not sure how true this was or is.......
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Ford built a "plastic" engine about thirty years ago-not put into production.The Ford Essex used plastic camshaft gears as did other manufacturers-Renault-for example.
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The Essex distributor drive gears were a fibre material IIRC and didn't last long.
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The Essex distributor drive gears were a fibre material IIRC and didn't last long.
the gears were the cam/crankshaft gears, and they were fibre teeth on a metal gear, the fibre used to breakup, causing the same damage as a cambelt failure......
an after market replacement was solid gears, safer, but noisier.
the distributor was driven off the camshaft by a gear, the oilpump was driven off the distributor, by a hexagonal shaft (bit like a bic pen) that used to round off leading to engine seizure......
Edited by the swiss tony on 14/06/2009 at 19:14
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In answer to NC and 659FBE:
The engine is described as 'force air cooled'.
Might be a bit of marketing blurb, but it sits atop the spinning blade, so I suspect it uses a bit of back draft from that.
Not sure of the exact material the shaft is made of.
The lawnmower man mentioned the cambelt running in oil.
He said they seemed to last forever provided the correct oil was used, which I think is synthetic, although that should be double checked.
Apparently, the wrong stuff will rot the belt in the end, although it will take years.
There was an earlier, but similar, mower in the workshop which I was told was eight-years-old and 'well used' by a customer who does some contract mowing.
It was in a for a carb rebuild, not that it had broken down, just wasn't running very sweetly.
Thanks for the feedback - all the signs are this is a decent, well-engineered product.
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Even the old Briggs & Strattons are 'force air cooled'! They put vanes on the flywheel and enclose it in a metal casing. Voila, force air cooling and some spare forced air to work the engine governor linkage via a hinged flap.
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Even the old Briggs & Strattons are 'force air cooled'! They put vanes on the flywheel and enclose it in a metal casing. Voila force air cooling and some spare forced air to work the engine governor linkage via a hinged flap.
And some more spare to suck grass cuttings into the cooling space and choke it up!
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"nylon sprockets for motorcycles"
I'd forgotten about those! It seemed like a good idea to me (for rear sprockets, at least), but I never got round to buying one. I notice that the rear drive sprocket/pulley/gear (?) on toothed-belt driven Harleys is made of nylon, or similar and they seem to last. Indeed, the whole toothed-belt drive idea seems so attractive (clean, quiet, smooth) that I can only assume that there is a gentleman's agreement between the bike and chain manufacturers that prevents its widespread adoption.
WRT camshafts, while I respect Honda's engine making, I do wonder if replacing a hard-wearing component with a less durable one that requires special oil is real progress. It can only be to save a few pence in manufacture...
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In reply to the thread title, some people see "plastic" as being an inferior material. Plastics used in engineering bear no resemblance whatsoever to those used for cheap domestic items and toys in cornflake packets.
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Most parts of the worlds most reliable handgun family the Glock G series are made from high durability plastic components.
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Toothed belts for motorcycles are not confined to Harleys; Kawasaki used them on their excellent little 305cc twins some years ago, and indeed they continued onto the bigger 440's until quite recently.
Some of the "Jap cruisers" also have belt drive, IIRC, but apart from Buells (which of course are owned by H-D) the practice has not spread to high-performance crotch-rockets.
As a matter of interest, belt life of 60 or 70 thousand miles is not uncommon on an Electra-glide, so long as they're kept well adjusted and you ensure that the guards (particularly the lower one) are kept in place. I have to admit that whilst they're less than ideal aesthetically they are so much cleaner than a chain, and less hassle too; until they break of course!
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