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  1. #16
    Join Date
    Jan 2004
    Location
    Mackay North Qld
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    6,446

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    hi BobL,

    Got one of those as well.

    It was the predecessor of the current Hoselink 2 outlet tap.

    My Holman was much better than yours- leaking profusely straight out of the package .

    Grahame

  2. #17
    Join Date
    Aug 2010
    Location
    Near Bendigo, Victoria, AUS
    Age
    72
    Posts
    3,102

    Default

    A week or so ago, I had to rebuild our 12 months old lawnmower, that started burning a lot of oil.
    So I ordered some new rings and pulled the engine down. It is a 150cc "good old" Briggs & Stratton engine in a "respectable" brand Victa.
    When I had everything apart, I couldn't believe my eyes: the CAMSHAFT WAS PLASTIC!
    So were the gears that drove it. So is the entire starting mechanism.
    The aluminium piston runs in a bare aluminium bore, the big end bearing is the aluminium conrod, the crankshaft is grey cast iron, the pushrods are 4mm dia. steel tubes, the rockers are pressed sheet metal. The piston "skirt" are two very narrow slides only, and the piston top finishes at the bottom of the oil ring groove, with cutouts so the oil rings are actually exposed in those spots to the crank case.
    Anyway, so after a year's use - at a rate of about once a month, taking maybe 1-1/2 hrs each time, the ring gaps were around 1mm.
    I fitted the new rings which closed the gaps to around 0.3mm. Checked everything else for wear (negligible) and reassembled everything.
    The mower runs fine again.
    Now I'll keep real tabs on its actual use and see how long it goes for.

    This is by far the worst engine design I have ever seem and the shittiest $500 mower I have ever owned!
    My last mower was a ($295 in 1986) Honda Buffalo that lasted and worked fine for 35 years. I wish I hadn't given it away and rebuilt that instead.... or bought a (now $1100) Honda Buffalo again....
    Cheers, Joe
    retired - less energy, more time to contemplate projects and more shed time....

  3. #18
    Join Date
    Apr 2012
    Location
    Healesville
    Posts
    2,129

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    Quote Originally Posted by jhovel View Post
    A week or so ago, I had to rebuild our 12 months old lawnmower, that started burning a lot of oil.
    Joe that would probably be an ill fitting ac element or often a shrub branch or stick can push or pull the breather tube off at one end or the other and the engine gets dusted out. Also use only SAE30. Briggs have used alloy cylinder bores for ever, except the IC engines (industrial commercial) that have cast iron sleeves. When re-ringing you never hone or abrade the alloy cylinders as the new rings will pick up the bore, the cylinders can be rebored and honed but the hone was something special that i never had eyes on.
    A number of small engines use plastic cam gears now, when i first seen the single cylinder 17-20 hp kohler engines i thought it odd that the plastic cam gears were never a problem but they often got a cracked crankcase, haha and this went on for years, dunno how many short engines that i replaced under warranty...

  4. #19
    Join Date
    Oct 2011
    Location
    Norwood-ish, Adelaide
    Age
    59
    Posts
    6,541

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    Quote Originally Posted by Grahame Collins View Post
    ... have the UV exposure that we have in the tropic zone, but I wonder how you are affected in the southern zone re plastics and equipment.
    UV resistance in plastic depends a lot on the formulation and of course, the additives that give it UV resistance (usually Titanium Dioxide I think) cost, so they are not added if not needed - as our Engineering Manager found to his embarassment after reviewing product test results before release (with the plastic grade he personnally selected)...
    The best 'natural' colour for UV resistance is Black, as the light does not get in as easily.

    Michael

  5. #20
    Join Date
    Oct 2004
    Location
    Southern Highlands NSW
    Posts
    1,894

    Default

    Quote Originally Posted by shedhappens View Post
    Briggs have used alloy cylinder bores for ever
    We know that generally you can't use the same metal bearing against itself, exception being cast iron.
    But many car and motorcycle engines and air conditioner compressors use what seems to be aluminium alloy parts rubbing together successfully.
    I believe the trick is to use an alloy with lots of silicon in it, then treat a surface with acid so as to deplete the top layer of aluminium, leaving hard silicon.

  6. #21
    Join Date
    Nov 2017
    Location
    Geelong, Australia
    Age
    57
    Posts
    2,651

    Default

    Interesting - I haven’t heard of that before. I always assumed it was just the lubrication that kept the surfaces separated.

    Steve

  7. #22
    Join Date
    Nov 2007
    Location
    melbourne australia
    Posts
    3,228

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    Quote Originally Posted by nadroj View Post
    I believe the trick is to use an alloy with lots of silicon in it, then treat a surface with acid so as to deplete the top layer of aluminium, leaving hard silicon.
    This is the process I'm most familiar with:
    https://en.wikipedia.org/wiki/Nikasil
    Chris

  8. #23
    Join Date
    Aug 2010
    Location
    Near Bendigo, Victoria, AUS
    Age
    72
    Posts
    3,102

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    My biggest surprise was not the cam gears, but the the camSHAFT. The actual shaft and cam lobes were plastic.
    Thanks Shedhappens for the hint about checking air cleaner fitting condition in the future.
    Cheers, Joe
    retired - less energy, more time to contemplate projects and more shed time....

  9. #24
    Join Date
    Jul 2008
    Location
    near Warragul, Victoria
    Posts
    3,718

    Default Bakelite

    Is bakelite used much these days ?

  10. #25
    Join Date
    May 2011
    Location
    Murray Bridge S Aust.
    Age
    71
    Posts
    5,942

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    Found this on google for you;
    Bakelite continues to be used for wire insulation, brake pads and related automotive components, and industrial electrical-related applications.






    To grow old is mandatory, growing up is optional.

  11. #26
    Join Date
    Aug 2008
    Location
    Melbourne
    Age
    34
    Posts
    1,075

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    We still make fibre-reinforced-bakelite (Tufnol) gears. They're often used as mechanical fuses in machinery, similar to a shear pin.
    Gear cutting specialists and general engineers www.hardmanbros.com.au
    Fine pitch gear cutting from 0.1 Module www.rigear.com.au

  12. #27
    Join Date
    Oct 2011
    Location
    Norwood-ish, Adelaide
    Age
    59
    Posts
    6,541

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    As Elan says, Bakelite is still used, but is a Thermoset plastic - made in a different way to most common plastic items and won't melt. But it is expensive, abrasive on tools and the dust is not good for you (phenolic compoounds). I think it eventually dries out in the sun and gets brittle or cracks though.

    Michael

  13. #28
    Join Date
    Aug 2019
    Location
    Revesby - Sydney Australia
    Age
    56
    Posts
    1,183

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    Joe's comment about the plastic camshaft reminded me of a Kmart mower (Gardener's Choice) mower I stripped:
    IMG_2275.jpg

    At the time, was intrigued that it had plastic gear and lobes. At least the cam shaft was metal, and the bores were iron, alloy cylinder cast around it.

    I share your concern about the starting mechanism (pulley, ratcheting pawl) being plastic - from memory it was well worn.

    Interestingly, the camshaft seemed wear free. The Nylon they used, or the oil splashing around in there, seemed up to the task?


    P.S. This is what failed:
    IMG_2276.jpg

    Mower had oil leak around main crankshaft seal. Previous owner had mown some long fibrous grass (flax?), that was stuck in there, so it might have been lubricant free for many hours operation. I replaced the seal and refilled crankcase, but when it got hot, it would drop power or die. Eventually seized.

  14. #29
    Join Date
    Jan 2004
    Location
    Mackay North Qld
    Posts
    6,446

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    Michael alluded to the quality of plastics and correctly matching them to the application.

    The Blue spare parts container is an Aussie Fischer plastics parts container.

    The red one from my Chinese made mobile frame with various sized parts containers and various bin colours. Frame was always IN THE SHED out of the sun.
    The front fell off it when I unclipped it from its mobile frame. -about 9 years old

    The blue one has been kicked around, dropped, walked on, crushed and generally mistreated for near twenty years. Its tatty,but intact. Michael was sooo.. right about the colour and UV effecting it.

    Grahame

    nasty asian bin.jpgOlder Fischer bin.jpg

  15. #30
    Join Date
    Oct 2004
    Location
    Southern Highlands NSW
    Posts
    1,894

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    Quote Originally Posted by jack620 View Post
    This is the process I'm most familiar with:
    https://en.wikipedia.org/wiki/Nikasil
    Liner-less aluminium alloy engine blocks had been in mass production in USA before the Germans developed Nikasil, which I think is an improved development.
    I'm not sure if the Repco-Brabham V8 F1 engines were linerless, but the Oldsmobile F85 aluminium blocks they were based on were. That's from early 1960s.

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