Author Topic: Engine finish  (Read 7781 times)

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Offline MrWright

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Engine finish
« on: 26 Dec 2005 at 23:57 »
General question:
I am restoring a T35 and would like some input on the engine case finish.  I have media-blasted the case, and the finish is that of a green-sand casting.  This is not bad, but I have seen some pictures of bikes with polished finishes.  I prefer an original finish as opposed to an “over restored” finish.  What is the preferred finish of a true “concourse” finish?  All opinions welcome.

Thanks,

Dave

Offline Doug

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Re: Engine finish
« Reply #1 on: 27 Dec 2005 at 00:57 »
Unless prepared for a trade show, the castings were not polished to a mirror finish.  They were smoothed off, more or less depending on accessibility.  While it may not be concourse standard, I find a pleasing finish is after cleaning the castings to 'polish' them up with successively finer grades of Scotch-Brite or BearTex silicon carbide abrasive nylon hand pads and lots of elbow grease.  This gives more of a satin finish than a polish. 

-Doug

Offline MrWright

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Re: Engine finish
« Reply #2 on: 27 Dec 2005 at 01:42 »
Doug,

Good suggestion, I also find 3M Scotch-Brite to work well, however, Bear-Tex is a new one for me.  Perhaps it is not found state-side.  I think that time has taken its toll on the case, it has many pits.  I will be forced to use a rotary Scotch-Brite on a die-grinder.  I will be sure to stock the frig with plenty of ale and set-up a bench in the driveway.

Dave

Offline KiwiJohn

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Re: Engine finish
« Reply #3 on: 27 Dec 2005 at 02:13 »
Dave, I have really only ever looked closely at one Douglas outside of a museum and this is my 80 Plus.  There are pits in the castings that I can only imagine where there when it left the factory and although various owners have each given it more or less of a polishing throughout its life there are still patches on the engine and gearbox casings that I can only describe as 'raw'.

I believe the sales brochures of the time spoke of the finish being 'semi-polished'.

Offline trevorp

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Re: Engine finish
« Reply #4 on: 27 Dec 2005 at 04:40 »
i think i will stick with the single grain of sand and a piece of bamboo
u put the single piece of sand under bamboo and rotate once and then check
takes about 200 years but what a finish

Offline Chris

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Re: Engine finish
« Reply #5 on: 27 Dec 2005 at 15:20 »
Some years ago the only media blast finish suitable for aluminium was glass bead blasting. (shot blasting was much too coarse and crude for small aluminium castings).
However, this gave an artificially uniform finish and was rather too matt and grey in colour. A process now available is "aqua blasting" where the abrasive media is carried in water under high pressure. The finish from this process is superb giving a very fine "new aluminium casting colour" without removing the original surface finish. Even pits are clean and shiny without being removed. The only problems at the moment are that firms with the necessary equipment are few and far between and it tends to be rather more expensive than shot or bead blasting.

Offline MrWright

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Re: Engine finish
« Reply #6 on: 27 Dec 2005 at 23:54 »
Thanks for the input.  I have located a media-blasting company, and they have a plastic media made for aluminum.  Also, there exists organic media made from peanut shells.  These tend to bio-degrade, posing little threat to the internals of the engine.  As for the bamboo and sand, there are therapeutic uses for bamboo and sand to relieve itching and burning and it takes less than 200 years.

Offline Doug

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Re: Engine finish
« Reply #7 on: 28 Dec 2005 at 01:39 »
As Scotch-Brite a registered trade mark of 3M, Bear-Tex is a registered trademark for Noton (Abrasives.)  The same product may go under other names, but I gave these two as the are both readily availible in the USA. 

-Doug

Offline alwyn

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Re: Engine finish
« Reply #8 on: 28 Dec 2005 at 02:32 »
Hi all,
I have had great success on engine and gearbox casings and rocker covers using a Cotton Wadding Polish called 'Brite Shine' made in Meadowbank, NSW by Kenco Car Care - needs a liberal application of elbow grease to go with it but surfaces come up like new!
Alwyn
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