Hi there, we see quite a few Norton's in our little shop downunder and after reading everyone's views on blasting I thought I might offer my two bob's worth.
I've somehow ticked over 40 years as an engine machinist & builder here in Melbourne Australia. Metal finishing is also a huge part of my life.
During that time I've tried just about everything you can think of to restore componentry back to it's original condition safely.
As far as engine parts go, dry bead or grit blasting is out of the question. The reason is simple. The dry media tends to imbed itself into the metal and is near impossible to scrub out.
Back in the 90's a rare Lancia crankcase we were building was ruined by the local sand blasting hero who just shrugged his shoulders when shown the damage inflicted.
Days were spent on the Bridgeport mill remachining every mounting surface ruined by the process. Just when you thought it was clean you'd discover more abrasive hidden somewhere.
We spent some time wet wire brushing which was at least a safe option, but it was then that we decided to investigate something better.
The wet abrasive blasting process had been used by aircraft engine companies for turbine overhauls for years, and we found it suited our
needs perfectly. Since 1995 we have tried this technique on nearly everything you can imagine. Our process is definitely different (and safe)
After hot washing or tanking a customer's parts the next step is inspection & masking. (Yes, some surfaces should be protected - like the slider in a carby for instance)
We often heat up and remove bearings and other small assemblies that customer's aren't comfortable touching on their own. The correct mix of media is then chosen for each particular
job depending on the surface finish required. The mix of media, water and detergent massages the part. With the water acting as a carrier as well as a barrier, it softens the impact of
the media preventing the ingress of abrasive particles into the metal surface. Next the part is transferred to another similar machine for final bright finishing. This results in a look as
close as possible to the original. If there is a better way I have yet to see it.
Now, the important bit!
The part is thoroughly washed off with water including every bolt hole, oilway, water jacket, etc. Still not good enough yet!
Checking each part over, we look for any hidden areas or passages and take a little tour of the oil system. If a manufacturer uses a peened in alloy oil galley plug it's drilled, tapped and
removed using a small slide hammer. A new galley plug is easily made - without removal there's always a chance that the first oil the bearing's see will be mixed with abrasive.
It all sounds a bit dramatic, but in the right workshop environment it's very straightforward and fairly inexpensive. Ahh where were we? After a solvent wash and another water wash
followed by a detailed air blowoff we're all done. Remember, wet abrasive doesn't imbed in the metal but still ends up in bolt holes and galleries, where it is easily removed (unlike dry blasting)
If you don't believe it requires all of these steps, then stay well away from blasting - it will end in disappointment.
Sorry if I'm getting away from bikes a bit here but this will make it clear to most.
An aluminium bore Mercedes Benz V8 runs less than half a thousandth of an inch piston to bore clearance, yet we regularly detail pistons utilising the wet blasting process.
Enough said. Please visit my website and form your own opinion.
http://www.woodyshydroblast.com
During my aircraft mechanics schooling, our grizzled old instructor was very adamant abount not blasting the interior of the aluminum cases with anything. As he surmized, once the alloy cases heat up, the surface pores open enough to release the dust/glass fracturings that were imbedded during the cleaning process. I've stuck with that ideology. Besides, who cares how pretty the insides are, as long as they're clean of gunk? Along those lines, I recently discovered that my Waterpick (for cleaning my teeth) doubles as a mini high pressure washer. I fill it with hot water and a couple of drops of dish soap, and start blasting the nooks and crannys. It's amazingly powerful. Granted, you probably wouldn't care to stick it back in your mouth after that, but it's a relatively cheap device to buy for your shop.
