Topic: Bead blasting a complete engine ... my cranky method

[AshimotoK0]

This is for one of my Honda Twin engines but relevant on here too for SOHC/4's . (I havea 10/69 CB750K0 diecast and CB400F too.

http://www.hondatwins.net/forums/1-project-logs/34374-969-cb350k1-4.html

This is the relevant part:

Here are pictures of another engine I have for my JDM CB250 Dream replica. Ignore all of the fasteners (they are scrap) as is the camshaft . The camshaft is scrap because of the broken off points advance mechanism shaft (that cam was posted to me in a polythene bag only by DK Spares and hence broken in transit !). The cam bearing covers too are scrap ones. Engine is assembled with no engine internals (except broken cam) but with all gaskets (greased) and fibre washers on the fasteners. All oil seal holes blanked off with plates and rubber sheet. Exhaust and inlet ports blocked off with rubber faced seals. The starter motor aperture is blanked off temporarily with the end cover of a scrap starter motor, with its oil seal hole blocked with rubber. There a brass rivets pushed into the the holes of the alternator wiring rubber seal.

Tomorrow I will pressurize with air into the breather cover, and then if no leaks, I am going to dry blast with /100 glass beads. (VIXEN blast cabinet, Vixosheen beads). The idea is to blast without glass getting into the internals of the engine. I have two more engines to do like this, if successful, which includes the K1 CB350 engine of this rebuild thread. Will report back tomorrow.

I also investigated the crankcase finish on the K1 cases and also on the covers etc. I also had a NOS 286 crankcase top to test for original finish. I put a bit of 'proper' paint stripper on all surfaces to see if silver paint or clear coat applied. The NOS crankcase upper definitely had silver paint on it (please see the last photo).

So, to my reckoning, the factory finishes  were as  follows:-

CB250/350K engine

Crankcase upper... Silver paint,
Crankcase lower ... bare alloy finish
Clutch & starter covers ... Silver paint
Alternator cover ... Clear coat
Oil Filter Inspection cover ... Clear coat
Cam bearing covers ... Clear coat
Cylinders and cylinder head .. Bare alloy
Head Cover ... Bare alloy finish
Breather cover ... Bare alloy finish
Drive chain cover .... Silver paint
Starter motor ... Silver paint

CB750K0 Engine

Crankcases ... Silver painted top and bottom halves
Head  ... Silver painted
Barrels ... Silver painted.
Clutch cover ... polished then clear coat
Alternator cover  .. polished then clear coat
Transmission ('mission') cover  ... polished then clear coated
Rocker cover  ... polished then clear coated.
Cam chain adjuster housing ... Silver painted.
Oil filter housing ... Silver painted
Breather cover ... Silver painted


Debating whether to do  the same bead blasting with the 750K0 engine  ..lets see how it goes.  COMMENTS PLEASE !!

I pressurized to 3PSI and it held pressure no leaks (see digital gauge attached to top breather port) so I locked in the pressure then blasted. I checked it for leaks at every joint / blanked off oil seal with bubble detector leak aerosol spray.
Two more engines to do now plus polishing the relevant parts and painting/clear coating where necessary.

Scored a NOS generator cover on eBay. They always get a scratched 'arc' because of contact with the gear lever.

[AshimotoK0]

Take your point and I do have a parts washer. I blasted the whole engine with high pressure compressed air for about 20 minutes before I stripped it again. My main worry was that beads blasted against any internals may embed themselves in the alloy and get released after assembly.  The way I did it, no beads would have been shot against any internals to embed themselves. I see a whole bunch of people on forums vapourblasting individual components, surely that's a lot worse.

[AshimotoK0]

Not really. Vapor blasting is a much different process using a "slurry" instead of dry media alone. Unless you blasted with glass/sand at extremely high pressure, you're not going to embed anything in the cast alloy. Certainly heating the cases while rinsing will release any contaminants, but I've never had a problem blasting and washing/rinsing broken down engine cases. In fact, apart, it's easier to insure full cleaning.

Don't know much about Vapour blasting apart from the people who do it here in the UK charge a fortune (understandable due to the price of the equipment I suppose) . My understanding is that the slurry is of water and abrasive and hence you are still introducing abrasive into the internals of the engine. If the dry beads don't embed themselves at lowish pressure what's the difference? I do  have a massive heated ultrasonic cleaner, is it worth putting the parts in there for a few hours do you think at the highest temperature setting?

[przjohn]

Maybe I am missing something here. Is the whole motor empty and you assembled it and are then going to bead blast it like that?

[AshimotoK0]

Maybe I am missing something here. Is the whole motor empty and you assembled it and are then going to bead blast it like that?

 Yes .. because I have 3 motors (CB250/350 style twins)  to do at once and getting them vapour blasted was going to cost a fortune over here (like 50 USD just for one cover) . There are no internals in that engine except the camshaft ( which is scrap anyway). I am on the second motor now and once you have the necessary sealing bits (like blanked off oil seals, starter motor end cover etc) it's a breeze to do the other motors armed with an battery impact screwdriver. The parts were cleaned in a kerosene degreaser before blasting. All of the fasteners are scrap ones just to hold everything together for blasting. When I stripped the first motor I blasted, there was no sign of glass bead inside due to the airtight sealing process and I blasted the whole motor with clean air before dismantling again.

[przjohn]

Interesting, I have always bead blasted parts individually in my cabinet. As they say, there is more than one way to skin a cat. Curious to see the finished product.

[chewbacca5000]

I blasted a couple whole engines, but the engine was in the bike and everything is attached so there is no way anything can get in the engine.  I used highway spheres, Northern Tool blast attachment, and a pressure washer.

Here is the result.

[AshimotoK0]

Done two 350K engines now onto the third. Pretty convinced no glass got in the engine as I blasted the engine afterwards with air for about 20 minutes and then washed down with solvent, then air blasted again.

[beemerbum]

A little trick I learned from blasting my Yamaha XS 650 motor. The intake and exhaust ports can be nicely sealed using freeze plug expansion replacement plugs from your local car parts store. They have several sizes available. Put in the plug, tighten the bolt to expand it, a perfect seal.

[fitzmotor]

I have also blasted complete engines, runners, just seal it up and blast, then it takes three times as long to wash, blow off, wash again and blow off over and over, then I have even painted it with case paint and threw it in a oven to cure.
My buddy thought I was crazy, he said it will blow up, I ended selling one of them to him and it was still running 15 yrs later.
It comes down to making sure it's 100% sealed, I make them watertight so I can high pressure wash them when done.

[Don R]

 I use soda, it melts when wet.