This “project bike” spent some time outside and was covered in oil and grease from leaking seals when I got it. So the engine block, along with many other parts, looked pretty bedraggled.
I have gotten a number of questions from readers over the years about how I refinish the aluminum engine block (and the transmission and rear drive aluminum cases). I don’t bead blast the engine as that requires complete disassembly of the engine and laborious cleaning of all the internal oil passages in the block. Instead I use a secret ingredient, a lot of elbow grease, along with various abrasives and Auto Sol Aluminum Cleaner.
When I restored the 1973 R75/5, I put together a document showing the techniques I use to refinish various parts.
I also put together a document on refinishing, repairing and painting when I rebuilt the 1983 R100RS and converted it into an RT.
For this R80ST rebuild project, I decided to shoot a video showing how I refinish the engine block. The products and techniques I use are also applicable to the cast aluminum transmission and rear drive cases. If all you want to accomplish is to refinish the cases, you can do that without disassembly of the transmission or rear drive.
As I mentioned earlier, the most important tool is elbow grease and a mental attitude that I can summarize as:
Endeavor to Persevere
This work can be tiring so I don’t try to do it all in a single effort. Instead, I work on the engine block for awhile over several days and quit when my arms get tired or my motivation wanes.
Besides a good mental attitude, I use a variety of brushes and Auto Sol’s Aluminum Cleaner. I have stainless steel brushes, a green Scotch Brite pad, brass brushes, “0000” steel wool and nylon brushes. I use blue shop towels to wipe off the dark residue after working on the block with aluminum cleaner. As a final step to remove any trace of dark aluminum residue from the aluminum cleaner, I use brake cleaner and a clean blue shop towel to get the engine block shiny clean.
I got these brushes at Home Depot, but you can find similar brushes in most hardware stores.
I wear rubber gloves when working to keep the aluminum cleaner and brake cleaner off my skin.
Here is a short video summarizing the procedure and the final result that’s very close to the factory original patina.
VIDEO: 1983 BMW R80ST Refinish Aluminum Engine Block
Degrease The Bike
I start by cleaning all the oil, grease and crud off the bike using Gunk Foamy engine cleaner. I used three cans of the foamy engine cleaner to get a lot of the the baked on oil and grease off the bike. It was pretty filthy.
I use a nylon brush to loosen the crud and if it’s really baked on I use a stainless steel brush on it. I applied the engine cleaner in the street as the engine, transmission ,rear drive and wheels were really filthy.
Degrease the Engine Block
After I removed the engine from the frame and the top end off the engine block, there was still a fair amount of baked on oil on the block, so I use the Gunk Foamy engine cleaner, a steel brush to get it off and a paint scraper on the shelf at the rear of the engine block that’s under the transmission as the oil and gunk was very thick there.
The Foamy got most of the gunk off the engine block. When I removed the top engine cover there was some oil and dirt at the top of the engine block underneath the cover. I used the Gunk pump spray engine cleaner and a nylon brush to remove that.
Here is the degreased engine block at this point.
Refinish The Aluminum Engine Block
Before I start, I plug the push rod tube and oil filter holes to keep debris out of the engine.
There are a lot of dark spots of hardened aluminum oxide in the pores of the casting.
I start with the brass brush and spray a little aluminum cleaner and work it with the brush. Then I clean the black residue off with a blue shop towel and inspect the aluminum.
I continue working on these areas with the brass brush and aluminum cleaner. If I can’t remove the dark spots of aluminum oxide I switch to the stainless steel brush in tight areas and the green Scotch Brite pad in larger areas. Then I repeat brushing the case with the brass brush and clean off the black residue with a blue shop towel.
Eventually the darker spots look like they are pretty faint and I switch to the “0000” steel wool pad and scrub the block with it and aluminum cleaner. The steel wool creates a nice patina on the aluminum and also gets bits of dark aluminum oxide out of the nooks and crannies of the casting.
If bits of steel wool are left behind, they will rust and create brown spots in the aluminum. I thoroughly clean the engine block with aluminum cleaner and brake cleaner so I remove all the small bits of steel wool.
At that point I use the brake cleaner and a clean blue shop towel and wipe down the case to remove the last traces of dark residue. It’s not uncommon to see that some of the dark spots I thought were gone, show up again, but they are fainter, so I’m making progress.
So I use the stainless steel brush on the small spots with a bit of the aluminum cleaner. Then I finish up with the aluminum cleaner and the brass brush followed by the “0000” steel wool again.
After a couple repetitions of this procedure, and a final application of brake cleaner, the engine block has an almost factory original patina again.
There are some nicks, gouges and scratches on the block that can’t be removed, but the rough casting areas are clean once again. I’ll clean out the inside of the bell housing where the clutch and flywheel are located when I replace the clutch, the rear main seal and the oil pump cover O-ring.
Here is the refinished engine block. I estimate it took me about 10 hours over five days to complete the work.
I have not refinished the front engine cover nor removed the red paint and refinished the oil pan yet.