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Discussion Starter · #1 ·
About 10 years ago, I purchased a 1981 CM400T with 12,733 miles on it. Blue. I'll get pics up when I can. Family, work stuff happening now. Not yet. Eventually.

Rode the bike for about 9 years, stopped April 1, 2009. It had 49,250 miles on it. It was a rather leaky, greasy mess (head gasket, the gasket at the base of the cylinder sleeve). And it smelled like burnt oil whenever I stopped somewhere (where the gearshift shaft entered the crankcase, oil was leaking onto the exhaust collector and smoking). So I decided to take it down for serious cleaning with no idea when I would finish.

A friend did something (bead blasting?) to make the fins (EDIT: of the cylinder sleeve) look nice and clean again. I cleaned the rest of the engine thoroughly, and it took a long time (the gasket shellac at the base of the cylinder sleeve was especially hard to remove). I got new piston rings and had the cylinder walls prepared. The first time I reassembled it, a piece of a piston ring broke and fell into the engine. I took the case halves apart again but never found it. The second time I reassembed, I tore the base gasket (between the upper case half and the cylinder sleeves).

As I was cleaning the carbs, one screw head broke off at the "top cover" or slide cover. I drilled a small hole, but broke the main carb casting when I used a screw extractor. Got used VB22A carbs off eBay, used these carbs with my original jets. I finally rode it to work one day in September 2009. It ran on one cylinder. Also oil continued to leak out of the gearshift shaft onto my exhaust collector. And some gas expanded and removed the paint from a small portion of my tank near the gas cap (DARN YOU LOUSY EPA and your winter gasoline!!!).

Got a pair of carbs off eBay (VB22G this time), and transferred my factory jets, etc. from the old eBay carbs to these new eBay carbs. I also cut and primered a piece of sheet metal and placed it between the engine and the (re-cleaned) exhaust collector. (And I got some really nice header pipes from eBay as well.)

I finished it last night (June 13, 2010) and ran it for a minute or two, but it still runs on one cylinder (air-fuel mixture screws 2.0 turns out). Both cylinders run more frequently than in September, however. Perhaps I have reached the limits of my carb cleaning skills and should try the factory carb refresh kits? (I suspect the problem is not dirt, but the needles.)

Future plans:

Now I am thinking about tearing it down again and replacing cam chain, and balancer chain. And someone suggested there is a chain inside the oil pump mechanism (visible inside the right side [clutch] cover?).

Since the camshaft is held on by the same bolts as the head (unlike a car), I was thinking about dropping the cam chain into the crankcase, rigging up a new cam chain and dropping most of it down inside the crankcase as well. Installing the head bolts exactly as before (use the silver anti-seize compound again, don't disturb the heads whatsoever) and I should be able to save the head gasket, base gasket, and rings.

Then remove the engine, turn it upside down, and split the case halves. Remove the assembly holding the crankshaft and oil pump, then remove the crankshaft (but don't remove the pistons -- they've only got about 75 miles on them and I want them to continue breaking in). Remove the old cam chain and rig up the new one I dropped in. Replace the balancer chain as well. Make sure the cam and balancer are in the correct positions during reassembly. Then install the carb refresh kits.

Does this sound like a plan? This isn't really "restoring a barn find", but just fixing up a daily driver that has developed oil leaks over the years.

P.S. Are these older air-cooled machines always going to start leaking oil between 12,000 and 20,000 miles? I asked about this over at allaircooled dot com (VW beetle, microbus) and they didn't really have any good answer. Does it depend on the engineering maybe?
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