Lower end flush?

[ZillahBill]

I have the renovated CB77 jugs and head back from the machine shop. My question is should I flush out the lower end before reassembly? I have taken the oil drain plate off and everything looked good, nothing in the screen, just a little very dirty oil residue. This motor has not run in 40 or 50 years. Should I fill the crankcase up with some solvent to soak and clean? What do some of you CB77 experts think? The oil drain cover plate had been off before because it had some red gasket sealer on it. I'm thinking they were just trying to reuse the old gasket. It doesn't take gasket sealer does it? Thanks in advance for answering my questions. Regards, Bill

[Michael Stoic]

I think flushing is a good idea. I'd use straight diesel fuel (it's a great solvent AND an oil) and then plan on several oil changes, in quick succession, with regular oil, once the motor runs.

[oldbikedude]

You certainly could use kerosene and flush out the cases. The gaskets should be dry on a clean surface. You probably already knew the answer to this. Good luck with your project and keep the pics coming.

[deuce_7]

Good idea for the Flushing. To consider:

Get a head start on the flushing and sludge removal by first removing and cleaning the under crankcase. Now would be the time, with engine disassembled. I did this a few years ago when doing the CL77 top end. With the under crankcase removed, found one of the 6mm knock bolts (and lock washer) that secures the cam chain roller pin had backed out and was lying on the bottom of the crankcase.

Also consider replacing cam chain and cam chain roller when under crankcase is removed.

[ZillahBill]

Thank you and I'm glad no one said, "No, you've got to take the whole thing apart." I don't want to do that. I want to see if I can get it running in its' current state. While the top end is off I think I'll buy a couple gallons of diesel, pour it into the crankcase, and let it steep a couple of days. Dry gaskets on a clean surface. Got it.

[Tim Allman]

I would be concerned about residual metal chips from the machining much more than I would about discolouration or 'varnish' from the old oil. If you change your oil regularly when you get it running, the old oil residue will be gradually removed by the detergents in the new oil without the need to flush.

In your situation I would closely inspect, visually and by feel, everything for metal chips. This refers to all of the interior surfaces, the oil pump and all of the bearings. Rotate the main bearings, the rod bearings and the oil pump while feeling the motion. All of these should be very smooth. The crankshaft and connecting rod bearings are almost impossible to inspect without a hydraulic press so feeling for roughness is probably all you can do. Visiting a repair shop that understands these old roller cranks might be worthwhile. I my case, I thought my rod bearings were too rough but during a visit to a shop I was convinced that the very slight roughness I felt was unlikely to be a problem.

Should you need them, finding replacement bottom end bearings is difficult and expensive but fortunately the originals tend to be in good shape if the engine has not been abused. Keep in mind that these engines are somewhat overbuilt as this same crank assembly was used in the CYP72/77 café racer and probably on the track as well. These engines are durable. The camshaft bearings are much easier to deal with as they are a standard size sold by any industrial supply place. I replace those if there's even a hint of roughness.

[Geoff Hastings]

While I agree with all the advice given regarding flushing I just thought I’d share a photo from a crank from a Yamaha RT2 my son bought. We knew the piston was seized due to corrosion but once freed off and the cylinder removed the crank felt ok and ran smooth with no signs of a problem. Seeing the amount of corrosion in the main bearings we got the crank pressed apart just to be sure, lucky we did! It was dire, yet it felt smooth with no play at all.