New (to me!) '77 CB400F - US model

[paul G]

Finally, the oil pan appears to be cracked (hmm... thumbnail upside down again?):

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It’s not, however, in the “usual” spot, around the drain hole.  Plus, no matter how carefully I look, I can’t see any evidence of it on the inside:

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Is it possible that there’s some sort of fracture that doesn’t go clear through?

I would get that welded up anyway or bin it and get another.
If that goes while you are riding then its a cert the rear Tyre is going to get a coating of its contents

[Bryanj]

It could just be a casting flaw

[mattsz]

It could just be a casting flaw

Have you seen this sort of thing before, Bryan?  If the lack of visible cracking inside the pan isn't convincing, would a "gravity" petrol leak test tell you anything?

[Bryanj]

I see casting marks all the time petrol on inside may show a leak or you could see if anybody local to you in engineering has a dye crack detection kit but if you are real worried can you not get a used one

[mattsz]

I see casting marks all the time petrol on inside may show a leak or you could see if anybody local to you in engineering has a dye crack detection kit but if you are real worried can you not get a used one

I know some engineering types who may be able to help with leak testing.

I wouldn't say that I'm "worried," since the inside looks fine to me.  I've shopped used ones on Ebay (US), not much there that isn't in worse shape than mine!  I'm actually more worried about the shrapnel that I removed from the sediment in the pan!

[mattsz]

I almost threw away the washer that fits between the oil filter and the big spring - it was stuck to the filter and I didn't notice it until I was dropping the filter into the recycling bin.

The washer is bent.  How on earth does that happen?  It's sturdy enough that I can't bend it back with bare hands... 

[Bryanj]

Never seen a bent washer (probably found on workshop floor after being driven over), lost of missing ones yes. The aint expensive to replace.

[mattsz]

Never seen a bent washer (probably found on workshop floor after being driven over), lost of missing ones yes. The aint expensive to replace.

Only very slightly bent... I'll flatten it back out with a hammer - or replace.  Actually, it's probably fine as it is... just surprised to see it.  I guess nothing should surprise me on this bike...

[mattsz]

Still pondering the possibly cracked sump...

I'm still not sure if the cam chain tensioner action is working, but at least I've found that the external nuts and bolts are free and functional, so that's something.  I know bryanj has described the simple procedure for setting the cam chain tension with the engine off, but is there a simple way of checking the action with the engine not running?  I've photographed the internals through the bottom opening revealed by the sump removal, but I cannot see the tensioner horseshoe or the other parts... I'm not sure it's visible...

[mattsz]

... is there a simple way of checking the action with the engine not running?

Anyone have any ideas about this?

[mattsz]

I don't know where this bike was ridden, but the gunge inside the sprocket cover is shocking - chain lube (I assume) flung everywhere, and dirt/sand/grit thickly mixed throughout!  The cover wasn't too bad to clean, as it's removable... but the engine, still on the bike?  What a mess!  Same gunk that was all over the rear of the engine, swing arm, chain guard...

I must admit I'm surprised to see the sprocket mounting splines on the end of the shaft displaying surface rust - everything else is coated with crap, but it's clean and dry (and rusty).  I guess chain lube gets thrown away from the shaft...

Before:

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After:

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Piles of crap scraped off:

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[K2-K6]

... is there a simple way of checking the action with the engine not running?

Anyone have any ideas about this?

If you uncinch the chain tensioner clamp bolt then put a telltale rod into the shaft hole,  now put the bike in (take out the spark plugs first) gear and turn the rear wheel backwards,  it should visibly push that rod out as the cam chain trys to deflect the tensioner and so rock the horseshoe backwards. 
Then re tension if you turn the engine forward to pull the front chain run tight again, leaving the slack at the rear run for the tensioner to follow suit.
In essence the tensioner rod should go up and down when using opposing direction of crankshaft travel if left unlocked.

[K2-K6]

Note;- you've only to turn the crank maybe 10 degree in either direction to see the above and not multiple rotation.

It's just to flip flop the excess play in the chain to front or rear orientation within the two runs inside the cylinder block.

[mattsz]

Thanks K2-K6, that's helpful!

[mattsz]

I followed your suggestion, K2-K6... there is upward movement of the "telltale" rod when I bump the engine backwards - but not much, maybe just a couple of millimeters... does this sound right?  I don't know how much movement is ideal...