Pulled the head and request forum's expert advice

[arbrnrngr]

FIrst off, not sure the photo links below do what I hope, which is to show the head and jug but I'll try to frame my question sans pictures in case:

Head removed primarily due to broken stud when retorquing to address oil leak that looked focused on front. Picture of head shows a fair amount of oil and a left side combustion chamber that's pretty crusted up with carbon deposits. The right side doesn't look as bad, though it too seems like it's not burning well - and I don't know the history on this as it was purchased from a middleman as a 'barn find'. Pistons are STANDARD and bike appears low mileage. So with head off, my question is whether best to send it out for a head rebuild (L/S intake looks like seal may be seeping oil), to verify the surfaces 'true'/flat, etc. - or just anneal a new copper gasket and go for it? In photo you can see it was shoddily sanded in a cross hatch manner (amateur?) so clearly there's improvement possible here. I'm leaning to a quality rebuild since it's off...

Same for cylinder. If you can see the photo, you'll understand: While both cylinder walls look smooth, aside from carbon build up at top, there is a shiny area on the left front cylinder about 1/2" from bottom dead center. I can feel absolutely nothing - it's just shiny yet smooth as is the rest of cylinder wall so I'm inclined to just leave it, however I'd hate to soon learn I could have avoided a blown piston (or?) for lack of a little preventive parts-replacement... Does anyone think there's a problem about to get worse here? Also, if I pull the jug, it could stand cleaning and paint.

I think I can hear Pink Floyd's "Money" starting off in the background with those awesome cash registers. Now, where is Roger to start that bass line?

Cheers,
Kev

[Image codes corrected - L.A.B.]
Cyl. Head:

Cyl. Head - different angle:

Left Piston:

Copper Head Gasket:

 

[concours]

From my small iPhone screen that looks like redeposited aluminum. But usually less defined that than. Muriatic on a Q-tip etches it off if that's what it is. You should, at this point, pull the cylinder, and measure it & the pistons. Have a engine rebuild shop measure if you don't have access to the tools/skills. At the very least ring end gap will condemn/validate. You're in the neighborhood, it'd be a shame to miss the opportunity.

 

[Rohan]

OK, its an 850, so I'm on familiar ground.

My barn find 850, with only 12000 miles showing on the speedo (??) had very worn piston rings and bores.
And looked to have been a real oil burner, like yours.

If the lip at the top of the bore hadn't been so pronounced,
I would have just been tempted to just re-ring it - with new rings obviously.

What was interesting was that it had only been standing several years.
But several of the rings were REALLY stuck in their piston ring grooves.
So for compression or oil scraping their contribution would have been zero...

There is also a school of thought that doing the top end in a Commando without checking
the bottom end is not such a good idea. This is up to you to decide...

Yep, money pit.
Although the bits are very reasonably priced.
And a lot of it you can do yourself.
And you get lots of advice from folks here who have likely done exactly the same stuff
Have fun !

 

[concours]

"There is also a school of thought that doing the top end in a Commando without checking
the bottom end is not such a good idea. This is up to you to decide..."

To your point, first thing I did was install an oil pressure gage, to have another clue to rod bearing health. Then, having learned "Super Blend" bearings had come standard, that helped me decide to stop teardown at the base gasket. Also allowed cam lobe inspection. :mrgreen:

 

[arbrnrngr]

Great advice all. Thank you. Was pretty much headed to pulling jug but will also try the Q tip as it DOES appear like it could be aluminium (sorry, had to use the Brit term since daughter lives in Scotland).

Once head's off, as suggested, will take a look at cam, and other bits. In for a penny...

This wouldn't be so bad if, on my other '74, we hadn't found A LOT of metal during an oil change following last summer's rally. So that engine's sitting next to this, awaiting tear down. Fortunately, through all of this, my '75 (that I bought new), still runs great! I'm coming to conclusion that unless you buy a C'do that was built and wrenched by a "known" name mechanic (and/or AccessNorton members of course), the best course of action is to just do the tear-down up front because my experience is that there are always problems with these bikes being incorrectly rebuilt. I've had to redo wiring, reroute cables, properly re-torque nuts/bolts, etc. on the 2 'used' bikes I have to eliminate safety problems (e.g. rear brake, misrouted throttles, even incorrect oil line routing).

Anyway, thank you for your suggestions. Ride safe.

Kev

 

[acotrel]

It doesn't take much effort to work your way through a motor and replace the essentials - rings and bearings, valve grind and replace the valve springs. If you do it slowly and thoughtfully, you should not have a problem. As in the world of computers, you can always phone a friend. Things such as excessive bore clearances and wear in valve guides don't have much effect, however you should carefully check the big end clearances.