I Spy With My Little Eye...

Cylinder walls of my '74 850:




Bike has done around 5-6k miles since first re-bore to 20 thou over. Are these to be considered normal or of concern?

Can't say for sure about yours with any certainties but it looks a he'll of a lot better than mine did

Can you feel them (head off?) Or view from a bore scope?

MikeG said:

Can you feel them (head off?) Or view from a bore scope?

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Head is not off...imaged via borescope.

They look fine.

MikeG said:

Can't say for sure about yours with any certainties but it looks a he'll of a lot better than mine didView attachment 118053

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Ouwie! Was that from a wrist pin clip going adrift?

I should state me reason for taking look via borescope was to find out if any obvious reason for 5-7psi lower compression on left cylinder. Bike has felt a bit anemic recent outings, less strong exhaust pulse out of left side. Plugs look good and similar.
Will try a retorque of head bolts....copper gasket on though and have done a couple of retorques shortly after rebore.

When I have my head off and using copper head gaskets I only ever retorque the copper gasket at 500 miles then forget, they aren't like the fiber gaskets that need retorquing many times over, them marks could be the ring gaps maybe, they don't look deep, as for 5-7 psi difference in each cylinder is not a great deal could be a few things to cause a difference, what oil are you running???

ashman said:

When I have my head off and using copper head gaskets I only ever retorque the copper gasket at 500 miles then forget, they aren't like the fiber gaskets that need retorquing many times over, them marks could be the ring gaps maybe, they don't look deep, as for 5-7 psi difference in each cylinder is not a great deal could be a few things to cause a difference, what oil are you running???

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Valvoline VR6 Racing 20w50. Engine doesn't smoke. good starting and idling. Just feels weaker than in the recent past, with a noticeable periodic hesitation while at steady speeds....my imagination goes to engine "nipping up" but have no first hand knowledge of what that would feel like.

Were the valve lashes checked ?

Maybe your just over thinking things and worrying about what may happen instead of just enjoying your ride times, 5-6k miles is not really that many miles, if you do regular maintenance you should get long life out of your cylinders/motor as for your motor nipping up it would have done that a long time ago if there was a problem with too tight of clearance between final piston to hone bore and most bike shops when doing rebores will always do the final clearance a bit more as their thinking is not knowing how the bike will be run in by the owner, any other time nip ups is when something fails or breaks.
A lot of things can cause a slight drop in PSI in a cylinder and how accurate is your compression tester or using it right, a valve not seating right on one cylinder, all guess work really.

Ashley

BERT said:

Were the valve lashes checked ?

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Yes, I did a check last year when I noted this issue. All seemed ok and resetting to spec made no change in the issue. The left side seems to also give more clatter from the top end so valve clearance was worth checking anyway.
When amoungst other 850's at club outings, my bike doesn't sound the same, no pop to the exhaust when firing up and idling like others seem to get.

Thinking to ask some club members if they can help me do a leakdown check (I've no access to a compressor).

ashman said:

Maybe your just over thinking things and worrying about what may happen instead of just enjoying your ride times, 5-6k miles is not really that many miles, if you do regular maintenance you should get long life out of your cylinders/motor as for your motor nipping up it would have done that a long time ago if there was a problem with too tight of clearance between final piston to hone bore and most bike shops when doing rebores will always do the final clearance a bit more as their thinking is not knowing how the bike will be run in by the owner, any other time nip ups is when something fails or breaks.
A lot of things can cause a slight drop in PSI in a cylinder and how accurate is your compression tester or using it right, a valve not seating right on one cylinder, all guess work really.

Ashley

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Well the compression guage was the same used side to side...so even if not giving accurate readings, it should at least be consistent btwn sides...and it's more about being within a few psi on each side, right? Perhaps the copper gasket is developing a blow out, like I had on this bike a few years back.

Normally copper head gaskets will seep before a full blow out and normally fixed by retorquing as well look at how a Norton motor is set up the left side has more weight hanging off the crank than the right side, has a stator/ALT and a triplex chain etc etc. so in reality the left side does more work lol so the right side is on easy street compared to the left side with load wise, I just look at things differently in my eyes and the way I do things, after 49+ years of ownership I just know my own bike and the way I built it and every motor is different in sound or what they do, one Norton will make noises more than others and some run sweeter than others and as I say you might be worrying over nothing, if its running sweet and starting easy, just ride it and enjoy it before it goes bang, no only joking, about the bang that is, the more you worry about things the more it will happen, well that's my opinion anyway.
I be more worried if those light scrapes be deep scrapes in your bore or finding metal in your filter or on your sump magnet.

Ashley