I Spy With My Little Eye...

Tornado

Tornado

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Cylinder walls of my '74 850:

I Spy With My Little Eye...
I Spy With My Little Eye...
I Spy With My Little Eye...
I Spy With My Little Eye...



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
I Spy With My Little Eye...
 
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???
Click to expand...
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.
 
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
Click to expand...
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
 
A few things come to mind. More about the loss of pressure and possibly power than the marks on the bore. I agree they are probably not an issue and just keep an eye on them with a boroscope.

Copper gaskets can be a bit difficult to seal 100 %. Hopefully you sprayed them with coper coat before assembly.

When you retorqued did you back off the nut first and then retorque. It takes some pressure to overcome the static friction if you just retorque and don't back off first.

Check the tappet clearance after retorquing.

Check the oil carefully for any sign of metal.

I'm almost paranoid about ignition timing. Don't know what system your using but if points check BOTH sides. Also don't know your compression ratio but full advance between 28 to 31 deg is good. 28 if your up at 10 to 1 or more.

Again don't know what carbs you have but always worth a careful check to see if things are OK. Except when a bike is highly tuned or raced the standard carb settings by the book works for me 99 % of the time. If your rich a visit to a dyno with a mixture analyser is often worth it.

Any popping always check for leaks in the inlet tract and exhausts, especially the header pipes.
 
I did not fit the head after the rebore, it was a restoration shop though I have since found some of the things they did were not right, so gasket might not have a sealer applied.
I do use the undo before retorquing method.
Running VapeWassell EI for past 8 yrs without issues. Amal Premiers.
Have not strobed timing for some while so will do that soon. But should be at 28 btdc still.
 
Tornado said:
Thinking to ask some club members if they can help me do a leakdown check (I've no access to a compressor).
Click to expand...
Please consider the possibility of a "leakup", i.e., valves not seating properly, or eroded seats/valve rims.

- Knut
 
mdt-son said:
Please consider the possibility of a "leakup", i.e., valves not seating properly, or eroded seats/valve rims.

- Knut
Click to expand...
I thought similar.

Not sure if it’s a trick of the light or not, but there looks to be a lot of thick, hard, carbon build up on those pistons.

Perhaps there’s carbon on the valve / seat reducing the compression ?
 
Tornado said:
But should be at 28 btdc still.
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Not that it explains the difference but for EI you can time to 31 BTDC at the EI's recommended revs not the 28 BTDC at 3K for points. Once fully advanced the points stop advancing, for EI its a curve where at high revs its still advancing very slowly but you can use more advance as the wander of the points is missing and there is no difference for side to side timing due to the self correcting of using 2 magnets on the rotor and 2 sensor coils on the stator.

Wassell instructions for Norton twins is 28 to 31 BTDC at 4 to 5K.
 
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