A Good Ride Spoiled

Torontonian said:

I've seen a drive side lobe on a 70 that had pitted hardening face marks on the ramps yet the highest point had no marks at all.

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That would be uncommon. There have been a number of photos of soft, wornout cams both here and on the other Norton site. All of those had lost a lot of lift.
If one absolutely must peer at every moving part, then there are cases to part, main bearings to check, conrods and Conrod shells to inspect and so on.
I wonder if some of these non-runner bikes are ones that came apart for inspection and never quite went back together again....

I’d advise caution asking a machine shop to inspect your bores. They may be sympathetic / sensible to the fact its an old bike, ridden like an old bike. But most are not, and will apply unsuitable modern, tight standards. So make sure you read the tolerance info in the workshop manual and ask them to check to that spec, NOT their modern opinion.

I once agreed with my machining guy that the valves and guides were clearly worn on my T160. So we fitted brand new, genuine valves and guides from a trusted source. When he’d finished, we were both surprised to find they were exactly the same as before !

Personally, if everything looks good, and if it’s all OEM stuff, I wouldn’t even change the rings or circlips. Cos unless you KNOW what you’re doing and what you’re buying, you could easily fit worse parts than you have.

All I’m saying is... if it were mine and I’d taken it down that far... I’d remove the barrels to allow inspection and cleaning for peace of mind.

Having now seen the bores on your bike I would be shocked if that bore/pistons/rings needed any work
I'd be shocked if the barrel needed skimming
And surprised if the head needed skimming
I wouldn't be taking any of it to a machine shop
You can deck the head by hand on some float glass if it needs it
It's not uncommon for the studs to be pulled a little causing a bump
This should be addressed imo
Personally I prefer a composite gasket with some wellseal painted around the pushrod tunnels mating faces

I always used standard composite baskets on my 850. I fitted them as clean and dry as possible. Meaning I’d clean the head and barrel face with brake cleaner and tissue until it was CLEAN. I didn't use any sealant. And I never had any leaks.

Composite gaskets aren’t available for 920‘s (and I wanted better control of the squish clearance) so I used copper. I used the JS method of copper wire and impact adhesive. It was an unbelievably horrid, fiddly task and I hated it. So far at least though, no weeps at all.

Tornado said:

In the last bore pic, is there much concern of the circular "center punch" mark on the A piston?

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umm... it's not a hole, is it?

It looks to me, that intake guide/seal allowed excess oil to burn, create deposits sending the compression ratio higher. When the throttle was opened (more than usual) the copper gasket that had been compromised by inadequate clamping (studs pulling) gave way under the higher pressure created by more complete combustion chamber filling.

JMWO

From the pics, the crosshatch pattern appears very shallow to me. IF the pics accurately show the crosshatch angle, I would reverse my previous opinion that agreed with those who said to just replace the gasket. If I pulled the head and saw that pattern (assuming it is accurately shown), I'd pull the barrels/resurface/install new rings.

Just curious - do you run a standard paper filter or a K&N/other aftermarket filter?

Crosshatching may be shallow, but it is "worn in" and I'd leave the barrel on and go with the pistons and rings you have now undisturbed. The problem was head gasket related.
Jaydee

Fast Eddie said:

I’d advise caution asking a machine shop to inspect your bores. They may be sympathetic / sensible to the fact its an old bike, ridden like an old bike. But most are not, and will apply unsuitable modern, tight standards. So make sure you read the tolerance info in the workshop manual and ask them to check to that spec, NOT their modern opinion.

I once agreed with my machining guy that the valves and guides were clearly worn on my T160. So we fitted brand new, genuine valves and guides from a trusted source. When he’d finished, we were both surprised to find they were exactly the same as before !

Personally, if everything looks good, and if it’s all OEM stuff, I wouldn’t even change the rings or circlips. Cos unless you KNOW what you’re doing and what you’re buying, you could easily fit worse parts than you have.

All I’m saying is... if it were mine and I’d taken it down that far... I’d remove the barrels to allow inspection and cleaning for peace of mind.

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Re the machine shop, there is a saying " If you go into the Bakery you'll probably come out with some bread"

The problem with removing the cylinder and not changing rings is that the existing bore to ring seal is lost. That's why it's recommended to install new rings and hone when removing cylinders.
I've tried putting things back together as-is twice. Got lucky with one and made a smoker out of the other.


Re crosshatch depth- I pulled heads on the Rapide a couple of winters back to replace inlet valve seals. The
crosshatching was more worn than in Mike's photos but still visible in places, surprising after 55,000 miles.
Total taper from the untouched very top of cylinder to the most worn part was just over 1 thou. Makes you realize just how shallow those hone marks are.
Hastings Ring Co recommends reboring at anything greater than 12 thou total taper.
I have some riding to do before rebore time.

Wow quite a mixed crowd we have.

All good advice and I know it is not ideal making assessments via pictures and second hand description.

What I think im settling on is to pull barrels and see ring state. We don't know what they are like and could be contributing to compression loss. Also, getting last bits of grit out from on top of the upper rings would be good idea. Plus I can then thoroughly clean the cam followers from any detritus that may have fallen in when pulling head. There was much crumbly crud on edges of tunnels where rods had to knock against during removal.
Im all for knowing state of the machine as much as possible for peace of mind.

MexicoMike said:

From the pics, the crosshatch pattern appears very shallow to me. IF the pics accurately show the crosshatch angle, I would reverse my previous opinion that agreed with those who said to just replace the gasket. If I pulled the head and saw that pattern (assuming it is accurately shown), I'd pull the barrels/resurface/install new rings.

Just curious - do you run a standard paper filter or a K&N/other aftermarket filter?

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Bike had paper filter when I acquired it two years ago, 7500 clock miles. Ive run K&N for most of next 7200 miles.
Now don't you go preaching about virtues of paper over oiled cotton, as I may have to dredge up old threads from you running velocity stacks in dusty Mexico

maylar said:

umm... it's not a hole, is it?

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Doesnt seem to be. Just a punch mark. Will poke it bit to see if crud filling an actual hole.

Tornado said:

Doesnt seem to be. Just a punch mark. Will poke it bit to see if crud filling an actual hole.

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Perhaps someone got carried away with a piston stop? Never seen a divot in a Commando piston before.

I lost a stellite pad on one of my followers 2 years ago while my bike was idling in the driveway... YES, I heard it break off and go clunk, clunk, clunk, so I shut the engine off. I pulled the head and barrels and there was the pad sitting on top of the cam lobe. I caught it in time, no damage to the cam.

I got a new pair of old stock followers from Jim Comstock and put the whole thing back together with the same rings... I got $10 bucks in my pocket that says anyone who wants to try and kick my bike over can't get it over TDC on their first attempt.... I don't know why you think you need to change the rings Glen.

Why would leaving it alone be OK, but pulling the barrels off to clean any grit off the pistons then putting the barrels back on be bad??

Sounds like you only think that you don't need bread if you don't go into the bakery... IMO, you don't know what you need until you take a look, then you go into whatever bakery your inspection dictates and buy what ever bread you need, and since you went into the bakery, you've visually inspected the cam, the followers, the pistons, the head bolt threads, and felt the rods for excessive big end play...

I'm going into that bakery to look around, and if I don't need anything, I'm gonna take one of their "sample" cookies on my way out!!!

If you read all of my post, or even just the whole paragraph about re-using rings, I explain why.

Loss of the bore seal with removal of the rings from bore is a well known problem , it's not something I made up.
My own success rate on this is 50% at the moment.

Also you misread the " Bakery and bread" analogy. Its in reference to Eddie's comment about his machine shop experience, not about an owner inspecting his engine.
I should add that there are lots of good machine shops out there and a few not so great.

Glen

some people would ride at 100 mph around a tight, blind corner.

Tornado said:

Bike had paper filter when I acquired it two years ago, 7500 clock miles. Ive run K&N for most of next 7200 miles.
Now don't you go preaching about virtues of paper over oiled cotton, as I may have to dredge up old threads from you running velocity stacks in dusty Mexico

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LOL, Excellent point! I am prepared to see bad-looking bores when the time comes... probably sooner rather than later!

Tornado said:

Wow quite a mixed crowd we have.

All good advice and I know it is not ideal making assessments via pictures and second hand description.

What I think im settling on is to pull barrels and see ring state. We don't know what they are like and could be contributing to compression loss. Also, getting last bits of grit out from on top of the upper rings would be good idea. Plus I can then thoroughly clean the cam followers from any detritus that may have fallen in when pulling head. There was much crumbly crud on edges of tunnels where rods had to knock against during removal.
Im all for knowing state of the machine as much as possible for peace of mind.

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Might want to look at the valves to see if they leak before you do that. You could be loosing compression there.

And since it is off, no big deal to get the mating surface skimmed.

Going over head today. Found no visible seeping when filling upper side of valves with WD40. Might try penerating fluid later.
Trying torque on three studs, using alu stock against head surface and stack of washers, book says 30 ft-lbs. Good at 20 but could not get click at 30, so appear to be pulling. Helicoil or other worked needed.
HG mating surface seems to have original casting roughness and not machined. Is that expected?
Got to get valve springs compressed and collets out to assess guides. Suggestions for suitable compressors?

Tornado said:

HG mating surface seems to have original casting roughness and not machined. Is that expected?
Got to get valve springs compressed and collets out to assess guides. Suggestions for suitable compressors?

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No, the head was definitely machined flat. I suspect that if you have at it with a scuff pad and kerosene it'll clean right up. I usually rub it against some 400 wet paper on my 1/2" thick glass flat plate.
My spring compressor is a generic thing that I picked up at the auto parts store. Had to make an adapter out of a short piece of black pipe to get over the top of the rocker.