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Lannis Offline OP
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Started out investigating carburetors, Rohan reminded me check compression first so I did, first with my old gauge and I didn't like the numbers so I bought a new gauge and ....

100 PSI on the right side, 55 PSI on the left. This is throttles open and engine cold, because cold is all I got unless I take a blowtorch or heat gun to it.

wrenches come out in the morning, check to make sure that lack of valve lash isn't holding a valve open (a forlorn hope), then a leak-down test, then start taking the top end off which I've not done on a Norton before and will be asking questions.

Of course, I was working on it because the BritBikeBeach Run is coming up in 7 weeks and I hoped to not repeat the ignominy and shame of 2012 when I led one of the ride groups on a modern Moto Guzzi and was roundly and properly chastised for it, which is why I own this Norton in the first place. I won't know until in the morning when I do the leakdown test if the problem is obviously a valve or obviously piston ring blow-by, but I'll be soliciting information if there's anyone in range who can do a Norton top-end job between now and mid-March if I deliver and pick up the head, cylinder, and pistons ... ....

So the process begins, I'll be in touch, and thanks in advance for your help.

Lannis


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If you tip a teaspoon of engine oil down each plughole and turn it over a few times, and test the compression again, this can tell you lots.
Doing it cold is not ideal, but if the compression jumps up much at all, this tells you immediately the rings aren't good.
You can usually hear if the valves leak. Plus the kickstarter ebbs away underneath you

Nortons are a little famous for the rings sticking in the grooves. Ask me how I know this.
I've still got a pair as removed, I never did succeed in freeing off the rings.
And, oddly, the Porsche Owners Club don't recommend Castrol GTX, because you guessed it,
it causes stuck rings. Hmmmmm ?

If you have a leaky head gasket, you can usually hear it too.
If its bad, even when running.

If you pull the pushrods up into the head, you can tip the head over and remove out off the frame.
Then remove the cylinder - this is an 850 ? - I forget.
Measure carefully - you may get away with just new rings.
That is a long trip the rings travel every rev...

Ain't old bikes fun !

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The left side rings wear quicker than the right side, rule of thumb is 2 sets of rings to one set of pistons. I re-ringed my MK2a after it started to smoke out the left silencer under acceleration.

If the bike has been standing for a long period it may just need a good blast to free up a sticky ring.

As a 75 it will have the RH4 head, very susceptible to inlet guide hole cracks in the head, so if its currently crack free and you plan to get work done on the valves then get the guides lined and not replaced. Driving old guides out and new guides in risks cracks in the head casting that are extremely hard to get repaired. Lining old guides removes that risk.

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Ya might want to check the camshaft…’75 are notorious for having soft camshafts. PO may have tried to compensate worn camshaft with valve adjustment…measure rocker movement on all valves before you remove head.
Rod

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I'm following all suggestions, and the results are as follows:

1) Tipped a tablespoon of engine oil into the low (55 PSI compression) cylinder. It only brought the compression up about 4 PSI to <60, so it's probably not a critical or stuck ring issue.

2) Checked the valve clearances before unbolting anything. They were a bit loose at .013 intake/.015 exhaust, on both sides. I'd never noticed the engine being noisy, though. But the clearances were not tight, which might have resulted in a valve being held open when hot.

3) Got out the leakdown tester and set up with 90 PSI air. The right cylinder (which had >100 PSI compression), showed in the middle of the gauge's green "Low Leakage" range at 25%. The left cylinder (which had 55 PSI compression) showed 65% leakage, well into the "Problem Zone". And air was puffing out of the left exhaust port, even though I checked and the valve was closed with .015" clearance. Couldn't hear any leakage out of the breather or the intake port.

So it looks to me like a leaky exhaust valve. I spent time printing out the manual to use it in the shop, fiddling the carburetors off, using RF's lovely heavy-duty exhaust ring removing tool, and was in the process of figuring out how the rubber mounts on top of the head worked when time ran out. Is there a trick to taking off the spring-loaded thingy on the front of the rubber head mount? The manual doesn't say anything about it.

Head off and measurements tomorrow.

Lannis


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Originally Posted by Lannis
was in the process of figuring out how the rubber mounts on top of the head worked when time ran out.

https://andover-norton.co.uk/en/shop-drawing/136/engine-mountings-spring-head-steady-
You remove the side plates #10. The rubber mounts can be left on the frame. Edit Or did you mean what it is they actually do?


Originally Posted by Lannis
Is there a trick to taking off the spring-loaded thingy on the front of the rubber head mount? The manual doesn't say anything about it.

Slacken nyloc nut #7 (above link) or you can just remove the three (5/16" BSF) head steady cap screws #16.

Edit: Make a note of the spring/trunnion gap setting and retainer plate hook position see manual Fig. C1(a) before slackening nut #7.

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Thanks, all ... I'm trying to treat this like we're in a parking lot working on this Norton .... I'll try not to ask you guys to be walking, talking Norton shop manuals, so if I can look it up, or find it with a simple web search, I will.

On the other hand, I'm not going to be the strong silent type that will spend hours figuring out some technique that other guys have figured out years ago and could just tell me.

I almost stopped to ask about that rear-most cylinder head stud that's way up under there .... finally figured that a 1/4W ring spanner, with the access panel to the airbox removed, has enough clearance and swing to get the nut off the stud. (By the way, I'm surprised that in 1975, a Whitworth wrench is still the right thing to use for all the cylinder head bolts, since 14mm and 9/16" don't fit. I thought the Brits had abandoned Whitworth about the time my '69 BSA was made). And I assume that I will use a bio-calibrated hand and wrist to get the 30 ft-lb torque that it goes back on with, since no torque wrench I've ever seen will get up in there.

I've been stumped on two of the front bolts. I got the 1 stud in the back, the four bolts flanking the spark plugs, and the 3 in the very front down inside a deep recess. The manual says "Leave the rocker covers on when you remove the head." But the manual shows 10 cylinder head bolts, and when I overlay the diagram onto the bike, they must be right under the exhaust valves (if they're there). I can't even see them with a flashlight. IF they're there, I would have to pull the exhaust rocker shaft to even see them, much less get a wrench on them.

ARE they there on a MkIII 850? Or is the manual speaking with forked tongue, and the rockers have to come apart (which precludes "Leave the rocker covers on when removing head")?

Thanks!!

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Well my 2 nuts under the exhaust valves are covered in black paint so also not to be seen. But if yours are cleaner than mine they can be seen poking out the bottom of the head and some barrel fins.

https://andover-norton.co.uk/en/shop-details/16029/cylinder-head-sleeve-nut-nm24260-nmt2034-

[Linked Image from andover-norton.co.uk]

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Originally Posted by Lannis
I thought the Brits had abandoned Whitworth about the time my '69 BSA was made).

Not Norton although not all are 'Whitworth'

Originally Posted by Lannis
And I assume that I will use a bio-calibrated hand and wrist to get the 30 ft-lb torque that it goes back on with, since no torque wrench I've ever seen will get up in there.

It can be done with the right tools.

Originally Posted by Lannis
I've been stumped on two of the front bolts.

But the manual shows 10 cylinder head bolts, and when I overlay the diagram onto the bike, they must be right under the exhaust valves (if they're there). I can't even see them with a flashlight. IF they're there, I would have to pull the exhaust rocker shaft to even see them, much less get a wrench on them.


ARE they there on a MkIII 850?

Yes.
Sleeve nuts below the exhaust ports so towards the bottom of the barrels with 7/16" A/F hexagons although 3/16W also fits.


Originally Posted by Lannis
I got the 1 stud in the back,
The manual says "Leave the rocker covers on when you remove the head."
the four bolts flanking the spark plugs, and the 3 in the very front down inside a deep recess.


The rear nut is No.2.
No.1 is the centre bolt at the front.
Remove all except for the No.1 bolt and use only that bolt to finally release the head as then it lifts squarely.



Originally Posted by Lannis
Or is the manual speaking with forked tongue, and the rockers have to come apart (which precludes "Leave the rocker covers on when removing head")?

No.

Last edited by L.A.B.; 02/04/22 5:17 pm.
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I'll go out and lay down on the floor and have another look.

kommando, IS that tool required to get those sleeve nuts off? If it is, my schedule is probably hosed, because I'll never get it from the UK in time ....

I've been reading L.A.B. and others input on "Access Norton" on various subjects relating to cylinder heads, and especially how to get the pushrods in when you get it back on, so I won't have to be asking about that, I hope .... !

Lannis


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Originally Posted by L.A.B.
Yes.
Sleeve nuts below the exhaust ports so towards the bottom of the barrels with 7/16" A/F hexagons although 3/16W also fits.


Originally Posted by Lannis
I got the 1 stud in the back,
The manual says "Leave the rocker covers on when you remove the head."
the four bolts flanking the spark plugs, and the 3 in the very front down inside a deep recess.


The rear nut is No.2.
No.1 is the centre bolt at the front.
Remove all except for the No.1 bolt and use only that bolt to finally release the head as then it lifts squarely.



Originally Posted by Lannis
Or is the manual speaking with forked tongue, and the rockers have to come apart (which precludes "Leave the rocker covers on when removing head")?

No.

Thanks! Off I go ... Got to leave to pick up the grandkids for the weekend in a couple hours, so may not get much work done unless I can convince my 6 year old boy or 8 and 9 year old girls that working on a greasy old bike with Grandpa would be more fun than exploring the creek or playing Caroms or Scrabble ...

Lannis


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Originally Posted by Lannis
IS that tool required to get those sleeve nuts off?

No, just a normal spanner.

[Linked Image from i.postimg.cc]

Last edited by L.A.B.; 02/04/22 5:38 pm.
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Quote
kommando, IS that tool required to get those sleeve nuts off? If it is, my schedule is probably hosed, because I'll never get it from the UK in time ....

No, normal spanner as LAB has said, it's just AN salesmanship.

Never used a torque wrench on a Norton twin head, but there are ways to use them even for these awkward nuts.

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Originally Posted by kommando
Quote
kommando, IS that tool required to get those sleeve nuts off? If it is, my schedule is probably hosed, because I'll never get it from the UK in time ....

No, normal spanner as LAB has said, it's just AN salesmanship.

Never used a Torque wrench on a Norton twin head, but there are ways to use them even for these awkward nuts.

Thanks. I've found that so far, I've had all the right tools, as well I should after 20 years of keeping my BSAs running, as well as buying RF Whatley's tools last fall. It's described on Access Norton how to cut and weld a 1/4W ring spanner so as to attach a torque wrench to get that nut back on right, but I really really think that I can hit it pretty close just by feel. That rear stud wasn't hard to remove ... after 1/2 turn with the wrench, it came off with my fingers. I'll clean the nut and threads good before it goes back on.

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Originally Posted by Lannis
I thought the Brits had abandoned Whitworth about the time my '69 BSA was made).

LAB: Not Norton although not all are 'Whitworth'
*********************************************************************************


For the most part with possible few exceptions.
1. All featherbed were still brit threads.

2 The new Commando designed components were introducing UN family threads. Therefore started in 67
however
The items and assemblies retained and carried over from before, mainly engine transmission retained the early brit hardware.

3. The next major engine crancase revision to have UN hardware changes was 200000 series. with new cylinder studs and internal timing chest hardware.

4. The 300000 series engine had more UN upgrades such as the 2 7/16 cyinder sleeve nuts in the pix above.

This is not an all inclusive list but a general trend that has become evident based on evolution research on original norton bikes.


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Originally Posted by Lannis
IS that tool required to get those sleeve nuts off?

Also...

That 13.1660 1/4"WW combo spanner...
https://andover-norton.co.uk/en/shop-details/16029/cylinder-head-sleeve-nut-nm24260-nmt2034-
https://andover-norton.co.uk/en/shop-details/18702

...fits the earlier 1/4" Whitworth hexagon sleeve nuts...
https://www.rgmnorton.co.uk/buy/cylinder-head-sleeve-nut_3907.htm

...therefore, does not fit the 7/16" reduced hexagon sleeve nuts used on later models including the 850 Mk3.

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Originally Posted by Dave Comeau
4. The 300000 series engine had more UN upgrades such as the 2 7/16 cyinder sleeve nuts in the pix above.

Only the sleeve nut hexagon size changed.

The (3/8") stud/nut thread wasn't changed to UN (at either end of the stud).

Same NM24389/067885 3/8" - 20 x 26 stud (x3) and 26 TPI rear stud nut NM24250/067870 from 20M3 to 850 Mk3.
https://andover-norton.co.uk/en/shop-details/17374/cylinder-head-stud-3-8-nm24389-
There's no equivalent 3/8" - 26 thread in any UN series as far as I know.

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Let me know if you need anything Lannis, I've got a freshly machined .040" over barrell with pistons, rings & lifters.
New cam

Remember to THOROUGHLY CLEAN the area between the barrell & head fins, full of sand, glued in by oil & cooked.
WD-40, compressed air, 3/32" welding rod to dislodge, etc.

Last edited by Howard Inough; 02/05/22 1:47 pm.

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Originally Posted by Howard Inough
Let me know if you need anything Lannis, I've got a freshly machined .040" over barrell with pistons, rings & lifters.
New cam

Remember to THOROUGHLY CLEAN the area between the barrell & head fins, full of sand, glued in by oil & cooked.
WD-40, compressed air, 3/32" welding rod to dislodge, etc.

Thanks, good advice on the cleaning. I know I've got a bad exhaust valve on the left side, but I figure that as long as I've got it this far, I may as well measure and look and maybe at a minimum install new rings. Hopefully I won't have to bore it or go to an oversize cylinder. I'm hoping that the cylinder that I have is standard bore ....

Lannis


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Originally Posted by Lannis
...I know I've got a bad exhaust valve on the left side...
Lannis, what does bad mean in this instance?
I've got some random missing on the left side and I'm thinking I need to look into diagnosing a sticking valve.


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Originally Posted by Hugh Jörgen
Originally Posted by Lannis
...I know I've got a bad exhaust valve on the left side...
Lannis, what does bad mean in this instance?
I've got some random missing on the left side and I'm thinking I need to look into diagnosing a sticking valve.

From a few days ago, above ...


3) Got out the leakdown tester and set up with 90 PSI air. The right cylinder (which had >100 PSI compression), showed in the middle of the gauge's green "Low Leakage" range at 25%. The left cylinder (which had 55 PSI compression) showed 65% leakage, well into the "Problem Zone". And air was puffing out of the left exhaust port, even though I checked and the valve was closed with .015" clearance. Couldn't hear any leakage out of the breather or the intake port.

So it looks to me like a leaky exhaust valve
...

Leak-down testers, like battery load testers, are very valuable but seldom used home shop diagnostic tools ... !!

Lannis


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Doh. Mea culpa.
Thanks.


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Originally Posted by Lannis
Thanks! Off I go ... Got to leave to pick up the grandkids for the weekend in a couple hours, so may not get much work done unless I can convince my 6 year old boy or 8 and 9 year old girls that working on a greasy old bike with Grandpa would be more fun than exploring the creek or playing Caroms or Scrabble ...

Lannis

Well, actually that plan worked. Emma grabbed a ratchet handle and a 5/16W socket and went to work

[Linked Image]
[Linked Image]

and after all the head bolts were out she held the pushrods up into the head while I tilted the head back .... 9 years old, I'll teach her to be a mechanic yet ...

[Linked Image]

Looks to me like the left side has been burning a lot hotter than the right, possibly the reason for a duff exhaust valve, I better check my needle/slide settings or just buy a Mikuni .....

[Linked Image]
[Linked Image]

Cylinder off Monday and valves out of the head and have a look, I guess ...

Lannis


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With one ultra oily pot like that, what you want to watch when you take the inlet valves out is whether the inlet valve
stem seals are still intact and sitting on top of their valve guide.
https://andover-norton.co.uk/img/imagescaler/b8/b8ad4d8c60209fb004ce0036f6961426.jpg

If not, that could explain the excessive oil.
If they are in place, you may need to dig a little deeper ...

Great little helper you have there !

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Originally Posted by Hugh Jörgen
Originally Posted by Lannis
...I know I've got a bad exhaust valve on the left side...
Lannis, what does bad mean in this instance?
I've got some random missing on the left side and I'm thinking I need to look into diagnosing a sticking valve.

This has absolutely buggerall to do with sticking valves, but if you are getting any leak down past the valves, some combustion chamber cleaner might be worth a try. If nothing else, there will be less crap to scrape off if you do tear it down. I’m anti snake oil and generally don’t use any additives, but do use combustion chamber cleaner. We used it prior to shimming the valves on the DOHC fours. I’ll spare you all the details, but Honda ended up supplying it to their dealers because it made a difference. Bike comes in with excessive valve clearance….run combustion chamber cleaner through it and then remeasure the clearance… made a difference. Now you could adjust the clearance properly with no risk of burnt exhaust valves.

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