Mk3 Primary

Hi,

I now have a few hundred miles on my new, to me, 850 Mk3. About 500 miles ago, the PO had a new sprag clutch and sprocket etc. I assume there was a failure. Lately, first start with the button, I just get a whirring. No clacking or grinding, just a spinning. Then it catches second attempt. It's also fine if I ease the motor past compression with the kickstart. I also have a healthy weep from the rear / bottom of the primary seal. I researched the primary and starter threads on here.

I drained the oil, it was dark, with a fine metallic content. Also, well below the drian plug level. I'd say c.200cc was in there. Being the hydraulic primary chain tensioner version, I think it should have more oil (to the level screw). Also the triplex primary chain looked quite slack. Just off the chaincase. I'm assuming that's because the hydraulic tensioners had bled down?

I am thinking:
- The anti backfire may not quite be torqued-up enough, causing the starter to slip;
- The metallic oil may be due to the previous sprag failure;
Reasonable?

I cleaned everything out. Read the Old Brits article on the anti-backfire adjustment, which put me off a bit. I don't weld and so don't have access to a tool for checking the backfire device torque setting. For the moment I've put a new (AN) gasket on, with Wellseal and put in enough oil to the level plug, leaving it a couple of hours, to make sure it wasn't still weeping (just over 300cc). I plan to run it for a hundred miles or so and then drop the oil again, to see if it is clean. I'm hoping there's nothing more sinister. Does that seem sensible?

I know the starter problem won't disappear on it's own, but want to solve one concern at a time. Assuming I'll still have the starter slipping problem, does the anti-backfire seem a sensible cause? How do you adjust yours to get it right? As I understand it, it is the nut on the spindle inside the alternator stator, that I need to adjust (tighten a touch)? Can I do this leaving the stator and everything in place in the Primary?

Thanks,

Martin

When the anti-backfire overload slips I believe it will make a loud clacking. I built the tool and found that my overload would must have been slipping at some time and then seized; it would have never slipped again until I disassembled and repaired it. When setting the slip torque it snaps on release, it's not a smooth release so if you're not hearing it, the sprag is probably failing to catch.

Any chance there was gear oil or some synthetic oil in the case?

If you don't replace ALL the mating parts when replacing a sprag it's likely to fail again at some time.

Mart UK said:

Also the triplex primary chain looked quite slack. Just off the chaincase. I'm assuming that's because the hydraulic tensioners had bled down?

Click to expand...

No, the springs inside the plungers should be maintaining chain tension Edit: so either the springs need replacing, the plastic inserts are fitted incorrectly (heads outwards instead of inwards?) or the chain is worn out?

Mart UK said:

The anti backfire may not quite be torqued-up enough, causing the starter to slip;

Click to expand...

Mart UK said:

Assuming I'll still have the starter slipping problem, does the anti-backfire seem a sensible cause?

Click to expand...

No.
Over-tightening the anti-backfire is one reason why the sprag gets broken if the engine does kick back.
If the anti-backfire device slips then you will hear it as it makes an unmistakable loud clattering sound (as JimNH mentioned) like the torque clutch on a battery drill, (only louder as that's basically what it is) not a whirring sound.

If the sprag is slipping then the sprag parts probably need to be replaced.

Mart UK said:

As I understand it, it is the nut on the spindle inside the alternator stator, that I need to adjust (tighten a touch)? Can I do this leaving the stator and everything in place in the Primary?

Click to expand...

It's the nut, item '9' on the starter driveshaft '14'.
The alternator outrigger plate Edit: (also rotor and stator and I think also the plate from the chain tensioner) must be removed in order to remove the starter drive shaft.


I've set the slip torque using a socket with short lengths of welding rod inserted to grip the splines.

Martin, there is a oil level plug (slotted screw, bottom center) in the Mk3 primary case. If you fill the primary with oil until it weeps out of this opening (per the manual) it is about 300 cc, not the 200 cc (pre-MK3 spec) in the manual. At 200 cc the oil level is well below this opening and does not come close to touching the chain. I fill to the oil level opening (~300 cc) to insure that the starter gears and sprag are lubricated and the hydraulic tensionerss are primed. At 300 cc, I have never had any issues with clutch slipping, which is the downside of too much oil.

I get some debate about this with some other MK3 owners who stick with the (Pre MK3) 200cc spec versus fill to the oil level plug. Their rationale is that the movement of the bike is enough for 200cc's to lubricate and keep tensioners primed.

In MHO, more lubrication is better for a MK3 given all the additional mechanicals in the MK3 and opt for filling to the oil level plug.

Slack chain may be causing the chain to contact the cases. That’s probably where the metal is coming from. I did adjust my anti-backfire device (over 20 yrs ago) and did not use any special holder. I just don’t remember how I did it, but it is do-able. If everything worked for a while and then started to act up you may have to replace all the working parts around the sprag also. I believe CNW’s has all new and improved parts. I would also make sure the tensioner is completely clean and has the gasket installed (this part is not shown on all parts diagrams).

I would definitely consider the new layout with new and better parts from CNW
Vidar

Mmm. Lots to think about. CNW is out of the question for now, on cost grounds.

After the oil refill, I did start it up this afternoon. It started first time. I have noticed the battery is only 12Ah and 4 years old. It takes a charge, but seems to need a charge after each ride. I think the alternator is working, the red ignition light does not come on with the motor at tickover. I'll measure the voltage across the battery with the bike running, to check. I'd expect to see around 14v?

Could lack of umph from the battery cause what I'm seeing? I have a nearly new 16.5Ah, same dimensions, I can swap in, to see if that helps.

I'd like to check the primary chain tension, now I've run it a few minutes, to see if the higher oil level has made any difference to the hydraulic tensioners . I can't see it is possible to do this through the small inspection cap (with the timing guage behind it)? It looks a bit too small. Is there a way to check with the cover on? I should have checked the tensioners, when the cover was off. I assumed they had bled down, explaining the loose chain. Schoolboy error! I'm hoping I can avoid dealing with the Wellseal and gasket again...

Mart UK said:

I'd like to check the primary chain tension, now I've run it a few minutes, to see if the higher oil level has made any difference to the hydraulic tensioners.

I should have checked the tensioners, when the cover was off. I assumed they had bled down, explaining the loose chain.

Click to expand...

The plunger springs provide the chain tension as I mentioned previously.

The tensioner, once primed, maintains a constant tension on the chain as it rotates, it doesn't 'pump' both plungers against the chain so doesn't increase chain tension as you seem to think.

Martin , I just spent a lot to upgrade my MK111 primary. Find the money for the CNW components. Hardened sprockets and gears. Hardened clutch center. Don't worry about the anti-backfire device. Clean oil is essential with more changes than the engine ! The tensioner will not tolerate contaminated oil with metal bits. $Spend.

How about trying the Alibaba sprag, mentioned on another thread on this forum? It's reported to be "worth it" in spite of it's cheap or low cost. Cj

L.A.B. said:

The plunger springs provide the chain tension as I mentioned previously.

The tensioner, once primed, maintains a constant tension on the chain as it rotates, it doesn't 'pump' both plungers against the chain so doesn't increase chain tension as you seem to think.

Click to expand...

Got it, thanks. So, the tension I saw, will be the tension it will run at. I really appreciate the input, as i get to understand what I've got....

It wasn't touching the bottom of the case, but it was within 5mm. Closer than I'd expect. I guess oscillation when running could easily take up that gap. I don't recall marking inside that area as I cleaned the case, but stupidly, I didn't think to particularly look for it. So, either my primary chain has stretched, or the tensioner isn't doing its job? Grasping at straws, if the top hat spacers the spring pushes on, are in the wrong way, I guess that could rob it of some of the spring adjustment. I need to look at it and check for the gasket But, looks like I will have to undo the case again. Groan!

On the sprag, I recently looked at CNW for silicone gaskets when i sorted the rocker cover leak. £54 just for post and packing put me off. Replacement innards would push it into customs duty territory too. The next month or two, i want to watch what i spend. Just concentrate on what i must do to enjoy some spring and summer miles on the bike. But, get the risk of false economies...!

Steven Griffith said:

Martin, there is a oil level plug (slotted screw, bottom center) in the Mk3 primary case. If you fill the primary with oil until it weeps out of this opening (per the manual) it is about 300 cc, not the 200 cc (pre-MK3 spec) in the manual. At 200 cc the oil level is well below this opening and does not come close to touching the chain. I fill to the oil level opening (~300 cc) to insure that the starter gears and sprag are lubricated and the hydraulic tensionerss are primed. At 300 cc, I have never had any issues with clutch slipping, which is the downside of too much oil.

I get some debate about this with some other MK3 owners who stick with the (Pre MK3) 200cc spec versus fill to the oil level plug. Their rationale is that the movement of the bike is enough for 200cc's to lubricate and keep tensioners primed.

In MHO, more lubrication is better for a MK3 given all the additional mechanicals in the MK3 and opt for filling to the oil level plug.

Click to expand...

Steven
Where did you get the 300cc spec?
The shot below (I've left enough pics so you can see it's for Mk3) is from the "Commando - Norton Riders Manual - 850 MkIII Models" and it clearly states "7 fl.oz. (200)cc of fresh oil. be careful not to overfill"

Mart UK said:

It wasn't touching the bottom of the case, but it was within 5mm. Closer than I'd expect. I guess oscillation when running could easily take up that gap. I don't recall marking inside that area as I cleaned the case, but stupidly, I didn't think to particularly look for it. So, either my primary chain has stretched, or the tensioner isn't doing its job?

Click to expand...

Think of the plungers as pistons each end of an oil-filled cavity that are constantly moving as the chain rotates. As one chain run tightens it pushes the plunger inwards which, due to the oil between them, forces the plunger on the slack run outwards so maintaining the chain tension.

At rest, the upper plunger and spring should be supporting the chain...

...the lower plunger and spring will be pushing against the lower run and there isn't much free space between the chain and the case when the chain becomes worn.

As the chain wears, with the upper run 'tight', the lower run can eventually touch the case...

Any scrape marks could be from a previous worn chain but can be checked by pushing down on the lower chain run where the marks are.

Whether it was a factory bodge to increase chain tension, the nylon plugs should be fitted with the heads against the springs.

robs ss said:

Steven
Where did you get the 300cc spec?
The shot below (I've left enough pics so you can see it's for Mk3) is from the "Commando - Norton Riders Manual - 850 MkIII Models" and it clearly states "7 fl.oz. (200)cc of fresh oil. be careful not to overfill"

Click to expand...

It's not actually a written "spec" but if the Mk3 chaincase is filled to the level hole then the quantity of oil will be 300+cc/ml which doesn't seem to cause any problems and the additional oil probably does help to speed up the priming of the tensioner.

LAB, thanks. Much appreciated.
I put in a touch over 300cc and then waited a few hours for it to stop dribbling out of the level. My chain is not as loose as the photos. My 5mm estimate was whilst putting finger pressure on the bottom run. So, there may be some life left in it?

I think I will do a short run today and then empty the oil and see what it looks like.

I will subscribe to the forum.

Thanks,

Martin

L.A.B. said:

It's not actually a written "spec" but if the Mk3 chaincase is filled to the level hole then the quantity of oil will be 300+cc/ml which doesn't seem to cause any problems and the additional oil probably does help to speed up the priming of the tensioner.

Click to expand...

Thanks Les - I hadn't checked the volume before overflow - but will!

Will put my hand up now (and bow my head?) but I put a measured 200cc in last time and am sailing on in blissful ignorance.
All seems fine......

...and I'm sure you'll be fine. I guess, provided your chain dips into the reservoir at 200cc, it can only make a small difference at initial start up. With the risk the extra oil coats the clutch. But the difference in level across the case between 200cc and 300cc must only be a millimetre or two, probably within the factory's initial manufacturing tolerances!

Steven Griffith said:

Martin, there is a oil level plug (slotted screw, bottom center) in the Mk3 primary case. If you fill the primary with oil until it weeps out of this opening (per the manual) it is about 300 cc, not the 200 cc (pre-MK3 spec) in the manual. At 200 cc the oil level is well below this opening and does not come close to touching the chain. I fill to the oil level opening (~300 cc) to insure that the starter gears and sprag are lubricated and the hydraulic tensionerss are primed. At 300 cc, I have never had any issues with clutch slipping, which is the downside of too much oil.
snipped

Click to expand...

Steven,
In Section A, Capacities, the Mk III Workshop manual does call for 200cc of oil. However, that is just another of the many errors. This info was simply copied over from the earlier manuals without change. Something that is done in a number of places in the manual.
Section C34, Step 37 simply states to refill the primary, with no mention of method or amount. However, Section K9 clearly describes filling to the level plug, as you have outlined above. I'm going to correct that 200cc statement in Section A of my edited Mk III workshop manual.
It stands to reason that the Mk III primary case will require more than the 200cc called out for earlier primary cases, as the longer crankshaft and added starter motor drive gear required a pair of wider primary drive cases.
Sections K2 & K3 state that the primary oil is to be changed every 3,000 miles.

Mart UK said:

snipped the difference in level across the case between 200cc and 300cc must only be a millimetre or two,sniped

Click to expand...

A 50% increase in oil volume will raise the level more than "a millimeter or two".

So, on 200cc vs. 300cc for a Mk3, after a 10 mile ride yesterday, to try and flush out any remaining particles, I changed the primary oil again. There was some metal dust in the oil. I measured the amount of warm primary oil that came out of the drain. Just about 200cc! I left it to drain for an hour. I put 200cc in, then added a thimbleful and it started to ooze from the level hole. So, in my case at least, an oil change was 200cc for a Mk3. From completely dry, I guess an initial fill would probably be more.

I don't get any strange grumblings or scraping from the chain case, but I will do 50 miles tomorrow and then look inside the case again at the weekend. I'll check the tensioners. If they look ok and the chain is still very loose, time to spend again. I find the AN parts diagrams a bit confusing. I have 4 diagrams open, flicking between to work through what goes where! Will be more obvious with the open case in front of me.

If I stay with the stock set up, and replace the primary chain, sprag, do I also need items 19 and 21 (starter drive gear and thrust washer) in this drawing? https://andover-norton.co.uk/en/shop-drawing/133/electric-start# Do I also need the needle bearing (item 20)?

To replace the primary chain, do I need to replace the triple sprocket: item 32 here: https://andover-norton.co.uk/en/shop-drawing/132/gear-linkage-chains-alternator-engine-sprocket# And item 2, clutch chain wheel, here: https://andover-norton.co.uk/en/shop-drawing/130/clutch, or, if they look OK, leave them in place?

Whilst there, I'll look at the tensioners / check for gasket. Anything else I should check / be sensible to replace?

I will read through the shop manual, NOC's service notes etc. And go step by step. If i have to replace the clutch chain wheel, I'll also need to buy the clutch tool. Any other special tools /anything else to be wary of?

Thanks,

Mart