MK3 CHAIN TENSIONER / SPRAG / OIL

Can someone help me with a few questions on the chain tensioning unit on a MK3..
I have just fitted the following new parts to my primary :

Crankshaft oil seal
Front engine sprocket
Sprag bearing unit
Gear crank wheel
Primary chain
Clutch drum bearing

1: On disassembling the auto chain tensioner I found the plunger unit assembled as per option 2 (see images below). I am wondering if they should have been assembled as in option 1.. I checked both my workshop and parts manuals but the drawings do not show the plunger as having a head.. Also on assembly does it mater which way the small hole in the plunger shaft faces? …

2: On fitting the clutch drum and front engine sprocket I aliened both with shims as per the workshop manual but I now find the primary chain is running very close to the ES gear idler, not much of a gap at all, is this correct (see images below)? Also there is a line running round this idler gear, should it face me or the engine?

3: Have I fitted the sprag bearing into the drum the correct way round ? ..

4: Once all is assembled do I fill the primary with the suggested 20/50 GTX or is there a better oil to use in regards to sprag etc..

I would appreciate all thoughts on any of the above…

Cheers
Paul

Hi,,

Can someone at least tell me which option to use from my images to refit the chain tensioner plungers back into the housing????

Thanks...

patience .....

the Mark3 experts are nice retired people and should be waking up from their naps pretty soon to help out

option 1
www.oldbritts.com/nor_mk3_75_10.html
Not shown clearly in this instance but option 2 is wrong

I'm awake (but I'm no expert!) so some thoughts:

Last time I took my tensioner to bits I cable tied the plungers to keep it all together, and that was a long time ago, so without taking my plungers apart, option 1 is correct. If you use option 2 it would compress the springs too much.
Just looked at the workshop manual, and it's not very clear!
When you assemble the unit test the movement of both plungers with the primary chain, and remember not to overtighten the three nuts on the tensioner outer plate otherwise the plungers could stick. That little hole isn't critical which way it goes.

The sprag looks good to go with the sprags leaning to the left.

Nice clean crankcase by the way

CB

The sprag bearing looks right, the flanged side goes in first.
The chain clearance is tight, I guess they had to squeeze it in there. Just make sure it doesn't rub.
Jaydee

Hi Paul.

1. You found them correctly assembled. Factory assembly pic extract below.



2. Do you have the factory gasket (thinking of thickness here)? Is the inner housing fully home, seeing as the retaining fasteners are only fitted after the stator carrier bracket is installed? Do you have the centre stud nut backed off? Is the front sprocket tight on the taper, as it may well go even closer when the alternator nut is tensioned? Is the crank "pushed in"? I have always fitted the idler gear groove out as you have it, but I cannot see that it would matter, as it is a "slab" gear.

3. The sprag has a "shoulder" that goes in, so it looks correct. There is the shouldered washer to go first, of course (which is not installed in your pic).


4. "Fill" as in 200 ml, I assume you mean. Like many, I have found engine oil better keeps the tensioners quiet. Just as an aside, I do think it is important to use eng oil that has 1200 ppm minimum ZDDP content in engines with FLAT tappets.
Oils that meet later specs than SG typically have less than 1000 ppm ( 300 or less even sometimes, depending on the oil), so you may want to check up on that. I use Motul 3000 4T (SG), which the product data sheet lists as 1200 ppm min ZDDP. Others likely have their own brand preference, but always with the zinc levels in mind.

Hope that helps,
Lyell

nznorton said:

Can someone help me with a few questions on the chain tensioning unit on a MK3..
I have just fitted the following new parts to my primary :

Crankshaft oil seal
Front engine sprocket
Sprag bearing unit
Gear crank wheel
Primary chain
Clutch drum bearing

1: On disassembling the auto chain tensioner I found the plunger unit assembled as per option 2 (see images below). I am wondering if they should have been assembled as in option 1.. I checked both my workshop and parts manuals but the drawings do not show the plunger as having a head.. Also on assembly does it mater which way the small hole in the plunger shaft faces? …

2: On fitting the clutch drum and front engine sprocket I aliened both with shims as per the workshop manual but I now find the primary chain is running very close to the ES gear idler, not much of a gap at all, is this correct (see images below)? Also there is a line running round this idler gear, should it face me or the engine?

3: Have I fitted the sprag bearing into the drum the correct way round ? ..

4: Once all is assembled do I fill the primary with the suggested 20/50 GTX or is there a better oil to use in regards to sprag etc..

I would appreciate all thoughts on any of the above…

Cheers
Paul

Click to expand...

nznorton wrote;

Also there is a line running round this idler gear, should it face me or the engine?

Click to expand...

I always put the idler gear in the other way round to how you have fitted it with the groove to the chaincase wall. My reasoning for this is I believe that the groove is able to hold a very small amount of oil for lubrication for the idler gear and the chaincase wall when you use the starter mechanism........but I'm no expert!

If anything can be fitted upside down, wrong way round, inside out, left or right, then I'm sure Norton will have had some input into it

The hydraulic plastic insert is so obviously machined or molded and made to go into the spring, with the head obviously made larger to fit into the bottom of tensioner. What is the point of machining a shoulder when just a plain rod would suffice! and be cheaper to produce!

The word 'obviously' is obviously to be used with extreme caution


CB

I was lucky enough to find the original patent information as "RENOLD ENGLAND - BRIT PAT. No.861741" is stamped on the underside of my Mk.3's tensioner plungers.

It appears the tensioner patent originally belonged to: The Perry Chain Company LTD., inventor: Nigel Henry Blakstad.
The description given precisely matches the operation of the Mk.3 tensioner.
http://worldwide.espacenet.com/publicat ... 1741A&KC=A

861,741. Chain and belt tensioning. PERRY CHAIN CO. Ltd. June 23, 1959 [Aug. 12, 1958], No. 25820/58. Class 80 (1).

To prevent snatch or jerking in a chain or belt drive on over-run, when the slack run becomes tensioned and the tensioned run becomes slack, and vice versa when the drive is taken up again, two spring-biased plungers 13 acting directly or through pivoted members on slippers 14 or on sprockets co-operate with the two runs of the chain, respectively on opposite sides of a sprocket, and reciprocate in hydraulie-fluid-filled cylinders connected with one another by a passage or an orifice 9, so that, in use, the two plungers move together in a controlled manner so as they effect a smooth change in the tensions of the two runs of the chain whenever a reversal or over-run of the drive occurs. The cylinders are kept filled with fluid from a reservoir 6 through clack-valves 20 in the plunger, as described in Specification 810,274, or a cylinder and plunger construction as described in Specification 788,500. In Fig. 4, not shown, the cylinders are offset one above the other and are joined by a bleed passage through the dividing wall. In Fig. 5, not shown, the tensioning units are positioned outside the chain runs and the cylinders are connected by a pipe of suitable bore.

Click to expand...

Complete document:
http://worldwide.espacenet.com/publicat ... cale=en_EP

The patent drawing clearly shows what appears to be a similar item to the plastic component orientated as in the "Option 1" photo.


To satsfy my own curiosity, I removed the tensioner mechanism from my own Mk.3 (that's when I noticed the patent number) and the plastic components were both fitted as in "Option 2". If Option 2 was in fact how the factory assembled the plunger assembly, then I suspect it could have been done to gain extra spring preload?

I can't recall the tensioner in my early MK111 ( 1/75 ) having those plastic guides. I wonder if they were a later modification ?

johno

petejohno said:

I can't recall the tensioner in my early MK111 ( 1/75 ) having those plastic guides. I wonder if they were a later modification ?

Click to expand...

Both of the plastic parts were stuck fast inside the plungers on my Mk.3 and I still haven't been able to remove one of them, so you may not even have known they were there?

That drawing that shows the plastic item up inside the moveable tensioner makes no sense.
Is it just an extra bit that they needed to use up? Not likely.
It makes more sense to put it in a position the would assist in metering the oil. Talk amongst yourselves.

The face groove in the idler is a puzzle indeed.
It serves no obvious purpose.
There is a boss that is proud from the clearance that is cut into the inner case.
The idler sits up against the boss, the diameter of which is far smaller that the face groove,
so the groove is never against any surface no matter which side is in or out.
And the groove is not an accident because it is in all the idlers I have seen.
To put it in requires intentional tooling. Strange.
On other parts, not motorbike in origin, I have seen grooves used for manufacturer identification where one meant metric internal threads and two meant imperial internal threads. The groove were also a registered trademark. Maybe it's meant to be a manufacturers mark of identity or to keep very similar but non-interchangeable items separate during manufacture.

The sprague position looks ok.

The chaincase oil can be engine oil or anything else that is compatible with the clutch linings and all the other moving bits.

All the best.

L.A.B. you constantly amaze me with your resourcefulness.
Many thanks for sharing that patent info and a tip of my hat to you sir.
All the Best.

A big thank you to you all for helping with your thoughts and suggestions on how these many primary parts should be correctly installed..

A few years ago I purchased this MK3 from the original owners son, during the stripping of the gearbox (to facilitate the renewal of the famous suspect lay-shaft bearing) I made contact with a friend of the son as I was told he doesn't use computers and is unreachable by telephone. The answers to my questions where relayed to me and I was told in the 26,000 miles of his fathers ownership to his knowledge nothing in either the gearbox or primary had ever been touched..

On stripping the gearbox I found at some point in the bikes life the lay-shaft bearing had in fact been replaced. I pictured it on this forum and was advised to replace it, which is what i did with the latest fag up-grad bearing.. I then stripped out the primary and found problems with the electric starting system, as you know I am now in the throw's of replacing these parts mentioned in this post, which lead me to the questions you guys have now kindly answered, it would appear these little plungers in the primary chain tensioner where installed incorrectly by the Norton factory or perhaps the son has forgotten about someone being inside this MK3.. One plunger is actually jammed in the bore so I will try and carefully remove it, hopefully this week..

I now find myself checking all parts I remove and not just taking for granted that all is factory correct and untouched.. I am so looking forward to getting the es working and my paint job back from the painter ..

Cheers
Paul ...

Regarding the orientation of the plastic tensioner inserts, is it possible that when assembled as in option #2 the head of the insert is in a proximity with the small bleed drilling so as to enhance the hydraulic action of the plunger? Sort of like a tiny front fork? It's odd that two of us found it assembled in the "obvious wrong way" along with the Norton assembly drawing as well. I vote for option #2.

The slipper plungers have a (spring) hole up the middle and a small bleed hole intersecting this at more or less halfway along the depth.
The location of the bleed hole means at least two things:
1. the top and bottom plungers can be identical.
2. the top plunger will trap air above the bleed hole.
The trapped air provides an air-over-oil cushion and smoother operation overall.
The plastic stud is plastic because it is quieter in a rattle situation than a metal part would be and less expensive than a moulded rubber part (no mould tooling cost).
This plastic part is about the right length to leave the bleed hole unrestricted.
The plastic part displaces some of the trapped air thereby providing the possibility of some tuning of the air cushion.
The diameter was likely determined empirically.
My previous statement about the factory drawing not making sense was premature. It does make sense.
All this is true or the best bullshit story so far.
Corrections are welcomed.
All the best.
ps I am fed up with snowstorms.

Both of the plastic parts were stuck fast inside the plungers on my Mk.3 and I still haven't been able to remove one of them, so you may not even have known they were there?

Click to expand...

Yeah I suspect your right. They seem to work OK.

Johno