MKIII Primary chain noise

Could use a little advise/help on a 75 MKIII.
Bike has not run in six years.
I've done the basic's - engine oil change, check/adjust valves, check/set timing, rebuild carb's, etc..
Dealing with a issue in the Primary.
I've flushed the primary oil a few times but continued to hear, what to me sounded like a chain rub noise at around 3K to 5K rpm while going through each gear.
Pulled the cover and found this.
Second pic shows what I may have been hearing.

I've read a couple posts on this but am hoping someone could school me on how much I need to disassemble to get at and check the oil passage's on the top & bottom tensioners. Seems like I also read about a check valve in the manual too.
I'm assuming the top one is not getting oil to hold it in a tensioned position? Allowing a slackened chain to rub agaisn't the lower case.

One issue at a time getting this back on the road.
Thanks in advance, Ken




Wear Marks


Top Tensioner


Bottom Tensioner

CR125Honda said:

Could use a little advise/help on a 75 MKIII.
Bike has not run in six years.
I've done the basic's - engine oil change, check/adjust valves, check/set timing, rebuild carb's, etc..
Dealing with a issue in the Primary.
I've flushed the primary oil a few times but continued to hear, what to me sounded like a chain rub noise at around 3K

Click to expand...

Hi Ken

To get easy access to the tensioner remove the generator rotor and stater and carrier and the backfire protection mechanism then the tensioner fasteners. Before you dive in have you tried priming the tensioner manually? Fill the well between the the steel deflector plate and the tensioner body with oil and pump the plungers once primed they should move as one from top to bottom.

best regards

Esme

There's supposed to be a gasket between the plate and the tensioner to help keep the reservoir from leaking out when the machine sits. The check valve is just a small ball-and-spring in the tensioner body that lets the tensioner plungers extend and then blocks off when they compress.
First time I took mine apart, there was no gasket, and I was not aware until later that it even existed. Once I found out and acquired one, I pulled the cover and plate and put the gasket in place. After that, the startup rattle was gone because the tensioner no longer loses it's prime over time.

Danno said:

The check valve is just a small ball-and-spring

Click to expand...

There is no "check valve", and no spring. There is a two way "shuttle valve". When the tensioner is dis-assmebled, and cleaned, the ball can easily be heard rattling back and forth when the tensioner is shaken. The ball moves constantly back and forth during operation, controlling oil flow in both directions. This is essential for the "hydraulic cushion" effect.

Classic Cycle Repair said:

There is no "check valve", and no spring. There is a two way "shuttle valve". When the tensioner is dis-assmebled, and cleaned, the ball can easily be heard rattling back and forth when the tensioner is shaken. The ball moves constantly back and forth during operation, controlling oil flow in both directions. This is essential for the "hydraulic cushion" effect.

Click to expand...

It seemed to me from the very lengthy discussion in the previous thread that the tensioner was full understood.
The ball/check valve is a one way valve only to fill primarily the top piston. Exit not allowed is the natural function of a check valve.
The top/master piston then transfers oil to the bottom/slave piston through the tiny transfer hole.

Oil only exits through each pistons oiler holes or leaks by the bore clearance.
I'm surprised that it works at all with the BLACK MUD contamination. I'd guess the bike has a fiber friction plates which I am beginning to think is a no-no for MKIII.

CR125honda:
hydraulic tension must come apart and both primary and tensioner must be inspected and scrupulously cleaned of mud + bronze plates

https://www.accessnorton.com/Norton...c-tensioner-assembly-doesnt-make-sense.27790/

dynodave said:

The ball/check valve is a one way valve

Click to expand...

Incorrect. It is a 2 way valve.

dynodave said:

only to fill primarily the top piston.

Click to expand...

Incorrect.

dynodave said:

Exit not allowed is the natural function of a check valve.

Click to expand...

True (but irrelevant here).

dynodave said:

The top/master piston then transfers oil to the bottom/slave piston through the tiny transfer hole.

Click to expand...

Oil passes through that aperture, but to state that it only does so via the action of the upper tensioner plunger is incorrect. It is not "tiny", it is adequately metered.

dynodave said:

Oil only exits through each pistons oiler holes or leaks by the bore clearance.

Click to expand...

Incorrect. The oil exits right back out past the ball bearing, until such time as the flow moves the ball to the outer end of the valve. This is because thew valve has no spring, as it is not a check valve, but a 2 way shuttle valve, designed to allow the oil to escape momentarily, providing the essential hydraulic cushion action to the primary chain tensioning.

dynodave said:

It seemed to me from the very lengthy discussion in the previous thread that the tensioner was full understood.

Click to expand...

That is clearly not the case.

Chain marks on bottom of case suggest a new primary chain is required

CCR
The emperor has no clothes

cross over port #68 drill .031"
There is no other direct connection from the inlet check valve to the slave side except the .031 drilling.
check valve inlet .146" to master cylinder only.
cross over passage is 4.4% size of inlet check valve port
or 22.3:1 ratio is tiny in my view though it is also adequate.
My point is restated and you are entitled to your ???? evaluation.

Thanks everyone for helping with this.
When I checked yesterday, the tensioners would move independent of each other.
I.E., I could squeeze them together, resisted only by spring pressure.
Have learned there needs to be oil in the "chamber" and pushing on one should move the other when operating correctly.
I'll disassemble today and see what I can find.
This help lets me know what to look for.

On the chain, wondering if a new chain would rub if the tensioner was inop?
Should I just get a new chain?? 18k on the mileage.
I've seen slack measurement limits for timing chains (on other bikes) but haven't seen any reference for a primary.

At first glimpse, I also thought under that the black goo at the bottom of the case was old clutch plate build up.
Ended up being a patch job on a cracked cover.
Found out today the owner did the patch many moons ago.

dynodave said:

There is no other direct connection from the inlet check valve to the slave side except the .031 drilling.

Click to expand...

There is no "master" or slave side. "Slave" means it only operates when the "master" causes it to. The lower tensioner plunger operates completely independently, and exactly the same as, the upper tensioner plunger. The "inlet" shuttle valve has to be physically located somewhere (that allows it to actually fit, and also that facilitates correct function), and fluid is provided to both plungers form that position. The upper plunger can remain completely still, and this has no impact whatsoever on the movement and operation of the lower plunger.

dynodave said:

CCR

cross over port #68 drill .031"
check valve inlet .146" to master cylinder only.
cross over passage is 4.4% size of inlet check valve port
or 22.3:1 ratio is tiny in my view though it is also adequate.

Click to expand...

There is no check valve. There is only a shuttle valve. Why is that the tensioner does not function as well with lighter weight oils? If the tensioner operated with a check valve, it would. But as it has a shuttle valve, the lighter weight oils do not "carry" the ball back and forth as effectively, allowing excessive fluid discharge.




It is not a "cross-over" port specifically, but rather a feed hole that due to the design of the tensioner also operates in a cross over manner.
There is no "master cylinder".
Of course the feed port to the lower plunger is much smaller than the shuttle valve, as the shuttle valve contains a ball bearing.
The plunger "oiler holes" are even smaller again, so do you refer to them as "mega" tiny? Is a 0.031 tappet gap "tiny". I disagree with your perspective.

I cannot assist further.

1) I don't care what you want to call the little thingy with the spring loaded ball in it on the tensioner but I will tell CR 125 Honda that with all of that "gunk" in the bottom of the primary case that the tensioner will not work because the "check valve" will be clogged up and little to no oil will be getting inside the tensioner to do its job.

2) I took out all of my sprag gear, back fire stuff when I pitched the useless starter years ago so I don't remember if you really have to take the alternator and carrier off first. My feeble brain remembers taking the three nuts off the plate and somehow manuvering the tensioner out saving hours of extra work. Then give it a thorough cleaning and inspection.

3) Search the archives for "primary chain tensioner" There is lots of usefull information to be found.

4) Although the workshop manual states that no maintenance is required we, the owners of MKIII's, know better.
Any sludge will clogg the tensioner so my chaincase gets the oil changed with the motor oil and the whole thing cleaned and inspected over the winter months.

5) Despite what some people will tell you the MKIII should have motor oil in it not ATF. ATF is not thick enough to work the tensioner properly.
Prime everything before reassembly and make sure you install a gasket between the shield and body (not shown in parts book) and fill the little trough in the rear.

The above 5 points are my opinion and not stated facts. I have worked my MKIII primary case and tenioner for 44 years so maybe I know a thing or two,,,,,,,or maybe not.

Ride On (to the rallye)
Dave

Norton's are new to me but I've also been wrenching 50 plus years.
Again, Thank you all for the help.
The experience on forums are great for the gotcha's the manuals don't explain.
Hope to get this sorted out tomorrow.
Will follow up when able.

Update time..

Disassembled the tensioner.
Found some crud in the passageway to the inlet port.
Did not have a gasket. Looks like the plate to tensioner reservoir was sealed with "aviation permatex".
No spring behind the ball.
I did flush out a small metal circular shaving behind the ball though.
The color of the primary oil was "milky" when I first drained it a two weeks ago. Tried flushing it 4 times. The oil out of the last flush looked much better but the noise continued so I decided to disassemble.
It's obvious now the oil was not reaching the oil port inside of the tensioner.

Plastic inserts installed in top and bottom tensioner correctly per research in this forum - (narrow end first, i.e. most spring tension).
All small oil passageways were/are clear (body top to bottom and each tensioner)
Also found a couple missing rollers in bearing FJ-2520. Strange. No galling on shaft. Didn't find the missing rollers.

New bearing and chain on order.

Clogged inlet / milky oil


Traces of old sealant (Aviation Permatex type?)


Top tensioner housing


Bottom tensioner housing


Missing bearing rollers


Misc

Thanks for posting all of this. It is especially interesting to me because this job is in my future. The P. O. decided to remove the starter and all associated gear, years ago. The parts came in a box with the bike though. Cj

I had a Mark 3 awhile ago.
It had a terrible rattle in the primary.
I replaced and fiddled with everything except changing the chain.
It got better to a just off idle rattle. The final fix was to raise the idle to about 1200. Worked for me.
I sold it before I got around to replacing the chain, it had about 25k miles.

I've often wondered if I had replaced the chain if it would have been fine.

My question is, properly set up, do these work fine with a normal 1k idle?

This one has wear marks on the case below the tensioner. Also just noticed in one of my pics above, it has wear marks above the tensioner. Pretty obvious a chain rubbing the case could cause noise. My tensioner was inop. Repairing that alone may have cured this problem but I'm replacing the chain too. That way, IF the tensioner ever fails to operate again, odds are better the chain won't be rubbing.

Hi Ken
Caught me off guard. My $100 MKIII (current primary runner) has not been apart since 95 and my 5 mile MKIII has never been apart. I would have to mock up an engine/primary/tranny to see If a chain will touch top and/or bottom if pulled tight on opposite run if the chain is to spec and not worn out.
Any chance you can get away to the michigan rally starting next monday? I'm bringing a box full of MKIII primary parts for one of the tech sessions.

dynodave said:

I'm bringing a box full of MKIII primary parts for one of the tech sessions.

Click to expand...

Just the tech session I've been waiting for!

So many people think they have all the answers to 'primary' questions but don't realize the MKIII is a completely different animal.
See you at the rallye.
Ride On (rain or shine)
Dave

dynodave said:

Hi Ken
Caught me off guard. My $100 MKIII (current primary runner) has not been apart since 95 and my 5 mile MKIII has never been apart. I would have to mock up an engine/primary/tranny to see If a chain will touch top and/or bottom if pulled tight on opposite run if the chain is to spec and not worn out.
Any chance you can get away to the michigan rally starting next monday? I'm bringing a box full of MKIII primary parts for one of the tech sessions.

Click to expand...

Thanks Dave,
With my left thumb's built in "torqueometer", I'm gunna say it takes about 15 lbs of pressure to make the chain touch the lower case. Would expect that probably take's less pressure as the engine and oil heats up. Didn't try upwards as I just saw those marks today in the pics. CYA says replace the chain. Strange on the missing needle rollers.
Would love to make it to the rally, meet the Norton crew and get in on the sessions. Enjoy that kind of stuff. This season has been non-stop with prior commitments / life. Doing my best to make it the British rally here in Cincinnati with my T120R, this fall.
I'll update again as parts are replaced. Will also try and compare chain stretch - old to new.
Ken

BTW - Found a great guy here locally that did a fantastic TIG weld job on the cover. Finished the job with an Xray inspection.

CR125Honda said:

.........Will try and compare chain stretch - old to new.
Ken

BTW - Found a great guy here locally that did a fantastic TIG weld job on the cover. Finished the job with an Xray inspection.

Click to expand...

IMHO its going to be hard to compare new and old chains, however I thought a new chain helped my bike with chain slap. Never had the chain rubbing though. Good job on the welding.