Mark III primary chain tensioner (2015)

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lazyeye6

lazyeye6

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I bought a '75 Mark III with 1500 original miles on it. It had been in dry storage for 30+ years. I recommissioned it with all of the appropriate work and replacement expendable parts. It starts instantly with the stock electric starter and runs and rides like a new machine. When
idling slowly cold the primary chain slaps a bit against the chain case. It goes away with more RPM and after warming up does not slap at idle. Any thoughts on why it would be doing this?
 
do you have the correct type and qty. of oil in the primary?

the MKIII has a hydraulic chain tensioner so the oil is critical.

Also the seals could be bad in the tensioner
 
There are no seals to speak of in the tensioner. There is a check valve in there and also a gasket that seals the flat plate onto the tensioner body. There is also a nylon spacer under the springs, if put in upside down it has less spring tension.
+1 on oil type. I use 20-50 MC oil that is designed for engine/transmission use, i.e. Honda engine oil for my Gold Wing.
Pete
 
lazyeye6 said:
When idling slowly cold the primary chain slaps a bit against the chain case. It goes away with more RPM and after warming up does not slap at idle. Any thoughts on why it would be doing this?
Click to expand...

Hopefully, what you are actually hearing are the un-primed and so un-damped tensioner plungers being thrown back against the tensioner body by the 'loose' chain rather than the chain hitting the case-as it takes a short while after starting for the hydraulic tensioner to re-prime again.


vuuduu21 said:
Also the seals could be bad in the tensioner
Click to expand...

There are no actual oil seals in the standard tensioner, so as soon as the primary chain stops feeding oil the hopper the tensioner slowly begins to drain.
 
My 2 cts how it works.
The tensioner function relies on the presence of oil in its "catchment cavity".
This cavity is formed by a recess in the top half of the body and steel plate in front of it.
The cavity catches oil thrown of the chain.
Near the bottom of the cavity sits the little ball valve in the body allowing oil only in, not out (so much).
During standstill, oil will slowly drain from the body past the bottom plunger.
There are no seals, only the gasket between body and plate.
The plunger springs are only there to keep the plungers in a start position.
So no oil (say just after starting, when cold), no tensioning.

Sorry, 2 faster posts while I was typing..
 
All info above makes sense. I'm pretty sure the nuts on the damper are a specific torque to avoid warping the body. Regardless, whatever is happening doesn't sound correct.
 
Deets55 said:
There are no seals to speak of in the tensioner. There is a check valve in there and also a gasket that seals the flat plate onto the tensioner body. There is also a nylon spacer under the springs, if put in upside down it has less spring tension.
+1 on oil type. I use 20-50 MC oil that is designed for engine/transmission use, i.e. Honda engine oil for my Gold Wing.
Pete
Click to expand...

Just looking at the parts manual and there is no gasket shown between the flat plate and the hydraulic tensioner body, but at the bottom of the list it says "not illus." and gives part #06-6570

Don't remember ever seeing a gasket there, but I guess I need to get one.
 
Thanks, Les. I have one on order from Old Britts. A least now I know what it looks like.
 
Hmmm
I have had ATF type F oil in the primary. I drained it thinking to put in 20-50 oil. Oil was below the level plug yet 11 oz of
oil drained out. The service manual states that oil capacity for the primary is 7 oz. It would seem that about 12 oz is needed
to fill the primary to the level plug. Which is right?
Norm
'75 Mark III
'74 Mark II
'69 Mercury
'70 Triumph Tiger
'08 BMW R1200R
 
lazyeye

your main seal between the crank and primary may be giving up the ghost and leaking engine oil into the primary

thus the larger amount of oil in there than when you filled it
 
That is a distinct possibility which I had thought of. Still, why the discrepancy between specified amount of oil (7 oz) and a level plug which allows up to 12 oz???
 
lazyeye6 said:
The service manual states that oil capacity for the primary is 7 oz.
Click to expand...

Just to avoid any confusion, the "7 fl. oz." in the manual refers to Imperial fluid ounces, 7 Imp. fl. oz. = 198.89 cc/ml.

1 Imp. fl. oz = 0.96 US fl. oz.

lazyeye6 said:
It would seem that about 12 oz is needed to fill the primary to the level plug. Which is right?
Click to expand...

If the Mk3 primary is filled to the level plug, then "12" fl. oz. (340cc Imp. - 354cc US) sounds about right.
I fill mine to the level plug and have not experienced any problems (using 20w/50) although others may recommended sticking to the 200cc/ 7 fl.oz quantity as stated in the manual.
 
No where in the workshop manual does it say whether to fill to level plug with bike on center stand or side stand. Seems there would be less in the primary if on side stand? Workshop manual "Note: under no circumstances allow more than 7fl.oz (200 cc) of oil in the primary case." Next paragraph "Pour fresh oil into the filler cap orifice until it begins to run from the level plug hole." Mine has about 10 oz. when alls leaked out of the level hole when on center stand. Maybe when I get it off the work lift I'll set it on the kickstand and see how much drains out.
 
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