Mk3 Timing Cover, for Pre- Mk3 applications (2017)

[RoadScholar]

A customer called me because he found that the Mk3 timing cover, purchase separately, wouldn't seat because the intermediate gear on his '74 Mk2 was .0065 too thick (thicker than the Mk3 intermediate gear.

I ask because I will be faced with this issue, possibly, when I assemble a '73 750. I purchased part # 06-6161, which is a kit from AN that purports to fit pre-Mk3 applications.

I noticed that the Mk3 pinion and intermediate gear have different part numbers than pre Mk3 examples.

So, here is the question: When fitting kit #06-6161 to pre-Mk3 models do you need to purchase the Mk3 pinion and intermediate gears? Or, was my customers experience a fluke?

 

[dynodave]

A customer called me because he found that the Mk3 timing cover, purchase separately, wouldn't seat because the intermediate gear on his '74 Mk2 was .0065 too thick (thicker than the Mk3 intermediate gear.

I ask because I will be faced with this issue, possibly, when I assemble a '73 750. I purchased part # 06-6161, which is a kit from AN that purports to fit pre-Mk3 applications.

I noticed that the Mk3 pinion and intermediate gear have different part numbers than pre Mk3 examples.

So, here is the question: When fitting kit #06-6161 to pre-Mk3 models do you need to purchase the Mk3 pinion and intermediate gears? Or, was my customers experience a fluke?

I only know of very few instances where the 6161 would work on other than MKIII, and that is where a very few pre MKIII engines were NOT fully drilled for normal commando OPV return to the oil pump inlet...since the MKIII covers dump inside the timing chest (like all pre commando) ...but you all knew that right!!!
I would not normally have any interest in trying to make mismatching parts work despite AN/norton having made this mistake of a kit. Might even need a MKIII oil pump to make the anti wet sump valve work??? The MKIII disc won't go on an early oil pump without machining.
There are lots of correct parts available on ebay. Creating crazy combinations is possible but WHY?

FWIW the regular commando gears is .980" and the MKIII is .917".
A lot more than .0065"
Have not yet finished this timing cover page ...
http://atlanticgreen.com/NHTtimcvr.htm

 

[RoadScholar]

A customer called me because he found that the Mk3 timing cover, purchase separately, wouldn't seat because the intermediate gear on his '74 Mk2 was .0065 too thick (thicker than the Mk3 intermediate gear.

I ask because I will be faced with this issue, possibly, when I assemble a '73 750. I purchased part # 06-6161, which is a kit from AN that purports to fit pre-Mk3 applications.

I noticed that the Mk3 pinion and intermediate gear have different part numbers than pre Mk3 examples.

So, here is the question: When fitting kit #06-6161 to pre-Mk3 models do you need to purchase the Mk3 pinion and intermediate gears? Or, was my customers experience a fluke?

I only know of very few instances where the 6161 would work on other than MKIII, and that is where a very few pre MKIII engines were NOT fully drilled for normal commando OPV return to the oil pump inlet...since they dump inside the timing chest...but you all knew that right!!!
I would not normally have any interest in trying to make mismatching parts work despite norton having made this mistake of a kit.
There are lots of correct parts available on ebay. Creating crazy combinations is possible but WHY?

FWIW the regular commando gears is .980" and the MKIII is .917".
A lot more than .0065"

So, the difference, according to your measurements is .063, my mistake for listing it .0065, I should have put it at .065, not nearly as I had listed. AN offers the kit # 06-6161 as a reto-fit for Pre-MK3 applications, I see this as an ability to check the cam chain tension without removing the timing cover, which is time consuming and often not necessary.

Given your encyclopedic knowledge of all things Norton, do I need to purchase the Mk3 pinion and intermediate gears to successfully implement the MK3 timing cover kit on a '73 750? I am going forward with this, but I'd really appreciate it if I could get a solution. Are the Mk3 drillings, in the timing cover, for the OPVR, really that different from the pre MK3? Why would a respected company like AN offer this kit if the fitment was so poor? I can send it back, and if the cam chain adjustment is a once-in-a-live-time experience then, Maya Culpa, with apologies.

The timing cover that came with the motorcycle is so beat-up (and pried off with screw drivers) it would need to be replaced anyway. Shot peened by 12 ga...Total junk. I can easily afford to replace ii with like kind, but I'd rather up-grade to a situation where I only pull the cover when the chain actually needs to be adjusted; this modification s NOT uncommon! Your thoughts?

 

[RoadScholar]

PS: I have a Mk3 oil pump (new) for the build.

 

[dynodave]

The running clearance is within the gasket thickness.
The intermediate gear should match the cases it is used in.
My guess is he tried it without the gasket. it locked up....as expected.
If it is a proper 6161, than you would be better to block off the return passage in the case.
1/4 20 set screw. though the normal gasket should block it off...do you feel lucky? :?

 

[worntorn]

PS: I have a Mk3 oil pump (new) for the build.

What is different about the MK3 oil pump vs earlier pumps?
I see that it supercedes the earlier pumps and is listed as the right pump for all Commando models right back to the earliest.
Will the early pumps work in the MK3?
I have a good early pump(1969?) here on the shelf that I was hoping to use on a MK3 engine with MK3 timing gears and MK3 cover.

Glen

 

[madass140]

what is the width of the MK3 crankshaft pinion?

 

[worntorn]

According to the Andover site, the Mk3 uses the same crankshaft oil pump worm gear as all other Commandos. That gear also is used for the 66 on Atlas and the 650 six start pump.

Glen

 

[dynodave]

PS: I have a Mk3 oil pump (new) for the build.

edited/numbered djc
1. Will the early pumps work in the MK3?
I have a good early pump(1969?) here on the shelf that I was hoping to use on a MK3 engine with MK3 timing gears and MK3 cover.
2. What is different about the MK3 oil pump vs earlier pumps?
I see that it supercedes the earlier pumps and is listed as the right pump for all Commando models right back to the earliest.


Glen

1. Not really correctly, they don't have the "Feed Bush, Oil Pump, MK3 & Eariler Upgrade 06-6191.

2. This bush is larger than the early one. The pump should be dismantled to enable a special tool to push out the old smaller bush. Then the early pump body must be machined to accept the new bush and let it seat properly.

 

[dynodave]

what is the width of the MK3 crankshaft pinion?

My first grab from the bins show:
MKIII .5065"
pre MKIII 1949-1974 .563"

 

[Danno]

According to Fast Ed, the gears in the Mk III timing case are narrower than Pre-Mk III gears to make up for the slightly wider crankshaft. This may make the timing covers slightly different, I would compare them side-by-side and take some measurements before attempting to fit the newer cover to older cases,

 

[worntorn]

Thanks for that information Dave.

Glen

 

[RoadScholar]

Thanks all.

So, it sounds like the gasket will give a running clearance for the pre-Mk3 intermediate gear, measurements between the Mk3 cover and the original cover for comparison will be done and no difference in the pinions (a mere supersession?) .

However: A Mk3 intermediate gear would give an additional .063 clearance according to DynoDave, is this too much? I would think that the cam sprocket "follows" the sprocket on the intermediate gear, and if both have loose fits can they injure themselves?

I am surprised that no members of this forum have, apparently, done this mod, or haven't stepped up to share their experience. I am also surprised that AN would sell this kit if it didn't fit well; I'll be writing them this coming week.

Having the ability to check the cam chain tension with out removing the timing cover saves a huge amount of time and whether or not the chain needs adjustment, the peace of mind factor is large...

 

[Fast Eddie]

Well, as I read Dyno Daves comments and the comments posted in the thread asking about MKIII strengthened areas, the thinner intermediate gear on the MKIII was done purely to accommodate the wider crankcases of the MKIII. It is therefore only required on MKIII cases irrespective of the timing cover used. The timing cover used has nothing to do with it.

The bigger question IMO is the oil feed machining differences as mentioned by DD. Was this mentioned in the instructions provided with the AN kit? Is the 'kit' timing cover already modified accordingly?

Re the 'benefit' of being able to check the cam chain tension in situ. I think you'd have to be a serious high mileage rider for this to be the case! But if it does concern you, are you aware you can buy a very effective auto cam chain tensioner from Comnoz? This does away with the need to check and adjust. Simples.

 

[dynodave]

Thanks all.


1. So, it sounds like the gasket will give a running clearance for the pre-Mk3 intermediate gear, measurements between the Mk3 cover and the original cover for comparison will be done and no difference in the pinions (a mere supersession?) .

2. However: A Mk3 intermediate gear would give an additional .063 clearance according to DynoDave, is this too much? I would think that the cam sprocket "follows" the sprocket on the intermediate gear, and if both have loose fits can they injure themselves?

3. I am surprised that no members of this forum have, apparently, done this mod, or haven't stepped up to share their experience. I am also surprised that AN would sell this kit if it didn't fit well; I'll be writing them this coming week.

4. Having the ability to check the cam chain tension with out removing the timing cover saves a huge amount of time and whether or not the chain needs adjustment, the peace of mind factor is large...

Bill
1. this a no brainer. ALL 20M3S and up...on the 3 types of covers, the support for the intermediate shaft is FLUSH with the cover gasket surface.

2. Why knowingly make/allow something sloppier than original? Are you going to fix all of nortons mistakes? I don't have a problem with the original setup or clearance.

3. I don't see it as much of a "mod". Did you get a comprehensive explanation sheet of the upgrade procedure and included or required extra parts needed? or just a big bill? It might reduce wet sumping past the threads of the OPV, but not through the retained stock oil pump.

4. :roll: one TC gasket is $3.65 06-6161 Timing Cover MK3 (can be used for Pre-MK3) $425.00
At these prices that means I have $9775 worth of timing covers. :lol: I don't get any peace of mind and maybe need to lock them up for safe keeping.

5. Anyone else notice on AN parts drawing that #38 oil pump gasket is drawn "flipped over"/backwards

6. Maybe we should come up with a mod to allow an early cover to be use on a MKIII :?: :mrgreen: The original MKIII check valve design and execution is quite problematic as reported to me by MKIII owners. An AMR type ball bearing/spring might be the real upgrade.


half joking half serious OK
dynodave (all small letters)

 

[dynodave]

The bigger question IMO is the oil feed machining differences as mentioned by DD. Was this mentioned in the instructions provided with the AN kit? Is the 'kit' timing cover already modified accordingly?

Are you refering the OPV release path?
A long time ago I once worked on a bitza engine. It has severe over pressure problems. Come to eventually discover the normal return path to the pump inlet in the cases was only drilled and tapped part way. This certainly would have been a motor for the MKIII type cover. The owner had the normal earlier cover which of course would not work. The cure would have been either to cut a small segment out of the timing cover gasket to allow venting into the timing chest or finish the drilling into the pump inlet passage.
A real head scratcher on that one...

 

[L.A.B.]

The bigger question IMO is the oil feed machining differences as mentioned by DD. Was this mentioned in the instructions provided with the AN kit? Is the 'kit' timing cover already modified accordingly?

There's no actual machining difference between the pre-Mk3 and Mk3 timing side case in that position, as the Mk3 T/S case still has the OPRV return gallery same as pre-Mk3 T/S cases. The difference is in the cover, as the Mk3 timing cover blanks off the gallery because the Mk3 cover vents oil from the OPRV directly into the timing chest unlike pre-Mk3 where it's sent back to the feed pump inlet, so although it can be beneficial to blank off the return gallery as DD suggested, it isn't absolutely necessary and wasn't done on the Mk3 model.

 

[dynodave]

The bigger question IMO is the oil feed machining differences as mentioned by DD. Was this mentioned in the instructions provided with the AN kit? Is the 'kit' timing cover already modified accordingly?

There's no actual machining difference between the pre-Mk3 and Mk3 timing side case in that position, as the Mk3 T/S case still has the OPRV return gallery same as pre-Mk3 T/S cases. The difference is in the cover, as the Mk3 timing cover blanks off the gallery because the Mk3 cover vents oil from the OPRV directly into the timing chest unlike pre-Mk3 where it's sent back to the feed pump inlet, so although it can be beneficial to blank off the return gallery as DD suggested, it isn't absolutely necessary and wasn't done on the Mk3 model.

No disagreement on what you are stating
On the problem engine I worked on, I had always wondered if the failure to fully drill the passage was a Norton defect or intentional.

 

[L.A.B.]

No disagreement on what you are stating
On the problem engine I worked on, I had always wondered if the failure to fully drill the passage was a Norton defect or intentional.

Who knows? :wink:
I'd guess it was probably a machining error. :?
Hopefully, we can agree that the full drilling is usually there, as it is on my reasonably late Mk3 and kept as a precaution against a pre-Mk3 cover being fitted (so the OPRV would then revert to pre-Mk3 operation).

 

[RoadScholar]

The timing cover that came with the '73 750 that I will be bringing back to life is not an option, it is beat to crap, and although it may be functional it appears to be good only for making into an intermediate gear support tool.

AN does not appear to offer pre- MK3 timing covers, but refers you to part # 06-6161. With current exchange rates the cost (195 Pounds) + shipping (to the East Coast) should be around $250 USD at retail. Shipping is hard for me to pinpoint as I purchased a new 850-type 750 cylinder and a bunch of other parts; total shipping for 28 pounds was under $100 USD. Short of purchasing the new Mk3 cover my options would lead me to E-Bay, or the like, where a good used pre-Mk3 timing cover could be had for ???.?? and need hours of sanding and polishing; at almost any shop rate the price of a new cover becomes peanuts. My goal in re-doing any motorcycle is to come up with an end product that is more reliable than factory production and is also stunning in appearance.

The (only) instructions that came with the cover state: "This timing cover, which is the standard fitment for 850 Mk 3 models, incorporates a plunger-type non-return valve and is supplied with all parts necessary to fit it to an earlier engine, i.e. one having an oil pump with a small feed bush. The small feed bush, which is a press fit in the oil pump body must be removed and replaced with the new large-diameter bush and matching rubber seal."

My experience, which is not nearly as global as some on this forum, leads me to believe that fitting (almost) any part to a Norton requires some fettling or at least close inspection. I have gathered, from this discussion, that, as long as the oil galleries are completely drilled the swap should go as stated by AN, although timing cover gaskets also vary in thickness, I'll come up with some method for measuring the free play of the intermediate gear to insure that it is not binding when the cover fasteners are at set torque.