BritBike Forum logo
BritBike SponsorBritBike SponsorBritBike SponsorBritBike SponsorBritBike Sponsor SteadfastCyclesBritBike SponsorBritBike SponsorBritBike SponsorBritBike SponsorHepolite PistonsBritBike Sponsor
Upgrade to: Gold Membership | Premium Membership | Vendor Membership | Site Sponsor Membership
Member Spotlight
Howard Inough
Howard Inough
Kensington, New Hampshire, USA
Posts: 445
Joined: May 2009
ShoutChat Box
Comment Guidelines: Do post respectful and insightful comments. Don't flame, hate, spam.
Search eBay for motorcycle parts in following countries
Australia, Canada, France, Holland, Italy, United Kingdom, USA
Random Gallery photo
a word from..
Manuals on DVD (Shipping included)
Previous Thread
Next Thread
Print Thread
Rate Thread
Commando Mk lll Questions
#784495 09/16/19 6:18 pm
Joined: Jan 2014
Posts: 105
Samsmc1 Offline OP
Britbike forum member
OP Offline
Britbike forum member
Joined: Jan 2014
Posts: 105
I'm curious about the timing cover on a Mk lll. Does it really stop the crankcase from wet sumping when it's not running?
Is the Mk lll timing cover interchangeable with the earlier (70-74) covers as long as you use the later oil seal on the pump?
Last - why is the timing idler sprocket different between the Mk lll and the earlier models? Are they interchangeable?
Thanks
Sam

Support Your #1 BritBike Forum!

Check out British motorcycles for sale: British Motorcycles on e-Bay UK, British motorcycles on e-Bay North America
Re: Commando Mk lll Questions
Samsmc1 #784503 09/16/19 7:33 pm
Joined: Sep 2007
Posts: 1,144
Likes: 2
Britbike forum member
Offline
Britbike forum member
Joined: Sep 2007
Posts: 1,144
Likes: 2
The MKIII timing cover has a non-return valve built into it. This valve is machined into the inside of the timing cover, behind the small bulge you can see in the surface of the cover.

The valve does work as long as the bike is ridden regularly ... so that the valve plunger does not seize. If the plunger seizes, it will usually fail safe and stick in the open position, meaning that it will not stop oil flow (but neither will it prevent wet sumping in such case). I've seen lots of the plungers stuck in the open position, which is considerably better than being stuck in the closed position and causing an engine failure due to oil starvation.

The MKIII covers are interchangeable with the older covers with a few mods (like the flat pump seal to allow the plunger to seat). I even updated a very early 20M3 Commando engine with a MKIII cover years back, though on that one I had to machine back the boss in the timing cover that supports the idler gear shaft.
.. Gregg


Spyder Integrated Technologies
Lucas, BTH, & Miller Magneto & Dynamo Restoration
SMITHS Chronometric Restoration
[email protected]
Re: Commando Mk lll Questions
gREgg-K #784509 09/16/19 8:04 pm
Joined: Jul 2001
Posts: 13,254
Likes: 16
Well'ard Rocker
Offline
Well'ard Rocker
Joined: Jul 2001
Posts: 13,254
Likes: 16
The non-return valve on the MKIII does work unless, as Gregg says, it sticks.

For a surprisingly small amount of money, an outfit called AMR-Tucson will take your timing cover, replace the "bucket"-shaped piston with a ball, machine the surfaces, and otherwise modify it so that it always works and never sticks. I've done it to mine and it's great; no blocking the pump inlet with a check valve and risking your engine, no putting a valve in the inlet line and forgetting it or the interlock failing.

Lannis


"Until it's safe" means "Never".
Re: Commando Mk lll Questions
Lannis #784520 09/16/19 11:33 pm
Joined: Aug 2001
Posts: 6,471
Likes: 14
Britbike forum member
Offline
Britbike forum member
Joined: Aug 2001
Posts: 6,471
Likes: 14
Originally Posted by Lannis


For a surprisingly small amount of money, an outfit called AMR-Tucson will take your timing cover, replace the "bucket"-shaped piston with a ball, machine the surfaces, and otherwise modify it so that it always works and never sticks. I've done it to mine and it's great; no blocking the pump inlet with a check valve and risking your engine, no putting a valve in the inlet line and forgetting it or the interlock failing.

Lannis



Wow, excellent advice. $80 + shipping for just that mod alone is quite fairand a no brainer. I know what I am having done over the winter...thanks Lannis !


Jon W.


1957 6T Thunderbird 650
1968 T100R Daytona 500
1971 TR6R Tiger 650
1970 BSA A65F 650
1955 Tiger 100 - Project
1971 BSA A65 650 - Project
1972 Norton Commando 750 "Combat"


"Every time I listen to AC/DC, so do my neighbors"

Re: Commando Mk lll Questions
Samsmc1 #784703 09/18/19 6:35 pm
Joined: Jun 2007
Posts: 6,820
Likes: 6
Britbike forum member
Offline
Britbike forum member
Joined: Jun 2007
Posts: 6,820
Likes: 6
Jon, while you're at it, send your tach drive to them for a proper lipped seal mod. Those buggers always seem to leak otherwise.
Cheers,
Bill


Bikes
1974 Commando
1985 Honda Nighthawk 650
1957 Thunderbird/T110 "Black Tiger"
Antique Fans: Loads of Emersons (Two six wingers) plus gyros and orbiters.
Re: Commando Mk lll Questions
Samsmc1 #784704 09/18/19 6:47 pm
Joined: Sep 2007
Posts: 1,144
Likes: 2
Britbike forum member
Offline
Britbike forum member
Joined: Sep 2007
Posts: 1,144
Likes: 2
Fortunately, the good people at Andover Norton seem to have "read the memo", and the new tach drive couplings they sell now come with a proper lip seal fitted.

.. Gregg


Spyder Integrated Technologies
Lucas, BTH, & Miller Magneto & Dynamo Restoration
SMITHS Chronometric Restoration
[email protected]
Re: Commando Mk lll Questions
gREgg-K #784705 09/18/19 6:53 pm
Joined: Jan 2014
Posts: 105
Samsmc1 Offline OP
Britbike forum member
OP Offline
Britbike forum member
Joined: Jan 2014
Posts: 105
I had forgotten about that mod to the tack drive.
Can anyone tell me what size seal they use - I can modify the housing easily enough if I have the seal.
Thanks
Sam

Re: Commando Mk lll Questions
Samsmc1 #784706 09/18/19 7:19 pm
Joined: Mar 2006
Posts: 4,365
Likes: 6
Britbike forum member
Offline
Britbike forum member
Joined: Mar 2006
Posts: 4,365
Likes: 6
Originally Posted by Samsmc1
Can anyone tell me what size seal they use - I can modify the housing easily enough if I have the seal.


The AN seal is 6 x 15 x 4mm although 6mm seems a little tight on the spindle.

https://andover-norton.co.uk/en/shop-details/16978/oil-seal-tacho-housing

Another seal often used for this purpose is Honda part 91207-222-000 (7 x 14.5 x 5mm).
https://www.oldbritts.com/11_065200a.html


The seal I used was 7 x 14 x 4mm.

Re: Commando Mk lll Questions
Samsmc1 #784707 09/18/19 7:19 pm
Joined: Sep 2007
Posts: 1,144
Likes: 2
Britbike forum member
Offline
Britbike forum member
Joined: Sep 2007
Posts: 1,144
Likes: 2
Sam, I can give you the generic part number of the seal.

The last seals I brought in were made by SKF, and came under SKF part number 2450. I'm pretty sure National or some of the other big names do it as well.

... Gregg

Last edited by gREgg-K; 09/18/19 7:20 pm.

Spyder Integrated Technologies
Lucas, BTH, & Miller Magneto & Dynamo Restoration
SMITHS Chronometric Restoration
[email protected]
Re: Commando Mk lll Questions
Samsmc1 #785035 09/22/19 2:40 am
Joined: Jan 2014
Posts: 105
Samsmc1 Offline OP
Britbike forum member
OP Offline
Britbike forum member
Joined: Jan 2014
Posts: 105
Gregg
Thanks - I have 3 of those puppy's coming.
Sam


Moderated by  Dave Comeau 

Link Copied to Clipboard
Home | Sponsors | Newsletter | Regalia | Calendar | Bike Project | BritBike Museum | Spiders Cartoons | DVD- Manuals & Parts books
Upgrade to: Gold Membership | Premium Membership | Vendor Membership | Site Sponsor Membership
Powered by UBB.threads™ PHP Forum Software 7.7.4