Mk3 Oil Tank bottom mount

p400 · Nov 14, 2019

My oil tank bottom mount is loose.
I pulled the oil tank, bottom mount difficult to access.
The pieces on this bottom mount (bolt, washer, sleeve) do not seem to make good mount sense.

Here is the oil tank and it appears in good shape.

p400 · Nov 14, 2019

Cleaned the oil tank, bottom mount bolt (1" long SAE NF ¼), washer, steel sleeve.
Chased the bottom mount threads.
The 1" bolt threads into the bottom oil tank mount and when it meets end, exposes about 0.460" thread.
When this group (bolt, washer, sleeve) is threaded in to the tank bottom fitting for trial fit, it does not fit up tight.

I am expecting this hardware to tighten up solid.
Sup?

Craig · Nov 14, 2019

I enhanced ( heavier rubber buffers) two top mounts and left bottom mount off , just some stiff foam jammed in ...

Danno · Nov 14, 2019

p400 said:
Cleaned the oil tank, bottom mount bolt (1" long SAE NF ¼), washer, steel sleeve.
Chased the bottom mount threads.
The 1" bolt threads into the bottom oil tank mount and when it meets end, exposes about 0.460" thread.
When this group (bolt, washer, sleeve) is threaded in to the tank bottom fitting for trial fit, it does not fit up tight.

I am expecting this hardware to tighten up solid.
Sup?

View attachment 13236

Looks like the rubber isolator is missing, hence the gap.

dynodave · Nov 14, 2019

p400 said:
The 1" bolt threads into the bottom oil tank mount and when it meets end, exposes about 0.460" thread.
When this group (bolt, washer, sleeve) is threaded in to the tank bottom fitting for trial fit, it does not fit up tight.

I am expecting this hardware to tighten up solid.
Sup?

I would hope you to realize the 1" bolt is the wrong one. A shorter one will be better... Bolt - lock washer - flat washer - spacer -tank. The nice new soft rubber grommet will help prevent the typical tank bottom cracking when using rock hard grommets.
Just remember the stiffer the oil lines are the more likely you will break the tank mounts. The engine is isolastic but the tank is frame mounted. Herring bone or stainless line are bad news in my book...

maylar · Nov 14, 2019

And there should be a grommet in the mounting hole, a bit taller than the spacer.

lazyeye6 · Nov 14, 2019

It has been extensively discussed on this forum about how using the bottom mounting bolt on the oil tank leads to
cracking (aside from the near impossible effort it takes to even get a bolt threaded into the tank boss). It seems
that many folks do not install the bolt, but do insure that the rubber isolation bolts which secure the tank
tabs at the top are in fresh condition (pliant rubber, not age hardened). Some have discussed grinding down the boss
at the bottom of the tank and applying a layer of rubber to the bottom to alleviate vibration. My bottom bolt fell
out 15 years and 20,000 miles ago after having removed the tank to weld up a cracked upper mounting tab. I've
had no problems since.

https://www.accessnorton.com/NortonCommando/bottom-oil-tank-bolt.15861/

https://www.accessnorton.com/NortonCommando/oil-tank-bottom-mount-options.8954/

p400 · Nov 14, 2019

Here are Andover pieces and they list the 1" bolt along with 5/16 thick spacer.
These are the two pieces i have off this original Mk3.

p400 · Nov 14, 2019

All the Access threads I find on this oil tank mounting are the usual nonsense prattle.
I was hoping someone has repaired this bottom oil tank mount and can relate to these pieces I have in hand.
I have ordered a mount kit from Andover.

I looked at Andover parts and it seems at least all the 850 use this bottom mount...probably all Commandos.

What with all these 45 years later PIOOYA fixes?

maylar · Nov 14, 2019

When you've had 3 oil tank fractures and oil spewing all over your Norton as I have, you might come to the same conclusion that many of us have - that the factory mounting scheme sucks.

kommando · Nov 14, 2019

That nonsense prattle will stop oil leaking from your tank, the bottom mount is best for rod of.

lazyeye6 · Nov 14, 2019

I truly respect the OPs opinion that many posters on this site spew "nonsense prattle" as well as I respect those who
wish that their machine remain pure and OEM. Then, also, there are those who have experienced some of the rather
peculiar design engineering aspects of Commandos and have sought to find a better way.

p400 · Nov 14, 2019

I see all Commandos from 1971 thru end of MK3 utilized the same mounts.

Madnorton · Nov 15, 2019

p400 said:
I see all Commandos from 1971 thru end of MK3 utilized the same mounts.

View attachment 13244

View attachment 13245

You need item 10 twice, either side of the grommet insert - job done. The parts book is wrong as it should show two washers, item 10, this I found from the MK3 build book.

p400 · Nov 15, 2019

My dimensions of my pieces would not benefit with adding a washer.
Meaning the steel pieces would still not pull up tight.

I am pretty sure this lo mileage MK3 has never been apart......and the bottom oil tank bolt was up tight (bottomed) in the mount.

What is an Mk3 build book ? Can you please post a picture of this information found in this book?
Here is the Workshop manual info I find.

"dont forget the spacer"

p400 · Nov 15, 2019

Since all of the washers for the upper rubber hex oil tank mounts are shown in the IPB,
why would washers be left out of the lower mount?
for 5 years of parts books in a row?

The oil tank bottom mount fitting, welded to the Norton Mk3 oil tank bottom, has an extra thick flange area that should not be expecting an additional washer.

maylar · Nov 15, 2019

Perhaps the bottom mount on that tank isn't threaded deep enough for the bolt to fully seat. As Dave mentioned in one of the posts here, a 1 inch bolt is not required, even though the parts lists say that's what they should be. If that's as far as your bolt will screw in, I would use a 3/4 inch bolt with a split lock and call it a day.

dynodave · Nov 15, 2019

Madnorton said:
You need item 10 twice, either side of the grommet insert - job done. The parts book is wrong as it should show two washers, item 10, this I found from the MK3 build book.

I guess the build book was secreted from the assembly line workers. My "never registered 5 mile" MKIII had only 1(thick) washer. The 1" bolt last 3 threads were quite mashed. The bike was unmolested when I got it, but is slowly becoming disassembled from investigating and answering so many questions...
The bolt access with the oil lines in place is horrible (I agree).
However I'd suggest (like Dave M) a 7/8 or 3/4" with a lock washer and call it a day. Use a 1/4 drive 12" extension and it is otherwise quite easy to do...but 2 plain washers?
Now I see why the assembly line workers did not follow the build "book", would you?

seattle##gs · Nov 15, 2019

My solution was to cut out a square from 3/8" or 1/2" rubber sheet available from Grainger at about $20 per square foot. It cuts easily in a band saw. Throw away the bolt and washer. The rubber should be thick enough to support the tank and the threaded spigot off the battery table. If not, trim off a little bit of steel with the disc grinder. The spigot will hold the rubber pad in position and the oil tank side panel will not allow the tank to swing out to the right side. Works great. CNW offers a version of this.

concours · Nov 15, 2019

p400 said:
All the Access threads I find on this oil tank mounting are the usual nonsense prattle.
I was hoping someone has repaired this bottom oil tank mount and can relate to these pieces I have in hand.
I have ordered a mount kit from Andover.

I looked at Andover parts and it seems at least all the 850 use this bottom mount...probably all Commandos.

What with all these 45 years later PIOOYA fixes?

Check it WELL for cracks....radiating from the mounting stud. It’s a known pattern failure....
I have pics of my repair... somewhere.

Mk3 Oil Tank bottom mount

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