Oil tank mod - Apologies to CNW

I'm modifying my oil tank to prevent the bottom fitting from fracturing as happened to a friend recently. If I lived in the US I would happily send the tank to CNW for their mod but living mostly in Mexico makes shipping things back/forth unwieldy, expensive, and fraught with tales of missing shipments.

So I'm doing it myself but have a question for those who have either DIY'd it or had the CNW mod. It appears from reading the CNW info, they remove the tank's bottom mount, reinforce the rear mount, use larger shock bushings and place a pad under the tank but do NOT bolt the bottom of the tank, it just sits on the pad. I have done these mods but the part where it just sits on the pad bothers me. The tank is still free to vibrate/flex sideways a bit, which also allows the side cover to move slightly with it. Is the idea to have the tank forced down so tightly on the pad that it essentially can't move or does the tank just sit and a bit of flexing is ok? Frankly it seems to me that it SHOULD be attached at the base but the only way I can think to do that would be with adhesive on both sides of the pad. But obviously this would make subsequent removal a little more difficult. OTOH, how many times does anybody remove an oil tank?

So what's the advice?

Mike,
speak w/ Russ(Batrider) on this forum.
He has had the oil tank mod done.
Marshal

CNW mods are over kill. Only real help is to leave the tank bottom free/unattached yet with some pressure on the rubber padding under it to both relieve the upper supports and allow some compliance so the sheet metal does not have to.
I glued a decent thick rubber gromlet to mine so easier to keep it centered when replacing tank. Wider the better. I do lots of very rough riding with too many to count drops or major deadly impacts, so far so goodie as braces nor tank bottom have fractured again.

I did fudge some with rubber under the brace ends at frame but tank ends up pretty darn fixed tight in place. Battery tray is pretty flexy in the support area and seems the main reason tank bottoms don't hold up. Pounding a fist on it can give sense of its tolerance.

I had mine done by CNW. It seems to fit very tightly and doesn't bounce around. The rubber mounting biscuits are much heavier dutier. They also beef up the back tab which was a problem on my original tank -- it broke off. There is another supplied pad against the back of the battery box. With the hoses attached it isn't going anywhere.

I saw an oil tank being "field repaired" with a torch and brazing rod on the bottom mount at the INOA rallye in Tioga and after that I decided it was time to head that problem off at the pass.

I'm usually sort of a mod hater and skeptical as hell but this one just fixes the problem and is otherwise unnoticeable.

Mike

if you prefer to have the lower bolt in place an alternative is to have a doubler plate welded to the base of the tank around the lower bolt hole to reinforce the tank in that area.
MIne has been done that way but i don't have a much mileage since - can let you know in 10 years time how effective it has been

Iain

I put a pad between the tank and the battery tray, one between the tank and the side cover, and one under the tank. The cover's rubber doodad cinches it laterally and the pad under the tank holds it up. 30,000mi no problems. The rear strap is known to crack the tank too. It would have helped if they had used a little heavier gauge steel on the tank. Colin Chapman strikes again.

The problems 35 years later are the rubber at the bottom of oil tank petrify to rock and vibrate the brazed in threaded insert to shakerland history. A lot of heat there from hot oil accelerates the prob of petrification so fit a thicker rubber to support the area , much work to remove tank but when braze goes oozing oil over tire makes life interestin.

Mike,

The idea is to address the weak original upper rubber mounts. Those are the ones that usually fail and then the lower mount takes the load. This will cause hairline cracks or worse, a complete fracture. So by taking the lower mount out of the equation and using better rubber mounts, this problem is taken care of. We also braze a large plate on the bottom to ensure that any hairline cracks are covered up. The tank is pressure tested after this is done.

Another common issue is for the rear tab (where the rubber mount is installed) to break off, and what is described above happens next. What we do is make a stronger mount that is up to taking the load of the tank.

By 'hanging' the oil tank you eliminate the issues caused by the solid lower mount. The rubber pad we supply just as a filler between the battery tray and the oil tank. Its not there to take any load.The oil tank is secured from swinging out by the side cover itself. Slight movement of the tank is ok and wont create any problems. Of course the upper rubber mounts should still be checked on an annual basis as they certainly arent, as any rubber part, designed to last forever.

We have done countless of these modified tanks and I personally think its a great fix for a common problem. Of course part of our fix is to boil the tank out first to get rid of all that sludge on the bottom, and when done with the mods we powder coat it so it looks great.

Matt / Colorado Norton Works

Thanks Matt,

Good info and I appreciate you sharing it so clearly.

As I said, I'd have shipped it to you if I lived in the US or was going to be there for a couple of months. But my next visit of that duration isn't until May. Typically I buy parts when I'm going to the US (I'll be in TX for Thanksgiving for a week), have them shipped to where I'm going to be, and then carry them back to Mexico in the luggage. With something like this tank, I would have to carry to the US, ship it to you; then you would have to ship it to some address in the US the next time I'd be there - it's just too convoluted and time consuming for items that are going to be machined/modified and returned.

The fact that a CNW Commando did the LaCarrera Panamericana with no mechanical issues at all while an oem Commando fractured its oil tank pretty much demonstrates the worth of the modification.

combat-proddy-build-t4186-120.html#p59866

Exhaust mounts up top.
No botton bolt.
Velcro.

Just got one back from them. I'd say grinding the bottom bolt off till flush and weld a reinforcing plate on the bottom and you're there with some foam support.

Dave, I like the velcro on the tank/batt box; good idea!

I purchased a new Commando 850 in 1973. Within 6 months the oil tank split and made a big mess on the garage floor. The tank was replaced and the new tank ruptured within a few months. I sold the bike as being unreliable (mistake!). I had the CNW mod done on the '73 Commando 750 I recently restored and it has now gone 18 months and 2000 miles with no problem. The CNW mod works and I'll definitely have it done on the '74 850 in process now.

Mike,

A few years ago I was flying to St Louis and with me I had a modified oil tank. Did not check any luggage so I had it stuffed in my carry-on luggage.

When they got a hold of it in customs I was promtly removed from the line, pulled aside, and questioned in detail about what it was that I was trying to take on board the plane. They probably thought it was a bomb of sorts since they never seen anything quite like it.

Interestingly enough I also had my Leatherman tool (with a knife and all) in my jacket but since they pulled me aside they didnt notice that one.

Thats airport security for you !

So I guess what i am saying is that dont try to carry on a Commando oil tank on board since it can get you in some serious trouble.

Matt / Colorado Norton Works

OK, got it - Knife: OK

Commando oil tank: NO GO!