Plastic Gas Tank getting bigger

[nsmith]

2007 Breva 1100, 45000 miles. Getting the rear bolt that mounts the gas tank lined up is becoming a problem as the tank is growing in length. So, can I simply drill the hole in the tank oblong to get things to fit easy again, or will this open a bigger can of worms. As of now I use a 36" pry bar and a C-clamp to squeeze it enough to get the bolt hole to line up. Thanks everyone. Have a great weekend.

[SIR REAL ED]

2007 Breva 1100, 45000 miles. Getting the rear bolt that mounts the gas tank lined up is becoming a problem as the tank is growing in length. So, can I simply drill the hole in the tank oblong to get things to fit easy again, or will this open a bigger can of worms. As of now I use a 36" pry bar and a C-clamp to squeeze it enough to get the bolt hole to line up. Thanks everyone. Have a great weekend.

You could oblong the hole to get it to fit.  As long as you don't remove so much material that you cause a leak.  Let your eyeball be your judge.

You could also cut off the bolt head, and turn down the bolt shank diameter, and thread it in by hand so that it becomes a smaller diameter locating pin instead of a clamping bolt.

How much do you trust gravity?  Does the seat provide a secure clamping surface for the back of the gas tank?

I have heard that some people have good luck with draining the tank bone dry and letting it sit empty for a few months and the tank will shrink somewhat.  Expecting it to return to original size is probably overly optimistic.

[guzzisteve]

If you have 2 rubber knobs that fit in slots on front of the tank you could cut some off in front to move tank back.
I used to cut the stuff off on small blocks.
Yes, on frame 2 rubbers, trim the front of it off for tank to go back.

[tris]

Don't get me wrong as it's well documented that these tanks grow, but I had some success in lubing up the mounting bungs at the front
On my bike they were sticky and causing the tank stop short of where it should locate to fit the bolt, plus it costs you nowt to try

[john fish]

The plastic tank on my MZ Skorpion expanded.  I fixed it by draining it and leaving it empty and with the gas cap open over the winter months.

As I'm sure you know, ethanol gas causes the expansion.

[nsmith]

If I trim the front mount rubber blocks that lets the tank move forward more but the problem is then relocated to the front. The space between other things under the tank may be an issue. I know ethanol fuel is a problem but if I have put that much corn gas in there, seeing as I try never to use corn gas in my bikes, the gas pumps are lying about their ethanol content. The location pin plus a hole drilling combination will be brought up to the committee at the next meeting. thank you all.

[guzzisteve]

Cutting the rubbers caused no issues 15yrs ago and was the fix for our shop to stop the pile of bad tanks under warranty, they quit covering them. Plenty of room under the tank, not like it's moving 2".

[guzzi ride]

One thing that I think helped me was to do the Euro vent conversion on my Norge. The vent valve got gummed up and didn't vent well. Never had to much of a problem with tank swelling. 

[sign216]

One guy on his 750, replaced the one rear bolt with a strong zip tie, giving him room to fit everything.

He hasn't reported problems (yet).

Joe

[Stevex]

As I'm sure you know, ethanol gas causes the expansion.

Incorrect. The ethanol absorbs water vapour and in turn the water is absorbed into the plastic. The water can also cause bubbling at the tank's surface.
As already stated, if a tank is drained and left open so the water can evaporate, the tank will shrink back to some extent over a few months.
Best practice is not to leave your tank full of fuel for extended periods when it's off road.

[Frulk]

Have an XR1200 in the garage with a plastic tank. Swelling is a well known issue with this model. If possible only run ethanol free gas. Look for stations which cater to boaters if you have problems finding it. I also park bike in shade and vent it frequently on hot days. No swelling of tank in 14 years. Seems like a hassle, but Since it’s an around town bike due to it’s extremely limited tank range It hasn’t been a problem for me.

[john fish]

Incorrect. The ethanol absorbs water vapour and in turn the water is absorbed into the plastic. The water can also cause bubbling at the tank's surface.
As already stated, if a tank is drained and left open so the water can evaporate, the tank will shrink back to some extent over a few months.
Best practice is not to leave your tank full of fuel for extended periods when it's off road.

[Bulldog9]

2007 Breva 1100, 45000 miles. Getting the rear bolt that mounts the gas tank lined up is becoming a problem as the tank is growing in length. So, can I simply drill the hole in the tank oblong to get things to fit easy again, or will this open a bigger can of worms. As of now I use a 36" pry bar and a C-clamp to squeeze it enough to get the bolt hole to line up. Thanks everyone. Have a great weekend.

I used a file. It is what it is.

[bad Chad]

Steve is right, don’t make this more complicated than it needs to be.

[Stevex]

Just re read your post...apologies.
It's just dawned on me that when you said gas you meant fuel/petrol; In the UK we use the word to describe...er, a gas.

[ohiorider]

One thing that I think helped me was to do the Euro vent conversion on my Norge. The vent valve got gummed up and didn't vent well. Never had to much of a problem with tank swelling.

Yes.

Bob