G'day all,
I see this problem was invoked in a couple of older threads. I believe I have an explanation for this occurrence, and a solution. I purchased my 2013 Benelli TNT1130R recently with around 3,700km on the clock, so practically a new bike. It already had the cracks in the tank covers. When swapping out the fuel injectors, I noticed the tank was difficult to remove and replace, but managed.
I subsequently purchased a new set of tank covers from Italy via eBay and thought these were reasonably priced for new/old stock.
Benelli got many things right with these wonderful machines but their adherence to fine tolerances had unforeseen consequences with the gas tank. The tank covers are made of Pocan (polybutylene terephthalate) injection moulded plastic. This is a fairly tough, stable and heat-resistant material. The fuel cell appears to be rotational-moulded polyethylene or similar. This material is known to expand by 3% or more in normal use.
This expansion tears apart the cover causing cracks at the weakest point - the screw holes. Mine has a dimensional difference of 10mm between the screw centres of the covers in relation to the fuel cell. So, despite popular belief, the cracks are not caused by over-tightening the shoulder-screws, but by the difference between the two materials.
This could have easily been avoided by elongating the mounting holes in the covers.
Here's what I did to avoid this with the new covers as I was not about to go to the expense of replacing a functional fuel cell:
The screw holes in the new covers were elongated as far as possible with a round file. This gained maybe 7-10mm of wiggle room. The mounting screws were swapped out for M6 x 15mm Black nylon screws (eBay) which were passed through 15mm neoprene washers (eBay) which are soft enough to give a bit yet retain the covers perfectly.
I applied a layer of aramid cloth with West System epoxy behind the stress points on the covers to avoid any reoccurrence of this cracking. This stuff exceeds the tensile strength of steel 10x on a per-weight basis so I don't expect any problems there.
Lastly the slots holding the rubber grommets were cut as these were now an impediment to attaching the new covers, and the slots around the metal bracket were relieved by 5mm forward to allow clearance.
The rubber grommets were deleted with no ill effect, as the screws adequately retain the covers.
If all of this is TLDR just refer to the attached images.
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I see this problem was invoked in a couple of older threads. I believe I have an explanation for this occurrence, and a solution. I purchased my 2013 Benelli TNT1130R recently with around 3,700km on the clock, so practically a new bike. It already had the cracks in the tank covers. When swapping out the fuel injectors, I noticed the tank was difficult to remove and replace, but managed.
I subsequently purchased a new set of tank covers from Italy via eBay and thought these were reasonably priced for new/old stock.
Benelli got many things right with these wonderful machines but their adherence to fine tolerances had unforeseen consequences with the gas tank. The tank covers are made of Pocan (polybutylene terephthalate) injection moulded plastic. This is a fairly tough, stable and heat-resistant material. The fuel cell appears to be rotational-moulded polyethylene or similar. This material is known to expand by 3% or more in normal use.
This expansion tears apart the cover causing cracks at the weakest point - the screw holes. Mine has a dimensional difference of 10mm between the screw centres of the covers in relation to the fuel cell. So, despite popular belief, the cracks are not caused by over-tightening the shoulder-screws, but by the difference between the two materials.
This could have easily been avoided by elongating the mounting holes in the covers.
Here's what I did to avoid this with the new covers as I was not about to go to the expense of replacing a functional fuel cell:
The screw holes in the new covers were elongated as far as possible with a round file. This gained maybe 7-10mm of wiggle room. The mounting screws were swapped out for M6 x 15mm Black nylon screws (eBay) which were passed through 15mm neoprene washers (eBay) which are soft enough to give a bit yet retain the covers perfectly.
I applied a layer of aramid cloth with West System epoxy behind the stress points on the covers to avoid any reoccurrence of this cracking. This stuff exceeds the tensile strength of steel 10x on a per-weight basis so I don't expect any problems there.
Lastly the slots holding the rubber grommets were cut as these were now an impediment to attaching the new covers, and the slots around the metal bracket were relieved by 5mm forward to allow clearance.
The rubber grommets were deleted with no ill effect, as the screws adequately retain the covers.
If all of this is TLDR just refer to the attached images.
