Spark Exhaust Bent Tube 90° Ø 35 × 1.0 mm Stainless Steel Universal G9131

Thirty-five millimetres at ninety degrees. The tight corner in a small-twin diameter — the piece that gets an exhaust under a crankcase and out the other side.

Key Features

• Mandrel-formed 90° bend, AISI 304 stainless steel.
• Ø 35 mm outside, 1.0 mm wall thickness.
• Straight tangents at both ends.
• Matches Spark's 35 mm straight tube, article G9011.
• Spark part number G9131, made in Mantova, Italy.

Under the Engine

On a small twin or a single the exhaust drops from the head, turns rearward beneath the crankcase and climbs again toward the silencer. The first of those turns approaches a right angle, and it happens in the tightest space the system has.

Ground clearance decides how tight. Measure it with the suspension compressed and a rider on the machine, not with the motorcycle on a paddock stand.

Flow Separation on the Inside

Gas going round a sharp corner cannot follow the inside wall. It separates, leaves a slow recirculating region behind it, and effectively narrows the pipe. That is where the loss in a right angle actually comes from — not from the change of direction itself.

A larger radius reduces it, and so does a straight section afterwards in which the flow can reattach.

Magnets Do Not Help

Austenitic stainless is non-magnetic, so the magnetic clamps and angle blocks that hold mild steel for tacking are useless here. Set-up means clamps, vee blocks, tape and a flat surface — which is worth knowing before the first joint rather than during it.

Cutting a Ninety in Half

Cut at the apex and a right angle becomes two forty-fives, each with a straight tangent at one end. It is the reason the sharper angle is the safer article to keep on a shelf: the saw only works in one direction.

After Welding

Pickling paste on the outside of the joint removes the heat-affected oxide and restores the passive layer. It is not cosmetic — the discoloured band beside a weld is chromium-depleted and it is where a stainless system starts to corrode.

Ordering

One bend per article. Available in 30°, 45° and 90° at this diameter.