The cause of the Idle Hammer
The IH noise and hammer felt through the bike is because the crank hops (lifts) up and down in the drive side (right of the engine) main bearings oil clearance.
There are a few contributory factors which when they occur at the same time and while ever the engine is not loaded (such as when at idle) create the lift.
Heavy flywheel being pulled downwards by gravity at the opposite end tends to lift the drive side journal.
Two pistons and rods mid-way between the bearings trying their best to make the crank journals rise and fall.
Scissor gear adjacent to the drive side main pushes the crank fowards and therefore upwards so the journal lifts.
Clutch with significant rotational inertia (acting as second engine flywheel) trying to lift the drive side main as it transfers inertia back into the crank via the primary drive gears.
Less prone to happen and quieter when engine is cold. Less expansion of the bearing which is in an aluminuim housing. Oil thicker so damps the knock.
More prone to happen and makes a very heavy and regular knock when engine crank cases and oil are hot through. Fully expanded bearing housing. Oil thinned due to heat so far less damping.
You could say it's just down to the layout of the engine. Perhaps if we had lighter flywheels, heavier cranks, less main bearing oil clearance, different design of bearing, a lighter and smaller diameter clutch (less inertia), deeper clutch oil bath or better oil cooling then the IH would never occur. Wait a minute! These are all the things Suzuki changed between TLS/TLR when they created SV and DL. Or what they have tweaked in SV and/or DL since their birth in 2002 and 2003. TLS/TLR had other problems but no reports of IH.
Try TBS (vacuum), new plugs, TPS, Valve check, different oil brands, different oil grades, Fuel Map tweaks, check the big nut on the crank and the rest. If you still have the IH in your SV or DL after this lot then your only way to cure it before now was to strip the engine and gamble that new mains would have some impact (or sell it in winter). Which is exactly what Suzuki were doing here in the UK to pacify owners until as late as 2006.
Something that works at just the right frequency to keep the "hop" in check at idle is required. It must also allow the crank journals to build and run on their wedge of oil in the mains when the engine is loaded.
Like the clutch basket re-engineering I kicked off some years ago, this IH solution has taken plenty or investigation, experimenting and testing over two years to get something fit to make available. Now wondering if it's going to be worth my time to tool up for low volume production to help those owners who until now just had to put up with the IH.
Last edited by svman; 08-13-2012 at 05:22 PM.