Thread: engine rattle?
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Old 05-23-2011, 06:45 PM   #19
JoelWisman
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Joined: Apr 2009
Location: STL, MO, USA
Oddometer: 1,392
Quote:
Originally Posted by itsatdm View Post
The bike has a spring/oil pressure cam chain tensioner. Mine doesn't do it, but it is possible the chain is loose and rattles until the tensioner if fully pressurised. Normal? no doubt some do it, but I really don't think it was designed that way. I would check to see you have the proper oil level and type of oil in it. Probably does not do a great deal of harm if it only happens for a short time at low speed without load, but I certainly would mentally note if it got worse.

There have been a couple of reports of bad tensioners and if left unchecked could be catastrophic for the engine.
This rattle, that lasts from 0-3 seconds is not a concern so long as it only hapens at startup and never at any other point. If conversely your bike makes this same sound at idle continuesly when the engine is hot, it's a sign of impending explosion.

The sound is from air in the timing chain tensioner. The air gets in as oil bleeds back through the oil filter check valve, or leaks through an internal gasket. The timing belt tensioner is damped by oil, and just like a brake circuit, functions poorly with air in it.

The oil filter check valve always leaks, but it leaks more as oil thins and fills with more particulate.

Also not all oil filters are equal, some bleed back quicker right from new.

If your start up death rattle seems long, change your oil and filter. If it shortens, don't worry about it.

The other major source of bleed back is a leaking gasket internal to the clutch cover. There is a torque spec AND sequence for the clutch cover. This is specd for a reason. Either a tech or owner not paying attention to the instructions for bolting on the clutch cover will increase the startup rattle AND reduce oil pressure to the rest of the motor as well as foam the oil.
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