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Old 10-07-2010, 05:44 AM
x_files x_files is offline
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2005 Quest
2005 Pathfinder
 
Join Date: Sep 2010
Posts: 6
Default $67 Cure for VQ35 Timing Chain Rattle in 05 Quest

Hi, My first post to this fantastic forum. Fortuantely I'm posting some good news about the fix I used to resolve a frustrating nissan quality problem: primary timing chain rattle. Here's my story.

Our '05 Quest with the VQ35 3.5L V-6 has 78k miles on the clock. About 3k miles ago I began to notice a fairly loud rattle from the cam drive side of the engine right after its first start of the day. The noise would go away after backing out of our drive, shifting into drive, and as the engine speed climbed above 2-3k rpm. Also, sometimes there would be a lesser, shorter duration rattle after shutting down and then restarting after a short period of time. Based on what I read here on the forum and what I heard coming from beneath the engine's front cover, I figured it was the primary camshaft timing chain slapping against the front cover housing.

Changing the oil & filter did somewhat reduce the intensity and duration of the timing chain rattle. I'm thinking this is mainly due to the new, clean filter and its reduced pressure drop resulting in faster oil delivery and therefore faster pressure rise at the oil fed primary timing chain tensioner. The tensioner needs oil pressure to push its plunger into the timing chain guide to remove the slack in the timing chain. Not enough plunger force = too much slack = chain rattling against the housing. Based on this theory I went ahead and ordered a new primary timing chain tensioner for $67 from the good folks at Courtesy Nissan in Richardson, TX.

The Waterpump replacement instructions in the Cooling System section of the Nissan service manual do a good job outlining how to change the tensioner without removing the whole front cover assembly. Basically it involves removing the small access cover directly in front of the primary chain tensioner, rotating the crankshaft slightly to get slack in the timing chain by the tensioner, and then removing and replacing the tensioner. I deviated from the instructions by leaving the front motor mount in place, and instead removed the power steering and coolant resivoirs to improve my access to the tensioner. Regardless, it was still tricky fitting 2 hands down there to move the chain guide to gain room for installing the new chain tensioner. In total it took me about 3 hours to do the job.

The new tensioner appears identical in form and fuction to the original. Regarding its installation, I did something not mentioned in the manual. The tensioner's piston has two very small oil bleed holes drilled into the "top" of the plunger/piston body: 1 directly centered in the "top" of the plunger, and a second drilled laterally into the "rim" of the plunger. I oriented this second,lateral drilling pointing straight up. The thought was that this orientation would trap more oil in the hollow ID of the plunger body on shutdown and therefore reduce oil pressure delay within the tensioner upon engine start-up. Unfortunately I didn't note the orientation of the old tensioner's plunger before I removed it. So this may not really matter, but I figured it couldn't hurt. I also fully dissassembled the tensioner and oiled all the internal components before installing it.

I did not notice any obvious wear in the old tensioner's plunger, plunger bore, spring, or the small piston & seal on the end of the spring within the I.D. of the plunger. There does appear to be small, one-way valve in the body of the tensioner at the base of plunger bore. This apparently controls the flow of oil from the oil rifle into the tensioner. Perhaps this was worn and allowed too much oil to drain back on shutdown??? Or, maybe just the opposite - its "stuck" closed and now takes more oil pressure to open the valve so oil could flow into the tensioner and cause the plunger to extend??? After writing it out, I think the second is more plausible. If I get really bored this winter I'll consider building a test rig to measure opening pressure and see what's really going on with this flow control valve.

In conclusion, for one week now its been starting like a champ without any rattle. I'll post back again in a few weeks with an update - hopefully still silent!

Scott
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