Why???
HDF Community Team
Joined: Jun 2006
Posts: 12,763
Likes: 2,597
From: san antonio
Lifter noise is very hard to diagnose; there are many sources of valve train noise that can be mistaken for lifter noise. Rocker arms can have too much clearance on the shaft or too much end play, pushrods can be making contact with the upper end of the push rod tube, valve springs can be tapping the inside of the rocker box, if valve spring pressure is high, you could be hearing valve making contact with the seats, cams with aggressive ramps will make noise as the lifter cannot maintain full contact with the cam lobe. See what I mean?
Lifter noise is the result of lifters "bleeding down", or losing pressure during operation in the valve body and allowing some clearance to be introduced into the valve train between the lifter and the rocker arm even though initially set at zero clearance. One reason why the service manual recommends replacing lifters at 35K mile intervals.
You can try taking them down another half turn or even another full turn. Some adjust from the bottom up by bottoming out the lifter travel and backiing off a full turn. Try re-adjusting, more preload on the lifter and see if that helps. If you can identify the offending lifter, replace it. If you can't get rid of the noise, you can change lifter brands; the new Woods directional lifters are manufactured to closer tolerances that the MoCo lifters and will eliminate or reduce the noise. If you can live with the noise, that's probably the easiest fix. Face it, an air cooled pushrod vtwin engine can be noisy; it's the nature of the beast.
Lifter noise is the result of lifters "bleeding down", or losing pressure during operation in the valve body and allowing some clearance to be introduced into the valve train between the lifter and the rocker arm even though initially set at zero clearance. One reason why the service manual recommends replacing lifters at 35K mile intervals.
You can try taking them down another half turn or even another full turn. Some adjust from the bottom up by bottoming out the lifter travel and backiing off a full turn. Try re-adjusting, more preload on the lifter and see if that helps. If you can identify the offending lifter, replace it. If you can't get rid of the noise, you can change lifter brands; the new Woods directional lifters are manufactured to closer tolerances that the MoCo lifters and will eliminate or reduce the noise. If you can live with the noise, that's probably the easiest fix. Face it, an air cooled pushrod vtwin engine can be noisy; it's the nature of the beast.
HDF Community Team
Joined: Jun 2006
Posts: 12,763
Likes: 2,597
From: san antonio
zero clearance = zero lash. Valve train has no lash/clearnce between lifter and rocker arm.
Banned
Joined: Jul 2008
Posts: 1,036
Likes: 67
I would try re-adjusting them before I threw out the baby. They are not complicated to adjust but can be tricky especially if you are not used to doing it often. Besides that, it costs nothing to re-adjust, assumbing you are doing it yourself.
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Elite HDF Member
Joined: Apr 2009
Posts: 3,780
Likes: 69
From: Al Bu Ker Key, New Mexico
djl, you stated "One reason why the service manual recommends replacing lifters at 35K mile intervals." Exactly what service manual are you referring to? I had someone tell me that pushrods should be replaced every 25K miles and said the "service manual says so" and still cant find that one. This was for an EVO motor. I am by no means a mechanic but I do try to understand the best I can. thanks!
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Tourer
Joined: Aug 2010
Posts: 320
Likes: 24
From: Hudson Valley
Also, on our twin cams if you pull your tappets you'll noticed that the sides have flat areas on them. The tappet anti-rotation device goes against these flats to keep the tappet from turning in it's bore. Sometimes you will get some noise as the from the factory tappets if the flat does not extend down far enough as the body hits the anti-rotation device at full lift. Many of these aftermarket tappets have longer flats for higher lift camshafts.
Last edited by inverse121; Feb 3, 2011 at 12:49 PM.
