Problem with lash closing up

nhramnl · 03-05-2020, 03:14 PM

Given all of what you say, there can only be a couple possible causes. To get my head around the problem, I think "which components would be capable of making the valvetrain get "longer" on the #4 cylinder?" The "longer" the valvetrain gets (from the surface of each cam lobe to the head of each valve on the seat), the less lash there would be. I would first very closely examine the lifters, because removing them will give you a chance to examine the cam lobes (which are not a likely cause), the lifter wheels, axles and roller bearings or bushings, and the lifter bore bushings. I wouldn't waste much time on pushrods, because they're under tension, and can therefore only get "shorter", through bending, breaking, etc., which would increase lash. Then look carefully at the rocker arms, again, looking for anything that could cause that theoretical, "overall length" to be reduced. Then, I'd look at the valves, springs, retainers, keepers and shims, to see if something has "shifted" (like the fit between the retainers and keepers, or between the springs and retainers); Look closely for metal flakes in the area. I would also look to see if the heads are beginning to pull off of the valve stems (they can stretch, which reduces lash) Weird-looking keeper grooves are sometimes a giveaway. Finally, I would look at the valve heads and seats for things like old-fashioned "tuliping", though with today's outstanding materials, I think that's virtually a thing of the past. If I had to bet $100 on the cause, I would say that you might just have an anomaly, which is part of running in a newly assembled engine. Sometimes, a cigar is just a cigar, and the only way you confirm (beyond a doubt) that you've actually got a problem is to readjust #4 to .018 cold, and put a couple more pulls on it. If it moves again, you KNOW you're in trouble; if it stabilizes, you can feel reasonably confident that you've dodged a bullet. Scariest thing of the whole deal is that the lash loss is confined to both valves on ONE cylinder. I have had a similar (though not identical) situation, and it is very worrisome. Hope that helps.

03-05-2020, 03:14 PM	#13
nhramnl Senior Member Join Date: Feb 2010 Posts: 507 Likes: 8 Liked 358 Times in 83 Posts	Re: Problem with lash closing up Given all of what you say, there can only be a couple possible causes. To get my head around the problem, I think "which components would be capable of making the valvetrain get "longer" on the #4 cylinder?" The "longer" the valvetrain gets (from the surface of each cam lobe to the head of each valve on the seat), the less lash there would be. I would first very closely examine the lifters, because removing them will give you a chance to examine the cam lobes (which are not a likely cause), the lifter wheels, axles and roller bearings or bushings, and the lifter bore bushings. I wouldn't waste much time on pushrods, because they're under tension, and can therefore only get "shorter", through bending, breaking, etc., which would increase lash. Then look carefully at the rocker arms, again, looking for anything that could cause that theoretical, "overall length" to be reduced. Then, I'd look at the valves, springs, retainers, keepers and shims, to see if something has "shifted" (like the fit between the retainers and keepers, or between the springs and retainers); Look closely for metal flakes in the area. I would also look to see if the heads are beginning to pull off of the valve stems (they can stretch, which reduces lash) Weird-looking keeper grooves are sometimes a giveaway. Finally, I would look at the valve heads and seats for things like old-fashioned "tuliping", though with today's outstanding materials, I think that's virtually a thing of the past. If I had to bet $100 on the cause, I would say that you might just have an anomaly, which is part of running in a newly assembled engine. Sometimes, a cigar is just a cigar, and the only way you confirm (beyond a doubt) that you've actually got a problem is to readjust #4 to .018 cold, and put a couple more pulls on it. If it moves again, you KNOW you're in trouble; if it stabilizes, you can feel reasonably confident that you've dodged a bullet. Scariest thing of the whole deal is that the lash loss is confined to both valves on ONE cylinder. I have had a similar (though not identical) situation, and it is very worrisome. Hope that helps.