Problem with lash closing up

[Larry Hill]

Did the seat sink or did the valve bend at seat contact area.

[nhramnl]

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.

[ss3011]

Probably should have said right from the start that this is a stocker engine with a flat tappet cam . Today we pulled the intake and examined each lifter and cam lobes . This is the second year on these parts and they still look brand new . It has cast iron heads , and the valve seats are not replaced , they are just machined into the casting . This year the valve job still looked OK so the valves were lapped and re-installed . Springs were not replaced and are still at 200 on the seat just like when it was reassembled . Engine has about 10 pulls since re-assembled . These are good parts , Trend lifters DLC coated , Steel cam , PAC springs .

The next step I think will be to try and measure the length of each valve , and see if Cylinder 4 valves are .003 longer than the others . I would think when the original valve job was done , all the valve lengths should have been ground to the identical length .

Thanks for all the ideas , it helps .

[Jeff Stout]

Could you swap a set of rockers from another cylinder and retest? Might find the source of problem or rule out 1 of the problems.

[Ralph A Powell]

Your Lash was off the first time? Maybe you should get your old P&G out and use it!

Originally Posted by ss3011

Probably should have said right from the start that this is a stocker engine with a flat tappet cam . Today we pulled the intake and examined each lifter and cam lobes . This is the second year on these parts and they still look brand new . It has cast iron heads , and the valve seats are not replaced , they are just machined into the casting . This year the valve job still looked OK so the valves were lapped and re-installed . Springs were not replaced and are still at 200 on the seat just like when it was reassembled . Engine has about 10 pulls since re-assembled . These are good parts , Trend lifters DLC coated , Steel cam , PAC springs .

The next step I think will be to try and measure the length of each valve , and see if Cylinder 4 valves are .003 longer than the others . I would think when the original valve job was done , all the valve lengths should have been ground to the identical length .

Thanks for all the ideas , it helps .

[ss3011]

After checking all the components , we ran the engine of the dyno again . Ran well so once the engine cools down lash will be checked again .

[Bob Mulry]

What was your EGT on that pull????

Stretching the valve or sinking the seat??????

[Todd Geisler]

Ran into this with my bbc with titanium valves. The sealing surface of the valve began to erode causing the lash to close up a little over time.

[ss3011]

Originally Posted by Bob Mulry

What was your EGT on that pull????

Stretching the valve or sinking the seat??????

If the valve was stretching due to getting really hot , I agree this could be a cause . This engine runs at WOT on the dyno for a very short time . A test is a sweep test lasts only about 10 seconds at WOT . So I have a hard time thinking that these valves get hot enough to stretch . Anything is possible . Don't have EGT's running , but the O2 sensors are saying the A/F ratio is around 12.8 .

[ss3011]

Originally Posted by ss3011

After checking all the components , we ran the engine of the dyno again . Ran well so once the engine cools down lash will be checked again .

So now, after all this grief , we checked the lash cold and lo and behold they all measure exactly what they were set at . Glad we checked everything , and don't regret being concerned , but all is well now . Thanks for all the ideas and comments .