valve lash increasing on 1 exhaust rocker.any ideas why?

I have an Arias chevy with Bac-Man billet heads. 522CI with mert HH14-71 at53%. 45 lbs boost at 8200 RPM.Comp ratio is 10.4 to 1. Seat pressure is 325lbs. My #5 exhaust lash increases .030to .050 beyond hot setting during run. No cam wear or lifter wear. Push rod shows no signs of hitting anything and not gauling on either end. It has Jesel rockers and the stands are welded together.Valve spring is not bottoming out and has 1 piece lash lock keeper with radial groove on titanium valve. I changed rocker arm and problem continues.While warming car up the lash doesn't change. The egt's are consistant with the other cyl. temps. Have a pro mag20 with 6-shooter and Lehey timing controler. Timing is 27 and I take 8 initally out at the hit and it is all back in at .08 into the run. Any ideas? thanks

 

take the rockers off and do a leakdown, see if any air leaks out of the exhaust port, possible bent valve

 

the leak down is 16% on that cyl. when cold. It has more than .100 piston to valve clearance

 

I just pulled the lifter out and checked it again. There are no hard spots when I roll it and there doesn't seem to be any more bump in that lifter than the others.

 

Lash Problems

This is just an observation and I don't know if this would have any effect on your lash problem but, I noticed your seat pressure is only 325psi, and running 45 psi boost is a lot. I was of the impression that boost that high should have a min of 350-360Psi seat.

As stated, this is just an observation.

Corey

 

Valve Lash

I just notice that this was an exhaust rocker, forget what I said.

Guess I should read before I speak.
Corey

 

Since you're running lash-locks, check the radial groove in the valve and see if it's spreading. This is a problem with the lashlocks, since they have the spring pushing them up, then the rocker pushing them down, then the spring pushing them up, ....................................
If this is the problem, it will eventually work back and forth until it tears the tip of the valve off.
Good luck,
Marty Thacker

 

I hear you loud and clear Corey. I used to run 425lbs of seat pressure on a pontiac 427 casting head and when I got these Bac-Man heads they were 325. So I left it alone and don't seem to be having any issues with that. I used to do heads on an alocohol f/c and we ran 425lbs. I am also tuning an early Brad nitro head combo with 280 lbs of seat pressure and is running quite well despite the low seat pressure.

 

you better listen to Marty he is soooo rite I have been ther and yes broke there it will shear it rite off..Dave
www.myspace.com/daveloweswr

 

On the subject of the lash locks...Manton Lash Locks work great....we don't run ours as hard as the Top Alcohol guys....8500 RPM max....but I check the radial groove in the valve and lock when the heads are apart for any "wiggle" and replace the valve if the groove gets "spread"....I've never seen the lock bead wear much, but the groove in the valve does move a little....

 

Ditto on what Marty said! I've seen a couple engines ruined because of lash locks. Snaps the valve off right at the keeper groove.There is not a constant pressure on the valve groove with them and every time the valve shuts it slams the keeper against the groove like a air hammer.
-Dale

 

the radial groove on the valve is good and doesn't show signs of wear. The lash locks are from Ferrea and are 3 pieces. I have found out that the measurement from the top of the radial on the valve top the tip of valve should be .250 +/- 0 . The problematic valve is not .250 it WAS to long. I fixed it so we will see if that was it. If that is not the problem it was definitly going to become one So thank you Marty for bringing that to my attention.

Have a good night, Chris

 

This may sound stupid but what are lash locks ? are they a type of valve collet or lash cap ?
Thanks,
Wayne

 

http://www.competitionproducts.com/prodinfo.asp?number=NME603751-16

 

Lash-locks

Give us a call and we will be happy to send a Catalog covering all of our products including the LASH-LOCK. We also manufacture a complete line of Valve Locks and Lash Caps.

The problem being talked about in this thread sounds like a valve tip length problem. I suggest taking the assembly apart and measure everything.

tel:951 674-2212

www.mantonengineering.com
www.mantonrockerarms.com
www.mantonpushrods.com

Noel Manton

 

Thanks for your input Noel. The tip lenght is a problem. Even with the increased lash the pushrods you made me show no signs of wear. You definatly make the best pushrods

 

I ran the car had last weekend and no more lash problems. Thanks for all the input. The tip length had to be corrected on all of the valves.