Valve Stems Slipping Past Keepers?

CWizard · #1 (**permalink**) 08-29-2006, 08:50 PM

Is there a way to tell if the valve stems are slowly slipping through the keepers with minimal disassembly? Like maybe removing the rocker arms and putting a straightedge across the valve stems and measuring the distance between the bottom of the straightedge and the end of the stem with a feeler gauge? I've done this measurement twice, 300 miles apart, and the data show a clear trend - the valve tips are getting farther away from the straightedge. Is this a valid diagnostic? Also, if the stems are slipping, how do you fix it? AFR 205 heads on a 418 stroker. Thanks.
Thinking I have a problem,
Jerry

Rick Parker · #2 (**permalink**) 08-29-2006, 10:17 PM

If you sincerely believe this is happening and have checked your dimensions accurately I would recommend you cease running the engine. You have a catastrophy on the verge of happening. It is possible that you have the incorrect retainers and keepers meaning they are not matched to each other. If a set of 7 degree valve keepers are used with a 10 degree retainer it is possible there could be movement as you describe. If it continues (and there is no reason to believe it won't) a valve will drop into the cylinder and be impacted with the piston and all kinds of nasty, noisy, loud, EXPENSIVE things will happen. If you are unfamiliar with this get some professional help. You may be able to remove the rocker arms and retainers without removing the heads or it may be decided the best corse of action would be to remove the heads, get some advice.

freddie · #3 (**permalink**) 08-29-2006, 11:34 PM

DO NOT RUN THE ENGINE anymore untill you find out the reason for this problem.
rick is correct this can and will be a very EXPENSIVE lesson if a valve does drop into the cylinder ...
You do not have to remove the heads to check the keepers or change them there are a couple of different ways to do this. without buying any expensive equpment. call me and I can explain to you 408-316-0199

once again DO NOT RUN THAT ENGINE AT ALL TILL FIXED!!!!!!!!!!!!!!!!!!

FREDDIE

CWizard · #4 (**permalink**) 08-31-2006, 04:14 PM

Thanks for the feedback guys. The car went to a local shop via flatbed this morning to have the keepers, springs, etc. checked out.

Rick Parker · #5 (**permalink**) 08-31-2006, 06:16 PM

Let us know what the diagnosis is.

troll · #6 (**permalink**) 08-31-2006, 06:54 PM

Hey I saw that happen.And there was a telltale sign it was going on.In my case it was the rocker arm hitting the retainer before the stem.(damned professionals did this work for did for someone I know)The valve dropping in the hole did happen but at low RPM and it only bent the valve.There was a lot of grey looking grit on the keeper.It was a 289 and I went and got some 390 springs,retainers and keepers and put them on,no more prob.Its now my engine and it has seen 8,000 rpm.Look for the grit.

Jerry Clayton · #7 (**permalink**) 08-31-2006, 07:09 PM

The old 427 fe engines used to have pistons that had bumps on them to hit the middle of the valves to keep from bending them!!

Do you have alum retainers? A spring with a flat wound damper will cut up a alum retainer like a hole saw

Jerry

CWizard · #8 (**permalink**) 08-31-2006, 08:14 PM

Troll said: Hey I saw that happen.And there was a telltale sign it was going on.In my case it was the rocker arm hitting the retainer before the stem.

Hey Troll - That's exactly the problem that started me off on the measuring valve tip and retainer heights. I had pulled the valve covers about 6 weeks ago to adjust lash, and decided to look at the rockers. Four of the 16 were hitting the retainer. At that time, it appeared to be a problem with valve geometry, so my engine builder provided new rockers and longer pushrods. I also talked to AFR (they supplied the heads complete with valves), and they thought everything was ok, but suggested remeasuring the tips and retainers after a few hundred miles. So two days ago, which was 300 miles later, I remeasured, and found that all but one valve tip was lower than in the first measurements. Actually, I believe a more correct description is that the keepers and retainers are sliding up the valve stems, rather than the valves getting lower. Anyhow, I'm glad I found it now, rather than after blowing the engine.

Jerry C. - My retainers are supposed to be chrome moly steel. I'll find out what they really are in a few days.
Jerry

Jerry Clayton · #9 (**permalink**) 08-31-2006, 09:00 PM

If the 2 keepers are touching on both sides, you have the wrong sized keepers--there should be clearance between the 2 keepers

If you have too large retainers the keepers will slide thru even if they are the size needed for your valves--

I suggest new chromoly retainers and heat treated-machined keepers, not the stamped variety

Check for retainer to guide contact as that will cause your symtom as willcoil bind

Good luck

Jerry

CWizard · #10 (**permalink**) 09-11-2006, 07:55 AM

A local engine guy examined the retainers and keepers and meaured spring tension. His conclusions: 1. Keepers are properly sized and wear is normal. 2. Spring tension is ok. 3. Valve geometry is still not right (I had replaced the rockers and increased pushrod length earlier attempting to correct this). 4. My measurements suck (ouch!). So he put it back together with .010 longer pushrods and added lash caps to the valve stems. This should fix the geometry problem. And he also came up with a jig to measure valve tip and retainer height. He did this just to demonstrate to me that the valve tips weren't slipping through the retainers. Said he knew I'd worry about it otherwise. Pretty nice guy! So after another 3-400 miles I'll go back and we'll compare height measurements to ones he took last week, and then I'll stop worrying. But it looks like a happy outcome.
Thanks again for the input!

Excaliber · #11 (**permalink**) 09-11-2006, 11:40 AM

Well CW, can you imagine how many of us will now be taking a hard look at our valve keepers next time we adjust the valves?

Paranoia strikes deep...

CWizard · #12 (**permalink**) 09-11-2006, 11:51 AM

Excaliber -
Probably not a bad idea. Suggestion: In addition to keepers, check the clearance between the bottom of the rocker and the top of the retainer with the valve closed (spring fully extended). Crane says you need at least .040 inches there. In a worst case, interference there could tilt the retainer, allowing the keepers to work loose, and Boom! Valve hits piston.