Why Am I Agonizing To Set My Valve Lash At .004?

coollx · 03-09-2008, 05:08 PM

I just started my first valve adjustment and, like many others before me, its a challenge to say the least.

I'm not in a big hurry since I'm using this as an opportunity to get better acquainted with my new toy and first 911. Plus its winter here and I can't drive the car anyway.

I've read tens of valve adjustment threads on this site plus I have Wayne's book and the Bentley manual for reference. I'm also trying the traditional and backside procedures to understand both approaches.

What I want to know is why am I agonizing, redoing, double and triple checking to get the valve lash exactly at .004 when the manufacturers sticker under the deck lid says "Int & Exh lash is .004 +/- .002" ??????

Can anyone cite a legitimate reason why let says .003 to .005 is not acceptable?

It would certainly make life much easier and I doubt performance or longevity would suffer.

Thanks

mca · 03-09-2008, 05:11 PM

Interesting ... I am curious too.

old man neri · 03-09-2008, 05:11 PM

Quote:

Originally Posted by coollx

What I want to know is why am I agonizing, redoing, double and triple checking to get the valve lash exactly at .004 when the manufacturers sticker under the deck lid says "Int & Exh lash is .004 +/- .002" ??????

I don't know if it matters but that sticker refers to emissions stuff. So maybe it has to be at that spec to be emissions compliant but still should be at a tighter tolerance. I don't know, but I somewhat feel the same as you.

Zeke · 03-09-2008, 05:55 PM

So it runs smoothly and quietly, that's why. Run one or two at .006 and you'll swear you can hear which ones are bigger.

Plus, by going for .004 on the button, most end up with +- .002 anyway. In my mind, most can't do this that well, or should I say perfectly.

RWebb · RWebb's Garage

smooth & quiet also means so it won't hammer the thing to death

death = mechanical failure ===> engine rebuild

but only if it is off a far amount

Crashly · 03-09-2008, 07:24 PM

Dom I would guess that it has something to do with the thermal expansion of the metal parts once they are up to operating temperatures, in addition to leaving enough space for oil to get between the foot and the cam. To little space and no room for expansion and oil. To much space and the parts beat themselves up. I have tried the traditional .004 method numerous times and once I learned the backside method with the go -no go guages I was a true believer.

coollx · 03-11-2008, 11:04 AM

Just a couple of observations.

I certainly agree that too much valve lash is bad and could cause the engine to hammer itself to death....but it would take a very big lash to do that...probably well in excess of .010.

I'm sure the engine will run just as smooth and quiet with a lash of .005 as it would at .004.

I think Milt really said it best and is my point in raising this question with his comment;

Plus, by going for .004 on the button, most end up with +- .002 anyway. In my mind, most can't do this that well, or should I say perfectly

Thanks for everyone's comments.

Jdub · 03-11-2008, 12:01 PM

The key is to adjust all valves, wait overnight, then recheck them. (Most of us) do this on an annual basis so it's worth the Friday evening / Saturday morning model to ensure your valves are at least as consistent as they can be 1) as a set and 2) overall to the .004 gap.

Green Loctite those little screws on the valve adjuster, whatever you do!

rusnak · 03-11-2008, 12:39 PM

are you guys able to get your feeler blade back in to recheck the clearance? I've always had to back the adjuster out before feeding the feeler in, and then once it's out, it's out.

Superman · 03-11-2008, 12:56 PM

I use a dial indicator, and the results I get are between .003 and .0035. Works for me.

nesslar · 03-11-2008, 01:58 PM

I thought it says +/- .001, not .002...
My engine was too noisy when a couple of valves were at .005. Now it is as close to .004 as is possible without going insane through the process, and the car sounds good, a bit mechanical yet rumbly. I like it. I think next time I'll shoot for fairy tight .004 (actually would use the backside method) so it's even quieter.
Someone here not too long ago wrote of the tolerance issue and said he always adjusts to .003 as I recall. He said the engine is nice and quiet, (SC) and he's never had any problem over the course of a million miles (exaggerating just a bit here).

Anyway, at first glance .001 seems like a lot, but I believe those design nerds and trust their engineering.

LakeCleElum · 03-11-2008, 02:48 PM

My take on it it: set them at .004 When checking, OK to leave alone if between .003-.005. There are these type of specs for many maintaice items.....

cab83_750 · 03-11-2008, 06:27 PM

I am surprised that no one made reference to the 'gay' valve-adjusment method!!!!

i.e., backside

alniki · 03-11-2008, 07:36 PM

Quote:

Originally Posted by Jdub

The key is to adjust all valves, wait overnight, then recheck them. (Most of us) do this on an annual basis so it's worth the Friday evening / Saturday morning model to ensure your valves are at least as consistent as they can be 1) as a set and 2) overall to the .004 gap.

Green Loctite those little screws on the valve adjuster, whatever you do!

Jdub,
Did you mean Loctite Threadlocker Blue Stick?
Also, wait overnight to let my brain cool down or let the screws and nuts set? I don't see why the clearance might change overnight without running.

I'm thinking of manually cranking the engine a couple turns and rechecking the clearance. But would that do any damage to the cams etc...

bell · bell's Garage

Quote:

Originally Posted by alniki

I'm thinking of manually cranking the engine a couple turns and rechecking the clearance. But would that do any damage to the cams etc...

just don't turn it backwards and you'll be alright

aigel · aigel's Garage

Loose may sound bad, but it is the tight that you are worried about. If the valve does not close fully any more, it does not cool well, gets hot, leaks and before you know it you are in for a valve job.

The clearance generally gets lower over time, especially on the exhaust side. This is because the valve is sinking into the seat from wear of the mating surfaces. The rocker and cam lobe do not wear significantly compared to the valve / seat wear you may experience.

Getting them too tight is hard to do, except if you get carbon stuck between the valve and the seat. Then it will look closed, even though it isn't. This is why you want to avoid changing plugs (or pulling them) before adjusting the valves.

Hope this helps. Don't over-analyze. No, I don't miss valve adjustments ...

George

Don Ivey · 03-12-2008, 04:55 AM

OK, what if you do get a bit of carbon stuck between the valve and the seat. Is there any way to get it out without engine disassembly. Thanks,

Don Ivey
'87 Carrera (undergoing valve adjust)

cashflyer · 03-12-2008, 05:35 AM

More gap = more noise (and more hammering effect)
I use the traditional method and set mine at .0035"

Quote:

Originally Posted by Jdub

Loctite those little screws on the valve adjuster, whatever you do!

+1 - but which product number are you using?

This one time... I set mine, drove it for an hour, then let it cool.
Opened it up the next day to verify that the adjustment had stayed as set, and I found one of the nuts had worked completely off of the adjustment screw!!! Luckily, it lodged in a safe place and did no damage.

Ever since, I am sure to use the Loctite.

When selecting a Loctite threadlocker, be sure that it is designed for the application. You need oil tolerance and heat tolerance. Their catalog suggests the following 3 products for oily environments:
Blue #246. Oil tolerant, medium strength (170lb-in break), and heat tolerant to 450F.
Red #266. Oil tolerant, high strength (270lb-in break), and heat tolerant to 450F.
Green #294. Oil tolerant, high strength (289lb-in break), heat tolerant to 450F. Additionally, this formula is self wicking.

hcoles · 03-12-2008, 07:32 AM

as a side note - I think the actual spec. is 0.1mm which is a bit under 0.004" - I try to adjust to get a fairly firm sliding feel... almost like you can't slide it without a bit of wiggling. So as mentioned above it is a bit difficult to get them too tight. With effort and practice you can slide the feeler back in there. I cut down the tool that holds the feeler... the stock tool config. was too long IMO.

charleskieffner · 03-12-2008, 07:51 AM

because if you do it WRONG you will have 19% leakdown on your #4 exhaust valve like mine is. at 120K miles because some dumb ass wrench set it too tight somewhere in its previous owners life.

and im stuck with an upcoming freeking ******* very spendy while your in thar rebuild.

DO IT DEAD NUTS .004 intake/exhaust or suffer serious wallet depletion! your wanker will fall off, your wife/g/friend will leave you and your dog will piss on your polished fuchs and generally you will be a miserable SOB for the rest of your life!