Valve Lash Adjustment - Cold v. Hot - Measured differences

[NewZed]

Has anyone actually measured the difference in valve lash from cold to hot? Or had to make large adjustments from cold to hot settings? Are certain cylinders more prone to change dramatically?

 

The materials and dimensions of the individual valve train components are the same, so it's not clear to me why there would be big differences. Component growth should be the same for each from cold to hot.

 

I ask out of curiosity and laziness. It's easier to set it cold.

 

Plus it seems like the individual settings should be more consistent with cold setting since they are made at the same temperature, as opposed to setting on a hot but cooling engine.

 

Thanks for any comments.

[at-jefft]

I don't know why, but I did have to make noticeable adjustments from cold to hot settings.

[olie05]

I ask out of curiosity and laziness. It's easier to set it cold.

 

BAH.

 

You just need to become speedier with the feeler gauges and man up to the scalding hot engine waiting to torture your knuckles.

 

That being said, I haven't adjusted my valves in a year, but I also have not driven more than 3000 miles since the last adjustment.

[PanzerAce]

I've never quite gotten the problem people have getting the hot measurements... Drive for awhile, stop, pop hood, remove valve cover, use starter to turn the engine, and it's easy.

[TimZ]

I've never quite gotten the problem people have getting the hot measurements... Drive for awhile, stop, pop hood, remove valve cover, use starter to turn the engine, and it's easy.

 

The problem I have with it is that people automatically assume that it's more accurate because everything is at "operating temperature", when in reality the engine is now changing temperature (and actual clearance) the entire time you are adjusting the valves. Working faster just says to me that you are spending less time per valve ensuring that you have a good lash setting, so what exactly are you gaining?

 

I believe that you are more likely to get repeatable results valve to valve when adjusting cold, since the engine temperature has stabilized.

[WildBill]

On my Dodge truck w/Cummins diesel, the valves are adjusted cold. I suppose you could adjust the valves when hot, then check clearances when cold and use that spec. for cold adjustment, then do a quick run through when hot to double check (at least the first time). Seems like OHC with screw adjusters have hot adjust spec, OHC with shim/bucket are cold spec, and OHV engines with solid lifters have a cold adjust spec.

[z-ya]

I believe that you are more likely to get repeatable results valve to valve when adjusting cold, since the engine temperature has stabilized.

 

How cold is cold? What is the ambient temperature for the "cold" lash specifications in the FSM?

 

I believe that adjusting them as close to operating temperature as possible is the most accurate way. It really is not all that difficult. Of course you want to adjust them to the "hot" specification in the FSM or on the spec sheet that come with your aftermarket cam. This of course this is 100% correct if you are running a stock temperature thermostat.

[TimZ]

How cold is cold? What is the ambient temperature for the "cold" lash specifications in the FSM?

 

How do you know what the temperature is for each valve when adjusting them hot, and what that spec was supposed to be? At least if the engine temperature is stabilized, the temperature is the same from start to finish.

 

I guess if I'm going to go to the trouble, I'd rather have the valve-to-valve settings consistent and just worry about being in the ballpark for the absolute measurement rather than the other way around. I just don't think that there is any real extra "accuracy" to be had from adjusting hot, and more potential pitfalls.

 

Nothings going to break if you are a thou off in any case - Nissan spec'ed it both ways, so do whatever makes you happy.

[JMortensen]

The problem I have with it is that people automatically assume that it's more accurate because everything is at "operating temperature", when in reality the engine is now changing temperature (and actual clearance) the entire time you are adjusting the valves. Working faster just says to me that you are spending less time per valve ensuring that you have a good lash setting, so what exactly are you gaining?

That sounds like you're saying you can't do a good job while going fast. My friend who worked as a Z mechanic and later for Nissan could do an L6 hot in just a couple minutes and they were all spot on, but he did nothing but work on L6's for several years. I suppose I agree that if you're slow, then do them cold. If you're not, I think hot is better because you're adjusting them where they run, although in fairness 911's are supposed to be adjusted cold, so you can make an argument for hot isn't absolutely necessary.

[z240]

You guys crack me up. Worrying about the tiniest of details of how to do it fast or slow, hot or cold and how other manufacturers do it and why. There is an even more important question people!

 

What I want to know is why the cold clearance specs are SMALLER than the hot specs? Don't Metal parts expand when hot, reducing the clearance between adjacent parts, thus strongly suggesting the hot specs should be to SMALLER clearance?

 

We'll also now sit back and hear from those that believe the cold spec is .010/.012 and the hot is .008/.010

 

Just thought I'de stir the pot today.

[PanzerAce]

How do you know what the temperature is for each valve when adjusting them hot, and what that spec was supposed to be? At least if the engine temperature is stabilized, the temperature is the same from start to finish.

 

I guess if I'm going to go to the trouble, I'd rather have the valve-to-valve settings consistent and just worry about being in the ballpark for the absolute measurement rather than the other way around. I just don't think that there is any real extra "accuracy" to be had from adjusting hot, and more potential pitfalls.

 

Nothings going to break if you are a thou off in any case - Nissan spec'ed it both ways, so do whatever makes you happy.

Well, one advantage of triples is that I can listen to figure out which valves are off before I even pull the valve cover. Obviously, some of the others might be slightly out of spec, but in general, other than one or two valves, it's usually just a quick run through to make sure everything is still to spec. Takes maybe five minutes tops if you've got help.

[DrSideways]

You guys crack me up. Worrying about the tiniest of details of how to do it fast or slow, hot or cold and how other manufacturers do it and why. There is an even more important question people!

 

What I want to know is why the cold clearance specs are SMALLER than the hot specs? Don't Metal parts expand when hot, reducing the clearance between adjacent parts, thus strongly suggesting the hot specs should be to SMALLER clearance?

 

We'll also now sit back and hear from those that believe the cold spec is .010/.012 and the hot is .008/.010

 

Just thought I'de stir the pot today.

 

 

 

The reason the hot clearance is more is because there is more surface area on the stem than on the ends.

 

Alan

[powershotnt]

Personally I don't adjust them..the ticking I get kinda gives me a rythm to hum to as its warming up..jeeezzz alright no more pain meds for me tonite

[TimZ]

You guys crack me up. Worrying about the tiniest of details of how to do it fast or slow, hot or cold and how other manufacturers do it and why.

 

Agreed - I seriously doubt that anybody would be able to detect a difference from either method - I just bristled a bit at the notion that setting the valves cold is "lazy" and "inferior".

 

What I want to know is why the cold clearance specs are SMALLER than the hot specs? Don't Metal parts expand when hot, reducing the clearance between adjacent parts, thus strongly suggesting the hot specs should be to SMALLER clearance?

 

We'll also now sit back and hear from those that believe the cold spec is .010/.012 and the hot is .008/.010

 

No, the smaller cold spec is correct.

Think of it this way - as the metal in the head gets hotter, its molecules move faster and get farther apart, hence the expansion. Everything gets farther apart, not just select parts of the head. So, for instance, any holes drilled in the head also get bigger (not smaller), since all of the metal circling the hole has to get farther apart too.

Same can be said for gaps and clearances in the head - so long as the whole head heats up at roughly the same rate, and the expansion coefficients for the parts of the head are not vastly different, then everything gets farther apart.

[HowlerMonkey]

With two crow's feet wrenches, you should be able to adjust all valves in less than 10 minutes.

 

15 if you use standard open end wrenches.

 

Keep a long pry bar handy in case you need more torque and make sure you use wrenches that are not worn.

[Zmanco]

FWIW, the cam card that came with my Schneider cam only listed cold clearance. I called to ask why and they said it didn't really matter whether it was done cold or hot, and since it's easier to do cold that's all they list now.

 

My own experience from installing a few cams cold and later checking hot is that there is no pattern to which valves "change", and usually it's about .001 or .002 difference so not a big deal. As I said in another recent post, if you're worried about valve noise, make sure that the wipe pattern is good, otherwise no amount of adjusting the valves is going to quiet things down.

[NewZed]

Thanks for all of the input. I recently set mine cold and wondered if it was really necessary to open things up again to recheck hot, hence the question.

 

In the future, if things get noisy and I want to drive right away I'll set it hot. Otherwise, cold seems like the way to go.

 

Thanks again.

 

By the way, will blood in the oil harm my engine? It's only a couple of knuckles worth....

[cockerstar]

Unknown to many, blood has a very high ZDDP content, and helps make up for the lack of it in modern oils. It should definitely help with cam wear

 

I adjusted mine to the cold spec, and found that I was still getting a lot of noise, so I adjusted them hot. Still had some noise, but it was better.

Has anyone else had to go tighter than the FSM specs to get everything to stay quiet?

[ozconnection]

Has anyone else had to go tighter than the FSM specs to get everything to stay quiet?

 

I did....once.

 

Don't go too tight, sure it's quieter but you can introduce other problems like poor manifold vacuum, rough idle and in a worst case scenario...burnt valves and valve seats. I had the first two symptoms and figured something wasn't quite right. Nutted it down to too tight valve clearances done by me! Once adjusted and the engine running properly, I could live with the little bit of extra valve train noise.

[cockerstar]

I don't think I over-did it, and as mentioned before, I'm not the quickest with the feeler gauges. I had to stop half way through and warm things up again, so adjusting some valves "warm" rather than hot might account for the difference. It definitely wasn't significantly tighter by any means.