# Why such large valve lash???



## brett (Jun 3, 2007)

Hey guys...

I've searched through the forum several hundred times and it seems like nobody really talks about WHY there is such a large clearance on the RB26 valve lash. More importantly why most people tend to follow the factory specs when they change everything in the head, except the actual bare head itself. When you put Ferrea valves, dual valve springs, ti retainers, and a high lift/long duration camshaft...why would you keep the factory lash settings? It doesn't make sense to me, so I'm hoping someone can shed some light on the subject. It's particularly strange that many people will eliminate the sodium-filled exhaust valve, yet keep the same lash setting. Again...why?? Thanks in advance for the discussion.

-Brett


----------



## BenR (Jan 28, 2013)

Well, first off, we don't retain factory clearances with aftermarket cams, depending on the severity of the profile of course. 

I guess the question really is what you would gain by altering clearances, what would you hope to achieve. More or less clearance, I'm assuming less by the way you're speaking. 

Or do we go back to basics and why we need clearances? 

Sorry, that sounded condescending. 

I mean do we need to quantify the clearance amount that a stock rb runs and maybe why you would call it excessive?


----------



## tarmac terror (Jul 16, 2003)

Thing is, the majority of mass market, machine-assembled engines have far greater assembly tolerances than, say, a hand built 'blueprinted' engine. (OK, not a big fan of the 'blueprinted' ideology but use it to imply attention to detail)
I would suspect that when assembling an engine for motorsport using aftermarket items and taking ones time to do it properly tighter tolerances (than stock) can be achieved.

I agree with BenR though that its a good starting place to understand the stock clearances and the rationale behind them first before trying to reduce them.

TT


----------



## BenR (Jan 28, 2013)

There is a tolerance on valve clearances, so I wouldnt call the clearance itself a function of tolerances. 

Its primarily due to thermal expansion rates, and in pushrod engines that could end up being quite large. Overhead valve setups only really have thermal expansion of the valve itself, the bucket/shim/camlobe are all basically immeasurable amounts. 

Valve length and material affect the total amount of expansion, and especially the environment they operate under. 

So the RB has a 100mm od valve length and operates under quite high EGT's, meaning a fair amount of 'clearance' is required. Once your up and running, clearances drop and valve motion control experiences less jerk and snap acceleration rates. 

When you swap to an after market single piece stainless valve the expansion rates are quite high with that material so you'd still require a fair amount of clearance. 

All up for discussion, but the primary concern isnt the cold lash setting, but the running clearance, which is minimal at high temps, and the cams have appropriate pickup ramps to accommodate this and the formation of a hydrodynamic wedge.


----------



## brett (Jun 3, 2007)

There may have been a little condescension, but I'll ignore it. We've started the conversation, which is what I asked for...so, thank you Ben.

My point is that when we start spinning these motors above the factory intended redline (9,000 RPM for example), and introduce a much higher lift with a much more aggressive ramp it seems logical to me that the shock to the valve train of the cam/bucket contact will be severe at the factory lash specs. 

If you take these heads to just about any machine shop that specializes in race applications and you tell them you want the lash on the exhaust set to .015" and the intake at .018" there is a look of confusion. "You mean the other way around right?", is the first statement that comes back. Then you explain the sodium filled valve scenario and it makes a little more sense. Second comment is, are you sure that's not millimeters? Most shops (in the U.S. anyway) want to run the lash at about .010" intake and .013" exhaust with SS valves on these heads. It works well on cars seeing 30-35psi of boost and 750-900whp. Any more boost/hp and the loosen them up another .001" or .002".

The main reason to my question is looking throughout this forum, and so many qualified engine builders this doesn't seem to be covered. Other than a few stating to use stock specs. 

I understand the expansion rates of the different metals, and the need for the valve to sit on the head to remove the heat, but .018" of lash at 9,000 RPM "seems" quite excessive. Which is why I wanted to start the conversation.


----------



## BenR (Jan 28, 2013)

Is it 18 thou when hot though? 

If we could measure true hot values that might answer some questions. 

Also, kelford spec 10 thou inlet with their 272 cams iirc. 

And are we spinning the stock cams to 9k? I wouldn't know, I've never done it. 

The factory cams and lash specs obviously have taken into account the reduction in lash with operating temp, and the cams will also have appropriate ramps to deal with the operating clearance they have built into the engine. 

I guess this is quite easily demonstrated by the traditional values used by aftermarket cam grinds. 

I guess the beauty of turbo profiles is that there is a, relatively, generous amount of time to play with, so ramps might be extra accommodating with stock cams. I've never held a set so have never had the chance to map a profile and run the numbers, so it's all speculation for me.


----------



## brett (Jun 3, 2007)

It's not 18thou when hot, but 18thou on an intake valve (cold) is excessive unless Nissan has some magical growing valve as it warms. The valve train in these things are noisy even bone stock. We aren't spinning stock cams to 9,000RPM, we aren't even talking about stock cams or valves at this point. I know that's the reference point that many want to use, but that's why I started this conversation. That reference point doesn't make sense once you throw all the OEM stuff out the window, yet there is very little conversation about this. I want to know what is best for higher rpm, longer duration, high lift cams. It seems better to throw OEM specs to the wind as well, and do what works well in similar engines, which may very well be tighter tolerances. Hopefully we get a few more engine builders in this thread and "drop some knowledge" so when someone searches this subject again, they have more answers.


----------



## Nexen (Jul 19, 2009)

When I bought my Tomei cams they came with clearances that were similar to the standard so thats what I used . I know Scooby's use smaller clearances but then our straight six seem to last longer .


----------



## brett (Jun 3, 2007)

I can see that being the case. Stock valves? The reason I decided to bring this up was because people that were no longer using sodium-filled exhaust valves were still setting the lash tighter than the intake valve. It makes no sense, so I'm hoping to get an answer on that and lash in general when changing to an aftermarket valve train.


----------



## Nexen (Jul 19, 2009)

Well I'm very interested and will be keeping an eye on this .


----------



## BenR (Jan 28, 2013)

brett said:


> It's not 18thou when hot, but 18thou on an intake valve (cold) is excessive unless Nissan has some magical growing valve as it warms. The valve train in these things are noisy even bone stock. We aren't spinning stock cams to 9,000RPM, we aren't even talking about stock cams or valves at this point. I know that's the reference point that many want to use, but that's why I started this conversation. That reference point doesn't make sense once you throw all the OEM stuff out the window, yet there is very little conversation about this. I want to know what is best for higher rpm, longer duration, high lift cams. It seems better to throw OEM specs to the wind as well, and do what works well in similar engines, which may very well be tighter tolerances. Hopefully we get a few more engine builders in this thread and "drop some knowledge" so when someone searches this subject again, they have more answers.


Ok, I think I am starting to follow your train of thought a bit better. 

I understand what you are talking about with 'excessive' values, especially when compared with either the exhaust side value or the values that other common DOHC engines run. 

Now, the determining the value as excessive is tough without having all the information. The stock value is what it is for reasons known mostly to either nissan, or someone who has investigated it thoroughly. Perhaps the profile has an extremely generous clearance pickup in its ramp profiles. Obviously a problem with the clearances does not exist in terms of valve train ferocity otherwise the wiping of lobes and lifters would be a common problem. 

The only people I can see putting time into the research of stock valve train motion are those who offer alternative cam profiles. 

And from a quick glance, there doesn't seem to be a trend within the available grinds. 

The jap tuners might follow in the OEM style profiles as it seems (and not many offer much info on their grinds) they run similar clearances to stock. Tomei pon and pro cam series both keep the OEM clearances inlet and exhaust of 0.45 inlet and 0.38 exhaust. 

Jun require 0.30 inlet and 0.33mm exhaust. 

Kelford cams require 0.25 inlet and 0.3 exhaust, apart from their top line drag profiles which requires the values reversed (0.3 inlet and 0.25 exhaust) so I'm not sure if its correct or a typo. 

Camtech offer some drop in cams which require 12 thou inlet and 14 thou exhaust, yet their more extreme profiles require 18 thou inlet and 15 thou exhaust. 

I cannot find data for HKS, Mines, Brian Crower or other cams as I assume their only come with the cam data cards in the box. 

From the data presented I would say that the clearances are not excessive in stock form and merely a function of profile design requirements. It is evident that nobody should be using stock clearance values for after market cam profiles as they all require and demand their own values. 

Irrespective of the valve/spring/retainer setup, the clearance values as a starting point should not deviate from the cam grinders recommendations. 

So I am perplexed as to the issue of people running and not questioning stock clearance values, as it seems they should not be run in any circumstances bar stock. And to be honest, with any cam change I have done in a variety of engines of a variety of valve actuation methods, the change requires the altering of clearances to those specified with the new cams. 

So, to quote you for a clearer understanding

"That reference point doesn't make sense once you throw all the OEM stuff out the window, yet there is very little conversation about this"

The reference point for stock clearances goes out the window along with all the OEM stuff when it gets changed. So perhaps this is why there is very little discussion about it, the problem does not exist?

Also to quote you and answer

"I want to know what is best for higher rpm, longer duration, high lift cams."

The 'best' is what comes on the cam card when you buy wilder cams. 

Or again, am I missing something else in the topic of discussion.


----------



## brett (Jun 3, 2007)

Thanks BenR. You are spot on.... So with the clearances being determined by the manufacturer of the camshaft, this means that the function of the lash is solely based on the profile of the lobe? Regardless of the expansion rate of the valve material?

As you have seen searching some cam information, there are some manufacturers that have kept tighter tolerances on exhaust than intake. I wonder if they are just following Nissan's lead, or they just assume the user is keeping the sodium filled valves. I was looking for HKS cam information when these questions started to make we wonder why .015"/.018" seemed to be the most prevalent answer. I never found the HKS cam information, an email may be in order.

So to carry this conversation forward, I do know a lot of tuners that run tighter clearances. I'm not sure of the benefit other than higher lift and a quieter valve train. The down side being if the tolerances are "too tight" (not sure how else to say it) there may be a valve that hangs open, or does not sit on the seat long enough to cool the valve?


----------



## BenR (Jan 28, 2013)

Some of the grinders could follow the cam profile philisophy of the OEM cam since Nissan would of put in more R&D than most other companies could ever afford. Or it might be a result of the fact that many of the aftermarket cams run relatively larger valve motions because they grind a smaller base circle, which requires much more gentle action to control valve motion. Larger BCD's allow more 'area' for control, but require modifications to the lifter bores for clearance or even machining for larger lifter bores. It would be interesting to compare those cams with their clearance requirements. 

Running smaller clearances does have the added benefit or a more gentle valve motion as there is less jerk or snap valve acceleration upon pickup, along with a lower chance of valve bounce. So long as you dont, at peak operating temps, hang a valve off the seat due to too little clearance then all should be fine. 

There are zero benefits to additional lift amounting to that you reduce in clearance values of say 5 thou. It might crack open the valve slightly earlier and close slightly later, but we are talking minimal amounts where nominal changes would occur to the cycle apart from those we can map geometrically. 

I would not think sodium valves would play a part in their design as they are only used on the exhaust side and do not explain the larger inlet clearances. 

I'm all for tighter clearances, but at what point are you just guessing during testing. I think the only way to find out would be to firstly map a profile, run the numbers, and see exactly what the pickup ramps look like, they are are longer than normal. Then check if under operating temps the ally head is expanding at a higher rate than the valves, or if the valve growth is more. Once you know the sum of both you can see if the total clearance gets bigger or smaller and if you can play with clearances in one direction or another. 

In a lot of the pushrod engines I used to play with you could gain minute advantages by running larger clearances, but valve control because so harsh that damage was certain. Likewise you could tighten things up and see if the engine ran better with 'more cam'. 

Valvetrains are extremely complex and I certainly dot know enough to accurately give any answers for definite. But I guess a problem in the area only exists if you create one. It seems there hasn't been a problem with longevity or even performance with the RB, and gaining anything by changing clearances isn't going to net you significant amounts of area under the curve, nor extend service life simply because they operate in such harsh environments. 

If problems were in existence, I would of thought answers such as larger lifter diamters and cams with significantly larger BCD's, thinner stem lighter valves of the 5.5mm area, or if your extreme DLC coatings.


----------



## BenR (Jan 28, 2013)

double post*


----------



## brett (Jun 3, 2007)

Thanks Ben, and I agree with all of your points...again. 

Obviously, my biggest concern occurs when deviating from the valve train's intended RPM and Lift. The shock of the valve train at Nissan's clearances makes me nervous. 9,500 RPM, 11mm of lift, a base circle of 31, and .018" lash is a little disconcerting (to me).

Like I stated earlier, I have seen these motors run perfectly with much less lash. (.008" IN and .012" EX for example) I personally like the peace of mind of less harshness and a tighter follower at at the high RPM's. (and less noise) 

Thanks again for your input.


----------



## BenR (Jan 28, 2013)

brett said:


> Thanks Ben, and I agree with all of your points...again.
> 
> Obviously, my biggest concern occurs when deviating from the valve train's intended RPM and Lift. The shock of the valve train at Nissan's clearances makes me nervous. 9,500 RPM, 11mm of lift, a base circle of 31, and .018" lash is a little disconcerting (to me).
> 
> ...


If deviating from the valve trains intended lift and rpm, surely you would have changed valve/spring/retainer setup to accommodate the use of wilder cams which can carry on making power at 9500rpm. I personally wouldn't be too worried, it doesn't seem like a problem has arisen from existing advised clearances. From the data I've seen, it seems its a function of cam design and grinders advice, as there will be quite the infinite variation of valve train components used with their cams. 

Although, on the flip side, if smaller clearances can be run without any worries, then I would be running tighter. 

Its either a case of run them tighter and see, or map the cam profile and run the numbers.

If you know some tuners that do run them tighter, see what they run them at, why and how it affects the running/longevity. Would be interesting. 

I have hydro lifters so dont have to worry haha.


----------



## brett (Jun 3, 2007)

BenR said:


> If deviating from the valve trains intended lift and rpm, surely you would have changed valve/spring/retainer setup to accommodate the use of wilder cams which can carry on making power at 9500rpm. I personally wouldn't be too worried, it doesn't seem like a problem has arisen from existing advised clearances. From the data I've seen, it seems its a function of cam design and grinders advice, as there will be quite the infinite variation of valve train components used with their cams.
> 
> Although, on the flip side, if smaller clearances can be run without any worries, then I would be running tighter.
> 
> ...




Correct. Dual springs with higher seat and open pressures, titanium retainers, stainless valves, etc... I've been talking to those shops that run tighter clearances. It's just interesting to me though that this topic hasn't been covered much on here before, but like you said it may be simply because there has not been a "problem". Thanks again for your insight, I'll be sure to post any results. Good or bad...


----------



## BenR (Jan 28, 2013)

It might be because a lot of the engines that are built on here by their owners are built by the book since they are not professional engine builders. 

The safety margin of building with suggested book figures takes a lot of stress and worry off home builders, as well as a lot of the responsibility of possible failures off the shoulders of both home and professional builders. 

I'd be tempted to heat a stock and stainless valve up to operating temp on the bench and measure growth. Likewise heat a cylinder head up to operating temp in the oven with a loose lifter in, then push in a valve and see if the clearance opens or closes up. 

Be a quick and easy test to see if clearances open or close, and less messy than checking on a freshly run car. 

Personally, I'd also be moving towards a tighter clearance, but I'd probably pick a cam that suggests a tighter clearance to start off with. The only engines I've played with that require huge clearances like that in the RB26 are pushrod race engines, and they are much easier to adjust on the fly to see the effects. Most DOHC engines i've played with have been roller or finger follower, or run sub 12 thou clearances with solid buckets.


----------



## R.I.P.S NZ (May 7, 2004)

BenR said:


> And are we spinning the stock cams to 9k? I wouldn't know, I've never done it.





brett said:


> We aren't spinning stock cams to 9,000RPM, we aren't even talking about stock cams or valves at this point.


I can't comment on valves, springs or clearances but just to clear up one thing that seems to have been missed........you are not turning the cams at anything like 9000rpm even with a screamer race engine with aftermarket/custom cams, at most they might see 5000-5500rpm.

Rob


----------



## brett (Jun 3, 2007)

R.I.P.S NZ said:


> I can't comment on valves, springs or clearances but just to clear up one thing that seems to have been missed........you are not turning the cams at anything like 9000rpm even with a screamer race engine with aftermarket/custom cams, at most they might see 5000-5500rpm.
> 
> Rob


Correct, I meant spinning the engine to 9,000RPM vs. 8,000 RPM, etc. We were being technical and I should have been more specific. The cam speed on a 4-stroke motor being half that of the crank.


----------



## BenR (Jan 28, 2013)

lol, sorry, I think my comment didn't come across as clearly sarcastic is intended. 

Whilst your here Rob, I cant think of many that put an RB under more duress than you do.

What do you run clearance and valvetrain wise? Do you worry about running anything but the suggested clearances from the cam grinder?


----------



## R.I.P.S NZ (May 7, 2004)

I am sponsered by Kelfords now and pretty much leave them to it with regards to cams, springs, clearances etc.

I know with our previous heads we would need to replace a set of exhaust lifters every 2 seasons, the lobes would be nice but the bucket would get wear on the surface, exactly what caused it we didn't get into, we just changed them.

Once I have done a couple of seasons with the new gear it will be interesting to see how they look.

Rob


----------



## BenR (Jan 28, 2013)

I'm really interested in Kelfords new split lobe designs, have you had any experience with them?

Its all quite expensive once you get it over to the UK though, and get caught by the duty man.


----------



## BenR (Jan 28, 2013)

R.I.P.S NZ said:


> I am sponsered by Kelfords now and pretty much leave them to it with regards to cams, springs, clearances etc.
> 
> I know with our previous heads we would need to replace a set of exhaust lifters every 2 seasons, the lobes would be nice but the bucket would get wear on the surface, exactly what caused it we didn't get into, we just changed them.
> 
> ...


Have you considered or tried DLC?


----------



## DrGtr (Jul 18, 2009)

so if used with the tomei procams which they recommend 0.45in and 0.38ex let say 0.30in and 0.33ex what kind of problems could arise theoretically ?


----------



## yodookie (Oct 22, 2012)

DrGtr said:


> so if used with the tomei procams which they recommend 0.45in and 0.38ex let say 0.30in and 0.33ex what kind of problems could arise theoretically ?


I'd like to know this also. I'm going to be doing a set of valves pretty soon, would be nice to know so I can quiet the noise down a bit. :smokin:


----------



## BenR (Jan 28, 2013)

Theoretically....Lifter/lobe damage or a valve that does not fully close under running conditions, and thus a burnt out valve/seat.


----------



## freakazoid3 (Jan 19, 2008)

I'd be very carefull with making the clearance that much smaller just like that...Unless you really got a taste in engine rebuilds and you're hoping for a"thrid time's the charm" with your engine rebuild DrGtr


----------



## DrGtr (Jul 18, 2009)

freakazoid3 said:


> I'd be very carefull with making the clearance that much smaller just like that...Unless you really got a taste in engine rebuilds and you're hoping for a"thrid time's the charm" with your engine rebuild DrGtr


 no please i cant take it out once more if it breaks again i will be throwing the stock engine which i still have and park somewhere in the basement and dont touch it for many years till i get the psychology again i am going with the tomei recommendation then. its 0.45in 0.38ex for me.


----------



## DrGtr (Jul 18, 2009)

BenR said:


> Theoretically....Lifter/lobe damage or a valve that does not fully close under running conditions, and thus a burnt out valve/seat.


i had plendy of these lol valve seats are here 2 supertech exhaust and 12 ferrea inlet going to the local machine shop tomorrow to start working on it.


----------



## freakazoid3 (Jan 19, 2008)

Following the recommended figures for a mild setup is always the safest option 
You can always take the tightest clearance specified...


----------



## doyle4281 (Dec 10, 2008)

Hello all, I know this is a really old thread, but I have the very same question as many of you. I just received an RB26 back from the machine shop, and the intake lash was set to .010 and the exhaust to .015. HKS step 2 cams, ported head, valve job, dual springs, retainers, stock valves. Is this .010 tight enough to remove and redo the intake side?


----------



## DrGtr (Jul 18, 2009)

After years of running my last set up of 9000rpm and over 900hp with the factory recommendation clearances my engine runs still as new without problems since it doesn***8217;t rattle when cold and no sound of loose valve lash I would stick with the factory spec settings, or at least the spec that your cam recommended for.


----------

