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Camshaft /Tappet settings

Camshaft /Tappet settings

Camshaft /Tappet settings

(OP)
Can any one tell me why the gaps on a  upgraded camshaft are bigger than on an  OE one

eg, standard TR 6 , 35 65 35 65, 250 cam lift, 10 thou clearance,  after market cam, same duration, but a little more lift, 25-40 more, but any thing from 16 to 24 thou clearance,

this is even if the cam is ground on a new ..blank..

also , why does one have to set the tappet settings ..wider.. with 1.65  ratio rockers, as opposed to  OE  1.5 ratio ones, or so i have been told, but not why,.

i have been told conflicting things, but seeing as we have some..camshaft type... Guru,s on here, maybe I ,and others will end up being a bit wiser!!!

regards Marcus

RE: Camshaft /Tappet settings

The primary reason that I'm aware of for having a gap at all in the cold/newly adjusted condition is so that you don't end up holding the valves open when hot/worn.  Holding the valves open even a tiny bit reduces their ability to transfer heat to the seat, which quickly results in failure.
 It is common (but not universal) that valve lash will decrease as the engine heats up.  It is almost universal (I am unaware of exceptions) that valve lash decreases as the valve/seat interface wears.  The right amount of cold lash to have is (enough to accomodate gap reduction as the engine heats up)+(enough to accomodate valve/seat wear between adjustments)+(a little extra for safety).
 If you produce more power with the same hardware, you'll likely see more reduction in lash in the hot state, so you need more lash in the cold state.
 When you increase the rocker ratio, you increase the amount of motion on the valve side w/respect to the cam side.  If your lash is adjusted on the cam side, then it would take less lash with a bigger ratio to accomodate the same valve expansion.  That's apparently the opposite of what you've been told, so I can't give you a good explanation on that one.
 

RE: Camshaft /Tappet settings

Tappet clearance is necessary to prevent the valve ever being held off the seat by the base circle of the cam. The amount of clearance required depends on the relative degree of expansion of the valves, head, block tappets and push rods and the accuracy to which the base circle is ground.

For the same clearance at the cam to tappet interface, you need more clearance at the valve for higher ratio rockers. Whether or not the tappet clearance or the rocker to valve clearance is the more important to maintain is arguable.

In reality tappet clearance can often be reduced considerably from recommended settings thus giving an increase in duration and lift and reduced noise and wear. To tight runs the risk of a total loss of power if a valve is held off it's seat.

Regards
Pat
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RE: Camshaft /Tappet settings

"To tight runs the risk of a total loss of power if a valve is held off it's seat"
... and burned exhaust valves, making the loss of power irreversible other than by overhauling the head.

RE: Camshaft /Tappet settings

Quote:

and burned exhaust valves, making the loss of power irreversible other than by overhauling the head.

Only if they are a complete idiot and continue to drive with something obviously wrong, Oh OK I see your point.
 

Regards
Pat
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RE: Camshaft /Tappet settings

(OP)
Thanks for the intrest, but I dont think Ive got yhe answers im after!!!!

Ivymike, youve come close, by saying that the bigger gaps in the tappets/ [rocker arms ] as we call them over here,  are for an engine with more power,

i can see where ye coming from with this, but read below.

Pat, i may have picked you up wrong, no offense meant, but I am well aware that engines need running clearances,, but ta for the reply any how, ,Maybe you can come to my help below!!!

But even on an  18-58-58 18 deg seat to seat duration, and 220 thou lift at cam lobe,

a very mild cam, peaking at 4500 rpm,and 100 bhp

 the settings are still the same for a OE cam of 35-65 65-35, with 250 at the cam lobe, and 5500rpm peak,and  142- 160ish bhp, depending on exhaust and air box,s

same engine/engines just different cams, on above

what Im trying to find oot, is why after market cams  , all have bigger running clearences, even when made on a ..new blank..., and even when they are ..very.. similar to OE cams, the running clearances are still nearly ..Twice .. as big,!!!

it just does not seem to be with my older type of engine either, but all across the board,

[ is it the same with the big V 8,s some of you Ladds run!!]

Why is this??????

regards Marcus

RE: Camshaft /Tappet settings

For the theory.

I thought this was implied earlier, but on the same engine, the only reasons one cam requires more tappet clearance than another are:-

1) The base circle has more run out.

2) Expansion of some parts closes the gap more. This can be because of higher temperatures of some components giving a higher temperature differential to other components. If the only change was the cam, I would not really expect any real changes. Maybe (it's a long shot) the exhaust valve might get a bit hotter, but I really doubt it.

3) The engine is used in a different manner, but even on a stock cam, the clearance has to cover all manner of operation.

For the practice.

Tappet settings are a catch all recommendation with safety factors built in so they are NEVER to tight. Maybe aftermarket incorporates a bigger safety margin and maybe the aftermarket thinks that clattery tappets sound like a race car, so they are desirable to the market sector.

I tune cars with up to 290 deg at 0.050" and over .700" lift making over 1000HP. At times, I close the tappets down to the minimum I can without holding a valve off the seat.

If I think I need all the cam I can get, I close the inlets to 0.010" and exhausts to 0.012" hot, ASAP after a full power run. If I think I need less cam, I will open them up to 0.030". I don't really consider the cam grinders recommendation, however if the grinder recommends tight, I have more confidence in him and his quality.

This is on a blown injected methanol SBC with 23 deg aluminium heads, roller followers, SS valves, CrMo push rods and 1.65:1 rockers.

I have never had any valve train damage attributable to any settings within that range.





  

Regards
Pat
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RE: Camshaft /Tappet settings

could it be that the aftermarket cam manufacturer has not gone to the effort to determine the "best" setting, and is just reciting a particular value which has worked in the past?
 

RE: Camshaft /Tappet settings

Let me add my two cents here...

In my experience with several racing engines, the valve lash has been different with almost every camshaft, even for the same engine.  The often quoted reason being as Pat and Isaac have stated...However, I have found that further research into the "engineer" that came up with the specs is a much better indicator.  Seems these designers have their own personal tastes (based on experience?).  Perhaps that can account for some of the variation we see in aftermarket cams?

As to MY current engines...The Austin A engines have most of the cams (Kent SP310 and SP296) lash called out for 0.016"+ range by design..In fact, I use .018 and .020 hot (determined on the dyno) and when cold they vary only by a couple thou.  Now the Lotus twincam settings are wildly different, anything from Cosworth's typically tight .002" to McCoys .008 and CTE's at .014"...In practice the cold setting of .002 work just as well as the .018" I have tried on the CTE G-3's.  This variation has been virtually the same in every engine I have ever built.  What I mean to say is, referring to my initial statement, the lash called out in an aftermarket cam can and often is a product of the designer/engineer's personal preference.  I am sure that blanket statement has a bunch of holes in it, but that's the way it looks to me.

I have spent countless hours on the dyno trying to make that big improvement by juggling the valve lash and timing...Generally a waste of time and money.  There simply is not much to be gained (much to loose) going to far afield the nominal specs.

Rod

RE: Camshaft /Tappet settings

"A slappy tappet is a happy tappet" A common saying amongst the older mechanics I know here in OZ.
malbeare

A tidy mind not intelligent as it ignors the random opportunities of total chaos. Thats my excuse anyway
Malbeare
www.sixstroke.com

RE: Camshaft /Tappet settings

(OP)
Thanks Ladds, I seem to get the jist of it,

I was running the cam at  17 inlet, and  19 ex,

but on recomendation, from some one, who said that cos im on , 1.65 rockers, instead of  1.50 ones, then the gaps should be opened up to  19 and  21

as higher ratio rockers need more clearance,

this I did, and the engine  now sounds very ..clattery..

does no seem to go any better , just a lot more noisy


A  slappy tappet, is a happy tappet,  never heared that one before, maybe have to tell the neighbours this, when they complain me cars too  ..clattery.. for them , hee hee hee

thanks for the info though all of you

regards Marcus

RE: Camshaft /Tappet settings

I read somewhere that cams for solid lifters include a 'clearance ramp', to gently take up the lash before intentionally opening the valve.  You should be able to see this with a dial indicator, zeroed when the lifter is definitely on the base circle, e.g. diametrically opposite the lobe.  As the cam rotates toward the area where the valve should start opening, the lifter will slowly take up the lash, and then begin moving the valve.  For this to work, the lash has to be set _exactly_ as the cam designer intended.  Too little lash opens the valve early; not far open, but enough to burn a valve.  Too much lash, and the cam whacks the lifter up noisily instead of gently engaging it.



Mike Halloran
Pembroke Pines, FL, USA

RE: Camshaft /Tappet settings

Back in the 1960's, Chevrolet released a 375 bhp 327 cid engine for their Corvette that found its way into other cars too.  It had a cam that quickly found its way into other engines.  It was named the "30-30" cam, for its 0.030" valve lash.

It was noisy.  One commonly used rationale was the wide lash allowed a little valve bounce without hitting anything.

Another cam had .018 int and .024 exh, called the Duntov cam, of the early 283 fuel injected engine.

Franz

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RE: Camshaft /Tappet settings

I think it has more to do with the ramps and velocity of the lobe pattern in that area. As well as expansion of parts.

RE: Camshaft /Tappet settings

(OP)
Mike,im with you on that, as i know that cams have  take up

ramps,the one i have has these on,  it says so in  a

diagram, that was in the box,

the cam runs  solid tappets/lifters
 
too tight and it puts undue pressure on the cam lobe.



Franze,  this is sound thinking,  but dont rev that high,


Dicer, , this is what im tending to think tooo, as I said

before, one a mild engine, one 50% more power,[cam and

injection only ] but still the same rocker arm gaps,  so

expansion is not really an issue, at least with the OE cams,


Have we a ..cam manufacturer.. on here, that can say why

their cams run wider gaps,!!!

thanks ,  Marcus

RE: Camshaft /Tappet settings

The amount of tappet clearnce must match the amount of lift on the opening and closing ramps of the cam lobe. The ramps can clearly be seen on a lift/vel/accel graph of a lobe. They show up a horizontal constant velocity trace if the cam lobe is measured without any tappet clearance. There is no point in making the tappet clearance greater or smaller than the ramp height.  Just why higher performance cams have higher ramps I am nor sure - maybe a high performance (or racing) engine might be expected to run at extreme temperatures?    

RE: Camshaft /Tappet settings

I agree different cams have different ramps in both design and length. So long as the tappet clearance keeps the follower hitting on the ramp and never holding the valve off the seat it will work, at least in my experience.

I have seen anecdotal evidence that the 30 30 cam ran better with tight tappets, but I only ever ran the the 18 25 or so called Green Grind Duntov. I have seen the 30 30 refered to as a Pink Grind Duntov.

Regards
Pat
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RE: Camshaft /Tappet settings

Just why higher performance cams have higher ramps I am nor sure - maybe a high performance (or racing) engine might be expected to run at extreme temperatures?

high temperatures are a worse application for tall ramps, since you'll be signficantly increasing the duration in the hot condition vs. the cold condition.  having a tall ramp helps you seat the valve on the ramp instead of simply dropping it onto the seat when you're running fast and the valvetrain is vibrating, so you'll put up with the change in duration to keep the valves from breaking apart.  

If you plot dynamic valve position v time overlaid upon kinematic valve position v time, you'll see that at high load/speed the vibratory aspects of the motion are of significant magnitude relative to the ramp height.  Since you don't want to slam the valve shut, you need to have a tall enough ramp to catch it when the whole train is wiggling.  

 

RE: Camshaft /Tappet settings

(OP)
One thing i forgot to mention, dont no if it affects other engines, but the ..rocker gaps.. get wider  by about 1.5-2 thou,  when the engine is hot

depending as to how hot it is, then the gap is bigger

its a cast iron head, block

I would have thought that the gaps would ..close.. up, as metal  expands, with heat,!!!

am i alone in this phenomonom !!

thanks for all the intrest so far

regards Marcus

RE: Camshaft /Tappet settings

If the block and head expand more than the push rod, the gap opens. How does your block temp compare to your oil temp when you measure. All other things being the same, exhaust valves normally expand and close the gap and inlets normally cool and open the gap.

Regards
Pat
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RE: Camshaft /Tappet settings

The cam profile is specifically designed such that hot lash will be taken-up at a sensible velocity with both acceleration and jerk at minimum values - this ensures minimal impact forces at this juncture.

The valve-lift profile is therefore designed with specific lash ramp characteristics that may change from one designer/engineer to another.
 

RE: Camshaft /Tappet settings

Ivymike - I think your last comment makes a lot of sense and I strongly suspect that this is the basic reason that racing cams have higher ramps/clearances etc.  

RE: Camshaft /Tappet settings

Well he may be a bit of a braggart as you seem to think, Pat.
However, all what he says id definitely old school and if my personal experiences are any indication, he is damn well right on.

In the beginning, say, with my '61 Vette race car in the early 60's...I was not knowledgeable enough to stray from the OEM specs (and, I did not trust my peers )...So, even though I used the Duntov cams, I stuck with the specs.
Now, for the last 30 or so years, when setting up a race engine, I always vary the timing by 4 or 5 degrees both ways and vary the lash by up to .004" both ways while doing the dyno run ups...Fiddle with ign. timing a bit, but that is usually less productive...

As to whether lash increases or decreases with temp change...There is no problem with setting pushrod lash cold, as long as you know the numbers...I set pushrods hot and OHC cold...Just a matter of convenience.  Some gain, some loose.  All by fairly insignificant amounts.

All this does not change my opinion that the clearance ramps and ultimate valve lash is often determined as much by the cam grinders experience as any technical reason. That is definitely old school as am I.

Rod

RE: Camshaft /Tappet settings

(OP)
Pat,  Off topic here, a little,

but have been looking for clues!!, and come across an article that says that   Crane Cams have noo gone  bust,

maybe you already knew this

regards Marcus

RE: Camshaft /Tappet settings

I knew that, and if I remember correctly, Harvey Crane despite being the founder had a bitter bust up with the company some years ago. He was probably pleased to see them go.

Regards
Pat
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RE: Camshaft /Tappet settings

Braggarts I don't mind if they know what they are talking about. Braggarts who don't know anything are the annoying ones.
  For more than 40 years I have accepted without thinking about it too much that a tappet's clearance reduces when it gets hot. But is this true? The rule in physics is that a gap expands as if it were solid material. Everything I have seen written about tappet clearance describes it as closing up as the temperature increases - but I now doubt if it does close up significantly.
 Treating the whole engine as a solid mass says the gap must increase with temp. Does the valve itself get hot enough (and expand enough) to counteract the overall effect of increasing the gap?
Possibly the gap is there to allow for wear, base circle runout and reasons other than than tappet clearance closing up with increasing temperature.    

RE: Camshaft /Tappet settings

To quote my earlier post, It is common (but not universal) that valve lash will decrease as the engine heats up.  It is almost universal (I am unaware of exceptions) that valve lash decreases as the valve/seat interface wears.  The right amount of cold lash to have is (enough to accomodate gap reduction as the engine heats up)+(enough to accomodate valve/seat wear between adjustments)+(a little extra for safety).

Note that you have a short and long side of the rocker which must be considered seperately.  If the valve grows by more than the surrounding bits of head, the gap shrinks.  If the head grows by more than the pushrod, the gap grows.  So on and so forth...  If you think that all the parts are the same temperature, then how do you explain the choices about what touches coolant and what doesn't?  It would certainly be easier to put all the coolant passages at one end of the block and be done with it (or skip the coolant altogether).  Remember the discussion about what happens to valves if they can't transfer heat to the head?  That doesn't apply if the valve and head are the same temperature (no heat transfer).

I can assure you that hot and cold lash are almost always different numbers, and that engine OEMs know pretty well (by measurement) how much lash changes from cold to hot.  The engine manufacturer I currently work for requires a hot lash measurement test as a matter of course on every new engine program.  For small changes it doesn't yield much interesting info - for larger changes... let's just say you skip it at your own (signficant) risk.
 

RE: Camshaft /Tappet settings

In my experience, engines with aluminium heads tend to open tappets when hot and cast iron heads tend to close them.

Engines with aluminium pushrods tend to close them. Notice I said tend rather than do.

Aluminium blocks will also have an effect vs iron as will relativity of oil to water temperature.

Inlet valves are more inclined to open and exhausts to close.

  

Regards
Pat
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RE: Camshaft /Tappet settings

I'm no expert but logic makes me think that on an overhead valve engine (side cam) like my little 850, if the (steel) pushrods expand less with heat than the cylinder head and block assembly (all alloy on my engine), the tappet clearances will increase with higher temperatures.

RE: Camshaft /Tappet settings

alloy... aluminium?  How much do the valves expand?

On large diesel engines (all steel/iron), the valve lash tends to decrease when they get hot.  Common lash settings (cold) are in the neighborhood of 0.5mm exh and 0.25mm int.  Common lash values (hot) are more like 0.2-0.3mm.  These are typically cam-in-block engines with mechanical (screw) lash adjustment.

 

RE: Camshaft /Tappet settings

The laws of physics say that a gap expands when it gets hot. (Just why this is I personally find hard to visualise - logic could just as easily tend to make one think that it got smaller). So a gap decreasing on an engine with increasing temperature must be generally considered to be something of an anomoly. I think the valve is the main cause of this odd behaviour.  The valve is constrained to expand only in one direction (like the mercury in a thermometer). Presumably the valve's amount of expansion is double what would normally be expected. Does this make sense?      

RE: Camshaft /Tappet settings

I will waste a little time trying to explain again.

1) If you have a block of one substance and drill a hole in it, THE DIAMETER OF THE HOLE DOES GET BIGGER AS YOU HEAT THE BLOCK UP. That happens. It is fact, not opinion whether or not you can personally envisage it. This is the most elementary of high school physics.

2) There are a number of different metals used in the components that influence tappet clearance. These different metals do have a different co-efficient of expansion. Between aluminium and iron, there is a large difference. Between various grades of steel and iron there small but real differences. This means that for the same temperature increase there is a different amount of expansion. This is advanced high school or first year uni physics.

3) Different components in an engine are at different temperatures while the engine is running. Even different spots in the same component are at different temperatures and these temperatures are constantly changing as the engine runs and goes through its compression, fire, exhaust and induction cycles. This is more complex but can be understood by anyone with basic uni physics and some knowledge of an engine.

We are not here to train those who do not understand basic engineering principles. Please read site policies.

Regards
Pat
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RE: Camshaft /Tappet settings

A three word explanation:

Uneven temperature distribution.

- Steve

RE: Camshaft /Tappet settings

I didn't intend my meaning to imply that a gap didn't get bigger as it got hotter - of course it does. My meaning was that it is hard to visualise why it does.
I suspect my knowledge of physics is better than most people on this forum.

RE: Camshaft /Tappet settings

(OP)
Ok ,ladds , been doing a bit of detective work here, and also got some good feed back, from some ..cam manufacturers..

but one thing is clear, the gaps that are given with a cam, all vary, as to what the cam grinder  thinks/wants

some say that the gap is needed to ..take..up the gap on a ramp

some say its for thermal expansion

some are saying its both

some are saying that it is because the cams have a lot more lift

but some cams have more lift, and less gaps required,.

all are right , and every one has there own opinion of it

there are so may variables.

EG, My engine, an old castiron lump, the rocker gaps ..doo.. get bigger with a hot engine,

also , when setting the rockers, as stated before, the gaps keep altering, as you turn the engine round, for final checking

this i thought was due to the cam base circle not being  a ..circle.., so getting the back of the cam on a high,or low spot, thus altering the setting

this was eliminated, by setting the rockers at the same spot ,  but still got conflicting readings

but what aboot all the oil on the different parts!!!

cam bearings, cam base/tappet base/push rod ends/inside tappet [full of oil ]/rocker tip/valve tip,.

all are covered in the stuff,

noo  when i was setting the rockers, i was getting different readings, so I pushed doon hard on the screw adjuster,  and the gaps opened up 1.5 --  2 thou more

so some thing was getting compressed!!, oil,me tinks,!!!

also when engine had been ..turned over , to re check the  rockers, then the gaps would also increase,

this is I think, due to the oil getting ..thinned oot.. by turning over, and no oil pressure to re supply the bearings,

so cam was sitting at the bottom of its bearing, and not  supported by as much oil film

and as for pushing doon on the rocker, then i was squashing all the oil oot frae the contact surfaces of the components

Plus , it all depends on how thick your oil is too

so all these things can and doo alter the rocker gap

I actuall ended up setting the gaps to 6 thou, on the original rockers, as 1.5-2 thou bigger when hot, and 2 thou bigger when compressed == the 10 thou OE setting, when not compressed,and cold

on the cam i got noo, and this is where the post was from,

the gaps are to be set at 17--19 thou,

the engine ran noisy with these settings, about twice as noisy  the originals set at 6 thou, as stated above

but when i put on the set of 1.65 roller rockers i got [v,v cheap,and new too ]  then the engine was a lot quieter

but when , as i found oot, that the gaps had to be increased ,by the amount of extra ratio,

then the gaps went to 19--21 not 17--19 as for original setting for new cam

the extra noise that has come with the  2  thou gaps is a lot,

how can 2 thou diff, make so much more rackett!!

so I have gone and set them to my old formula , as mentioned further back, and took 2  thou off the original setting of 17-19, to end up with 15--17, this should i think still give me enough ..left over gap, to compensate for the extra ratio change

The  engine noo, is very quiet, and seems to go as good with a small gap as a big gap

Also as people have siad, the valve timeing has also increased a little

with the big gaps on the roller cam, the ..actuall valve.. was opening at 23 degs btdc,  now with my closed gaps its 26 degs btdc,  which is not far off, the 28 of what the cam is supposed to do,

So as you can see/read, there are so many variables in a cams gaps specs, that it is best to try and find oot, what works best for you,.

and thanks for all the feed back, well done

regards Marcus

 

RE: Camshaft /Tappet settings

Marcus, sometimes you just have to tinker a little to find out what the engine wants.

I've got this very same job to do on this rainy afternoon ... tightening up the exhaust valve clearance just a smidge on a Honda single with an aftermarket cam, which has been making a bit more mechanical noise than I'd like.

RE: Camshaft /Tappet settings

Something that no one has mentioned...

It is assumed that we all know how to set valve lash, that we all have "the feel"....That is simply NOT true.  Unless you are one of the few "techs" that actually CAN set valve lash by feel (I find these individuals few and far between) or are in possession of a P&G or some tool like it, then I could easily understand why you could have the variety of measurements you seem to be getting.

This ability is not something you can learn from a book, it must be taught by someone that already knows. Some very competent mechanics I have known never seem to get the knack!  Good thing about all this, in reality, a few thou one way or the other on a pushrod engine, at least, won't make a huge difference in the long run.

Rod

 

RE: Camshaft /Tappet settings

I think The go-no-go feeler gages ground to 2 thicknesses ( 0.002 inch step) are pretty handy for evaluating where I am.  Before I got a set of those I spent too much time deciding what was a tight 0.006 inch, etc, etc.  

RE: Camshaft /Tappet settings

I absolutely agree with Rod. Most cannot get repeatable readings closer than a few thou, but also that it does not matter. If you could get away with as little as 0.006 and you set at 0.010, no problem if it really is 0.008 or 0.12.

Regards
Pat
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