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
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
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
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
... and burned exhaust valves, making the loss of power irreversible other than by overhauling the head.
RE: Camshaft /Tappet settings
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
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
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
RE: Camshaft /Tappet settings
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
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
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
Mike Halloran
Pembroke Pines, FL, USA
RE: Camshaft /Tappet settings
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
RE: Camshaft /Tappet settings
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
RE: Camshaft /Tappet settings
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
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
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
Regards
Pat
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RE: Camshaft /Tappet settings
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
RE: Camshaft /Tappet settings
http://harveycrane.com/lashloop.htm
Regards
Pat
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RE: Camshaft /Tappet settings
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
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
Regards
Pat
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RE: Camshaft /Tappet settings
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
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
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
RE: Camshaft /Tappet settings
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
RE: Camshaft /Tappet settings
Regards
Pat
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RE: Camshaft /Tappet settings
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
Uneven temperature distribution.
- Steve
RE: Camshaft /Tappet settings
Regards
Pat
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RE: Camshaft /Tappet settings
I suspect my knowledge of physics is better than most people on this forum.
RE: Camshaft /Tappet settings
Regards
Pat
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RE: Camshaft /Tappet settings
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
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
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
RE: Camshaft /Tappet settings
Regards
Pat
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RE: Camshaft /Tappet settings
Regards
Pat
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