Here is a discussion regarding some of the issues involved in selecting a new camshaft for your TR4/4A engine. The same issues apply to the earlier engines,  but variation in intake port design may alter the balance point for trade-offs.

First, do you really need to change your cam?  Maybe not.  The engine designers did a good job with balancing the trade-offs of the camshaft. Certainly they knew how to make a "hot" cam, but chose the one they did for very good reasons. A "hot" cam works at higher RPM, but sacrifices low RPM flexibility (i.e low idle speed and grunt at low rpm in higher gears.  However, the hotter cam allows more power at the upper rpm range.  Unlike some modern short stroke engine designs, our Triumphs are not able to get safely past what is now considered a mid-range rpm range.  So, the really hot cams that allow good power over 6000 rpm are not really useful here.  The cams we will be working with are in the range of stock to mild to moderate. The choice of cam will also be influenced by what other modifications have been made to the engine to allow the cam to work the way it was intended.  It is almost like buying a person with a bad heart a racing bicycle.  Even though the bicycle can go very fast, the person using it can not sustain the effort to make it go!

What does a "hot" cam do differently from a "stock" one?  It does nothing differently at all, it just does it at a different time. Time is of the essence, particularly with cams.  The cams open and close the valves which allow the mixture to be drawn into the engine and the spent exhaust to leave the engine.  At low rpm, it is not hard to get the mixture into, and the exhaust out of, the engine.  As the rpm gets higher it is progressively more difficult to get the gases in and out due to drag throughout the system. At high rpm you have to wait proportionally longer to get the gasses in and out. This wait is the time that the intake or exhaust valves are open.  That is the entire issue.  Higher RPM requires longer valve duration for good performance than low RPM.  In addition, when optimized for one range, it is not as good for the other range.

As I said above, the use of the hotter cams requires other modifications to the engine to put the cam to good use. Specifically, you may need a "better flowing" head.  This requires that the ports and valves be treated to reduce low resistance.  This will allow the gases to move more easily so you get a larger volume in and out of the engine in the same period of time.  Again, there is a trade off here.  Very large ports allow huge slugs of gas to be expelled without having a lot of drag induced by very high flow speeds.  Unfortunately, the flow can be too slow as well, so large ports can allow the gas to flow so slowly that problems can occur.  When these problems occur it may be impossible to obtain a low idle speed.

Another modification that a hot cam often requires is a higher compression head.  With excessively low compression it may not be possible to get the combustion efficiency that the engine requires.

So, is it reasonably possible to get a "better" cam without having to modify the rest of the engine? The answer is a qualified yes. Certainly you can get some more performance from the engine, but will the cost of the cam removal and reinstallation be worth the 6-10hp difference? Only you can answer that one. I, unfortunately, subscribe to the "more is better", or "in for a penny, in for a pound" philosophy.

I have not yet made the dive into the engine, but since my engine rebuild will require at least new valve guides, why not shave the head to increase the compression, and explore the cost of "porting and flowing" the head?  Once I spring for that cost, it would make sense to install larger intake valves. Larger intake valves require that the head gasket and block be relieved around the edge of the valve orifice.  Since the engine has quite a few miles on it, and the pistons and liners are aging fast, maybe I should put in 89mm pistons to increase displacement from 2138cc to 2187cc.  Certainly after all these modifications the carburetors themselves are causing a restriction, and some other carbs would be necessary.  Maybe 2" (instead of the stock 1.75") SU's, but Webers or Weber-look alikes are better.  Webers make sense here because I have lost some of the low-end anyway with a "hot" cam.  Needless to say, I now need a better exhaust manifold.

You can see where this is going.  Since I am not looking for a ton of horsepower (its not a Corvette after all!!), I will stick to a more mild cam where I do not have to worry too much about porting, flowing, new manifolds and the like.  I will run a moderately increased compression, and moderately improve the head to go with the moderate cam I will install.  This will be only moderately expensive (I hope).

Which cam is which?
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How do all these variations make a difference?  Well, they vary the time that the valves open and close.  To understand why the timing is important, you have to understand a little of what is happening inside the manifolds and cylinder.

In a model of engine function where the intake and exhaust gases have no momentum nor and drag, then all you need to do is open the intake valve at the beginning of the intake stroke and then close it at the end of the intake stroke, then compress the mixture, fire when the piston hits the top and then open the exhaust valve when the piston is at the bottom.

In the real world the gases do have momentum and drag. We can use momentum to our advantage so the engine does not have to do all the work pumping the gases in and out. Using momentum, the gases will (to a certain extent) blow themselves in and suck themselves out.

For the intake stroke, we can use the partial vacuum created by the exhaust gases as they are shooting out of the cylinder to help suck in the new mixture.  In order to do this, we need to open the intake valve before the exhaust valve is closed, and we can even open it before the piston has come to the top of the exhaust stroke!  At higher revs we need to open the valves earlier and keep them open proportionally longer in order for the same  amount of gas to be moved.  At low revs, prolonged valve overlap will cause some if the new mixture to be sucked out with the exhaust, causing no end of problems, and reducing performance.  This is the first instance of why a cam timed for high revs does not work well at low revs.

Now a little later into the intake stroke the exhaust valve has closed and the mixture is being sucked into the cylinder as the piston moves downward. When the piston hits the bottom of the intake stroke, the incoming mass of mixture has momentum driving it into the cylinder, so we can keep the valve open even after the cylinder has begun its upward compression stroke and allow momentum to drive even more mixture into the cylinder.  The length of the intake runners will help in this matter as the echo of the intake valve closing on the last stroke can come back and compress even more gas into the cylinder.  The echo is a wave of gas bouncing back from the carburetor end of the intake runner just as a wave bounces off a wall in a swimming pool.  Again, at higher revs we need to keep the valve open proportionally longer in the cycle to get the full charge of mixture.  The added charge of mixture entering the cylinder is a poor man's supercharging.

On the compression stroke the valves are closed, so there is no magic here as far as valves are concerned until near the end of the firing stroke.

After the spark has fired and the mixture combusted, the piston is driven downward and eventually it is time to open the exhaust valve.  We can open the exhaust valve before the piston hits the bottom of the stroke without losing much power.  The early opening of the valve gives more time for the exhaust to leave the cylinder.  The early opening also allows the exhaust to be shot out of the cylinder with a little more force and speed.  This is important later in the exhaust stroke.  Again, at higher revs it is necessary to open the exhaust valve proportionally earlier, but at lower revs, that will result in noticeable loss of power.

Now the piston is moving upward expelling the exhaust gases. The length of the exhaust runner is important since the blast of exhaust has momentum and can help suck the exhaust out of the cylinder at the end of the exhaust stroke, and can even help suck in some of the new mixture.  The length of the runner is important since if it is too short it will develop less suction (extractor effect) than it should.  If it is too long then it will cause excessive back pressure.  This is how "tuned pipes" work, and why they are a mixed blessing.  If you are going the right (high, usually) RPM, then the extractor effect is very useful (as long as your cam is timed appropriately).  At lower RPM, the pipes are too short and you lose the extractor effect.

Now we have been through the entire four strokes of the engine, and it is more clear why cam selection is important and such a difficult decision.

What is an "asymmetrical" cam?  In the old days, and even today, cams were usually symmetrical.  (E.G. the 17-57/57-17 stock TR4 cam)  This means that the intake valve opens 17 degrees BTDC of the intake stroke, and closes 57 degrees ABDC of the intake stroke.  In this case the exhaust valve opens 57 degrees BBDC of the exhaust stroke and 17 degrees ATDC of the exhaust stroke. Why are the numbers the same?  I am not sure, but I suppose it was easier to machine that way (before computer controlled machines) and with an infinite number of possible asymmetric settings, they stuck with the more limited choices of the symmetrical style.  Nowadays we have computers! This allows us to make any cam profile we want with very little extra effort.  We just type in a different set of numbers into the computer and let it make the machine run.  In addition, we have supercomputers to do advanced modeling of the complex flows in the engine.  In my description of the 4 strokes above I never said anything about the exact time the valves were supposed to open.  There is no special reason why you should open the exhaust valve 17 degrees BBDC just because you opened the intake valve 17 degrees BTDC.  As a matter of fact, there is every reason to suspect they should NOT open at the same number.  It would be a mighty coincidence if the optimal numbers were the same.  More of a coincidence than you having the same phone number (except area code) as your sister living in another state!  Advanced computer modeling allows designers to discover the optimal timing of all valve opening and closings.  Actually, the most advanced engines have no cam at all, instead, the valves are solenoid actuated and can be opened at varying times based on engine demands.  We do not have that luxury.

Note:   I have found that the asymmetry can be in the ramp profile of the lobe. It can open and close at different speeds.  I.E.  It can open fast with a steep  ramp, then close more slowly to minimize valve bounce by using a more shallow ramp angle.

Well, that is it.  I hope this explanation helps you understand cams and cam selection a little better.  I still have not decided which cam will be the best for me.  Probably unless I make a BIG mistake, any cam I choose (even the stock one) will keep me happy.

The rope trick helps to break the cylinder head seal on the block. Remove the rocker shaft complete with it's rockers and then the spark plugs, and feed in a length of thin soft rope (maybe 5mm dia) into the cylinder chamber, and with the head nuts removed turn the engine over a couple of times on the starter. The rope is compressed up and fills the cylinder head chamber and the piston crown pushes it up against the cylinder head lifting it maybe 3mm.

You can be hopeful and try the double nut on the studs and try turning out the studs in reverse. Some may come out dry, if not use your best quality anti seize fluid and pour into little reservoirs made by using plasticine or other sticky pliable putty substance around each stuck stud, diesel works really well. Leave it for a day or so to disappear down the stud and then try the double nut method on the stud...wiggling it both tighten (to break the seal) and then try to undo. If the double nut won't break it maybe a more professional stud remover might do the job, and then of course warming the stud (careful if you've used anti size or diesel on the head) can help when used in the process.

If you get the studs all but one out, then an overhead crane or lift onto the head along with a twisting motion helps screw the head up a stuck stud. Perseverance pays off in the end, I've rebuilt over 20 of these engines, some which obviously came off the Titanic ! and although they threaten resistance the normally give up begrudgingly.

A little idiosyncrasy of the engine are their wet cylinder liners which should protrude between 3-5 thou above the block surface, make sure you follow the workshop manual and get used to fitting and pulling the cylinder head whilst you juggle the clearances and machine. An area where many "pro" workshops fail, they do one build and measure and then strip and machine components and refit ...bish boff biff done...wrong. The clearances are dynamic and change orientations so build, measure, strip, machine and BMSM again, until you get them correct.

TR Four-Cylinder Series Torque Sequence

First make sure the head and block surfaces are clean and flat and that all of the threaded holes in the block have good clean threads. With studs, screw in the studs hand tight only. Do not tighten studs into a block unless you are sure that the bottom of the stud can hit the bottom of the hole. On a TR4 type engine, the studs do not have as long a bottom as the hole is deep, the stud will thread into the block stop where the threads on the stud end. If you continue to torque the stud into the block, the threads will try to pull the stud down into the hole and the stud will act like a wedge. It will cause the block to crack from the stud hole to whatever the nearest open area is. This is the reason most "tractor" blocks have cracks at the left rear stud hole going to the water jacket. There are improvements to be made here, but that is another story. So just tighten the studs hand tight.

We have found Permetex "Anti-Seize" when used as a lubricant on the head bolt thread, washers and nuts, does not change the torque that is applied, but does help prevent the "sticktion" mentioned in the earlier posts, so that it becomes less necessary to loosen the nuts first during re-torquing. So on a TR-4, we apply the anti- seize to the fine threads on the top of the stud, to the top surface of the washer and to the inside of the nut and its' bottom surface. Tighten the nuts using a normal torquing sequence to about 30 lbs. ft., then 50, then 70, then we go to 85 or 90. We use this as a maximum torque. WE no longer torque heads to 105 lbs. ft. as we have not found it necessary, and it only leads to broken and stripped studs and head nuts.

Run the engine to get it fully up to operating temperature, then retorque the head hot, to the same torque figure as the initial torque. With a solid steel head gasket, you can try again, but we have found nothing will tighten any more. With a composite (copper/asbestos) or other "non solid sheet" gasket, we hold re-torque the head again after a couple of heat cycles. If you wish to loosen each nut before retorqing, there is certainly no harm in doing so. It is good to mark each nut with a scribed line before you loosen it up, so you can tell if it tightened to a position that is tighter than it was in the begining. If I try to tighten a nut or stud, and it will not move, then it is definitely good practice to loosen and then re-torque. These general instructions ( except for the torque figures quoted) will hold true for any cast iron block and head combination. Using ARP moly based assembly lube paste on the head nuts and studs will require a reduction in torque of over 30% because it is so slippery. We have tried using the ARP lube and one time actually crushed the raised boss on a TR-4 head above the intake ports. The Anti-Seize works very well.

On modern engines the manufacturers no longer (generally) use torque figures for head tightening. The engineers have calculated how much "stretch" on the head bolts they need to get the clamping pressure on the head gasket that they want & the procedure is to torque to 20 lbs, ft.or less, then use a protractor and tighten the bolt a certain number of degrees from that point, the desired pre-load is calculated by the pitch of the threads of the bolt. This procedure avoids the variables caused by the friction of the bolt or nut on the threads or the washer and achieves a more consistent clamping force on the gasket.  

I forgot to mention a couple of things. Make sure that the fine threads on the studs are not distorted. Wire brush them clean and then inspect them under bright light against a white wall. The threads should not tilt upward, but should be nice and uniform. After 50 years of head gasket replacements the threads will eventually become distorted and will bent upwards. Any studs like this should be discarded. Another way to check them is to take two studs and fit the threads together. Hold them up to the white wall and there should be no light visible between the threads of the two studs. If the threads of one stud are distorted, light will be visible. Check the bottom of each nut. feel the inside of the hole. The threads should not be pulled downwards. When a nut is machined, there is always a little bevel on the inside of the hole leading into the first thread. As the nuts are torque again and again, the thread will pull downwards. If these threads are distorted, discard the nuts. Replacing the nuts with good Grade 8 "high nuts" is a good idea. A "high nut" is a nut that is about 1 1/4 times taller than a normal nut of the same size. Curtiss Industries makes good ones that are heat treated to have a tensil strength of 180,000 psi. Lawson Industries also distributes similar nuts. Of course all ARP hardware is top notch, but I do not like the look of 12 point head nuts on a Vintage race car, they just don't look right. I do not believe that ARP make a hex "high nut" Finally make sure that the nuts will spin on to the studs easily with your fingers before using them.