Triumph Stag Maintenance

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this page updated 24-Oct-01

Overview

Differences MKI vs MKII (by Peter Howells) and (by Glenn Merrell)

Remember that Mark I and Mark II are not "Official" Triumph or British Leyland designations. This is why the hazy differences between what we have all come to know as Mark I and Mark II. Most assume that there is a clear dividing line between chassis/engine numbers and Mark I / Mark II features, where there is actually not. Infact modifications were built in on an availability or stock base.

The main differences that are obvious are
MkI has
Chassis number less than LD20,000
MkII has
Chassis after LD20,000
Not all the above is on all Mk1, as we have a hybrid often called 1 and a half, even after chassis 20000. Which leaves the question, where does the full Mk2 start?
There are lots of other differences which are not immediately obvious, under the bonnet etc.
Sometimes Mk1 owners, as I am, have to fit Mk2 parts because the Mark one stuff is not available.
My last example of that is Steering rack. Mk1 original was 4+ turns lock to lock. Mk2 is only 2+half.

Peter Howells

Stag Cooling (by Glenn Merrell, 73 Stag)

Since lately I have been studying the cooling system of the original Stag engine, the generally accepted methods of maintaining cooling on a Stag that I've found are:
  1. have the radiator recored to a 3 or 5 row core or modified cross flow;
  2. make sure the original style thermostat with blanking disk is used on a Mark II induction manifold designed with a bypass hole in the back of the manifold. CAUTION - If you have an early Mark I manifold that does not have a bypass hole behind the thermostat hold, DO NOT use a blanking disk style thermostat as it may NOT OPEN. This is due to the fact that the shaft of the thermostat has no place to travel when opening, where in Mark II induction manifolds, the blanking disk shaft travels into the bypass hole when opening;
  3. retorque the intake manifold and cylinder heads every 3000 miles, 6000 miles maximum;
  4. pressure flush the cooling system once a year, replacing the antifreeze coolant with new;
  5. rod out the radiator every two years, or with #4;
  6. use only original style molded reinforced hoses;
  7. se only a 20 psi radiator cap on a Mark II, 13 psi cap on a Mark I;
  8. properly bleed the air out of the system.
From the previous research and articles I've read, most folks seem problem free with the Stag cooling.

Adequate Maintenance:
It appears that only systems that have not been maintained, or not had a quality engine flush to remove the engine block sediments are actually having problems (I found about an inch or so of crud my engine block when disassembled). My nose is tuned to the smell of antifreeze, and I panic when I smell it. Most of the time it is a passing car with a leak, but I always check it out.

Six vs. Twelve Vane water pump impellers:
The reports of the 6 to 12 vane pump impeller swap increasing cooling I would be suspect of, without first performing all the generally accepted maintenance and modifications first.

Racing use:
If any use of the Stag engine would cause a problem in the cooling, I would think it would be racing. Hart Racing recommend refitting of a higher capacity radiator. The information on cooling from Hart that I have read, and since Hart races Stags professionally, I would take their advice for cooling system maintenance. Removing the heat from the engine compartment through exhaust modifications should help also, which I bet that none of the racing engines at Hart have other than tubular exhaust manifolds.

Cylinder head gaskets:
I've also noted several different types of cylinder head gaskets. I do not know the manufacturer of each, but one style I've seen does not have hole openings that match the water jacket's semi circular holes in the block and cylinder heads. Where there is a semi circular opening in the metal, there is only a small round hole in the head gasket. The intake manifold gaskets also have a smaller hole than the hole for water flow from intake manifold to the cylinder head. These restrictions would impead the flow of water through the water jacket, causing less heat removal.

Engine Block casting problems:
On one block, the water passage leading to the water pump suction on one side had some casting flash bent up obstructing the pump suction by about one-half. I've read other reports of this problem.

System Filling, air bleeding:
Since the high points that can trap air in the system are in the heater coil and intake manifold, jacking the front of the car to cause the air to find its way out should be done over a period of time while at idle, and topping off the radiator. An air bubble in the wrong place in the cooling system could possibly interrupt flow on one side of the engine, and cause overheating or over pressure.

Summary:
To date, I think the above is a summary of what has been done by just about everyone who has owned a Stag. It only takes one time to overheat and rupture a head gasket or warp the cylinder head. From what I have read, the cause leading to the overheat was lack of proper maintenance. The best recommendation so far is...regular periodic maintenance.

Who knows what I will come up with down the road, maybe only to verify that the general maintenance works fine.

Regards,

Glenn Merrell, 73 MarkII Stag (in surgery)

Annual Cooling System Flushing (by Glenn Merrell, 73 Stag)

When preparing to perform the annual flush of the cooling system, obtain a good quality flushing detergent. Make sure it states that it is not harmful to aluminum, and ones with corrosion inhibitors seem to work the best.

Prestone has a two part flush powder - one half is detergent for the flush, the second part is corrosion/rust inhibitor used in the rinse flush.

First disconnect the heater core from the flushing by removing the feed and return hoses. Reverse flush it later by using a cut off garden hose attached to the heater return port (normally connected to a pipe that runs to the water pump cover) and connect a length of hose to the supply side of the heater core (normally connected to the left hand head) and route it into a drain.

Reconnect the two engine side heater hoses using a suitable length of copper tubing, or if using a power flush connection, this is a good place to connect the tap. This bypass of the heater core will keep you from depositing the crud from the engine and cooling system right into your heater core. (You would only notice this when the weather turns colder and you were wondering why the heater does not work, as you panic to think that the cooling system has gone too.)

Drain the cooling system and radiator by removing the lower hose on the radiator, disposing of the coolant properly. Remove the thermostat and reinstall the "water elbow" or "gooseneck". Follow the directions for flushing the system, being careful not to boilover or overheat the heads. If using a power flush system using the garden hose, make sure that the water is on for the whole engine flush cycle. Never pour cold water into a hot engine, as you will surely warp the cylinder heads and possibly crack the block.

While the cooling system is flushing, take a good look at the thermostat. If is is clean and tidy, test the thermostat by placing it in a sauce pan of water and bring it to a simmer on the stove. Use your wife's candy thermometer (you do this when she is out shopping, of course) to observe the temperature when the thermostat opens, and make sure the thermostat opens. It should open fully, and if the boil is not too agressive, it is a kick to watch it open and close for the first time. After verifying that the thermostat opened at the proper temperature, remove it from the burner and add cold water to the pan to slowly cool the water. Observe that the thermostat closes. If the thermostat is dirty, or does not fully open or close, discard it and buy a new one with a new gasket. Most are less than 5 pounds sterling or $8 US, which is somewhat less costly than replacing a burst hose on an outing, or, the cylinder heads and gaskets.

By now the flush has progressed nicely and your neighbors are wondering why there is a steaming river running through the development. Shut down the engine, allowing the engine to cool normally. You will find that the garden hose kept the engine from heating past one quarter on the gauge (now just how long is that hose, anyway?). Now is a good time to flush the heater core as described above. After flushing, reconnect the heater core to the supply and return lines, open all drain taps to drain out the flush and making sure that the taps are clear and flowing, repeat with fresh water if necessary.

Replace the thermostat and gasket, carefully positioning the jiggle pin or bleed hole at the 12:00 o'clock position. Replace and tighten the drain taps in the block, and tighten all the hose clamps. When the engine is just warm to the touch, refill the system with a mix of 50/50 destilled water/antifreeze. Use antifreezes that have corrosion inhibitors. I have found that the environmentally friendly antifreezes do not last more than 6 months, and eat your engine.

Regards
Glenn Merrell, 73 Mark II Stag

Cylinder Head Removal (by Glenn Merrell: 73 Stag)

The Rope Method: Preface: The intent of using this method is to remove a stuck cylinder head. Suspending the vehicle on the engine pulling tabs will only stress other components; wedges will trash the cylinder head beyond repair; and the head pulling bracket may not work in all occurrences.

I have used this method on several engines, one with all five studs seized, and in all cases, the heads lifted about +1 inch, enough room to jab saw the studs up close to the head. Also in all cases, no connecting rods were bent.

Depending on the reason you are removing the heads, it would be wise to pull the tappet buckets and pallets to see if any valves are bent. If so, expect to find a broken valve in the cylinder, and do not crank the engine without a length of rope in the cylinder. Otherwise, the valve piece will imbed itself into the soft aluminum once for each rotation, and most likely trash your head.

Do not bother trying to soak the studs, the penetrant never goes more than 1/2 inch past the surface, no matter what the claim of the penetrant. But, if it makes you feel good, go ahead and spray away, the runoff will help loosen the grease cake on the side of the engine. Also, DO NOT attempt to weld anything onto the broken off stud(s), it will only damage the bolting washer surface which needs to be perpendicular to the stud axis. It would be a good idea to view Tony Hart's timing chain video first, available from Tony Hart, the SOC, or Rimmers. Tony does not stock US formats of the video.

Materials needed: Initial Procedure: (basically, remove everything from the engine) Overview:
The basic idea using this method is to use the power of the starter to move the piston at velocity, compressing the nylon rope against the cylinder head. Not to worry, combustion explosion in the cylinder exceeds 2000 psi. This compression, when repeated several dozen times, will break the stud free enough to lift the cylinder head about one inch. The sequence to be followed is open to the user, but I have found it best to start with the front cylinder and work my way back until I see how the head is lifting. If some studs are giving you a particularly hard time, concentrate on the cylinders on either side of the stuck studs. RESIST ALL TEMPTATIONS TO USE A PRY BAR AND WEDGES.

Removal Procedure:
  1. with one hand, place the long screwdriver or dowel into the spark plug hole of the stuck head;
  2. rotate the crank counter clockwise (CCW) with the other hand until the piston is at the bottom of its stroke, using the dowel as an indicator;
  3. remove the screwdriver and carefully feed the nylon rope into the cylinder through the spark plug hole, leaving a loop exposed to remove the rope...DO NOT INSERT ALL OF THE ROPE INTO THE CYLINDER, AS YOU MAY NOT BE ABLE TO RETRIEVE IT!!!;
  4. rotate the crank by hand to compress the rope in the opposite direction (CCW) from the normal rotation. Tick over the engine using the starter. RELEASE THE KEY/REMOTE BUTTON AS SOON AS THE crankshaft STOPS ROTATION, OR YOU WILL BURN OUT YOUR STARTER. The engine rotation sill stop with a dull thud. The starter is not strong enough to push the head up with normal rotation. It needs the counter rotation to bet enough momentum to strike the head with the rope in the cylinder
  5. Rotate the crankshaft CCW in the full opposite direction by hand to compress the rope in the opposite rotation:
  6. tick over the engine using the starter, again releasing as soon as the crankshaft stops rotation;
  7. rotate the crankshaft CCW to the bottom of its stroke, feed in more rope if necessary (you will know if it is necessary if the engine cranks several full rotations);
  8. rotate the crankshaft CCW by hand to compress the rope in the opposite direction;
  9. tick over the engine using the starter, again releasing as soon as the crankshaft stops its rotation:
  10. REPEAT steps 5-9 until you see some movement of the cylinder head, which may be 10-20 times, then;
  11. rotate the crank CCW to loosen the rope, remove the rope from the cylinder, move to the next cylinder, start at step #1;
  12. when the head has lifted to a distance of about one inch, move the cylinder head gasket up against the bottom of the cylinder head. This is to insulate the head from the jab saw;
  13. carefully, jab saw the stud as close as possible to the head, being careful not to contact the head;. This will give you a one inch stud to grab with a stud extractor or vice grips.

    The fun part...
  14. support the cylinder head on some wood blocks;
  15. drive the head studs out of the head with the drift pin and 10 pound mallet (ohhh..yes, this feels soo good, wear some good gloves and goggles)
  16. repeat for second cylinder head
  17. go sit in the sauna, drink a beer.

Regards,
Glenn Merrell
Keep Your Stag Cool, Install a NEW Composite Cowl Today

Cylinder Head Fastening (by Glenn Merrell: 73 Stag)

A On the Stag engine, the cylinder head studs are not perpendicular to the block, where the head bolts are perpendicular to the block. Expansion and contraction forces are not equal on the lower threads that penetrate into the block to the upper stud threads. There are 8 threads into the block on the stud fully inserted, but only 3.5 threads engaging the upper stud by the head nut. There is more force per square inch taken up on the nut thread area than than distributed across the threads into the block; that is, assuming similar force on top and bottom parts of the stud (which is actually different because of the diagonal insertion into the block at the bottom), the bottom of the stud has a larger thread surface contact to spread out the force, the upper stud has less thread area by more than a 2.2:1 ratio bottom threads to top. The nut takes more than two times the force due to less area.

B The cylinder block is cast iron, the cylinder head is cast aluminum. The cylinder head studs are hardened steel. From my basic physics, I recall that aluminum expands something like 3:1 to steel for the same heat applied, and contracts in the same ratio. Every time the engine goes through a heat/cool cycle, the expansion/contraction dynamics occur on all of the components. The studs, threads, and nut actually stretch, but being of hardened materal, do not return to their normal position. "N" number of heat/cool cycles later, the nut will be loose on the stud unless other factors keep the nut from backing off. Hence, locknuts, nylocknuts, etc are employed to resist movement after proper torque has been applied.

The more temperature cycles the engine goes through, the faster the loosening. Retorquing is always done within 100-500 miles of a new gasket set or head removal, then at an average point for the average driver creating the average number of temperature cycles...or in other words, a scientific wild A@# guess or wide range of mileage to be considered safe without failure of the component. If fasteners were perfect, we would not have cylinder heads blowing the gaskets. Why retorque after 100-500 miles? First, proper mechanical application of a threaded fastener is; once it has been torqued, the expansion forces stretches the fastener, but does not distort the threads. The threads actually hamb together. This stretch factor is then accounted for by retorquing the fastener back to original spec, plus a bit. This creates a proper mesh of the ID/OD threads to jamb tight. In a perfect application, that should be the last word, the fasterer should hold forever. But, threads, once distorted, now have a different torque and holding rating then when new. When taken apart, new fastening hardware should be used, the old ones discarded and replaced with new. This is because once a thread is properly torqued, it has distorted and actually matched its mating thread slightly. You can only distort a thread so many times before it fails from over torque, and the more times you distort it, the less holding force it has, giving it a tendacy to move under loads.

Now that whe have torqued properly, lets talk gaskets.
So why do gaskets fail? As stated, the steel cylinder block and the aluminum cylinder head expand at different rates, but what does the gasket do? If properly applied, the gasket sticks to the steel block on the bottom side, sticks to the aluminum on the top side, and the fiberous core flexes with the expansion and contractions. This is why a gasket is used in this type of application. Cylinder head gaskets are not used to take up the "space" from groves and imperfections in the metal, but to allow the surfaces some movement from temperature cycling. When the engine is machined, there is less than a half of a thousants of an inch across the surface of the block or head face for tolerance. The head gasket is thick to allow this normal movement without infringing on the integrety of the seal..

Back to the original question, why do gaskets fail?
There are four fluids involved passing through the gasket; coolant, fuel, oil, and air. Fuel being combusted runs through a wide range of pH properties during its brief life, eroding the aluminum at the gasket junction. This is why there is a metal ring at most block holes to the head holes which allows both a physical and electrical bond between the two surfaces. The metal rings also help hold the gasket together so it does not separate top to bottom layers. Early coolants had some similar coorosive properties and is why deionized water was recommended when filling. Oil too, when reaching its end of life, has a higher coorosive character that eats the metal surfaces. Clearances are pretty slim between some of the water jacket holes and cylinder to cylinder distances. If, during assembly, any contaminate like oil or water was left on either block or head surface, the gasket may not adhere properly. This is why the service experts do not recommend any sealant on head gaskets, but clean the surfaces with a non residue cleaner like brake cleaner or alcohol. This is also why the repair manuals recommend sanding clean both surfaces, and throughly cleaning both surfaces before applying the gasket. Add a loose torque area and the gasket separates in at the contaminate between gasket and metal, or if adhered, in the middle, top from bottom layers, creating a small space. If this separation just happens to occur in the gap between the water jacket hole and the cylinder or oil hole, the high pressure high temperature coolant or combustion gasses see a huge pressure differential and follow the path of lower pressure. In the stag engine, also up the stud holes in the head.

For those of you rebuilding your engines, if the gasket has become fixed to the mating surfaces of the block and head, you will notice that dissassembly destroys the gasket, literally pulling it apart. As you curse the scrapping and sanding effort, note that the gasket was most likely working, but improper torque allowed the gasket to fail in the middle layers. If you take the head off and it is loosely sitting there, it was either perfectly matched to both surfaces, or totally useless. Or, you may see that the gasket worked in some areas, but did not adhere to the area where it failed due to contaminates.

Some gaskets have a coating that is activated by petroleum, and they recommend a thin wipe of fuel with a clean rag prior to fixing, then they become slightly sticky. Others have coatings that are heat activated, and adhere when things heat up for the first time.

Not keeping proper torque on the fasteners will only allow the gasket to fail more rapidly around that loosened area. Undertorque will allow a blowout/blow through, overtorquing will distort the cylinder head. Torque spec's in the ROM were guestimates based on typical application of the fastener and thread pitch and size, used for the initial fastening of all new components. Experience shows that maybe +5 ft pounds maximum from ROM specification may be more correct on first retorque and then that same value on subsequent retorques. More may collapse or distort the head.

So, begging to differ, please retorque your cylinder heads, just don't move things about expecting the gasket to keep together and keep a good seal. Move the head, replace the gasket. Alwasy follow the retorquing instructions in the ROM.

Regards,
Glenn Merrell
Keep Your Stag Cool, Install a NEW Composite Cowl Today

Oil Pressure and Oil Pump (by Tom Jell, 74 Stag), Addition (by Mike Wattam, Stag)

As all Stag come with a generally low pressure I would like to add some typical good (collected and discussed in the Stag Mailing List) readings:
Oil Pressure
RPM
Engine Cold
Engine Warm
Engine Hot
Engine Trash Warm
Idle
35-40 psi
15-20 psi
10-15 psi
10-15 psi
1500
40-45 psi
35-40 psi
psi
30-35 psi
2500
50-55 psi
45-50 psi
psi
35-45 psi

Additional Rimmer Bros, Tony Hart and others are selling uprated oil pumps (I think they are from a Turbo Volvo) and the price is a couple of more pounds. So definitely worth.

Full Size Picture (400k)

Enlosed find a picture why you might encounter a sudden drop of your oil pressure. This oil pump already sucked some metal parts in. Oil pressure when cold is almost the same, with hot oil you're down to 0.5 bar ( psi).

Btw. examination of the engine showed no damage to the crankshaft bearings or camshaft... so the oil filter does what it is supposed to do (at least for a period of time)
Tom

Additional Comments (by Mike Wattam, Triumph Stag Register)
The best thing about oil gauges is, the Stag doesn't normally have one! I don't, because:
  1. they are something else to worry about
  2. they are never accurate
  3. oil pressure is of hardly any consequence
  4. They don't measure oil flow
  5. oil pressure is controlled by the relief valve, more than the bearings
It is possible to have very high oil pressure but no oil flow through the bearings, leading to failure. Conversely, nil oil pressure may mean there is plenty of oil going through the (sloppy but not failed) bearings.

If the bearings are worn out, you'll hear them. Because the camshaft chambers are fed by oil bled from the main bearings, if the bearings are worn out the camshafts don't get fed oil, so noise rapidly develops.

I can more or less guaranteee that if you take off the oil pump and strip out the pressure relief valve, you will find it is not correctly or fully seated in the housing, and has badly worn on one side. This causes poor oil pressure idling when hot in particular and has caused many to strip their Stags unnecessarily, rebuilt with new bearings and then found no change in the oil pressure.

The spring used in later Stag oil pump relief valves is a terrible design with about one third of its length being coil-bound. It helps the valve stick in its housing and has almost no movement, the spring rate is also very high. Re-engineered springs give a good consistent oil pressure at all engine speeds and the valve does not stick.

So, what I am saying is don't worry about the oil pressure unless you have other symptoms. If you must still worry, look at the oil pump pressure relief valve.

Mike Wattam
Triumph Stag Register

Tires Sizes (by Brian Tink, 73 Stag)

A Michelin dealer gave me the following details regarding rolling circumference. 
Standard 175    * 14  =  634 millimetres

         185/70 * 14  =  616

         195/75 * 14  =  630
So it would seem that the 195's are the closest to the 175 originals, with only a 0.63% negative difference, whereas the 185 have a 2.99% negative difference
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