ISOA Tech Tips - 2003

Last updated April 1, 2003

The tech articles on this web site are written with the understanding that you have some mechanical and/or electrical knowledge, and that you know and assume the risks and responsibilities involved in working on your own car. If you decide to make a modification to your car based upon one of these articles, you assume total responsibility and risk for those modifications. In no event will ISOA or any of its directors or officers be liable for any direct, indirect, incidental, or consequential damages arising out of your making modifications to your vehicle based upon the contents of an article provided in this web site. It's your car, and it can affect the health and safety of yourself and others - work and drive safely and wisely! To put it bluntly, if you don't know what you're doing under the hood, then you shouldn't be there.

Quick Index

• TR2 - TR4 Water Pump Pulley Puller
• The Right Screwdriver Tip
• Adjusting Triple Webers
• Adjusting a Spitfire Differential
• Stag/TR8 Temperature sending unit June 1, 2003

Last summer I had two instances of failure of the water pump pulley on my 1964 TR4, and a third related failure. In June I drove over to the Triumph Register of America convention in Wadsworth, Ohio and by the time I arrived the water pump pulley was wobbly on the pump shaft and noisy. Fortunately I was able to reach the TRA convention and remove/replace the water pump and pulley in the hotel parking lot. Just after I removed the fan belt to proceed to remove the pump and pulley someone handed me a neat little purpose made puller to remove the water pump pulley, which I quickly used and returned. A common 2 or 3 jaw pulley can't easily be used for lack of space and when I'd once before replaced the water pump (which requires removal of the pulley to get at the 3 pump fasteners) in the 1970's I had to remove the radiator. The simple puller someone handed me made the job very easy and eliminated the need to remove the radiator.

While returning home from the VTR convention in Red Wing in July, about half way between Madison and Janesville, the pulley I'd put on the month before shattered. This time there was no need to pull the pulley off since the only part remaining on the pump shaft was the central core. Both of the failed pulleys were the "Made in Taiwan" reproduction parts commonly sold today. In each instance the key way of the pump shaft was severely damaged but the pumps otherwise seemed fine and never leaked coolant. Again I replaced the water pump and pulley - although this time with NOS StanPart pump and pulley. I didn't accurately weigh the StanPart pulley vs. the Taiwanese pulley, but the NOS StanPart pulley is noticeably heavier and a much better looking casting.

In October, while enroute to the South East VTR Convention in Jekyll Island, GA, a blade of the cooling fan broke off and went into the radiator - most likely caused by an invisible crack created when the water pump pulley shattered in July and chunks of shattered pulley struck the fan. Due to the time it took to obtain a replacement fan I never made it to Jekyll Island.

Earlier this month, since it's warm in my basement and cold in my garage, I decided to make a Water Pump Pulley Puller, along the lines of the one I'd borrowed and used at the TRA Convention. The simple puller was made of materials I had on hand, and consists of 3 pieces of 1-1/4" x 1-1/4" x 1/8 steel angle and 4 ea 3/8" hex bolts and nuts. There is nothing critical about these materials dimensions and merely were what I found in my basement. I used a drill press, bench grinder, hack saw and hand files to shape the angle pieces - about an hour of sawing, drilling, filing and grinding. The next day I tack welded the 4 nuts to the angle pieces to make the tool easier to use and prevent loss of the nuts. The puller breaks down, nests together and goes into a cloth roll sewn up with a tie, about the size of a large candy bar. With this puller as part of my "self help" kit I suppose, like carrying an umbrella prevents rain, I'll never again have occasion to remove and replace a water pump and pulley. But, if I do, it'll be easy! "The main trait that separates man from animal is tools." Author unknown

By Jay Holekamp

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Like most of us, I originally thought that Triumphs had a lot of Phillips head screws throughout the car. I later found out that they are not Phillips head but instead Pozidrive® head screw. While they look similar, they are quite different and account for why there are so many seemingly "stripped" screw heads in our cars.

Pozidrive® heads differ in several ways from Phillips head screws. One is that the end point taper is much less on the drive head or bit. Also, the center of the where the slots cross each other has a small square (see figure #1) rather than the point found on Phillips head bits. This give the bit and screw head a much better mating and significantly reduces the possibility of stripping out the cross slots.

Pozidrive® screws can be identified by the small thin lines that are present on the screw head surface between the crossed slots. I have shown those lines in figure #1. You can order these bits from Snap-on Tools for your magnetic screwdriver. The part numbers are:

Bit #1 - part no. SMD251C	$.82

Bit #2 - part no. SMD252C	$.90

Bit #3 - part no. SMD253C 	$.82

You can order them on line from Snap-On or if you know a mechanic or shop that will order them for you in there next order, you can save on shipping. I talked to a Snap on rep but they do not carry them in their trucks. You can also buy the Pozidrive® heads as screwdrivers with plastic handles but they are much more expensive running from $10.00 and up. In this way you can always screw correctly in your Triumph!

By Tim "Yacker" Smith

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"So, what seems to be your problem?"

• Engine runs real hot, really hot in warm weather, really really hot in stop and go traffic
• Poor performance between 1500 to 2200 rpm
• Popping sounds through intake/exhaust header at cruising speeds

Now, the car is very difficult to start, won't idle once started, no power, and gas is dripping out of carbs #2 and #3 while engine is running.

I got in touch with Rich Cwik of the local Lotus Club. He had conducted the Weber Tech Session at the BCU last fall, 2002. He said, "So, what seems to be your problem?" He listened and suggested he make a house call. He immediately determined that we needed to operate. One by one all three Weber Carbs came off. He stated that the idle screws were never adjusted, the mounting washers (insulators) that were installed were rubber, not the metal Thackery washers which he prefers, the butterfly in carb #3 was mis-aligned and would not physically close, the middle carb was "jetted" differently than the front and back carb??, fuel pressure was a little to low so the gas pressure regulator setting was increased to 3 .75#, floats were not at the proper height, the floats were plastic not the metal ones which he prefers, and the O-Rings at the intake manifold were stretched.

Rich tested the accelerator pumps, added the metal floats, adjusted the height of each, jetted them all the same, and re-assembled them. We were done for the day. I will order new "Viton" O-Rings and Rich suggested I clean the outside of the carbs with brake cleaner.

The next house call was a few weeks later, when the O-Rings arrived. Rich used a moly lube on the O-Rings before he attached them to the intake, the metal Thackery washers were put into position and the carbs were bolted back on the intake manifold.

The accelerator cable was connected, the fuels lines re-connected, and Rich asked me to start the engine. Woooooooommmmm. The engine started immediately! Wow! Rich started adjusting the 9 adjusting screws. We saw some interference between two of the linkages. We used an angle grinder to increase the clearances. See Photo. Rich suggested the addition of another return spring to aid in bringing the engine speed back to idle speed quicker . It was getting late so the next house call would be the next morning.

We reviewed the jetting as shown in the Weber Repair Manual, Rich was concerned about this popping sound and the overheating condition probably caused by a "Lean" fuel mixture. He asked one last question, "What is the application of this engine?" I told him it will be a street driven, it's not a race car. He decided to switch the following Weber Components from F11 emulsion tubes to F2, and added 130 main jets and removed the 120 main jets. These side draft webers can be "easily" modified to any application by switching out a number of the internal components.

Rich has two really big tool boxes (they look like tackle boxes) and they are very heavy and stuffed with Weber parts. In those two boxes, he had everything to tune the Webers to my newly rebuilt TR6 engine with a custom cam. I suspect he has really big money invested in those parts. Rich has been working on Webers for 30 years.

We started the engine. With his air meter, he started adjusting those 9 screws while monitoring the rpm's and the sound of the engine. After maybe 20 minutes, Rich counted his tools and closed the bonnet. It was time for a test run.

This is one quick car, a 1972 GT6 with a 75 TR6 engine, with a very high lift cam, shaved head, along with these three DCOE Webers, and a differential geared for quickness (meaning traveling at a speedo reading of 55 mph, ground speed is reduced to 46.6 mph (.8474576 multiplier). I returned with a really big smile on my face.

Since the tune up, the 160 degree thermostat does not heat the cockpit. Who ever heard of a "thermally cool" GT6? I can't wait for warmer winter days to drive this car to work.

Rich, thank you for your support, your help, and your interest in British Cars!

by Phil "The Factor" Fox

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Alum. No, not really. It was done with $5 spherical washers.

Before discussing how the job was accomplished, it might be useful to review a few more basic things. First, two reasons to rebuild: 1.) It leaked oil very badly, and 2.) it was very noisy. Not the standard differential 'whine', more gear clatter, especially when going into reverse from a stop, or cornering at normal speeds. When the car was jacked off the floor, there seemed to be excessive free play when turning the rear wheels-one could rock one tire without movement in the other. After rebuilding the entire rear end-hubs, bearings, axles, U-joints, nothing seemed to resolve the problem. There were no real performance problems, however. So once again, a Triumph owner with nothing to do.

The differential was partially disassembled at the 2002 Transmission clinic, and incorrectly diagnosed excessive wear as the cause of the free play. We noticed that the small gears (see parts 7&8 in the drawing) had excessive free play. Especially problematic were the side gears (8) which could move nearly 0.1" in and out. They could easily be twisted off axis as well. The smaller pinion gears (7) appeared tight on the shaft, but moved in & out quite a bit-maybe 0.03". At the time, we determined to discontinue the rebuild and go on to other Triumph adventures. (A second-hand differential was purchased and installed into the car and driven last Summer.)

In thinking through the design and function of this wonderful device, it seemed reasonable that a few small shims appropriately installed could remedy the situation. The rationale being simple: The side gears (8) actually are centered by splines in the axle stubs, and shouldn't really wear much against the diff cage. Next, because both side and pinion gears are conical (tapered), free play will increase dramatically if a gap is allowed to develop between them. But more importantly, none of these gears actually turn during normal operation, so wear should be a minimum even in a Triumph! More on that latter in the Design & Operation section. So, off to the Victoria British catalog, and Bingo! Replacement washers available. Sort of a 'one size fits all' strategy, since all that's available for my car were 0.041" thickness, but that's a start. Now before starting out on a differential rebuild, it becomes immediately obvious that there's a lot more written cautions about this assembly than any other. And that's where the famous "Stagmeisterspreader" comes in. Joe made a special press (or puller, as it might be) to attach to the top casing of the differential to allow assembly of the cage back into the housing. The tool is an absolute "must use" due to the very tight (no clearance) fit. So with little to loose, and knowing the transmission clinic was upon us for 2003, disassembly started at home.

Removing the cage from the housing was easily done with a drift and light hammer taps. All parts were carefully marked and bagged to keep left/right sides separated. We'll need to know the total spacer stack-up (parts 12) to be able to set appropriate crown/pinion free play on assembly. Unfortunately, to remove cross pin (5), the crown gear first needs to be removed from the cage. That was actually a difficult operation since the attachment bolts were lok-tighted in. The gear orientation was marked on the cage to guarantee reassemble as the original. By the way, treat the crown/pinion with respect-no heat or rough handling here. Victoria Brits sells the set for $190, and they are matched. I don't know of other sources, except in complete assemblies. So a nicked tooth is about a $200 problem.

Once the crown was removed, the cross pin easily tapped out, and all four smaller gears could readily be removed (7&8). Sure enough, the washers were well worn, confirming suspicions. As it turned out, the two new washers (.041", parts 9) were added and combined with the thinner of the original set to produce an assembly with what felt like appropriate gear play. Application of the "Stagmeisterspreader", and Bingo! (again), the assembly was complete. Fortunately, crown/pinion free play was good. Add new oil seals and we're done. Considering the differential did not whine when last used, this all seems to make complete sense. So, as soon as the snow melts (?) and the car comes out of storage, we'll find out more.

Differential Design & Operation. Why is the gear mechanism so complicated? Actually, it's quite simple, and very ingenious. I believe it took the auto industry quite some time to perfect the concept, and since then all cars use a similar design (although hydraulics have modified a few things recently). The key benefit provided by the differential is to allow the tires to rotate at slightly different speeds when cornering, when both wheels are still firmly connected to an engine (transmission) operating at a constant speed. It also makes bumps a bit easier to absorb. The first cars had a simple crown/pinion gear attached to a solid shaft between both tires. That works well when going straight, but as the vehicle turns, the inside wheel needs to turn slower since the arc is a shorter distance compared to the outside wheel. Not only is handling poor, but both wheels slip on the pavement (The outside wheel goes too slow, the inside too fast). That makes for bad tire wear. The next step was to split the axle, and power only one wheel. Not such a good idea either. Kinda like one leg longer than the other.

The differential design solves these problems at minimum cost. Here's how: The crown/pinion gear assembly always rotate with the speed and direction of the transmission shaft, as they are directly connected to it, except for the gear ratio to the crown. The differential cage is bolted to the crown gear, so it also rotates at that speed. Cross pin (5) is captive in the cage so it always rotates with the speed of the transmission, as geared down by the crown/pinion ratio. Under normal, straight ahead operation, both wheels rotate in the same direction and at the same RPM. Because gears 8 are splined to the axle shafts, they also rotate with the same direction and speed as the wheels. However, the two smaller pinion gears (7) can not rotate with respect to each other on the cross pin shaft since they are meshed into opposite sides of the side gears. So what've we got? No relative movement among any of the smaller gears INSIDE the cage. Power is transmitted from the transmission to the crown/pinion, into the cage and out to the wheels. It works like a solid rear axle shaft with equivalent power to each rear wheel and we're happy.

Now, to understand the operation during cornering, think of yourself as a bug stuck on the rim of a tire. When you look at the other tire while traveling straight ahead, the other tire travels at the same speed as you, so it appears to not turn at all. (I'd guess, the bug would think of it as the whole world is turning, but not him/her/it). Then as the car turns, the inside wheel must slow, and the outside wheel must increase RPM. Again, from the bugs perspective, it looks like one wheel goes backwards while the other goes forward. (If this is difficult to understand, now is a good time to get a beer, as I did when writing) So during cornering, even though both wheels generally go forward, one travels slightly backwards with respect to the other. Back to the drawing. Side gears (8) can easily move in opposite directions because they ARE meshed on opposite sides by small gears (7). So even though the cage rotates at the transmission speed, which generally turns the wheels, the smaller gears inside the cage rotate at an RPM of the DIFFERENCE between the wheels. Power is divided appropriately, and again, everybody is happy.

So what happens when the car is jacked off the floor and a rear wheel is turned by hand? Only the differential gears can turn, and the cage remains stationary. That in affect requires them to turn in opposite directions. What happens when the car's stuck in snow, and one wheel spins? As the transmission RPM is increased without sufficient drag on one wheel, the cage turns only that side gear and the other is allowed to remain stationary. Because this is the extreme and unusual condition of operation, it is also the only time that significant wear is placed on the shims (9) and is the likely cause of failure in my differential. By knowing which shim was badly worn, we can even determine which tire was stuck. Be reminded that as cage RPM increases, centrifugal forces press gears 7 hard into the shims, and are likely to wear quickly. In other words, don't spin tires when stuck in snow, or reserve the Stagmeisterspreader.

Thanks again to Bill and Sherri Pyle for hosting the clinic, as well as all the helpful people that made it great fun.

Well, I'm done with the beer now. I wonder why this mechanism is called a differential?

by Steve Schultz

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Download the StagTemp.xls spreadsheet (MS Excel format) with these OEM resistance values.

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