Written by Ivan Bailey
Towards the end of the summer it would seem as if I had abandoned the Triumph. Parked in the garage, usually blocked by a car or two, it was just easier to jump on the motorcycle for my daily commute. Winter had arrived in New England and the car was officially in storage so with a little spare time on my hands I began the annual ritual embraced by countless enthusiasts - the winter teardown and rebuild. This year focused my energy on improving the performance of the TR6’s engine.
A little history regarding the current engine is important at this point.
When I rebuilt the original engine in 2003 I used the Competition Preparation Manual for TR250/TR6 as a guide. The engine was removed by me and my daughter, disassembled , then brought down to E&G Machine Shop in Wallingford, Connecticut. Frank, the owner of E&G and I spent many hours considering the rebuilding process. Eventually, I settled on a high-performance engine preparation but with a modest compression ratio.
The engine was completely cleaned, line-bored, and then the cylinders over-bored .030”. The original rods were reconditioned with new small end bushings, the I-beams were polished, lightened and shot-peened, and new ARP bolts were installed. The pistons were blueprinted, matching the weights as well. The crankshaft stroke was corrected and cut .010” undersized and then the journals polished. Oil passages were cross-drilled and chamfered to improve lubrication.
Prior to assembly the block was decked; the factory 4.550” thickness head was milled to obtain a 9.5 compression ratio per the Competition Preparation Manual instructions. The head was then given a three way valve job and a modest port and polish. The rotating assembly of crankshaft, flywheel and clutch assembly was balanced before the engine was assembled. The camshaft was installed and degreed, custom valve spring retainers were machined from small-block Chevy alloy retainers and new pushrods were cut to obtain the proper valve geometry angle.
The engine ran trouble free for nearly 3,000 miles, it started immediately and revved quickly and smoothly; so you may be thinking, “What could he possibly want to improve?” It didn’t pull as hard as I would like it to through the gears. Not wanting to rebuild the engine again, I was looking for affordable, bolt-on projects that would modestly improve the low- end and mid-range performance; upgrades that could be completed during the winter months. So began my search for a header, maybe trading the factory dual Zenith Stromberg Carburetors for dual SU’s or dual Hitachi’s from Paltech and other related performance components.
I haunted the 6-Pack site, researched the books, notes and articles I have in my collection of Triumph literature, and enquired to vendors for recommendations. I settled on a stainless oil pressure line and Brad Penn Oil from Ted Schumacher at TS Imported Automotive, a harmonic balancer rebuild and balance offered by Wishbone Classics, the quick and popular engine fan eliminator kit developed by Rick Patton (which offers a gain of 6 horsepower by removing the rotating mass from the front of the engine), and the installation of an exhaust header to improve low-end and mid-range performance. During my conversations with Kai Radicke, the owner of Wishbone Classics, he recommended additional tuning of the factory ZS carburetors with different needle profiles, and porting of the manifold instead of replacing them with an SU carburetors conversion.
Stainless Oil Pressure Line and Brad Penn Oil
The stainless oil pressure line was obtained from TS Imported Automotive and although not necessarily a performance improvement, I felt that the stainless oil pressure line was a worthwhile investment to protect the car’s interior, namely the carpet, dash and gauges that have been newly installed. Installation of the oil line was simple, and made even easier because it was done while I was fitting the new dash and refurnished gauges back into the car.
For some time I have been following the debate regarding oil products for the TR6. The concern regarding the loss of ZDDP1, the anti-wear component that protects our flat tappet camshaft engines (solid lifters); in available off- the- shelf oils led me to investigate alternative oils. ZDDP additives are available; however, I wanted oil that I could use without modification which contained the proper anti-wear properties. As an alternative, after the initial engine break- in period, I had begun using Shell Rotella 15W40 Multigrade Oil in the TR6 engine. This was the oil recommended at the time by vintage racers and other Triumph enthusiasts. Surprisingly, while viewing the TS Imported Automotive site, I rediscovered the Brad Penn Oils. Made in the USA, Brad Penn Oil is refined from Pennsylvania crude oil. Pennsylvania crude oil has a high paraffin level that makes it uniquely suited to be refined into performance oil. In addition the Brad Penn Oils contain a high level of ZDDP, addressing the concern over its loss in most off- the- shelf oils.
1 Zinc dialkyldithiophosphates (often referred to as ZDDP). ZDDP was originally added to create a cushion between the camshaft lobe and the lifter, today’s modern engines are designed to use rollers in these components, therefore high levels of ZDDP is not required. In addition I have been told that ZDDP was removed from modern oils because when it is burned in the exhaust it can shorten the lifespan of catalytic converters.
|With the two simple projects completed it was time begin disassembly of the engine components and get them sent out for rebuild.
Harmonic Balancer Rebuild
Looking into the engine bay, it is pretty obvious that to remove the harmonic balancer the radiator has to be taken out of the car. It is definitely a tight fit and no amount of contortions or tools would save me the time of having to remove nearly everything visible in the photograph, Figure 1. Comprehensive instructions to strip down the engine are covered in the Bentley TR250-TR6 Manual.
|Once the radiator was drained, the factory shroud removed, and the fan unbolted, a long breaker bar and a 1 1/8” socket were used to remove the center bolt Figure 2. This required shifting the car into gear, setting the parking brake and chocking the rear wheels. You can now apply enough force to the bolt to allow it come free without the engine turning over. After removing the center bolt and fan extension, I was able to easily slide the harmonic balancer forward on the crank snout until it bumped up against the alloy quick ratio steering rack and the cross-tube in front of the engine, adding ten more bolts and two more items to the list of parts which now had to be removed. Once these were out of the way, the harmonic balancer was removed easily and shipped off to Wishbone Classics for rebuilding and balancing. While waiting for the harmonic balancer to be returned, I removed the intake manifold to have it ported1. This is a service that is also offered by Wishbone Classics.
Engine cylinders 2 & 5 are shrouded by the casting wall in the center of each half of the intake. The result is that these cylinders are starved for the air-fuel mixture. A proper port job entails cutting back the internal divider and giving it a large nose radius to increase the performance of the stock intake manifold.
The original intake was removed figure 3 and a close up photograph figure 4 clearly shows the rough casting of the opening that the carburetor is bolted to.
In contrast, figure 5 and 6 show how the material has been cleaned up and the cast structures reshaped to optimize the fuel /air flow from the carburetors into the intake ports of the engine head.
|The ported intake was reinstalled onto the head with new studs, lock washers and nuts. High temperature anti-seize was used on the studs- both head side and then on the nut side. The new copper coated studs were screwed finger tight into the head and the nuts torqued to: 20-25ft lbs. for the exhaust manifold and 15-20ft lbs. for the intake manifold, Figure 7.|
Engine Fan Eliminator Kit
With the reinstallation of the newly rebuilt harmonic balancer, the three components that comprise the engine fan eliminator kit were bolted in place of the crankshaft extension and factory fan.
I had a new fan belt shipped out with the rebuilt harmonic balancer. After securing the balancer to the engine, I slipped the new belt around the water pump, alternator and harmonic balancer pulleys, only to discover that the new belt was a little too wide for the water pump and alternator.
The replacement fan belt I originally installed in the car was a 3/8” belt, not the correct ½”, having purchased the 3/8” belt based on the water pump and alternator dimensions.
I have been told that the 1972 through 1976 Triumph TR6 should have ½” pulleys and therefore require a ½” fan belt. I believe that since the balancer is the proper ½" width, and that it is the most difficult piece to changeover, the previous owner(s) put the other 3/8" parts in at an earlier time out of expediency, or they were just not aware of the right size.
This was a minor setback to getting the car back on the road, as now I had to find the correct pulleys for the alternator and water pump. Parts are available; however, I didn’t want to have to buy a new water pump to get the correct pulley. I contacted Wishbone Classics with this dilemma. Fortunately, the parts I needed were on hand. A new pulley was pressed onto my water pump and the 3/8” alternator pulley was swapped out for the correct ½” pulley. With overnight shipping, I had the corrected parts back, and ready to be installed quickly.
Final Assembly and Tuning
The factory Zenith Stromberg carburetors were reinstalled using the stock B1AF needles. The initial timing, mixture, synchronization and idle speed were set. The mixture may still have been little lean; when I lifted the carrier piston in the carburetors, the engine began to stumble. This is indicative of a lean condition, according to the TR6 Bentley Manual.
Unfortunately, little adjustment was left within the current needle carrier. Being stumped at this point, I posted a topic on the Six-Pack Forum for some advice. As usual our membership provided some possible answers: double check the float levels, check to see if the timing(2) is advanced too much, revisit my technique on performing the air valve test as I may have been holding the carrier piston up for too long. After rechecking these options and not finding any single one as the outstanding issue I moved on to the first road test.
After the test drive, I pulled the Champion RN12YC spark plugs. They seemed to be the "normal" color for a good mixture. The possible lean condition (3)discussed above did not seem to be a problem.
The engine idled with a nice lope at just a tick over 1,000 rpm. The RPMs rev up quickly and the engine begins to really start pulling at 2700-2900 RPM. After a little road testing, I went back through everything again (timing, mixture, and idle) and established this as a baseline to start from as I experiment with the different needle profiles to obtain maximum performance from the recent upgrades. It was then off to the Dyno.
2 Timing initially set 10-14 degrees BTDC without the vacuum retard connected.
3 Further conversations with Six Pack members revealed that the non-stock Kent Camshaft may not provide enough manifold vacuum to use the “lift the piston” test.
Conclusion & Dyno-tuning
I took the TR6 to local Debaise Brothers’ Custom Cycles and Hotrods in Meriden, Connecticut to have the car dyno-tuned. Originally, I had anticipated having three pulls on the dyno; however, my TR6 was the first Triumph the shop had ever seen so we ended up with nine runs. I think the guys running the dyno had as much fun as I did. First, the car was backed onto the top of the dyno and strapped down, front and back, and then test equipment was attached to the car. Finally, the tests and tuning began with shifting the engine through to fourth gear, then flooring the accelerator pedal and letting the engine build power and speed. After each run we evaluated the information and made adjustments to the timing and carburetion. By advancing the timing from 14 degrees BTDC to 16 degrees BTDC and enriching the mixture the last available ¼ turn in the needle carrier gained us nearly 7 horsepower and obtained the best run of the day with just under 104 horsepower and 122 ft. /lbs. of torque. See Dyno Results Below..
I have to tell you that I was disappointed with the numbers - I had expected a little more. In any case, the car sounded great, and the power, although less than I had anticipated, came on smooth and fast. We determined that the engine began to lean out; that is, it required more fuel at the higher RPM then the current stock needles could provide. The current camshaft, a Kent TH2/6, has a power band of 2500-6500 RPM. During the testing, the engine performance flattened out at 5500 RPM. Therefore, a needle change is planned as part of future additional tuning. At some point additional camshaft lift may be required.
Not having an original dyno test to compare my results with, these horsepower and torque figures become the starting point for future upgrades. These include the installation of the header, possible camshaft change, and 1.55 roller rockers. Now that the warm spring weather has finally arrived to New England, I will put down the wrenches for a few weeks and enjoy. As one Six-Pack member remarked, “Let’s drive.”
HP (horsepower), and torque figures are rear wheel figures. Factory stock HP and torque figures are estimated at 70 HP and 100 ft. /lbs. of torque.