1961 Triumph Speed Twin, 5TA - Part 2 – Rebuilding the Wreckage


So the old Speed Twin was pretty rough by the time the number plate was eventually sold.  Since the short runs I had used it for couldn’t have added more than 100 miles to the bike, it was clear that the last owners claim to have rebuilt the engine was a lie.  Selling it in this condition back then would have eaten into the profit I had made on the number plate, and besides, despite its problems, I had grown to like it.  Well, parts of it anyway, but you will read more of that later on.

Since the bike now cost me nothing, I decided to reinvest some of the number plate profits in fixing the engine.  At that time, I had a few big advantages when starting such a project.  Firstly, I worked for an engineering firm that had a very well equipped tool room.  Better yet, my boss, to whom I and many others will be eternally indebted, was bike mad, a damned fine engineer, and always willing to share both his knowledge and time.  His name is Bert Johnston, and at one stage in his career he ran a tuning shop catering for local bike and kart racers.  It was unprofitable probably because of Bert’s generosity.  He ran it as almost a charity, always willing to aid impoverished racers; the time he spent on projects was more than he could ever have hoped to recoup.  To give readers a taste of how good Bert was as a tuner, one of the achievements he was most proud of, was that it was he who tuned and built the 125cc engine used by Joey Dunlop in the 1993 IOM TT races.  This bike gave Joey his 15th TT win, and broke Mike Hailwood’s record number of race wins at the TT.

Meanwhile back to my Triumph.  Although the rest of the bike was far from immaculate, it all worked, so this rebuild concentrated on the engine.  When the engine was stripped, I found that one small end bearing has worn very badly, mostly to one side, meaning it was conical in shape.  Further inspection revealed that that con rod was slightly bent!  So much for the mechanical prowess and honesty of the previous owner!  So, this rod was replaced, the crank reground, the cylinders rebored, and new bearings were fitted throughout.  It also got a rather nice Morgo oil pump.

Originally these engines were designed to use older style monograde oils.  A straight comparison between mono and muiligrade oils can only be based on the range of temperatures within which they work effectively.  Monogrades work within a very narrow heat range, hence in times gone by; vehicles had their oil changed for summer and winter use.  But, oil specifications have changed in many more ways than just this, and these other changes can cause problems for those who want to use old vehicles.

Older oils lacked the additives that are present in modern multi-grades.   On early engines, this led to particulates caused by wear or carbon from combustion, dropping out of suspension from the oil as it pumped around the running engine.  These deposits caused localised hot spots and additional wear in engines.  Until the development of oil additives brought better solutions to this problem, many designers used the centrifugal effect of the rotating crankshaft to spin the particulates out of the oil.  Edward Turner, the designer of my Triumph, did just this.  There are inherent problems with such a system though.

Firstly, the particulates accumulate inside the crankshaft and will eventually block the oil supply within it that goes to the connecting rods (for the uninitiated, these connect the pistons to the crank).  This means that this design of engine needs to be taken apart at relatively low mileages to clean out the crankshaft sludge trap where these particulates accumulate.  It also means that these old engines are not compatible with modern oils, since modern oils have additives which keep particulates in suspension.  In modern engines, the oil passes through a filter which removes any contaminants.  Since my Triumph has no real oil filtration as standard, over time and mileage, modern oil would become an abrasive, contaminant-ridden mess, which would destroy the engine.

There are two solutions to this problem.  Replicas of old type oils are available for vintage engines, but I cannot understand why anyone would want to ignore the last sixty years of oil development?  The second option is to fit a proper oil filter, and use modern oil.  Since the dry sump design of my Triumph makes fitting an additional oil filter easy, this was the option I chose.

After all this, my Triumph ran well for many years, although I never did manage to cure all of the notorious Triumph oil leaks.  I ran it after I left the engineering company, and took myself off to get a university education.  I ran it to rallies, and on longish runs, including a number where we covered 350 plus miles in a day.  In fact, during one notable year back in the 90’s, we covered over 15, 000 miles, and the worst thing that happened during all that time was the wire from the car capacitor, (mounted on the rear mudguard to replace the then hard to get one in the ignition distributor), broke, causing a misfire.  This was easily fixed by the roadside, and we drove on.  I liked this bike.  It was light, economical, and had real charm.  A true pleasure to ride.

There were a few bad points though.  First the oil leaks, which were not too bad just after the rebuild, but were getting worse after a few years of use and abuse.  Next the lights.  The original six volts were probably feeble enough, but now that the bike was older many of those volts seemed to have shuffled off this mortal coil.  I remember travelling back home one Sunday night from a rally.  We had deliberately chosen the main road from Newry towards Belfast because it was wider, had street lights in parts, and was more likely to have other traffic that I could try to follow to use their lights to show the way.  That was a damned difficult ride, and I swore then that the next rebuild of the Triumph would include a 12 volt, negative earth conversion.  Eventually, as the millennium drew close, unleaded petrol loomed, and the Triumph’s mileage crossed that magic 100,000 mile mark (see the picture), I decided on another rebuild.
That is round the clock, not low mileage.  Who said that plain bush main bearings don't work?


This one was to have taken account of a number of things that limited funding had not permitted first time round.  These included 12 volt electrics as mentioned, the cylinder head, including valves and valve guides that were by then long past their prime, and a few more intricate jobs like balancing the weight of the con rods, remember that one bent one had been replaced, so they were not a matched set.  So I stripped the engine once more.

I had just finished the cylinder head, with new valves, guides and a repair to a long broken cooling fin when my wife suddenly found the house where we live now, and decided we were moving.  The house was a project, being pretty much untouched since it was built in exactly the same year as the Triumph.  It even still had its original 1961 kitchen!  So funding and time for the Triumph disappeared, and I am afraid to report that despite a few tentative thoughts of restarting the rebuild, very little has happened to it since.  We had lived in a flat, and had no garage, so all work happened a few miles away at my mothers house.  Once our own house was ours (and it does have a small garage), I brought round the Triumph’s mechanical bits, but left the rolling chassis where it was.  They have only been reunited location wise for a couple of years, but there still seems to always be another call on time and money, so the Triumph remains a work in progress.  The point of putting all this in public is to make some sort of commitment to get the bike back where it belongs by the time it is sixty years old.   There, it is out now, so I must be committed to it, mustn’t I?  ;-)

Next time, a plan….of sorts.

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