October 2023

A mate from 'oop north' sent his favourite T150 my way for some treatment. There were a few items on his list, and the parts to achieve them, but as is my modus operandi you simply have to check everything to see what you're dealing with before heading off in the best informed direction.

As it was a runner, I took it for a brief ride around the neighbourhood to see how it behaved. In a word - very well. Ok, two words. The carbs seemed a bit out, so I spent a few minutes tweaking them and equalizing the intake airflows. That made it a happier idler, but also elicited some exhaust smoke. That usually means valves/guides.

Next I did a compression test, as the engine had done well over 30,000 miles since last build. It had not showed any reluctance to get up and go when asked, but the results really surprised me. All compressions were 165psi, which is not only excellent, but they were all the same within a psi. This led to a brief conversation with the owner to see if he wanted the cylinder he sent down fitted if this one was still viable. We shall see what shape everything is in when its apart and can be measured.

Of course, any top end work loads the bottom end, so next step would be an oil pressure check. The "L P Williams" gauge was attached and the bike wheeled out into todays sunshine. It started easier than the first time, perhaps happy with its new carb settings, and the oil pressure looked as I would have hoped, despite the lowest idle ever at around 500rpm.

The low idle speed also elicited some new symptoms, a rather loud and unpleasant rattle-cum-knock from the primary drive area. A new clutch plate had come with the bike, although I had no complaints about the current one. This sounded more like it was a complaint from the primary drive itself.

With a few revs the noise stopped, so I took a leisurely cruise to warm things up so the oil pressure could be checked in worst case conditions. The pressure remained at 80+ while in use, and the hot idle when we got back was good enough to rule out any need for a bottom end strip.

I let it cool down a bit after that, as the exhausts would be the first things to come off, and then, before you could say antidisestablishmentarianism it looked like this.

Today lifted the head and barrels. It was a fraught process. The allen screws inside the rocker boxes threatened to snap several allen keys, and rendered one unfit for further use. I suspect loctite was used in the fitting, judging by lots of sealant used in other places, but to overtighten these screws is asking for trouble, as they have less than half an inch of alloy thread to retain them.

I finally gave up on the last one altogether. Fortunately it was in the exhaust rocker box, so I was able to take the head off with the rocker box still attached, and will pass it on to my engine reconditioner for his genius to find a solution.

Having removed the inlet stubs I could clearly see that the inlet valves were liberally coated with carbonised oil, so it seems that it has been getting sucked down the guides for some time.

While there did not appear to be undue wear in the cylinders, the pistons slid up and down the bores with very little resistance at all, so at the least a hone and a set of rings would be required to return them to service.

If the bore to piston clearance is reaching max tolerance then new rings will only be a stop-gap measure, so it is looking likely that the new barrels will be going on. A measure up will elicit more data.

Otherwise, rods and camshaft lobes and followers look to be in great shape. More good than bad today.

The head and new barrels went off to the engine reconditioner for his attention. Besides getting the reluctant allen screw out of the rocker box, the head likely needs valves and guides, and we need to see if it needs oversize guides. The barrels are like new, but the tapers at the bottom of the liners need to be increased slightly in order that the new piston rings will easily enter the bores when it goes on. I feed them in by hand rather than use compressors, and the taper dictates whether it is a smooth operation or a risky business. I prefer the former.

While that all waits for progress to be made by someone else I shall remove the primary drive and see what lurks within.

Later - actually it all looks great, and everything is well tight.

Perhaps I should not have chosen the last words. The crankshaft sprocket nut is tighter than Dean Martin on a Saturday (period joke..), and even my rattle gun failed to make any impression. While awaiting inspiration I inspected the cush drive, and sure enough, I found a small amount of rotational play. Not enough to indicate that the rubbers had turned to mush, and the oil I drained out said much the same.

So I opened up the cush drive to find something I had heard of but never seen. Some form of perhaps polyurethane 'rubbers' had been fitted, and they had migrated around the separators rather than the vanes, which appeared to have been built up.

While this explains the knocking noise at slow idle it does not help me remove the crankshaft nut, and I want to inspect the clutch. While I pondered I went and pulled the primary off another Trident, just because I was in the mood.

Having thought about maximising the impact of the rattle gun, I first refitted the cush drive retaining nut, and put a socket with a power bar over the nut while using the rattle gun with my left hand and my knee on the rear brake pedal for good measure. It did not look at all impressed.

Ah. Then I realised that I was using a conventional socket on the rattle gun. Perhaps the 12 point socket would impact the nut less dramatically than a proper impact 6 sided nut. Fortunately I tracked one down, and first go it came whizzing off. Marvellous.

The inner primary cover came off next, and the clutch followed suit. The spline in the clutch plate was quite a loose fit on the hub, so the clutch assembly could be rocked side to side some amount, which may have also contributed to the knocking noises.

It all looked to be in good condition, though the line of oily deposit around the inside of the clutch housing would indicate that a small amount of oil has been leaking along the pullrod and getting flung out of the asembly, and may have reached the lining material on the plate.

The clutch got stripped immediately, new clutch plate laid in place while I removed the clutch bearing to insert an angular thrust type. As these bearings are similar to a taper type, the centre can be pushed out of the bearing in the opposite direction to its intended thrust. While I doubt that this clutch will ever be apart again in our anticipated lifetimes, should it ever be necessary to get it out, two holes need be drilled through the pressure plate so a small punch can be used to drive the outer race out of its location.

Like so...

The old plate did appear to have an oily surface, so I think we are curing a number of ills in here.

The clutch assembly got all bolted up and is here ready to go back in place, with a light smear of grease on the hub first, and an O ring slid back over the splines to prevent any oil tracking down the spline into the clutch housing in future.

I also dressed the end of the pullrod where the edges of the screwdriver slot had been burred to the point they were interfering with the nuts.

So the inner cover went back on with a new oil seal for the cush drive and a new O ring around the oil pump.

Oh - and a manky green gasket. Why do they make them green on the outside.? Its black on the other side. No sense of aesthetics these people.

Now begins the battle of the cush drive rubbers. The previous set were quite soft and malleable, which is why they migrated so successfully. Must have been a joy to install.

The new ones I just know were British made, because they will never surrender. Hard as a hard thing, and I am going to soak the last ones in hot water to try and make them a tad more pliable. They are putting up one hell of a fight.

Heating the remaining rubbers did help, as did perseverance, so I eventually won. I bolted the cover plate on and off several times to make sure none of the rubber was preventing the cover going completely home. It is certainly a firm fit so bye bye noises in both departments.

Locking tabs applied and the chain assembly got refitted to the bike, with a bit of rotational trial and error as I found the splines that were the happiest match. I left it here for the time being, and cleaned the two threads which will get a sensible amount of thread lock when the nuts go back on tomorrow.

Some tomorrows later I fitted the new oil seal into the cush drive retaining nut, wrapped some insulation tape over the pullrod threads and slid it into place. A bit of thread lock and a long bar were pressed into service as I kneeled on the brake lever and gave it some torque.

The crankshaft sprocket nut got some thread lock and the same tightening treatment, then I had a devil of a job getting the edge of the locking tab to lift so I could fold it properly whereupon the job was done.

With a new gasket in place the outer cover was easily convinced to go home, and the fixing screws got a clean as each one found its place. I don't do any up tight initially, as often the gasket sags a bit somewhere and obscures the hole. Forcing the screw in can then break the gasket, but it can be persuaded back in place while none of the screws are yet tightened fully.

Once it was all complete it got a lick of polish just to keep the motto intact - everything ends up better than when it came apart.

Further progress is now in the hands of the miracle machinist, who I saw today to compare notes. His benches are very full at this time of year, but I gave priority to the barrels, as I can at least move forward if I get those first.