January 2020

A later date arrived.

I had decided that the cylinder head would need to be removed to find out why the drive side piston crown was very shiny and apparently covered in oil. This may lead to some rather expensive discoveries but it was necessary. As I prepared to remove the exhaust system I was considering how the very low mounting of the mufflers was the most unfortunate styling cue on this bike. A lot of work had been done to lift the visual appearance of the bike overall, and this was totally letting the side down. Not to mention the lack of cornering clearance it resulted in.


A quick look revealed that some different mounting plates had been fabricated, but it seemed that there was room to drill some new holes higher up the brackets. Unbolting the mufflers showed that this would indeed work, so I found the highest location that would be possible on both sides.

Just my personal preference but I think its a winner.


I then removed the exhaust system and the cylinder head.


Next job was to remove the barrels and pistons. The left side piston which had evidence of much oil activity seemed to have a fair bit of play so I was hoping that the bores would be ok, especially as the pistons were already .040" oversize. Removing all the studs revealed that a number of helicoils had been fitted, and it seemed there were large helicoils with smaller ones inside them. A couple of these had moved up in the barrel so were now proud of the surface. That may require some remedial treatment.

Once the barrels were off I could see that the bores were ok but perhaps somewhat glazed. The pistons appeared to be of recent fitment, but had cast oil rings, so that may be the explanation to both the glazed surface and some of the excess oil.


Inspecting the cylinder head I could see that oil had been getting drawn down the inlet valve guides on at least two cylinders, which suggested that either the guides were worn or the wrong type of guides had been fitted, or perhaps the valve stems were worn. An old chap who used to do machining for me had once observed that every time he was given a Trident head to repair which had seals fitted on the guides, the valve stems were always worn badly - obviously due to being robbed of enough oil.

And indeed there were guides fitted which required seals, and there was play between the valve stems and the guides. Normally I would fit the original type guides which have a steep taper at the top to shed oil without the need for a seal. The seals fitted here were of a type which had no spring to hold tension against the valve stem, so oil was still getting past the seal. I will fit the original type guides so It would be nice if the valve stems were good enough to be reused.


Removing an exhaust valve revealed original type guides and no appreciable wear, so at least these would not require anything more than refacing the heads and seats.

That thread in the shot which retains the rocker box is partially stripped and will require helicoiling.


I am currently able to obtain ring sets with 3 piece oil rings which do a good job of controlling oil in these engines, so if the bore to piston clearances prove to be ok we may get away with a hone and a set of rings, plus a set of inlet valve guides. The answers to these questions will be revealed once my engine reconditioner has measured it all up and given me his verdict. I will not purchase the valve guides until he has removed the old ones, in case oversize items are required.

Could have been a lot worse, and I get the impression that the pistons and bores will be fine.

Improving the top end of an engine puts more stress on the crankshaft bearings, and I had no real idea what shape they may be in. I fitted an oil pressure gauge and kicked the engine over to see what pressure I could get. 60psi was all I could manage on cold oil, which is a bit lower than I would have liked, but not disastrous. I shall leave the gauge in place until it gets fired up for the first time and we will know more.

I also discovered today what appears to be a leak from the rear of the oil tank. There are brackets brazed to the tank to support the coil tray and it seems that oil is weeping from one of those, so it may need brazing again. No better time to deal with such things than when it is already in bits.


Today the task was to entirely strip the head and barrels in order that they may receive whatever machining is deemed necessary so they behave themselves in future.



Progress to 8 January 2020.