November 2024
1975 Triumph T160 Trident 750
Since I first helped to prepare this UK import T160 for use in NZ I have not had to work on it from memory, or if so it would have been minor as there is only one other entry on the site for it.
It was a bit neglected at that time, and besides necessary work to make it compliant and run properly I had just repainted the instrument holders and tidied up the muffler mounting arrangement. It has run pretty well overall since, and I have no idea what work may have ever been undertaken internally, though it enjoys the reputation of having visited the Isle of Man for between 10 and 15 TT's.
During the last two or three visits I had noticed it was idling more on two than three cylinders, but otherwise performed well enough. Now the idle had deteriorated further so it was here to find out why. I suspected that there may have been some compression missing, and gently kicking through all three I could feel that one was decidedly lower. As I had decided to remove the carbs for checking I figured I would do that first as it makes compression testing easier.
The carbs still looked a lot better than the first time around, but there was some slight variation in slide heights at idle position.
With the carbs off I used a mirror to look down the inlet ports. Although the camera was not able to see what I could, you can just detect a glistening black deposit on the top of the inlet valve head, and all three were much the same.
This indicates oil getting sucked down the inlet guides, which in turn suggests that the valve stems are significantly worn. You would expect the softer valve guide material to wear first, but it is invariably the valves, although it makes little difference as both will need replacing. This now gives me an idea of potentially how much mileage the engine has done since last top end attention, if indeed it has ever had any at all.
The spark plugs are quite recent, and all are showing life to have been a bit on the sooty side of things, as one would expect. The pain of it is that the oil arrives as the engine is deccelerating, and will often soot up just as you stop and expect it to idle, and Chris said that he has had to keep revving it to avoid a stall recently.
Mixture wise I would say it is not far off being happy, so I think the carbs might be above suspicion, and I already know that they are in completely standard trim from my original strip and cleaning back in June 2019. That is a commendable service period for what had seemed to be a rather well-used bike when it arrived.
Next step was to do the compression test, and while the results were not alarming in any way, the middle cylinder was the offending item, with the outers looking healthy enough. With no real evidence of worn out rings it seems possible that a head refresh might be enough to solve the immediate issues.
Having said that, once you're in there you are up for whatever you find.
The engine gives the impression of being a well used unit from a less friendly climate than ours, and I guess that is just what it is. As I have a T150 race engine in a hundred bits right now I am not well placed to pull the top off this one, so I intend to put it back together and see if I can tune out the most troublesome behaviour.
To add to that, my engine reconditioner is under pressure with bigger things than triples, so if I send the head his way it might not reappear until after the relatively new warrant of fitness has expired - better to get some sunny miles out of it I reckon.
With the carbs refitted the bike started easily but was still an unhappy idler, so I played around with the vacuum gauge, slides and pilot screws until I found the happiest position for it, and it seemed to be pretty happy all round during a brief test ride.
Whether the low compression issue is just valve related is still up for grabs but lifting the head will be the proof when it eventually happens. Meantime the owner reports that it no longer stalls at idle which is making it much more pleasant to ride.
I guess that is good enough for now.