The Triumph 2000 / 2500 / 2·5 Register Forum

A 1975 2500S would normally have a viscous fan, unless it has been removed by a previous owner, and put back to a fixed fan.

The viscous type is the one with the 'fins' behind the fan is it not? Im sure mine doesnt have that... taking the cover off tomorrow so will have to remind myself!!

Yes, the viscous coupling is positioned behind the fan blades.
If its functioning correctly and not seized, you should be able to spin the fan freely by hand with little effort without turning the engine over as with a standard fixed fan. There should be no play in it.
If it is not seized, but the centre bearing has collapsed, if you grab a couple of the fan blades you may be able to rock the fan itself in a sideways motion which will confirm its failure.
It makes a horrible noise when it fails and should be easy to diagnose.
Here's a picture of a viscous coupling for your info.

Not had chance to pull the cover off today to have a look, i thought that was what i had in mind, and i am 99% sure i do not have that type fitted. Mine was a very early demonstrator as i am led to believe, and have noticed over the years it does appear to have several things that were not ' rolled out' when this model was finalised, although i could well be wrong.
Talking to a chap earlier, telling him of my issue(s) - after listening to the start up etc he implied, taking all the other bits in, possibly a lazy oil pump.....which kind of makes sense , but again could also be wrong !!!!

Johnnydog - i stand corrected by you !!! Hands are clearly up. This is obviously really bugging me and although things did not quite go to plan again this weekend ive just been out to remove the cover from the front end, pop the bonnet to double check which fan type is fitted. First thing i did was pushed the fan blades - and they moved fairly easily I always thought the fan sat clearly IN FRONT of the viscous coupling, thus easy to see. It is actually WITHIN the fan, so NOT easy to see, with the limited viewing space to the rad. So using fingers to feel first off, then a slim mirror and torch it does indeed have a viscous fan set up . Age is obviously creeping in .
Soooo.... checking movement whilst grabbing opposing fan blades .... no movement fore and aft ( front to rear), side to side (wing to wing ) i can feel a very slight movement, maybe a few millimeters. .....
Ran the start up video past a second friend today, he also said the noise does not sound like big ends, but top end..... the confusion continues !!!

If you are certain the noise is at the top end, I would do a compression check, then remove the rocker cover, and check for / rule out a broken rocker, broken valve spring etc etc. Also, especially if you have an alloy rocker cover fitted, it has been known for a rocker arm to catch the inside of the rocker cover - the evidence of this should be evident if you check the inside when removed. It doesn't explain the long delay before the oil light goes out, but you might as well do some checks at the top end that only require the minimal amount of dismantling first!

Ok so been and had a lengthy chat with my guy this eve , ran through the story / played the video and staight away his opinion was NOT the big ends, its definately an oil feed issue to the top end - as in too slow in sending oil ' up top' - the oil filter being # 1 suspect - by what has been gathered is the short GFE166 from Moss does NOT have a non return valve, and mine being the longer throw 2500 engine with auto trans,and the filter is not hung completely upside down.... so drain back occurs quite quickly, and thus has to refill every time.... so step one is throw that filter out and fit C.W. Bosch 0 451 103 101 longer unit already in my store. At least he has shown me earlier the difference between no valve/ has a valve - he keeps an unused Crossland filter on the shelf to show customers - no valve, do not fit. He then showed me one that DOES have a valve fitted so at least i know what i am looking for ! And yes C.W. filter has a valve. So tomorrow after work, that GFE 166 is coming off......

So a bit of an update. A little longer than i hoped but eventually found the time to drop that GFE166 off - what a pig to remove, being a short filter, and so close to the chassis and pipes no way could a hand get on it, even my oil filter chain strap was useless - time i took up the slack i was up against metal !!!! Never known a filter so difficult to remove. Ended up faffing with a monkey wrench type tool at the base.
Anyway that filter most certainly did not have a valve in its base, which in a funny way was encouraging. I pre - primed the one i brought from C.W. , as much as i dare put in on an angle to fit it to the adaptor. As i had disturbed the oil system again i thought i will take the sensible route and dis-able the coil lead again and go for a wind over to put the oil light out before a full start. This time the light went out quicker. Then went for a normal start, all good.
A few nights later i thought i would go out for another start up, this time everything connected,no priming but no choke either. Again, the light went out a good few seconds quicker than the last time. Once out, pulled the choke whilst still churning over,fired up, again no rattle...
This evening i had a chance to get her out for an hour so i did an initial wind over for 3/4 churnings, light still on at that stage, pulled the choke, a couple more churn overs and at the same time she fired up /light went straight out - no rattle...After a bit of running around, popped to the shop that kind of thing ( so now well up to running temp) i thought i would try the 'in gear and hold' situation that last time made the oil light flicker.... no flicker....
Was it purely that filter ? Time will tell i suppose . But right now i am taking that lot as a positive.....

That sounds a REAL positive to me!! Fingers crossed it will have made a hugh difference!

I do find it a little odd that just the non return valve 166 filter alone could be a single cause in this situation..... and to learn through this episode that you have never converted any of your 2000's to adaptor filter, carrying on with the original set up , without an issue.... cant say i am fully settled just yet if i am honest.