Coked Up?

yeah i have a timing light - when idling at c500rpm the advance must be about 15degrees btdc - without marking out the wheel in segments it's hard to tell exactly but the mark is about 15-20 degrees back from the tdc pointer

Check the exhaust manifold is not blowing at the block. Is the fan belt in good condition?

sorry for delayed response - been ill - and cheers all for help so far...
the truck had a new manifold fitted not long ago - done as per the manual (gasket on inlet only; bolts tightened to torque setting) - and I don't think there's any leak. Can't see or hear one at least (is there a test for that??).
Fan belt was replaced recently too and tension seems correct.
Been out on a long run again today and the noise is still there but I'm perhaps not sure if it is pinking or some other sound. I don't really know what pinking sounds like but the noise i have is a sort of 'clicking' sound. It only really happens at highish revs under strain - there's no sound when at full throttle on the motorway for instance, even if i really push it to top speed; but pulling up a hill in 3rd and it appears (click, click, click, click, click - rapidly).
I'm at a loss to think what causes it if the general feeling is not coked up...any further advice / steps I might take next??

Pinking is very distinct and unlike anything else but its hard to describe if you have not heard it. If it is pinking then it will happen when the engine is hot, loaded up in the mid range and in a high gear. Typically on a long hill in top. It is not in time with the engine and sounds like someone shaking a small ball bearing in a can. It is a sure sign of a weak mixture and slightly richening the mixture together with a slight retarding of the ignitions should stop it.
If what you have matches this you probably do have pinking, if not, you probably don't. Pinking is not "ticking".
One other option if a slight increase in richness does not fix it is to go to colder plugs, just one step. Bit this is usually more for highly tuned engines rather than a Series.

i'll richen the mixture and see if it goes away - i will also listen out again over the next few days and see if it resembles a' small ball bearing in a can' - thanks for the description.. i don't really know what i'm listening for!!

rob1miles said:

Click to expand...

That's great, thanks Rob - it would seem that I don't have pinking after all! Least it doesn't sound like that. Which I guess is good, especially as the remedies suggested didn't make the sound go away; but also annoying as I now have no idea what's causing my noise...I will continue to investigate and maybe if i can figure out a way of doing it, try and get a recording of it.
While I'm here - newbie question - but how do I tell if my motor has been adapted to run on unleaded in the past? I have just been sticking usual 95ron petrol in with no additives for the past few years and it 'seems' to run fine so I'm assuming it has been altered to suit at some point; but is there of way of knowing definitively and should I be using some kind of additive occasionally / regularly? Does everyone else add stuff to their fuel? (reminder I'm in a 21/4l petrol c1980).

It may or may not have hardened valve seats put in at some point.
If it has, great. If it hasn't, then it may or may not be quite happy for many years to come.
Leave it be unless you start to see signs, then get the valve seats done it a reconditioned head. Don't leave it or it'll get worse and the valves will burn eventually

kermit_rr said:

It may or may not have hardened valve seats put in at some point

Click to expand...

- any way of telling for sure?

kermit_rr said:

Leave it be unless you start to see signs

Click to expand...

- signs like what?

thanks!! I'm trying to learn what's what!

jasonmarks said:

- any way of telling for sure?

- signs like what?

thanks!! I'm trying to learn what's what!

Click to expand...

take the head off, valves out and look
signs.. blow/suck from the rocker cover.. poor compression.. poor running.. all depends on how much wear there is

Un-leaded and old engines is an ongoing debate. I've ran old engines on unleaded with no problems. Many old engines were designed to run on pool petrol which is truly awful stuff. The low compression, relatively retarded ignition and low power make them tough. If the values do eventually pocked a bit that's the time to get some hardened seats put it, if they don't no need to do anything. I recall when un-leaded came in and all the scare stories, but we knocked the timing back 5deg and never had a problem. I put a can of fuel additive through once every couple of years to keep it all clean but not as a matter of course.
Here's my noise checklist (attached).

rob1miles said:

I put a can of fuel additive through once every couple of years

Click to expand...

As a matter of interest what additive do you use? I might copy you on my 109...

I use a fuel system cleaner - for the diesel (Series) this is only a cleaner but the petrol one (an old Merc) its a cleaner and an octane booster. I use the redex ones.

I'm skeptical on cleaners prefer to call them preventers. As for octane boosters various tests have shown them not worth the money.. last time i checked

Thanks!

I have no poor running and nothing blowing from the cover and am loathed to get in and fiddle about with the valves more than just setting the gaps, so I think I'll assume that I have either had hardened seats fitted already or the ones I have are still in good nick: if I get any of the signs mentioned then that's when I'll take a look at the valves in detail - seems safer that way.
meantime

rob1miles said:

Here's my noise checklist (attached).

Click to expand...

- This is great, thanks - really appreciate it. I will work through it soon as I get out and about again and report back; will also get a bottle of redex and stick that in too.

+1 on that, don't fix what's not broke