Asking for a friend!

[JohnD]

A friend and neighbour has a Sunbeam Alpine, Series 5, 1725cc, with twin Webers.  It runs very rough!   I've been poring over it with him all morning, and we cannot work out the problem, so once again I turn to the Common Room of Sideways U!

The Webers have been rebuilt with the same sized jets tubes etc in the range appropriate for this engine (I know nothing of Webers).    He has fitted a new Optronic distributor, leads and plugs.   The engine has appropriate Weber intake manifolds, an original cast exhaust manifold, a new exhaust system, and has new piston rings.

The symptoms.  (trying to give you as much info as possible)

Consistently misses  at idle, the miss is on cylinders 3 and 4 (no effect when the plug leads are removed)  Revs freely, but no power, unsurprisingly.

Plugs all sooted, No.4 less so.  After cleaning, replacing and doing some more running, Nos. 1 & 2 clean, No.3 wet, No 4 clean.

On the Webers, there is a screw adjuster for idle running.  Screwing those for 3 &4 right down (no fuelling, Dave tells me) had no effect.  Doing the same on 1 or 2 stopped the engine.

 

Now, the inexplicable!    Blocking the intake to 3 or 4 has NO EFFECT!  We did this because there seemed to be less flow there. The same on 1 or2 stops the engine.

Is there an obstruction to flow?

 

Investigations

Looking into the 3 & 4 intakes with a mirror and torch and the butterfly is moving normally, so no obstruction there.

With the rocker cover off, and the engine at TDC on No.1 firing stroke, the rockers of No.4 are both slightly open, and the valve gaps on No.4 are nominal when checked by Rule of Nine.       So the valve timing is true, at least not enough to stop air getting into the cylinders.

Dave tells me the ignition timing is nominal, that he has done the compression pressures across the block, they are all within 5psi of each other, and leak-down tests, which were fine.  He has some experience of classics, so I believe him.

 

So this engine is aspirating much less air from 3 & 4 than 1 & 2, presumably too little for ignition on their firing strokes.    But why?

Neither Dave nor I can work it out.   Over to you please?

John

 

[Nick Jones]

More questions

Do you think 3/4 are firing at bigger throttle opening? Could just be a basic balance issue.

Do 3/4 actually suck when you block them?

Plugs newish NGKs by any chance? Try swapping around maybe?

Plugs 3/4 connected right way round?

[JohnD]

Thanks, Nick!

Dave has those LED light things on all four plugs and they all light up (and don't when  unplugged).  Not sure if that means actual firing or just X Kilovolts to the plug.

Please explain "a basic balance issue"?

I can't find my carb balancing  tool, but rigged up a water manometer.  1 & 2  suck so hard that they nearly pulled the water out, while 3 & 4 barely moved the level.   I think they suck hardly at all.

We swapped 3 & 4 for  1 & 2, no change in miss fire.

Yes plugs connected correctly.      I presume that the dizzy goes anticlockwise?

John

[RedRooster]

I would say he has the wrong engine fitted but I won't. 

Try the old dizzy with points if he has it. Guessing there's no trickery engine management inplace. 

[JohnD]

"Wrong engine"??  Oh, of course you mean the Alpine "Tiger".  My Dad had one of those.

Old type dizzy?    This is an obvious aspiration problem!     What will another dizzie do?

 

[RedRooster]

He's fitted a new dizzy at the same time, put the old one back in to rule out sparks is what I was pertaining too. 

Unless your Dad lived at Buckingham palace that Tiger wasn't his.. 

[RedRooster]

Also check the rockers for correct clearance, you never know. 

[Hamish]

I’d be removing the rear carb to ensure you can see down the manifold to the head intake. Can you see the valve stems like the tr ? If so do they move with engine turning over ?

 

compression checked and good- there must be a blockage in the down suction stroke ?

a weird one definitely 

[Nick Jones]

3 hours ago, JohnD said:

manometer.  1 & 2  suck so hard that they nearly pulled the water out, while 3 & 4 barely moved the level.   I think they suck hardly at all.

Large inlet leak 3/4. Servo or breather connection?

[JohnD]

Nick, I tested for an inlet leak with some "KwikStart" spray - no effect on idle.

I should expand his story.  He bought this Alpine some years ago, it had been  neglected by the PO, but kept under cover and it looks gorgeous.  But he couldn't get it running smoothly, as above, and hence the new dizzy, new rings, rebuilding the Webers etc. - and it still runs rough!   He says that this is how it was when he acquired it, and as Hamish suggests, its as if there is some blockage in the ducting to (or  from) 3 & 4.  But what could be blocking?   Dave assures me he's had the carbs off and the manifold just recently, to fit a new starter.

RR, as above, I checked for (more or less) correct TDC marking on front pulley, by a screwdriver down the plug hole, and for "ELoO" on No.4 at the same time.   I then did the opposite, TDC on the No.4 firing stroke - No.1 ELoO, and both No.4 valves fully shut.    And, on No.4 the valves go down as far as on No.1.   "It is a riddle, wrapped in a mystery, inside an enigma; perhaps there is a key" but I can't see it!

JOhn

[Hamish]

Thinking allowed. If it wasn’t for a good compression test I’d be thinking no.3 has a holed piston or a lost valve head. due to the lack of suction air flow and wet plug on no.3.

But a wet plug on no.3 suggests the mixture is reaching the cylinder but not firing. 
 

the non firing can be understood. 
what is the weird bit is the lack of intake velocity 

can you borrow an enderscope  type camera to see down the intake track to valve head and in plug hole.

 

otherwise I’d be looking at the cam ?

keep us informed John. 
 

 

Edited September 9, 2023 by Hamish

[mpbarrett]

Hamish might be right. Can you turn it over with the rocker cover off and see if you are getting the correct movement of the valves on 3 and 4?
Could it be a problem in the head, leak or crack somewhere. If its always had this problem then he needs to check stuff he hasnt changed or touched.

intriguing problem! 

[JohnD]

Indeed, mpb!   He asked me to sort his Webers, as if I knew them, but from his history I had to persuade him that the problem must lie elsewhere, which led to finding this low flow.

Yes, Hamish, "obviously" it's ring failure, holed piston or catastrophic gasket failure between bores, but Dave has only recently had head skimmed, new gasket etc, and that hasn't affected the old problem.     Running without the rocker cover is something we did not do!   Worth a look, deffo!

Another point, arising from my Weber ignorance.    Dave has venturi pipes on their inlets, with a 'sock' filter on each (due to the length of the Webers, when SUs were there from the factory, there's very little room between them and the wheel arch.   They pull out, and I did so to look inside the throats.    While running, I could see liquid fuel dribbling from the inlets, of both.  Is that normal, Webers are traditionally buckets to pour fuel into the engine, or not?

John

[Hamish]

1 hour ago, JohnD said:

 

Yes, Hamish, "obviously" it's ring failure, holed piston or catastrophic gasket failure between bores, but Dave has only recently had head skimmed, new gasket etc, and that hasn't affected the old problem.     Running without the rocker cover is something we did not do!   Worth a look, deffo!

 

but you have compression - that's what i don't understand ......

 

1 hour ago, JohnD said:

 

  While running, I could see liquid fuel dribbling from the inlets, of both.  Is that normal, Webers are traditionally buckets to pour fuel into the engine, or not?

John

if its on tickover then no you shouldn't see dripping - I've just been looking at that after my "fire"

this guy has done a series of videos on webers (and sooooo much more)

 

 

[flatter4]

I know it shouldn't be, but look at the ignition again.  Sometimes things are counter-intuitive.

Wet plugs / dry plugs, and optronic.....  I know it's new, and I know it should be fine, but put the points back on  - just to prove the point (no pun intended)

21 hours ago, JohnD said:

No.3 wet, No 4 clean.

I've had some very weird symptoms from a failing Lumention system.  It was obviously carburation, rough idle, spitting back, wouldn't run without blipping the throttle.  Obvious.....
I ditched the electronics and put a set of points in and she ran beautifully.

[flatter4]

Once you've discounted that then look at the complex bits.

Is there any balance pipe between front and rear carbs?

Is it a standard 4:1 cast exhaust manifold?

[JohnD]

Flatter4,

No balance pipe, in my ignorance of them, I don't think Weber's have them?

Yes, original cast manifold.

John

[Escadrille Ecosse]

Webers don't have a balance pipe.

The low flow issue suggests that it is NOT the Webers.

If you have compression and no flow I would suspect valve timing and/or lift and suggest you check both of these thoroughly before getting into anythig more exotic.

Especially since the engine has been apart.

[JohnD]

Yes, valves and timing were my thought too.   But as above, using ELoO, it seemed to be about right.   And surely, vastly poor valve timing would affect all cylinders, and not just 3 & 4?

This engine is very similar to the Triumph, but has a rocker shaft in two parts with in the middle a fitting that receives a tiny oil pipe coming up from the below, that directs oil both ways down the hollow shaft, as per Triumph.  To have in effect two rocker shafts made me wonder if that was a clue, but if the cam in the block is correctly timed, I can't think how 1 & 2 could work well and 3 & 4 so badly!

There was a thread recently over on the TSSC board, where the end collars on a Herald rocker shaft were missing (!!!) No.4 exhaust rocker had fallen off,  dislodged the spring collar and the valve had dropped.     Unsurprisingly, the owner reported  "Zero compression on cylinder 4"    Surprisingly there was no serious damage!   https://forum.tssc.org.uk/topic/11845-zero-compression-on-cylinder-4/    But I can't think that is relevant here.

John

Edited September 9, 2023 by JohnD

[Nick Jones]

Equal compressions and two happy cylinders implies that the engine is mechanically fit.

I assume that compressions were tested with the throttle wide open? Might be interesting to retest with them closed and see what gives. I’d put a small wager on the fronts going down and the rears remaining unchanged…..

I asked this before but does it run on all 4 at bigger throttle openings?

[JohnD]

Yes, that would be an interesting test.   I was able to see down the Weber throats with a mirror, and the butterflies open fully at WOT.     Couldn't see beyond them, down throats of either carb, so a blockage between them and the valves???   But if 1&2 went down with the throttles closed, but 3&4 stayed high, what would that indicate?   A vast leak between the Webers and the inlet valve??

If I can find my flow meter, that would be a better test of flow than my DiY water manometer, at idle and faster.

Fast running.  It runs very rough at idle, the engine vibrating on its mounts in a most distressing way, as might be expected if only two cylinders were firing.    This smooths at higher revs, but it might still be missing, as I'd attribute the lack of vibration to a higher frequency of impulses not resonating in the engine mounts.   Certainly, it seems to still miss, as Dave says that on the road it lacks power, so much so that he was reluctant to take it for the "Italian Tune-up",  a blast down the Motorway that I first suggested when I saw the how sooted up were the plugs, at first.    

My thanks to all in the CR!   I shall take the suggestions back to Dave shortly.

John