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Engine Mix in a Spitfire


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Mates called me, thinking I would be an expert, but I´m  clueless.

This car is an example  of its own. 

Thus seeking advice from the adience, for a Spitfire that is a real challenge (basket case).

The recipe: Spitfire MK4 with Herald 1360 engine, twin HS2 with AAN neddles, Spit MK3 inlet manifold, Spit MK3 distributor with accu spark ignition, mechanical rev counter.

What we cured so far (only the very top of the list) : burning loom replaced, chain tensioner was lying around below the crankshaft chain wheel, timing wrong by one tooth, head gasket, many   M8 M10 screws, .......

Got it now running, but it sputters above 3000. Up to 3000 absolutely fine.

Could it be the crankcase ventilation / PCV ??

The car has the PCV, but  the Spit MK4 non vented oil filler cap. Can the PCV just be screwed out? Never hat a Spit MK3.

Of course, it was always running fine in the past, whenever that was :wallbash:

Martin

 

Spit Gold.jpg

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Herald 13/60 engine (GE) is very much like the Spitfire Mk3 engine (FD).

Bottom end - really only that has cam bearings and the 25/65 cam profile.

Head has different valves, springs and spring retaining method. Compression ratio lower IIRC.
 

If still the 13/60 cam then the twin carbs won’t add much and the AAN needles might actually be too rich at 3k up, though not enough to make it fall on its face I wouldn’t have thought…….

Distributor / timings sound about right. Could maybe take a couple more degrees of advance.

What exhaust manifold/exhaust, what air filters?

I doubt there’s anything wrong with the PCV if it runs ok up to 3k. Apart from split diaphragm there isn’t much to go wrong - provided the parts are assembled in the right order.

And you have three superb Triumphs, mostly hand built with your own two hands, which is going to appear like serious expertise to most people :smile:

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Thanks for the flowers Nick,

but this Spitfire, a mess. The worn threads in the alloy sealing block at the Front of the Engine one  opened up to M10. Not square , of course . The other a M8 stud glued into it.  A real mess.

May it be that the Not vented oil filler cap leads to a too high pressure in the inlet manifold? 
 

Standard exhaust, standard airbox. 

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1 hour ago, Martin said:

Thanks for the flowers Nick

You're welcome.

Not sure whether the cars with the Smiths PCV valve are supposed to have vented caps or not?  Have you tried just venting the rocker cover stub to a catch pot and blocking the PCV pipe to see if it solves the running problem?  Might also reveal whether you have loads of blow-by, which is of course a whole new problem if there is!

The alloy block condition sounds..... quite typical unfortunately :ermm:

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17 hours ago, Nick Jones said:

Not sure whether the cars with the Smiths PCV valve are supposed to have vented caps or not?

They are supposed to yes, and I believe the size of the vent hole is fairly important. Can't remember what is the correct size - something like 1/16"...?

That might explain the poor running; I had to significantly change the carb mixture when I temporarily blocked the Spitfire's PCV off a while back. Without the vented cap I reckon you'll get a dramatically leaner mixture as crankcase pressure rises with RPM.

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19 hours ago, Martin said:

May it be that the Not vented oil filler cap leads to a too high pressure in the inlet manifold? 

Martin I think it also means you have to set the idle mixture richer, as additional air is drawn in via the filler cap vent. This then compensates higher up the rev range when crankcase fumes are forced into the intake. At least I think that's how it works. 

With a working PCV you definitely get vacuum via the oil filler cap; you can test this by taking the cap off while idling and putting a sheet of paper over the hole. The engine should start spluttering as soon as you take the cap off, as the inlet mixture gets too lean. 

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Hmm, so a cure could be removing the PCV, blocking the manifold and letting the crankcase fumes  into the air or as in the later Spitfire into the carbs where actually these tubes are blocked.

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