S2 4.2 L engine rebuild - any other things to consider at this time?

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kevhillyer
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#1 S2 4.2 L engine rebuild - any other things to consider at this time?

Post by kevhillyer » Fri Sep 04, 2020 11:23 am

I am having my engine completely overhauled and rebuilt - long story - but the block is back from re-bore and the crankshaft is freshly ground and was fitted today.


Are there any other jobs/mods that I really should consider asking for at the same time? It is an expensive job already BUT would be annoying to miss something now that would have been much easier at this stage.


I have specified electronic ignition and hi torque starter motor already


I have considered an uprated oil pump (thinking more oil pressure would be good for longevity)
It was suggested I get a 6 branch exhaust manifold made to connect to my existing exhaust


I am an E-type novice so would welcome any suggestions or advice


Thank you
Kevin

1970 S2 2+2 Manual

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christopher storey
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#2 Re: S2 4.2 L engine rebuild - any other things to consider at this time?

Post by christopher storey » Fri Sep 04, 2020 12:02 pm

Have you made sure that the crankshaft sludge plugs have been drilled out, the galleries cleaned, and the plugs replaced with new ones which have been staked ? This is absolutely essential in any rebuild but, as a number of threads here will attest, sometimes it is overlooked

More oil pressure is neither necessary nor even a good thing. It is flow which is important. And, I don't know how old you are but I would lay a bet that a newly rebuilt XK will see you out!! :bigrin:

6 branch manifolds are a mixed blessing . They may ( and I stress may ) provide a small increase in top end power above about 4500 rpm - but how often do you go there? What they certainly do provide is a nasty hole in the torque curve in the 2250 to 2750 rpm range, and a noticeable ( and unattractive ) tinkling noise which is the sound of combustion

1 part which sometimes is overlooked is the bronze distributor etc drive gear. This sometimes is worn , with resultant timing scatter at low rpm particularly

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malcolm
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#3 Re: S2 4.2 L engine rebuild - any other things to consider at this time?

Post by malcolm » Fri Sep 04, 2020 1:24 pm

Just to repeat what the very knowledgeable Christopher said about the oil pump; mine is the original pump, so 51 years old. My oil pressure is above Jag specs, with hot, slow tickover at 25-30lbs min, and 60lbs at all revs over 2500. Wouldn't want it higher.
Malcolm
I only fit in a 2+2, so got one!
1969 Series 2 2+2
2009 Jaguar XF-S

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#4 Re: S2 4.2 L engine rebuild - any other things to consider at this time?

Post by Heuer » Fri Sep 04, 2020 2:46 pm

just to repeat what Christopher said, avoid the tubular manifold like the plague because it screws up the beautiful torque curve of the XK engine. The heat produced by the tubular manifolds will almost certainly bubble the paint on your frames and may even do so to the bonnet. The cast manifolds are a perfect match to the engine - Jaguar knew what they were doing!
David Jones
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RogerM
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#5 Re: S2 4.2 L engine rebuild - any other things to consider at this time?

Post by RogerM » Fri Sep 04, 2020 3:47 pm

I would recommend replacing all the cylinder head studs. They pass through the water jacket and can corrode and break.
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#6 Re: S2 4.2 L engine rebuild - any other things to consider at this time?

Post by Tom W » Fri Sep 04, 2020 5:00 pm

Updated oil pumps have greater flow than the standard pump, not greater pressure. It’s the pressure relief valve and the clearances on the bearings that will affect your oil pressure. An updated pump should give a bit more pressure around idle, but as soon as the relief valve opens the pressure is capped. It may take a bit more power to drive though.

Whilst the engine is out, it’s worth looking at anything that’s impossible to change once it’s back in. Clutch and gearbox seals for example.

I have to disagree slightly with David and Christopher on the tubular manifolds. Whilst David experienced a dip in the torque curve on his car, it’s not guaranteed to happen, and it’s not all down to tubular manifolds. I have them on my car, and there’s no big hole in the torque curve, it goes extremely well from 2000rpm upwards to the red line. The exhaust is a Bell system, so nothing too fancy.

The problem comes not because of any inherent flaw in the tubular manifold design, but because the complete engine system needs to be designed to a considered spec. Jaguar did this very well, so the cast manifolds, along with everything else they specified, complement each other and the engine works well for its intended purpose. Swap out only one component, such as the manifolds, and you’ll likely find where you gain one area, you loose in another. You might not even achieve any benefit for your change, unless you start changing other components to make the most of the improved characteristics. If you do make a gain, make sure it’s in an area where you’ll actually see a benefit when you use the car.

The whole system needs specifying holistically, and with an intended usage in mind. This includes air filter, carburation, camshafts (timing, duration, lift etc), compression ratio, ignition advance, exhaust manifolds and the exhaust itself. Personally, I enjoy the challenge of trying to eek a bit more from the engine, and learning about engine tuning as I go, so I’m sticking with my tubular manifolds, along with all the other engine tweeks.
Tom
1970 S2 FHC

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#7 Re: S2 4.2 L engine rebuild - any other things to consider at this time?

Post by Heuer » Fri Sep 04, 2020 5:12 pm

The problem with tubular manifolds occurs when a big bore system is fitted. With standard 1.75" bore pipes the 'extraction' of gases at low revs is not as much of a problem. Classic Fabs overcame the problem by using venturi's in the silencers which works to an extent. But if you are going to fit a standard bore exhaust then you may as well stick to the cast manifolds.

Bubbling paint on the frames is still an issue though!
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#8 Re: S2 4.2 L engine rebuild - any other things to consider at this time?

Post by Tom W » Fri Sep 04, 2020 5:54 pm

That paint’s really suffered. So far, my original factory frame paint is intact. Has that car been repainted? Maybe restored cars are more susceptible? There does seem to be a trend to apply far more paint now than ever seemed to be used originally, probably in search for a better finish than they ever had when new.

The classic fabs venturi is a clever little device. It allows the exhaust system operate with some of the benefits of an interference system by introducing some resistance to the flow. Done properly, it will delay the negative pressure wave in the exhaust manifold, so it coincides with the overlap period, and helps cylinder scavenging. It only works up to a point though, and at high RPM, it starts becoming too restrictive. It probably works particularly well on the XK as it’s not too high revving.

Standard design E-type silencers already have the same feature built into them, as the cast manifolds don’t operate on the interference principle. Pure straight through silencers (the ones with only one continuous perforated pipe) don’t. Once again, Jaguar knew what they were up to.

Tubular manifolds can, of course, make proper use of the interference principle to aid cylinder scavenging, so can offer a performance benefit. The torque dip doesn’t occur specifically because the manifold is tubular. It’s just at that particular RPM, you have an unfavourable combination of exhaust pressure wave, valve timing, and possibly ignition advance. The exhaust pressure wave magnitude and timing being the thing that’s different between one manifold and the next. Change one of the other parameters, and you might well be able remove the dip, and possibly see an increase. Though the change will obviously have an effect elsewhere too.
Tom
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#9 Re: S2 4.2 L engine rebuild - any other things to consider at this time?

Post by abowie » Fri Sep 04, 2020 9:57 pm

While the engine is out look at and remedy problems with anything you can't usually reach.
  • Clean and repaint firewall, tunnel, engine frames etc as necessary
    Gearbox seals front and rear
    Replace tailshaft uni joints
    Replace the clutch unless it is brand new, and R&R clutch master and slave
    Check hydraulic lines and wiring mounting points and fix as necessary
    Send radiator off for R&R as needed. Replace all radiator hoses.
    Consider rebuilding carbs
    Check the mounting points on the engine frames for the engine mounts for cracks and get them repaired.
I have used "uprated" oil pumps on engines in the past and remain a little sceptical.

The simplest of these are stock pumps that have been ported a bit to remove a few corners. The claim is 30% more flow but presumably that's on the bench with no load.

Whether the pump actually delivers increased flow when installed and confronted with the resistance of the oil galleries and bearings is anyone's guess.

And as mentioned above, there is an oil over-pressure valve that stops the pressure going above a certain point.

Applying Qhm's law, flow equals pressure divided by resistance. So if pressure can't increase, you need to decrease resistance by enlarging pickup pipes, porting all the oil galleries etc and as a result I suspect that the actual increase in flow is a lot less than the claim.

I suppose that the one situation the pump might offer more over the standard is if oil return to the pump decreases or the oil is very hot (read racing) and in this situation the pump's increased flow capacity might buy you a bigger margin of safety.

WRT tubular manifolds I'd stick with the cast iron ones.

Firstly the original manifolds look the part. It's a classic car.

Secondly, they actually work very well, whereas a set of tubular manifolds may not improve performance at all or may worsen it.

To work properly they need to be a certain minimum length and equal length and what you buy off the shelf may not be very well designed. A properly engineered set of manifolds is useful for the full race car but probably not much use otherwise.
Andrew.
881824, 1E21538. 889457..oops. Jezza the V12 XJS race car.
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