My newly-acquired Mark IV 3.5 liter runs very rough. I discovered the vacuum line for the distributor vacuum advance is missing. There also appears to be no vacuum source to connect the missing line to. I connected a rubber hose to the distributor vacuum line port and tried to pull a vacuum. No luck. The distributor vacuum advance unit is shot. Does anyone have one they’d like to part with, or are they available aftermarket?
Thanks,
George
Hi George
To my very minimal knowledge, MK IV distributors did not have a vacuum advance system fitted, also there is not a vacuum take off from the inlet manifold (apart from, for the starting carburettor).
Others may have more knowledge than me.
Regards David
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George
Please see the below post from Roger Payne.
If you refer to SPC J.6 for 2-1/2 & 3-1/2 litre LHD cars (only) published in November 1948, you will see there were four different Distributors, albeit complicated by the fact that they show both SS Jaguar pre-war ‘all numeric’ part numbers mostly, and only a few postwar Jaguar ‘C-prefix’ part numbers…
But the four distributors are:–
- 40092/D (no Jaguar Part Number) DISTRIBUTOR (Lucas DXH.6A Type GC.36) (Complete with Micro-Adjustment Control 41490)
- These were fitted to 2-1/2 litre cars only, 530001 to 530029 (Saloon) and 537001 to 537019 (Coupe)
- 40093/B (no Jaguar Part Number) DISTRIBUTOR (Lucas DXH.6A Type GC.37) (Complete with Micro-Adjustment Control 41490)
- These were fitted to 3-1/2 litre cars only, 630001 to 630183 (Saloon) and 637001 to 637163 (Coupe)
- 40156/D (C.2584) DISTRIBUTOR (Lucas DVXH.6A Type GC.40) (Complete with Micro-Adjustment and Vacuum Controls)
- These were fitted to 2-1/2 litre cars only, 530030 and subs (Saloon) and 537020 and subs (Coupe)
- 40149/D (C.2529) DISTRIBUTOR (Lucas DVXH.6A Type GC.42) (Complete with Micro-Adjustment and Vacuum Controls)
- These were fitted to 3-1/2 litre cars only, 630184 and subs (Saloon) and 637164 and subs (Coupe)
For RHD cars you have to refer to J.2 for all 2-1/2 litre cars, but published in August 1947, so not fully up to date, so you need to also check the J.2 AMENDMENT LIST No.1 and No.2 that does take you through to the last… Note J.2 also retrospectively applies to pre-war SS Jaguar from the 1938MY cars as well of course to the postwar ‘Mark IV’… but you have three different Distributors…
- 406550 (no Jaguar Part Number) DISTRIBUTOR (Lucas **DUH.6A/O ** Type GC.14/1)
- These were fitted to 2-1/2 litre cars only, with Engine Nos L.1 to L.2055 - less 1 to 17)
- 40066/A (no Jaguar Part Number) DISTRIBUTOR (Lucas **DXH.6A ** Type GC.30)
- These were fitted to 2-1/2 litre cars only, with Engine Nos 1 to 17 and P.18 to P.200)
- 40096/B (no Jaguar Part Number) DISTRIBUTOR (Lucas **DXH.6A ** Type GC.38)
- These were fitted to 2-1/2 litre cars only, with Engine Nos P.201 and subs)
J.2 AMENDMENT LIST No.1…notes…
page 71. 40096/B Alter remark to read:- “Fitted from Eng. No. P.201 to P.618”
and adds…
4. 40092/D (no Jaguar Part Number) DISTRIBUTOR (Lucas **DXH.6A ** Type GC.36)(Complete with Micro-Adjustment Control 414950)
- These were fitted to 2-1/2 litre cars only, with Engine Nos P.619 and subs)
J.2 AMENDMENT LIST No.2…notes… nothing, relevant to Distributor
For RHD cars you have to refer to J.3 for all 3-1/2 litre cars, but published in December 1947, so not fully up to date, so you need to also check the J.3 AMENDMENT LIST No.1 (that’s it, no second AL) that does take you through to the last… Note J.3 also retrospectively applies to pre-war SS Jaguar from the 1938MY cars as well of course to the postwar ‘Mark IV’… but you have three different Distributors…
- 406550 (no Jaguar Part Number) DISTRIBUTOR (Lucas **DUH.6A/O ** Type GC.14/1)
- This is same as fitted to 2-1/2 litre cars, but for 3-1/2 litre cars to Engine Nos M.1 to M.1600 - less 1 to 25)
- 40080/A (no Jaguar Part Number) DISTRIBUTOR (Lucas **DZH.6A ** Type GC.31)
- These were fitted to 3-1/2 litre cars only, with Engine Nos 1 to 25 and S.26 to S.1501)
- 40093/B (no Jaguar Part Number) DISTRIBUTOR (Lucas **DXH.6A ** Type GC.37)
- These were fitted to LHD cars above, and 3-1/2 litre cars only, with Engine Nos S.1502 and subs)
J.3 AMENDMENT LIST No.1…notes…
page 72. 40093/B Alter Heading to add - "(COMPLETE WITH MICRO-ADJUSTMENT CONTROL 414950) and Alter remark to read:- “Fitted from Eng. No. S.1502 to S.2621”
and adds…
4. 40149/D (C.2529) DISTRIBUTOR (Lucas **DVXH.6A ** Type GC.42)(Complete with Micro-Adjustment and Vacuum Controls)
- These were fitted to 3-1/2 litre cars only, from Engine No. S.2643 and subs…
So Timothy - your car is a 3-1/2 litre RHD with Engine No. S3067, thus should have a 40149/D (C.2529) DISTRIBUTOR (Lucas reference number GC.42), thus same as later LHD 3-1/2 litre cars…
So that should resolve the mystery, and indeed there is additional detail in the J.3 Amendment List No.1, but if you really want serious detail/photos you should refer to the LUCAS MASTER CATALOGUE 710 which provides considerably more detail than any of the Jaguar catalogues, albeit the Jaguar catalogues of course advise applicability… (These are part of the MASTER CATALOGUE 400 series, but for the 1945-1950 period the nominal 400C, was actually published/divided up into four separate Master Catalogues - the 710 being for IGNITION SYSTEMS - indeed I think I may have a duplicate/spare 710 somewhere)
Roger
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Hey David, thanks for forwarding all the info posted by Roger Payne. I have not yet found an engine number, but by the serial number, 630124, the car (RHD saloon,) should have been manufactured late 1947. If it has the correct engine, then it should have the same vacuum distributor as mentioned for Timothy…40149/D (C.2529). I’ll check for a serial number on it to confirm. But it definitely does have a vacuum control on the side. Where exactly should I find the engine number? George
George.
The engine number is on the right (exhaust) side of the engine, at the rear, on a flat machined face, basically just above where the dipstick is.
Regards
David
Nope. No numbers there. 
Tried posting pictures of where the number plate should be and of the distributor, but can’t…maybe because I’m a new member.
There should be a flat boss on the right side at the rear above the starter motor and block drain valve. The engine number is normally stamped with hand hammered stamps there.
According to Roger’s research, your 630124 would have been made with a manual advance lever on the steering wheel, before the change to a vacuum advance at 630184. That would explain why there is no vacuum pipe fitting on the carb. It would have been on the underside at the throttle plate.
Distributor types without the letter V are the manual advance types.
The letter V indicates vacuum advance.
Possibly your distributor was changed by someone but they did not change the carb.
The vacuum advance is the same as XK120 so should be available from Moss and others. Be aware the reproductions have a different thread on the mounting studs than the originals, and are easily broken loose from the case when attempting to install.
Hello George, rough running will be unrelated to no vacuum advance at distributor. If distributor mechanical advance works correctly with vacuum disconnected, then rough running is not due to distributor. With a timing light and vacuum disconnected, check timing advance at idle and at different rpms. Look for correct total advance and jitter in timing strobe.
Vacuum advance is a luxury to help with mileage and is not fundamental to smooth engine running. Cars had smooth engines for decades before vacuum advance was used. Sounds like you may have a replacement distributor with unneeded vacuum advance.
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George, 630124 is (or was originally) a LHD Saloon and indeed was manufactured on 1st March 1948, so is your car now RHD as you advise, or was that a typo???
If your car has been converted to RHD that creates all sorts of potential problems/explanations…
As per my summary of Mark IV Distributors 630124 would have been originally fitted with a Lucas DXH.6A Type, 40093B Lucas Part No Distributor - can you check/advise/photo all the numbers stamped on the body of your currently fitted Distributor. If your car is now RHD whose to say what small and major components may have been sourced/changed during the conversion?
Roger
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Major typo on my part. Car serial number is 612024. RHD Saloon car initially exported to New Zealand and then imported to the U.S. in 1985.
612024 makes more sense, a RHD 3-1/2 litre Saloon built 26th Sep 1947.
I don’t know Engine No. as new, but adjacent cars of similar late 1947 age indicate Engine No. would have been less than S.2643, and greater than S.1501 so will have the third listed Distributor…
Lucas Part No 40093/B (no Jaguar Part Number) DISTRIBUTOR Lucas DXH.6A Type GC.37
COMPLETE WITH MICRO-ADJUSTMENT CONTROL 414950, as fitted from Eng. No. S.1502 to S.2621.
Roger
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Hi,
Also cars originally built as LHD had an L in the engine prefix, so mine is SL.2199, exactly like a regular RHD engine but it had the remote oil filter housing due to steering column clearance.
Cheers!
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Thanks for all the great information. I bought the car 6 weeks ago in Los Angeles. I’m on a 5-day antique car tour with it in Ocala, FL, right now, about 130 miles from home. Car running rough, but running. I’ve had many problems with it up to this point, but working through them all one at a time. I found the boss where the engine number should be stamped. Need to clean the paint off to find the number.
I have not yet found a timing scale or marks. I’m guessing the scale should be attached to the timing chain cover and the corresponding mark on the harmonic balancer. Book says with points gapped at .012", timing should be set at 10 degrees advanced. Is this correct?
There was no timing scale or anything else on the front. The timing mark is on the flywheel and visible through a hole in the top of the bell housing.
I found this inconvenient and made my own marks on the front pulley and chain cover.
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Hi,
Yup, when these engines were new there were no timing lights. 
I also used a white paint marker pen to draw three lines onto the front damper for 0 deg, 5 deg and 10 deg BTDC.
Cheers!
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Thinking about it, I imagine it was because these engines were designed with manual advance, with which setting by a timing mark was only used when setting up the engine during an initial build or major rebuild, not with ordinary tune-ups.
Even with vacuum advance, they provided a manual micrometer setting.
We had 2 days of spring here Wed and Thur so I started up the '38 SS and drove around a bit. Took about 3 seconds of cranking before it caught, after sitting still about 5 months. Now we’re back to winter.
A sunny 86 degrees here today in Ocala, FL. Jag didn’t do so well. Multiple times engine completely cut out, on acceleration, backfired either through tail pipe or carbs and then restarted. I’m thinking it’s most likely the condenser breaking down. Didn’t bring one with me, so will park it and use the Escalade for the final tour day.
I have completely cleaned the raised boss where the engine numbers should be stamped. It’s bare, shiny metal…nothing there.
