Heavy jumping / jerking shifting from Park. Series 1 XJ6

XJ
1

Other than the need to possibly adjust shift linkage, which is probable as the motor and trans were obviously removed at one point, what are other causes?

Band adjustment?
Vacuum leaks?

On another note, i wished to ask as well, there is an aluminum tube attached behind the transmission dipstick coming up from the transmission somewhere.

While I am quite certain this end at the trans dipstick attaches via some hose at the rear of exhaust manifold, where does it attach at the other end at the transmission? BW12

What is its purpose?

Excuse me, but I havenā€™t had a moment to get under the car as of yet to see.

Thank you very much in advance.

2

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What is your idle, Demianā€¦?

The main reason for jerking when gear is engaged from park is too high idle - accentuated by drivetrain slack. Which also makes the jerk more pronounced if you parked in forward and are engaging reverse from park - or vice versaā€¦

There are no relevant adjustments for the box itself or shift linkages. Lowering the idle reduces the jerk, but an inspection of the propeller shaft U-joints is prudent. Which box do you have? And does is shift smoothly while driving - and at the correct shiftpoints?

Frank
xj6 85 Sov Europe (UK/NZ)
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3

I think the aluminum tube you are describing coming up from the Borg Warner Model 12 transmission is the vent tube. On my XJ12 which has the same trans it has a rubber hose down to the trans. It lets air out as you add fluid. There is supposed to be a C.34258 cap on it to keep the dirt out.

4

Hi there
thank you both very much for your kind replies.

@Frank: I understand. Appreciate itā€¦itā€™s been a while. Had to throw it out there. I actually have more to ask, but wish to organize my thoughts first.

Yes, itā€™s kind of a mess at the moment. it has been sitting for ages, and I have done my thorough Jaguar reincarnation/bring back from the dead process, yet I am certain the engine must be pulled due to both a head gasket and rod knock ā€¦

Therefore idle is rough, unstable, and although compression is good across all cylinders, it is making a squeak, slight metal knock sound. And I do seem to be losing coolant.

Iā€™ve changed plugs, flushed out fuel lines, filters replaced, oil changed, adjusted upper timing chain, rebuilt and tuned carbsā€¦

ā€¦but also the nitwit PO (!!!oh these fools!!!) who pulled the motor as it was stated to have been rebuilt a few years ago, just cut all the hoses so I have gone through plugging all possible vacuum leaksā€¦

Hard to trace these things. yet the deciding factor must be that when I detach the #5 plug the knocking sound disappears. Tried pushing the cylinder down with a screwdriver to see if I could determine with certainty if it was a spun rod bearing, but there was no slack or movement when pressing down to make any determination.

My thought is that it had a blown head gasket and the amalgamation of coolant in the oil ruined the bearing while sitting and sittingā€¦

ANYWAY ā€¦ there was no sign of coolant in the oil, but there was sludge in the coolant, like mud, and Iā€™ve flushed the heck out of it, and again with vinegarā€¦and that there was no thermostat at all in it answers why it was not overheating using my infrared thermometer.

Using the hose to the ear while idling trying to pinpoint knocking did lead to a louder noise at the sump area of #5 soā€¦but it is hard to say.

At any rate, it is idling rough, difficult to get stable, and when starting when warm, it seems like it is missing as if plug wires are in wrong orderā€¦or perhaps overheated??

I cleaned up and went through the original carbs, but bought another set of CD175 ZS online which were rebuilt and are form a Volvo. Only the rear has a choke channel drilled. Hard to start when cold.
Although I have thoroughly cleaned the fuel system and running from gas can as the tanks must be flushed and sealed properly, it makes me feel perhaps a float needle may be stuck perhaps?

Iā€™ve driven it around neighborhood, using left foot for brake and right for gasā€¦to keep it goingā€¦and it does have good power, and as a result of all my meticulous cleaning, goop using to possibly unstick valves (seafoam soaking in valves for a week a few times and marvel mystery oil) there is no longer any smoking from exhaust.

HOWEVER ā€¦although only local neighborhood streets and it was difficult to get up past 40mph, it only shifted into 3rd once.
As much as I tried to massage it, it would not go into 3rd. Could be vacuum related or need time to free itself after sitting a while as these BW12 models seem to do after sitting unused a long while.

This all said, and more than you wanted to know, thank you ā€¦
You seem to be one of the experienced members in this group so any other thoughts are greatly appreciated.

intend to make separate posts with specific questions with photos which will be good for the community at some point.

@Rob: Thank youā€¦I imagined as much. It is not on the earlier cars I noticed.(mine is 73)

However from other images found online as the nitwit PO cut all the hoses off everywhere when pulling the motor, and now I must figure out what goes whereā€¦

ā€¦I did note that it connected to the rear exhaust manifold using an apparent flexible hose from that tube.
As a note however, this appears to be a continuous aluminum tube going down to the trans. FWIW

Kind regards

5

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While awaiting your specific questions, Damian - some initial musingsā€¦

On the BW12; vacuum is required to control shifting. A vacuum control unit on the box is connect by a vacuum hose to manifold vacuum by a vacuum hose - which the PO likely cut. Check and reconnect - and the box may upshift as it should Crudely; without manifold vacuum input, the vacuum control unit will read atmospheric pressure - and the box interpret this as a floored pedal, and wonā€™t upshiftā€¦

If the compression is even, within 15% between cylinders, there should be no problems with the head gasket and valves. The rough idle should then have other causes - uneven idle is a common xk feature, with no patent answer, and no single fix. Idling in gear, some 750 rpms - how much does the idle varyā€¦?

Loss of coolant. This require very careful ā€˜measuringā€™ and proper procedure. So how did you diagnose loss of coolant?

Diagnosing sounds is difficult. Not only do sounds travel around, making location difficult - but the type of sound is difficult to identify. That it disappear when #5 plug wire is pulled does not necessarily mean a worn big or small end - just leave it while you do other thingsā€¦

Hard starting when cold is of course carb related - but enrichment, choke, and fast idle cam is required for cold starting The Strombergs you have should run the Jaguar engine OK, but there is still necessary to get adjustments right. Do you know which Volvo version it came from?

Just initial comments - and you have put in a thermostatā€¦?

Frank
xj6 85 Sov Europe (UK/NZ)
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6

Hi Demian, we have the same car and I have just been through your symptoms on our car recently. Frank is right a steady and low idle is your friend. There is a little bit of pinion to crown wheel backlash on our car and I feel a gentle nudge each time I change from park to a driven gear but it is much less pronounced than before the engine was properly tuned. All seven uni joints behind the transmission have been changed. As noted these can contribute as well, if worn. Ours had vacuum leaks - identified 'in total" using a vacuum gauge and then worked out of the system - it now changes smoothly (for a BW12). Once you have connected the vacuum line to the modulator on the back of the transmission (per Frankā€™s note) you can experiment with shift points using a small flat head screwdriver - should be done measuring vacumm etc, per manual. Note that ā€œkick downā€ is electrical per a little microswiitch mounted on the accelerator inkage - when you get that far. Paul

7

EXCEPT!!!

If the PO also did a lousy rebuild and a big end aka rod bearing is loose, bigger trouble awaits!!! It will get worse and worse, til it decides to part company with the crankshaft and seek an exit to the open atmosphere!!!

Rough test, Rev it up til about 1500 slowly, then let off quickly.
A loose big end, aka rod bearing will rattle like shot in a tin can.

The seem to run quiet under load, but wheh load is relieved, they sound off !!!

Been there, too often!!!

Major work involved in a fix.
Carl

8

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You are dead right, Carl - which is why one should not fiddle with the bottom end of the xk, unless a problem is positively identifiedā€¦

Great care is required to get the bottom end right, and if it is already OK as is (the xk bottom end is rock solid ex factory) - a careless move, or lack of precision, while overhauling it has repercussions. This is an area where preventative maintenance, change of parts, is counterproductiveā€¦

Frank
xj6 85 Sov Europe (UK/NZ)
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9

Thank you all again very much.
Again, excuse delayā€¦no computer.

Iā€™m not one of those who adks questions and disappears.

Iā€™m right with all of youā€¦completely get it and understand.
Thank you.

Actually Iā€™ve never had a problem with the xk not idling smoothly.

And Iā€™ve had them in different displacements from the 50s to 80sā€¦

And Iā€™m a perfectionist, and do nothing halfway.

I wish i could hope it wasnā€™t a rod bearing or crankā€¦i can think of no other reason if sound goes away when plug detached?
Only possibility was some sort of pre ignition, but after taking much time coaxing patiently and soaking valves in seafoam, marvel, running it through for days, it is running cleaner, stoppedsmokingā€¦i replaced plugs with a highly recommended hotter plug etype guys recommend after removing the cheap new plugs used for testing.

They run much cleaner.
But no, still there.

I see messy gasket sealant around sumpā€¦someone f**ked with it.

Yes, these sounds are difficult to discern.
Hose to ear revealed only noise at sump, at #5. Other areas no sound.

I do recall a thread replied to on jaguarforum by some experienced australian fellow mentioning loose damper?

Anyway, yes i replaced thermostat, but it has no hole at the top and i want to drill one.
Canā€™t recall wher i read, some xk engine page online discussing block and overheating issuesā€¦youā€™d find it w a search.

He stated drilling 3 of the small holes would aid in even cooling during warm up which caused block cracking issues.

Anyway, i had filled up on white vinegar, let it sit a week, and draining it all seemed clear until i notice rust stained driveway now.

Then i notice some hard deposit at opening of upper hose.
Try wiping inside with rag, it is hard.

So for first time i squeeze hoseā€¦crunch crunch.

Bottom 2 as well, crunch crunchā€¦

Water pump to intake jacketā€¦same.

F**k

All hoses coated with hardened crap.

So i am not doing anything more until all hoses are replaced, and water pump.

Poor thing.

Then flush again.

So perhaps sludge was this crap lining the hoses, and who knows where, not head gasket symptom.
Ir maybe head gasket was replaced and all not flushed wellā€¦

I donā€™t knowā€¦u hate people that donā€™t take care of things or do them well.

Better not to do anything!
Iā€™ve brought old jaguars back to life after sitting for many years when just abandoned or left aloneā€¦and they were fine after doing what i doā€¦sigh.

Cobsidering donor car or just rebuild myself. Parts are cheapā€¦but i found a 72 s1 locally, needing resto. It depends though, why is it better than mine?
At least i could bring motor back to originalā€¦if that is even a good thing?

Anyway getting off topic here. May require its own thread.

Thank you allā€¦any thought very much appreciated.

PS tach doesnt work, but i can feel it from past experience that at low idle 700 it is unstable, louder squeak, bit of knock, then at abour 1500 it is more stableā€¦goes away, revs well otherwise, has great power driving.

Letting off suddenly as suggested yielded no knock.

Will experiment again when new hoses and pump arrive as weather is getting warmer.

Such a difficult thing to discern. So vagie i must always return to remind myself.

I just donā€™t have the space or time Iā€™m afraid.

10

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Only one comment, Demianā€¦

There is a specific warning for the V12 regarding the thermostat; the hole with the jiggle pin MUST be on top in the thermostat housing. This relates to air venting of the V12 - the xk does not need the hole as it is much better vented. There is no need to drill a hole - and it may be counterproductiveā€¦

As an aside; either you have been blessed with smooth idling xk engines - or your definitions of ā€˜smoothā€™ is less demanding. An xk without some ā€˜beatā€™ is scarce indeed but disappears with increased rpmsā€¦:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)
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11

Thx.

Right, Iā€™m aware of the v12 issueā€¦bleed valve up.
On the xk, this fellow described how on these 70s problematic thru stud engines prior to 81 when passages were drilled, the block would develop hot spots prior to thermostat openingā€¦

ā€¦and cold coolant would cause block to crack.

He suggested drilling an additional hole on each side of the one already there, removing the little tail on that one, making 3 holes, twice the size of that original tiny bleed hole, and this would allow some coolant to flow within block and ease any temp shock of the block when cold coolant comes following thermostat opening.

12

Just throwing it in here, have you checked the distributor for worn bushes?
One of our club members has recently finished his ā€˜Dā€™ replica and was attempting to set th points gap, what he found was that he could set the gap to the required amount, rotate the engine and there would be a difference of up to.005"
This guy used to be a flight engneer for the airforce so I believe he knew what he was up to.
Long story short he had the distributor rebuilt by a local guy who had all the correct equipment to set the advance curve for his engine. Runs much smoother now.

1 Like
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Hi Demian

I have some problem with my engine, and the way i identified this for sure was to hook up a simple vacuum gaugeā€¦they will expose many engine problems

my needle fluctuates rapidly ~16-19"

I then placed a hose up against each carb, and can hear the rear carb has turbulent air, and the front carb is smoothā€¦further investigations needed

If you hook up the gauge and the needle is steady ~ @17-21" and also passes a couple of simple tests, that can rule OUT (or pinpoint) many issuesā€¦(but possibly not a rod knock!)

1 Like
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@Robin_O_Connor
Thanks. It has been a sordid process, bringing back to life after many years, carb rebuild, plugs wires cap rotor, flushing, cleaning, vacuum leaksā€¦
Although i need to re-do that wiring in that area, i believe, yes, once i get it back together, i will find a difference as i found big arcing btw points of all things.

Distributor needed to be gone through, cleaned, wiring, points, condenser replaced.

We shall see. Have bigger fish to fry with motor, but should mk quite a difference i expect.

@awg
Thanks. Sure, thatā€™s good, true a hose to the ear is a good tool too.
Nothing like that for me, though removing butterflies from secondary carbs, those bushing ends may be leaking.

I do use that old style carb float balance tool.
Will need to give it another look when distributor back in and static timing done.

As described above, and as i read somewhere, 90% of carb issues are electrical.

15

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You could first check for an air leak, Tony - squirt of oil (less volatile than petrol or propane) at suspected areas, while observing the vacuum gauge. Carb gasket springs to mind - and carb externals, itā€™s not really the sort of vacuum gauge reaction expected with just a carb maladjustmentā€¦

Frank
xj6 85 Sov Europe (UK/NZ)
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16

Once I install the steering column, after replacing disintegrated lower column bush, I intend to swap out the entire rear carb and see if that makes any change,

even though I can balance airflow using a Gunson balancer, the turbulent sound of the airflow is disconcerting, the closest match on the vacuum gauge chart is worn valve guide or weak spring.

the needle fluttering means the engine is not working properly as an air pump.

I will work thru the issue step by step

17

"the turbulent sound of the airflow is disconcerting, the closest match on the vacuum gauge chart is worn valve guide or weak spring.

the needle fluttering means the engine is not working properly as an air pump."

Tony youā€™re on the right track and have a good feel/understanding.

If youā€™re gut is telling you itā€™s wrong, then it probably is.
Hope for the best, plan for the worst.

Donā€™t think carb change will mk differenceā€¦but why not.

I felt exactly the same reading plugs, if not for discovered distributor issues of all the simple things, it would have had to be something serious.

So you never know.

18

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Have you checked gauge reading at steady high revs, Tonyā€¦?

A compression test might be advisable, to confirm engine state; while the carb area is a suspect - I cannot see it causing vacuum variations as describedā€¦?

Frank
xj6 85 Sov Europe (UK/NZ)
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19

cranking compression is good at 170psi on each cylinder (9:1), which you would think lessens the chance, but does not rule out valves

the needle does oscillate at higher revs

otherwise shows no ā€œbadā€ symptoms from vacuum gauge chart

I put a short video on the XK Engine forum under ā€œintepreting vacuum gauge readingsā€

after changing out carbs, I will remove the cam covers, measure clearances, and change out intake springs if needed.

If that doesnt fix it the head will have to come off

20

Indeed, a vacuum guage can be very helpful. I have two in my ā€œtune up boxā€. Way back when, a GM tech taught me how to use them to balance the two carbs on my Corvair.

Also useful in testing old tech mechanical fuel pumps. Just attach to the tank side. It measures vacuum and that translates as to FP. on those about 3.5 PSI was desirable. Less poor or no running engine. More, float valves in the carbs over come and the engine floodsā€¦

Odd, I started this post yesterday. The computer blipped and I thought it was lost.

Carl,