Almost ready to start the XJ after doing up the head, turned on the ignition & found one of the SUs are leaking petrol from the bottom. It's one of the newer types with apparently a tiny float chamber at the bottom of the SU. Does this happen if a float is stuck? I haven't done anything with the carbies except had the whole manifold assembly off the head & out of the car (upside down etc)

 

If memory serves, the SU carburettors do indeed have a float chamber below or to the side with a sealing ring or gasket that can perish with age. Check also for cracks or poor sealing if there is a small hose from the float chamber to the bottom of the main jet.

A sticking float will sometimes cause fuel to pour out from the main jet or from any vent holes in the top of the float chamber.

NBCat

 

Open it up. You might even find that the float itself has disintegrated. They become very fragile with age, and turning the manifold upside down etc could easily have damaged/dislodged it.

At this point in the rebuild you'll want to do a spot of R&R on the carbs anyhow. Check piston for sticking, play etc. They are not exactly complicated.

An indication of float damage could be that if you start the car it may race to red line and beyond in an instant. Not recommended. Scared the pants off me first time around.

 

Here you are, the website with all the bits you need. You need to identify the type, but if it has an integral float chamber at the bottom, and concentric with the needle, it must surely be an HIF. (IF for Integral Float, I would think !)


SU Carburetters | SU - The SU Carburetter Company

 

Quote Translator "An indication of float damage could be that if you start the car it may race to red line and beyond in an instant. Not recommended."
Wish I could get it to start let alone redline
Anyway Fraser is right, it's a HIF type, when I took it apart the float chamber was full of petrol, of cause it's hard to tell if it was stuck & dislodged the moment I touched it but the float seems intact.
The petrol was actually exiting via the air filter, this may have been happening before the rebuild but is worse now & more apparent as I've replaced the ugly old monster air filter with little Ramflo ones.

 

Seems academic now, I've just checked the compression on the motor & found the compression/cyl is down around 40-60PSI. What have I done??? It had good compression on all but 2 cyl before I took the head off- sick of this, should have put a chevy in it like all the know-it-all rev-heads have been saying

 

The true reason anyone would put a cast-iron, pushrod lump into a Jaguar is a lack of technical knowledge and ability.

Due to the amount of petrol entering the cylinders, there may be a 'wash' situation that's occurred. Try squirting some engine oil into one or two of the cylinders, rotate the engine several times WITH A SPANNER to distribute the oil within the cylinder and then retake the compression test for the cylinder(s) in question. If the compression returns, there may have been a momentary loss of compression due to the petrol. If the compression does not return, there is a problem with the gasket or cylinder head if the valves were serviced.

One further thing, are the valve clearances correctly set so the valves are sealing properly when closed?

NBCat

 

I just noticed your signature line about having a Series II car with a Series III motor. If you've simply bolted the carburettor manifold to the Series III motor without changing to the Series II camshafts, the motor will not breathe correctly as the cam lobes have a different profile for lift and duration for the Bosch/Lucas L-Jetronic used on the Series III.

NBCat

 

Is the valve timing correct ? Did you set the cams using the correct tool, and did you put the cams back correctly (exhaust and inlet), and haven't swapped them over ?

Is the ignition timing correct; it is possible to be 180 degrees out if you're not careful.

'Whilst 'NBCat' is probably right about differing cams Series 2 and 3, I would have thought the engine should at least start and run, albeit roughly.

 

Fraser is thinking ahead and asked the question I was about to ask about the camshaft timing. If the sprockets were for some reason removed from the camshafts, it is entirely possible that the circlips retaining the sprockets to the camshaft coupling may not have been correctly installed and have caused the valve timing to be incorrect.

I suggest you remove the camshaft covers, place a spanner on the crankshaft pulley centre bolt and rotate the engine to obtain TDC on the number six cylinder (closest to the radiator). Once TDC has been obtained, check to see if the notches in the cams just behind the sprockets are facing up with the cam lobes set to a position resembling 'wings'. If the camshafts are in any other position, the valve timing is incorrect and will affect compression on some cylinders. This is also a good time to inspect the valve clearances so they are set a close as possible to the middle of the specification.

The 4.2 Litre XK engine fitted to the Series III cars has slightly different castings from those used in Series II XJ6s, so there is also a possibility that the wrong head gasket was installed, but I'm not entirely sure that would result in a low compression reading.

Ignition timing, whether incorrectly set or not, will have no affect on compression, but may not allow the engine to run, or run roughly.

One performance modification I've seen done to the Series III 4.2 XK engine is to install the camshafts from a Series II carburetted engine for improved breathing. This is a modification that does improve performance with additional low rpm torque, but will most likely result in excessive emissions, should the vehicle need to undergo any such tests.

NBCat

 

All good advice, I'll be mostly working & sleeping the next few days but Sunday I'll be back at it.
Firstly I suspect I will find the cams timing has moved. I've tried oil in the cyl. (The serIII motor was fitted by a previous owner (no injection)) The reason I removed & lapped & reshimmed the valves was 2 cyl were down on compression. On dismantling found a huge build up on the valves- I hope I haven't "overlapped" the seats.
Thanks for the help, first step in the process that I dread is getting to the crank to turn the engine to TDC

 

It may be easier to reach the crankshaft pulley from below with the vehicle securely raised on ramps or with stands.

Did you also reface the valve seats or remove any material from the top of the valve stems? When the cylinder head was reassembled, were all the valve clearances correctly set so there is no possibility of a valve remaining slightly open when the back of the cam lobe is against the tappet face?

NBCat

 

Yes I removed & refitted the cams dozens of times, I BELIEVE I got the shims spot on BUT! As others have confirmed you think it should be simple taking a gap measurement & then installing the correct shim but it never seems to be that simple.

 

I have found it much simpler to do all the valve clearances with the cylinder head removed and mounted on a stand so the valves are not fouled against the bench.

After inserting the valve and adding the springs and securing collars, I've used a soft-faced mallet to strike the top spring seat several times to ensure everything is securely in place because, as you've noted, even with extreme care, setting the valve clearances may still require several attempts.

If you're adjusting the valve clearances with the cylinder head in situ, be certain to rotate the crankshaft four or five times prior to checking and then rechecking the valve clearances.

NBCat

 

There is just enough room for a 1/2" drive and socket, (at least there was on my '80 XJ6 4.2), but the socket size is absolutely enormous on the end of the crank, something like 1 & 15/16"I think. I used to have one sitting in my socket set box. You only use one of these things about 5 times in your whole life, unless you are an XK engine mechanic ! DOn't forget the remove all the plugs, it makes turning the engine over easier.

Have you got a camshaft checking tool ? These are very cheap to buy and is the only way to get the cams in the exact correct position. A dial gauge is also useful to get TDC smack-on.

Finally, have you got the Jaguar workshop manual for the XJ Series 3 ? Another essential item, worth its weight in gold.

These engines were made from 1948 - 1986, and at one time there were lots of mechanics and amateur "experts" like me who had been through the hoop, but now we are all starting to die off, or at least retire ! Memories on how we did things unfortunately are fading; with me it was all in the 80s and early 90s.

 

I'm not very good with the fractional spanner sizes, but if I remember correctly, the bolt was a 27mm or perhaps a 28mm. Some things are English fractional sizes and some things are metric! I believe Jaguar referred to it as a 'process of metrication' over the years. I did have a set of Whitworth spanners many years ago as I sometimes found myself working on an English car or two, but I sold them long ago and have since never used fractional-sized tools, although, they probably would have come in quite handy when working on an XK engine!

NBCat

 

Not a happy chappy.
Suspect A: The timing is fine (the crank can't be accessed from underneath as the auto fluid cooling pipe is in the way) & the fan bolt I have again taken off & refitted. (you can get cramps in funny places trying to get that bolt out & back in
Suspect B: To dry, put oil down the plug hole in greater quantity & compression increased from 40PSI to 120 PSI, put oil in all cylinders & it almost seemed to want to start then not, rechecked compression & it's back down to ~ 45PSI

Suspect C: did I over lap the valves? or do something else wrong on the head overhaul? (shims?)
Suspect D: did the pistons/rings all lose there sealing ability sitting there over a year dry?

 

Will it start on Easystart ? This stuff will wake the dead so if that doesn't work it's time for deeper investigation.

If you have clearance on all valve tappets, the valves will be sealing OK if you have just ground them in. Only other thing is the piston ring seals; the oil trick seems to show these are not sealing very well. The trouble you have is that you have no idea of what happened before you owned the car. This Series 3 engine could also be knackered.

 

There are strong opinions on this forum about the ability of engine oil to cling to cylinder walls and and other engine parts to provide lubrication at start up when the engine has not run for a long period of time.

The fact that compression comes up after oil has been added indicates stuck rings or worn cylinder walls. Either way, it appears the bottom end of the engine will need attention. This often happens when an engine has many thousands of kilometres and the cylinder head is serviced thus raising compression and then revealing poor sealing ability by the piston rings.

At the risk of creating another lengthy discussion by other forum members on the subject, it's my opinion that you should try using an additive with the oil and run the engine to see if the rings eventually are freed up should they be stuck after sitting for some time.

NBCat

 

Two new questions-- If I swapped the cams ( I thought I was careful but dumber things have happened), If I swapped the cams would it bind up, bend valves etc? because that's not the case but if the result is near nonexistant compression then that is what I've done (I hope) (PS How do I tell one from the other?)
2nd question TDC is going to be highest point of travel of front cyl yes? & the rear cyl reaches TDC at the same time ??? If so Cyl 1 or cyl 6 reach TDC at the same time soooo you could find TDC by Jaguars No 1 cyl orr the front cyl, is this correct?
Thanks for your help & patience