Displaying items by tag: Engine

Some of you may have noticed my wanted ad in last month’s issue of the JDCQ magazine. I was chasing a 12 blade MK 2 radiator fan and a club member has responded with a couple of fans available. The story behind that ad is that the early MK1 2.4 cars only had a simple 4 blade fan which is adequate for normal use on the open road and general use but it is absolutely hopeless when caught in heavy city type traffic.

I attended Geoff and Gerry Underhill’s Australia day BBQ at Tingalpa on Sunday 23 January and it was a typical Queensland summer day with the temperature around the 30 degree C mark. I was travelling from Pine Rivers on the Gateway Arterial and sitting on the 100k speed limit with the water temperature gauge steady on 75 degrees. However I got caught in a surprising amount of traffic and a number of red lights around the Capalaba area and by the time I reached the Underhill estate the temperature was around the 100 mark.

Expecting the worst I let the car cool down and borrowed a bucket for water off Geoff [queries he - not another breakdown?] however it had not lost any coolant. The return trip home was uneventful with the temperature gauge sitting as before on 75 degrees.

I have had this problem before in my first MK1 2.4 in 1986 and the fix of putting a late model radiator fan on the car solved most of the traffic overheating woes. I expect it will make a major difference in this case.

A club member was having trouble with his XK series engine as it refused to fire up after having the carbies overhauled, new points, plug leads etc. put into the system along with a distributor overhaul. The engine refused to run and wouldn't even do the courtesy of giving the occasional backfire or cough. Club member was getting a bit frustrated with the whole thing

Enter yours truly and a few basic points were looked at. Spark plug removed from the front [number 6 cylinder in Jaguars] and a crank over to the compression stroke showed that the distributor rotor arm was pointing at the lead going to number 1 cylinder i.e. all of the leads out of the distributor cap were 180 degrees out. The spark plug leads were reattached in the correct order but still no signs of life when cranked. Careful checking of the float levels in the SU HD8 carbies showed no major discrepancies. There were lashings of sparks as yours truly got inadvertently zapped while holding onto a plug lead and noting that the spark would jump a ½ inch or 12 mm gap. A rough check on the timing showed it to be within the general running range of a few degrees before top dead centre. The fuel strainer bowl was checked for water and it came up clean so basically we had fuel, ignition and compression but still not a running engine.

When all else fails suspect any thing so I pulled the plugs out which were decidedly wet. I can only presume this occurred as petrol evaporated causing water condensation on the plug insulation. After washing them in petrol and drying with an air gun they were reinstalled. A dash of ether start assistance had the engine firing but refusing to idle. Keeping a fairly wide open throttle setting helped keep it running and eventually it stabilised at 1500 RPM, - still not right.

By now it was obvious there had to be a major air leakage in the inlet system as no amount of fiddling with the main jet enrichment system was having much effect on the idle. By sheer luck while suspiciously looking at the engine running from all angles I spotted a joining hose on the starting carbie pipe inlet system that had become disconnected and had left a significant opening for air to bypass the carbies. Apparently the hose had been installed but the hose clip wasn't tight and a backfire in the inlet system had most likely caused it to come off.

Reconnection of this pipe brought some order into the system and after this final mechanical skirmish we had the car idling. There was still a little leak somewhere in the inlet system as the engine was happily idling with both carbie idle air bleeds completely shut off! The best way to chase these leaks is by using a piece of thin hose held to the ear while the other end is moved around the inlet manifold and carbies. However time was running out and I had to leave this up to the owner to pursue.

Ben Stafford had another problem with his 420. There was generally very poor oil pressure of only 20 to 25 PSI when hot and cruising on the open road that dropped back to almost 0 at idle. The engine did not sound "clapped out" and the oil consumption was quite reasonable. The electric oil pressure gauge was suspected but substitution of a hard line gauge only confirmed that the electric gauge was telling a true story.

I suggested that before he did any thing drastic like an engine overhaul he should check the condition of the oil pressure relief valve. I have had two occasions in Jaguars where low oil pressure was traced to relief valve problems.

Ben found that the oil pressure relief valve spring had been bent. This resulted in the valve itself sitting at an angle on the relief hole and a groove had been worn into the face of the valve. He used a lathe to clean up the face of the valve and subsisted a straight spring for the bent one

The results were fairly dramatic with an improvement to 45 PSI on the open road and 15-20 PSI at idle when hot. In his own summation of the situation he "was surprised that such a small gap in the relief valve had led to such a dramatic loss of oil pressure."

Whither goes thy oil pressure? (continued)

MY Mk2 3.8 Auto has had a slightly low oil pressure and I was a little concerned that the engine may have been "loose" i.e. getting worn. I took a trip to Ben Stafford's to use his hoist and get easy access to the pressure relief valve.

Upon removing the relief valve it became immediately obvious that the valve face was not seating properly. A quick trip in the lathe to face off the valve resulted in an increase of 10 pounds per square inch over all of the operating range.

However I now believe the real problem lies in wear on the upper flutes of the valve which allows it to sit in the bore of the valve body at an angle and the final solution will be to replace the valve itself with a new part and possibly even re-sleeve the valve body.

As a result of the problems I had with the spark on the MK 1 3.4 auto while headed for the display day which I never got to [see Oct 03 Nuts and Bolts] I had a serious think about the ignition system in this car. It is very simple and on a par with the FJ Holden employing a coil, points, condenser and distributor. In fact alongside the modern day electronic systems it is downright crude. I pondered is there a better way?

There are modern electronic ignition system which can be fitted to run without points and deliver a massive spark however I detected some reluctance from a couple of commercial distributors of these devices when I wanted firm guarantees that they would fit a MK1 distributor. In fact they asked what was a MK1!

Using my vast background of Datsun 120Y experience I decided that the simple way was to retain the system, as it was however I would introduce a ballast resistor and coil. As I had lots of 120 Y used components in the parts bin including ballast resistors and coils I thought that a simple no cost experiment would be worthwhile. The results were quite spectacular. This car, which was always finicky on the start roared into life immediately. From dead cold it would catch on the first revolution of the crankshaft. Encouraged by this I purchased a new coil, ballast resistor and relay and the car has not looked back. In fact tonight I had to move it around in the shed and it still stated immediately although it is at least one month since the last time it ran.

How it all works is quite simple. When you are cranking over an engine on a 12-volt system the actual battery voltage drops to about 8 volts. This means your 12-volt coil will not work very efficiently when starting but is OK when running. If you substituted an 8-volt coil it would be good when starting but would burn out with continuous running. However a resistor designed to get rid of 4 volts when continuously running will protect the 8-volt coil. That is the ballast resistor. The relay is used at start up to short out the ballast resistor. The coil of the relay is connected to the starter motor voltage supply and activates when the starter is turning. The points in the relay are connected to either side of the ballast resistor and when they come together the relay shorts out the ballast resistor and full battery voltage is available at the 8-volt coil.

As we get more sophisticated I will try to introduce circuits and diagrams but at the moment I am stuck with a pretty basic computer and you will just have to bear with me on the description. While the foregoing information is not rocket science it appears to be a worthwhile modification to older Jaguars and is relatively inexpensive. Anyone who is really stuck can phone me and I will see what I can do to mail them a circuit diagram.

A fellow club member who regularly drops in to my place had been having some trouble with a series 3 XJ6 blowing head gaskets. He eventually checked the engine block and found the typical warp which in this case was about 9 thousandths of an inch [.009]

He finally bit the bullet and removed the engine for some serious machining work to get the engine block re-decked i.e. ground back to get rid of the warp. . Along with that he had a typical problem with a broken head stud when he removed the said studs for the machining work. He requested the workshop carrying out the machining to extract the broken stud.

He was put onto an alert by the workshop that he should also check the length of the old head studs as they do have a history of stretching. When he did this he found that they had in fact stretched. This may not sound serious but it is a problem in that Jaguar use a domed [acorn] nut to hold down the head.

If the stud has stretched the nut may feel as if has tightened down onto the head but it may have only tightened down onto the stud and may be exerting little or no pressure onto the head. This is a condition known as becoming “thread bound”. I.e. the nut is tight on the thread but is not holding the parts together with sufficient pressure.

Upon checking the head studs he found that they had all stretched beyond limits and a new set of studs was definitely needed. The XJ workshop manual does give guidance on checking the stud length but how many of us amateur mechanics read the manual before tackling the job?

In fact one wonders if the stretched head studs were not the problem in the first place as the engine had not really done any serious distance since an “overhaul” by a previous owner

In discussion with this member who like myself has lived in remote areas we agreed that if we struck this stretched stud problem well away from any reasonable engineering facilities we would either add an extra washer onto the head and use the Jaguar acorn nut or ditch the acorn nut and use common plain nuts. That would at least allow us some chance of carrying out a repair sufficient to get us home.

This modification is done to take advantage of the larger (1-7/8” ) inlet valves on the later cylinder head, although the earlier heads can also be modified to accept the larger valves. Issues which need to be addressed are as follows:

1. The inlet manifold on 3.8 litre motors differs from the 4.2 litre manifold. This article assumes you have the 4.2 litre inlet manifold.

2. The later cylinder head has extra holes for coolant flow between the block and the head. The two rear holes have to be welded closed. Any cylinder head reconditioner should be able to do this.

3. The later cylinder head casting is more upright at the front. Therefore, if you are using the earlier polished cam covers you will notice that the machined mating surfaces on the later head extend about 5 mm forward of your polished cam covers. Fortunately, if this offends your æsthetic sensibilities (as it does mine), there is enough metal to permit filing back in a nice radius followed by polishing. The fit of your early cam covers will then look just as it should.

4. You will also find reduced clearance or interference between the U-shaped aluminium breather and the cylinder head. You’ll have to take a file to the rear of the breather in the appropriate places.

5. If you want to retain your old tachometer generator, you’ll need to drill and tap three holes for it on the inlet side. Similarly for the camshaft blanking plug on the exhaust side you’ll need to drill and tap two holes.

6. Keeping the tacho’ generator means you’ll have to retain the old style camshaft covers, but for aesthetic reasons you’d probably want to keep these anyway.

7. The rear inlet camshaft bearing cap on the earlier head is longer than its later counterpart. It extends rearward out through a machined half circle in the polished cam cover, whereas the later shorter bearing cap does not. (This is because the later cam cover is not machined to accept the tacho’ generator.) The old bearing cap can’t be swapped onto the Series 3 head because it won’t mate correctly with the head. Therefore the half annular gap between the polished cam cover and the tacho’ drive has to be filled. The easiest way to do this is to cut the end off an unwanted early bearing cap. Alternatively, you will have to get an appropriately dimensioned ring turned up in a lathe, cut approximately in half and filed to accurate size.

8. If you don’t want the original tacho’ generator, but do want the old style polished cam covers you’ll have to arrange for an aluminium plug to be turned up.

The fitting of oil seals to the inlet valve guides of earlier cylinder heads is a common practice. Nevertheless, details of the necessary changes are not widely known even amongst Jaguar professionals.

The inlet valve itself is not affected by this upgrade. The most obvious change is the fitting of the later style inlet valve guides which have an external groove near their upper end to retain the seals. The other necessary changes are as follows:

· Use the later Valve Spring Retainer which is 0.530” high whereas the early retainer is 0.630” high. The part number of both retainers is C27480.

· Use the later Valve Spring Collets which are 0.345” high whereas the early collets are 0.438” high. The part number of both collets is C27482.

Unless these changes are made, the higher old-style valve spring retainer will contact the top of the oil seal.

· The later valve spring seat is shallower than the early valve spring seat, but either may be used.

· The later tappet is shorter (0.843”) than the early tappet (1.00”), but either may be used. The early tappet has the advantage of giving a greater bearing area in the guide at the expense of being a few grams heavier than its later replacement.