XJ6 & XJ12 Series I, II & III 1968-1992

Problems after new head gasket

 
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Old 07-12-2019, 03:14 PM
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Default Problems after new head gasket

Im the owner of 84 XJ6 with about 180 thousand miles on it, although enough of the car has been replaced that the date is somewhat questionable. A new engine went into it in 94 at 45,000 miles and a rebuilt engine in 03 at 131,517 miles. The transmission was replaced with a 6 speed standard in 97 and again with a 5 speed standard in 2000 .

It was in excellent running condition when I bought it more than a year ago. Then I took it to Quebec City for our anniversary. Great trip until we came back to the states. The US customs has eight lanes but only one agent. I didnt yet understand that 84 Xjs didnt take well to long periods of idling in hot weather. By the time that I got back into the states an hour later I, or rather the Jag had a warped head!

When I got it back to Virginia, I took it to my very good mechanic, who unfortunately has little Jaguar experience. He had the heads shaved and put a new head gasket in it. It ran, but power was down with occasional misses. The misses slowly got worse until 0-30 mph was on the order of twenty minutes.
Timing was rechecked. New injectors went in. The back 3 cylinders have low compression. . The plugs on those cylinders are black from low compression. A leak down test indicates50% leakage on the back 3 cylinders, but one cannot hear the air escaping anywhere

He asks Is it possible that the cams are swapped? What are the numbers on the two cans?

Were both at our wits end! Any ideas would be much appreciated!

Bob Cham

Faber, VA

 
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Old 07-12-2019, 03:36 PM
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I suspect a stack-up of different issues but my first thought is that the camshaft timing is outta whack. That's easy enough to verify, and that's where I'd begin. Then move on.

As for the cams, when installed and properly set (there's a setting tool), and #6 piston at TDC compression, the forward-most cam lobes of each cam should be pointed outwards like rabbit's ears. But, I don't think the engine would run at all with the cams reversed

Cheers
DD
 
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Old 07-12-2019, 05:06 PM
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A new engine went into it in ‘94 at 45,000 miles and a rebuilt engine in ‘03 at 131,517 miles. The transmission was replaced with a 6 speed standard in ‘97 and again with a 5 speed standard in 2000 .
That's a lot of rebuilds ! A 1984 engine should have the slotted block, which was an attempt to stop the block cracking between the bores. You might care to ask your mechanic if the block had slots between the bore when he lifted the head. Although the slotted blocks were better, the engine can still suffer headgasket failures, usually around 80-90k miles. However I would be very suspicious that all three cylinders are low at the rear. The later XK engines had two groups of bores, with each group of three siamesed together with no water passages cast in. Earlier blocks had these machined in with resulting cracking problems, (tell me about them, I had a 1980 XJ6 !!!!). The later blocks had narrow water passages in the form of slots machined in from the top of the block.

The other thing puzzling me is you talking about 5 and 6 speed transmissions. The XJ Series 3 cars only ever had 3 speed auto transmissions made by Borg Warner, the Model 66 being the last type fitted. So can you clarify exactly what model you have as it sounds like the later model, the XJ40 (called an XJ6), that had an all-aluminium engine and a 4 speed auto transmission. If it is a Series 3 then somebody has done some extensive modifications by the sound of it. If you could post a photo of the car and its engine it would help.
 

Last edited by Fraser Mitchell; 07-12-2019 at 05:09 PM.
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Old 07-12-2019, 05:58 PM
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The manual transmissions were after market items.
 
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Old 07-12-2019, 06:50 PM
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Originally Posted by Doug View Post
As for the cams, when installed and properly set (there's a setting tool), and #6 piston at TDC compression,
I meant to say #1 piston.

Cheers
DD
 
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Old 07-13-2019, 10:24 AM
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Caveat:

No. 1 is at the fire wall. Not up by the radiator as in USA cars.

Low compression does not necessarily mean black plugs.

Clear leak and a low number as to compression in the rear 3 mean a mechanical issue. Or issues. Excess ring wear and or leaking valves.

That over heat cooked them. Back three got the worst of the overheat, furthest from the pump and radiator.

Squirt some oil in the back three. .Test compression again. Any gain means poor rings.

A bit late, but, when confronted again with slow traffic. pop the bonnet to the partly open position. Allows more hot air to escape the engine bay. Lotsof stuff in these bays and air flow not good.

Good luck...

Carl
 
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Old 07-15-2019, 12:38 PM
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Default Cylinder Head Woes

Also, as if the above hasn't given you enough to think about, it sounds as though you might have had a seriously warped head.

Since the camshaft bearing supports are integral with the upper part of the head, any warping can also affect these, and unlike the surface that mates the engine block, they cannot be brought back into line by a simple milling operation at the typical auto parts machine shop.

So if your mechanic had to "cheat" to prevent any bearings from binding, and he did not actually verify the actual valve stem/tappet clearances as well, you could actually be looking at possibly finding a replacement head.

Here is a link to a good video showing this that I found on YouTube titled "
":

https://www.jaguarforums.com/forum/e...askets-220491/
 
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