XJ40 ( XJ81 ) 1986 - 1994

Poorly Head

 
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Old 06-12-2019, 03:39 PM
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Default Poorly Head

Hello Everyone,
I'm currently half way through a Cylinder Head Gasket swap and have come across a couple of issues...

The Head casting itself has eroded around a couple of the Coolant passageway ports.
Why, WHY do the Block and Head have triangular ports and the Head Gaskets have circular apertures with a much smaller area...??

Erosion and Porosity
Even the new Head Gasket I've bought (Payen) has 'just holes' - this can't be correct, can it..??

My second query is this - there is a little 'thing' on the Inlet Manifold which is something to do with the Crankcase Vent system.
There are three pipes connected to it - 1 Tees into the pipe between the inlet Elbow and the Oil filler neck and the other two, which come off the Inboard side are just a couple of inches long then open-ended.
Upon peering down to see where they should go I can see two more flexible pipes that come up to meet them (?) but which are 'jumpered-out' by what looks like an old piece of Brake pipe.

The thing in the middle - two pipes coming from it on the left are open-ended.
Is this a known mod, a good thing, bad thing or a total bodge..??

That's it for now.
Thanks in advance for any info/advice.

Cheers, Dave.
 
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Old 06-13-2019, 09:21 AM
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I remember a TSB (probably an old paper one) that described using an EPOXY to fill in the corroded spots if they did not encroach on the combustion chamber. (outside the head gasket chamber ring)

Make sure it is applied and smoothed/sanded FLAT.

I have done this to my 1992 XJ40 when I replaced the head gasket. There were a few corrosion spots so I applied some JB epoxy (not the kwik set) and then lightly sanded it FLAT.

The engine ran for years before I sold it.

bob
 
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Old 06-13-2019, 01:29 PM
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Bob, Many thanks for your reply.
I am picking up a 'good, used Head' off a chap that races an XJS but am not keen on rebuilding it unless i'm happy with the Gasket - are there any makes of gasket that have better apertures for the coolant passageways..??

Any thoughts on the Crankcase vent thingy..??

Cheers, Dave.
 
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Old 06-13-2019, 03:29 PM
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Dave,

Ditto on Bob's suggestion regarding JB Weld epoxy. I've used it on two XJ40 heads with the same type of corrosion. Clean and degrease your corroded head areas for good adhesion and use the standard cure or high-temperature JB Weld. I apply a small amount and smooth it, then when it begins to stiffen up but before it is hard, I use a safety razor blade to carefully trim it flat and level with the surface of the head, using the surrounding surface to help control the blade. If there are any voids remaining, I add another smaller application of JB Weld. Take care not to scratch the head gasket surface. If you hold the razor blade at the right angle, its bevel will be flat on the head so it won't cause scratches. If you have to sand the epoxy as Bob suggests, use very fine sandpaper (400 or 600 grit) on a small dead-flat sanding block.

I also used Permatex Copper Spray-a-Gasket on both sides of the head gaskets to help seal minor imperfections and it seemed to work well on both cars. The '88 was still good when I sold it, and our '93 went 90,000 more miles before the head gasket failed again, which is fairly typical of the AJ6.

The "thingy" in your photos is the partial load breather restrictor, which is part of the crankcase breating system. It is coolant-heated to prevent icing in cold weather. I am attaching the relevant section from the engine management manual.

Cheers,

Don
 
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Last edited by Don B; 06-13-2019 at 10:34 PM.
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Old 06-14-2019, 11:28 AM
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That's excellent advice - thank you Don and many thanks for the attachment.
I'm amazed by how complex these cars are - I dread to think what a modern one is like .....

This Head gasket is worrying me - does the smaller area of the hole in the gasket not cause flow issues with the coolant..?? This obstruction must surely be the cause of the erosion/pitting.

Cheers, Dave
 
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Old 06-14-2019, 12:58 PM
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Originally Posted by Evil Elsie View Post
That's excellent advice - thank you Don and many thanks for the attachment.
I'm amazed by how complex these cars are - I dread to think what a modern one is like .....
A Mercedes GL350 I service has 44 computer modules, and the first time I worked on it there were DTCs stored in 26 of the modules....

Originally Posted by Evil Elsie View Post
This Head gasket is worrying me - does the smaller area of the hole in the gasket not cause flow issues with the coolant..?? This obstruction must surely be the cause of the erosion/pitting.
You may be right that the smaller holes promote the corrosion, but I seem to recall noticing the same issue on the gaskets I used, so I don't believe it's a defect in the gaskets you received. Check photos of other gasket sets if you can find them - try SNG Barratt's website, Rock Auto and PartsGeek - they're all usually good for including photos of the actual parts.

Cheers,

Don
 
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Old Yesterday, 04:29 PM
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44 computer modules..?? My brain hurts just trying to imagine that..!!
Once upon a time all you needed was fuel and a spark (and maybe a spare set of points and a Condenser) now all you need is a mobile phone so that you can call the Repair Technician so he can plug his computer in. The latest generation of drivers won't even bother looking under the bonnet.....

I've had a look at various other gaskets and they're all pretty much the same.
Bizarrely, the gasket for the earlier 'Series' XJ and also for the AJ16 have 'shaped' coolant passage openings but the ones for the AJ6 are nearly always round.
What's that all about..??

While i'm asking ..... the 'Partial Load Breather Restrictor' - With my current set-up it's not being heated by the coolant. Would this only be a problem for a vehicle that was used in very cold ambient air temperatures..?? It does get cold(ish) here but only for a few weeks in the winter. Most of the time it just rains......

Cheers, Dave.
 
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Old Yesterday, 05:02 PM
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Originally Posted by Evil Elsie View Post
While i'm asking ..... the 'Partial Load Breather Restrictor' - With my current set-up it's not being heated by the coolant. Would this only be a problem for a vehicle that was used in very cold ambient air temperatures..?? It does get cold(ish) here but only for a few weeks in the winter. Most of the time it just rains......
It seems unlikely that your partial load breather restrictor not being heated by coolant is unlikely to cause issues, except possibly in weather cold enough that the moisture contained in air drawn from the crankcase could freeze on its way to the intake manifold. It certainly seems as though conditions when this could cause drivability issues would be rare, but that's my uneducated assumption. Jaguar engineers test their engines in every climate on the planet, from desert heat to Arctic cold, so they must have encountered conditions that prompted them to include the coolant jacket in the restrictor, but for all we know that may have been in Iceland.

Cheers,

Don
 
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Old Yesterday, 07:18 PM
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Originally Posted by Don B View Post
Jaguar engineers test their engines in every climate on the planet, from desert heat to Arctic cold, so they must have encountered conditions that prompted them to include the coolant jacket in the restrictor, but for all we know that may have been in Iceland.
Don -

According to the 3-part video on the XJ40, the cold weather testing was done in the middle of winter in Timmins, Ontario, Canada

https://en.wikipedia.org/wiki/Timmins#Climate

Larry
 
 
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