I have a spare early 3.6L engine (probably off a 1985 XJS) and it looks like it might have a good cylinder head. Since the cylinder head off my 4.0L 1994 XJ6 is warped, I was thinking of using the cylinder head off the 3.6L AJ6 motor on the 4.0L engine.
The valve sizes look to be the same but I will be measuring them to confirm. I would most likely be using the cams from the 4.0L head. After having the 3.6L head checked for warpage and it passes, does anyone here know if there would be any reason a 3.6L cylinder head couldn't be used on a 4.0L block?

 

Hi Steve,

I've sent a Private Message to our member motorcarman (Bob Gauff), a former Jaguar dealership technician and longtime independent Jag mechanic. He is probably the one person most likely to know the answer to your question. Hopefully he'll chime in.

Cheers,

Don

 

I have never tried a 3.6 head on a 4.0 but the later XJ40 heads are different from the 1990-1992 heads.

The cam covers are completely different.

The cam cover on the 3.6 has no provision for an oil fill cap. Cam cover from Engine number 179542 has the oil filler cap integrated. The 3.6 and earlier 4.0 has a tube into the block for oil fill.

The 3.6 head would likely fit the 4.0 up to engine number 179541.

That is the difference I remember.

bob

 

Also those later cam covers have 13 hold down bolts while the earlier ones have seven.

Larry

 

Thank you all for these informative replies.
Unfortunately the 3.6L cylinder head is also not flat.
After removing the head from the 3.6L engine and stripping the cams out of it, I took it to the machine shop.
They checked it and it has a 0.012 gap in the center of the head when a straight edge is placed along the length of the head.
So I am back to trying to figure out what to do about a straight cylinder head since I now have two warped cylinder heads.
I did call a very knowledgeable Jaguar and exotic car expert in NE Ohio and he said that a 0.010 to 0.012 gap like this is not a terrible problem and should not cause an issue with the cam journals.
He did advise that while I have the engine apart I should definitely replace the valve seals.

 

The 1994 Valve stem seals were a 'known-fault' and I replaced almost a dozen sets when I worked at the dealer because of the 'puff-of-smoke' at startup.

The aftermarket insurance did cover the repairs if people purchased the policy.

bob

 

Hi JensenHealey,

It's true that the maximum allowable warpage for straight six engines tends to be greater than for shorter heads. I haven't looked up the Jaguar specs recently, but a few months ago I did a head gasket on a BMW straight six, and if I recall correctly the maximum allowable warpage was 0.002 in. / 0.05 mm. I measured 0.0015 in. on that head so I reinstalled it and it sealed just fine. As to whether a head with nearly 10 times that warpage would seal or if you'd be at risk of a cam breaking, I can't say.

If you could find a machine shop that can straighten the head with heat as Bob has described in your other thread and perhaps skim the minimum amount of metal possible, that might be the best solution.

EDIT: I just took a quick look at the XJ40 Haynes manual and it doesn't give a maximum allowable warpage, but it gives a maximum resurfacing limit of 0.010 in. / 0.25 mm, and a minimum thickness of a 3.6L head of 5.101 in. / 129.6 mm, and a minimum thickness of a 3.2L/4.0L head of 5.108 in. / 129.7 mm.

Cheers,

Don