Go Back  Jaguar Forums - Jaguar Enthusiasts Forum > Jaguar Models ( Classics ) > XJ40 ( XJ81 )
Reload this Page >

3.6L AJ6 cylinder head on a 4.0L AJ6 short block?

XJ40 ( XJ81 ) 1986 - 1994

3.6L AJ6 cylinder head on a 4.0L AJ6 short block?

 
  #1  
Old 04-22-2019, 10:10 PM
Senior Member
Thread Starter
Join Date: Sep 2013
Location: NE Ohio, USA
Posts: 151
Received 28 Likes on 22 Posts
Default 3.6L AJ6 cylinder head on a 4.0L AJ6 short block?

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?
 
  #2  
Old 04-23-2019, 08:13 PM
Join Date: Feb 2014
Location: The Beautiful Mid-South, U.S.A.
Posts: 16,518
Received 7,519 Likes on 4,201 Posts
Default

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
 
  #3  
Old 04-24-2019, 09:44 AM
Join Date: Dec 2009
Location: Decatur,TX
Posts: 7,790
Received 4,064 Likes on 2,668 Posts
Default

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
 
The following users liked this post:
Don B (04-24-2019)
  #4  
Old 04-24-2019, 10:29 AM
Veteran Member
Join Date: Sep 2012
Location: Victoria BC Canada
Posts: 1,857
Received 1,164 Likes on 736 Posts
Default

Originally Posted by motorcarman View Post
Cam cover from Engine number 179542 has the oil filler cap integrated.
Also those later cam covers have 13 hold down bolts while the earlier ones have seven.

Larry
 
The following users liked this post:
Don B (04-24-2019)
  #5  
Old 04-24-2019, 12:51 PM
Senior Member
Thread Starter
Join Date: Sep 2013
Location: NE Ohio, USA
Posts: 151
Received 28 Likes on 22 Posts
Default

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.
 
  #6  
Old 04-24-2019, 07:02 PM
Join Date: Dec 2009
Location: Decatur,TX
Posts: 7,790
Received 4,064 Likes on 2,668 Posts
Default

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
 
  #7  
Old 04-24-2019, 10:59 PM
Join Date: Feb 2014
Location: The Beautiful Mid-South, U.S.A.
Posts: 16,518
Received 7,519 Likes on 4,201 Posts
Default

Originally Posted by JensenHealey View Post
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. [snip] 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.
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
 

Last edited by Don B; 04-25-2019 at 06:56 PM.
The following users liked this post:
motorcarman (04-25-2019)
 
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
juha_teuvonnen
General Tech Help
0
05-11-2016 12:36 AM
jaguars4r
S-Type / S type R Supercharged V8 ( X200 )
6
05-06-2015 08:44 AM
Skelly
XJ6 & XJ12 Series I, II & III
11
04-10-2015 05:14 PM
hoodun
XJS ( X27 )
0
10-12-2014 06:39 PM
hoodun
XJS ( X27 )
1
02-09-2012 07:13 AM

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 

Thread Tools
Search this Thread
Quick Reply: 3.6L AJ6 cylinder head on a 4.0L AJ6 short block?


Advertising
Featured Sponsors
Vendor Directory

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: