I am rebuilding my spare cylinder heads and would like to get some advice on the following:

- The tappet bores have 33.02 mm diameter (measured with a high precision bore gauge).
- The original tappets have 32.99 mm diameter - clearance 0.03 mm
- The new tappets (from Barratt, OEM, AJ83694) have 32.975 mm diameter - clearance 0.045 mm

I am surprised that the new tappets actually have slightly smaller diameter than the original ones that came with the head. I am concerned about the extra clearance if I use the new tappets as it may result in tappet noise (ticking). I would appreciate any advice/experience as to whether the (radial) clearance of the tappets is critical as far as the tappet noise is concerned. Should I stick with the original tappets (0.03 mm clearance) or will the new tappets be fine (quiet) even though their clearance would be 0.045 mm?

 

Are these spare heads an AJ26 or AJ27? The reason I ask is because I know there’s a difference in the height of the buckets between the 26/27 and the shims for the 26 are a lot thicker. I don’t have the numbers but, maybe there’s also a width difference between the two buckets??? It’s my opinion that .015 smaller X 32 buckets can overall reduce your oil pressure but, I don’t have the tolerances on me. I know we have an AJ26 engine repair manual at work that my boss got from Jaguar school when he was at the dealer. I can get a few pix with tolerances when I go to work tomorrow if you want? The only other person that I can think of who would know more about this would be Bob.

 

That would be great if you could post info on the tappet and bore diameters and tolerances. My spare heads are AJ26.

I have read about different tappet thicknesses between AJ26 and AJ27 but I have been unable to correlate this to the information in the Parts Catalogue and the Barratt and DMG websites.

Tappet up to VIN 853935, AJ26 - NCA2543AB - my 1999 AJ26 SC engine original tappets are 4.50 mm thick (and so are all tappets from my spare AJ26 heads)
Tappet from VIN 853936, AJ27 - NCE2543AA ==> AJ83694 - tappets are also 4.50 mm thick (the new AJ83694 tappets I bought)
So, the tappet thicknesses appear to be the same in AJ26 and AJ27.

Shims up to VIN 853935, AJ26 - shim thicknesses range from 2.18 to 2.90 mm, in 0.02 mm increments
Shims from VIN 853936, AJ27 - shim thicknesses range from 2.18 to 2.915 mm, in 0.015 mm increments
With regard to shim thicknesses, it appears that the only difference between AJ26 and AJ27 is that the AJ27 shims are made in smaller (0.015) increments but the thickness range is practically the same as in the case of AJ26.

It would be good if we could clarify when exactly the different thickness tappets and shims were introduced for the X308 AJ27 engines.

 

No luck..... the engine guide had certain specifications but, nothing related to tappet and bore tolerance. I was wrong about the 26 & 27 buckets being different. I have a set of 26 & 27 but measured the same between the two. I’m scratching my head because years ago when I rebuilt the heads in the 98’ XJR, I put a set of AJ27 buckets in it and the shims I transferred over from the AJ26 buckets I remembered having a substantial clearance issue. Anyways, I went back with the AJ26 buckets and all was fine. I will say that the metallurgy between the 26 & 27 buckets are different in sound as I suspect the 27 bucket to be lighter. I wonder if there’s a difference between the AJ27 and the 4.2L buckets? 🤷‍♂️ Sorry I couldn’t help out more.

 

I just found info that I extracted, cannot remember from what document (must have been one of the Jaguar documents):

"If more than 0.003 in (0.08 mm) side play in the tappet guides is present, the guide should be reamed out and an oversize tappet fitted.
If the lifter is dished or out of round by more than 0.002 inches (0.05mm), or if the lifter binds in the bore of the cylinder head, it should be replaced."

 

So it says use your original guides and send the new ones back, the second part would imply a size range? It's been superseded out of stock on JLR's site...
I just threw a bag out in the house move....I knew I shouldn't have.
The 27 heads if you can locate a pair cheaply would be an improvement, the inlet port design is improved, along with nickel alloy guides for no expansion, as A2B noticed I think the seats got an upgrade? Count Ibis is the guy to give us the specs -.4.2 multi layer steel head gaskets. blank the 2nd cam sensor, or just nip the tail off. 3.2 & 4.0 are the same part number NA & SC all the same. They only need a spring and valve stem oil seal refresh at 300,000 miles from what I've seen, the cylinder heads fit in the dishwasher perfectly, but only when she's out of the house!

Did you still have the info on a the tool to shim the valves in situe?

 

In August 2003 we got a 'tech_tip' about the tappet variation and transfer of tappets.

 

Thanks Bob! I knew there was something off about the 26 & 27 buckets.

M.S., I don’t know about where your at but, here in the US, we have several coating companies that can apply a specific coating on used engine parts that can give you back the clearance figures that your looking for. For example, there’s a place here called “Line2line” coatings. It’s just like the coatings on supercharger rotors. I know it’s a lot of extra effort, time and of course money. But it would sure beat trying to get some sort of inserts in all 32 holes.

 

Thanks for the document regarding change of tappets.

The VIN of my car (June 1999) is well after 853935 (the change-over point AJ26 to AJ27) but my engine is still AJ26 because it is SC (Daimler Super V8). Is it possible that in 1999, even though the SC engines were still AJ26, the cylinder heads installed on them in the factory were actually AJ27 heads? Most likely this is the case because the original RH head on my AJ26 engine has an aluminium plug where the second cam sensor is installed on AJ27 engines. This explains why the tappets in my original heads have the same thickness as the AJ27 tappets NCE2543AA (AJ83694). So, it seems that the different thickness tappets (NCA2543AB) were used only in the 1997-1998 engines ("full" AJ26) and that, from 1999, all engines had AJ27 tappets because the cylinder heads were AJ27, even on the AJ26 SC engines.

In that case, my spare heads are also AJ27 (not AJ26 as I thought) because the RH one has an opening for the second cam sensor and their tappets have the same thickness as the new AJ83694 (AJ27) tappets I have.

I do not have a problem with too much side clearance of the tappets in the spare heads. The clearance of the original tappets is very good (0.03 mm) but I just thought it would be good to install new tappets. However, since the new tappets (AJ83694) would open-up the clearance to 0.045 mm because they have, for some reason, slightly smaller diameter (32.975 mm vs. 32.990 mm of the original tappets), I have decided to go with the original factory tappets.

 

I bought the tool (303-540) some time ago from Bosch Automotive Service Solutions. I emailed inquiry to CSS.UK@Bosch-Automotive.com and got a reply from intl.inquiries@service-solutions.com directing me to Australia (Alison.Feely@au.bosch.com) as I am in their region. I do not know if they still sell the tool.

I am actually now selling this tool on Ebay (https://www.ebay.co.uk/itm/195977831726) as well as some other Jaguar parts.

 

99 model year is aj26.5

i have some aj26.5 heads at home they have the second cmp cutout and the valve covers are the thin gasket ones. oil pump is different too i think