Hi everyone,

I've been searching the depths of the web about my problem but haven't found some definitive asnwers so far so i hope you guys here can help me.

I've blown my 1998 XJR AJ26s engine by badly overheating it (total coolant loss @ 130mph) . Went for an exchange engine but didn't realize the AJ26s/AJ27s differences and got a AJ27s engine as a replacement. My mechanic has exchanged the engine (see below) but the thing wont run properly (misfires, fires on exhaus stroke).

Current situation is as follows:

- vehicle is a 1998 XJR, old engine was an AJ26s nikasil block
- swapped block+heads with an AJ27s
- refit SC and inlet system / intercoolers from old engine
- refit flexplate from old engine
- refit coil packs and ignition loom from old engine
- left old ECU in place
- refit old throttle body

I'm aware of the differences in the camshaft sensoring between AJ26s and AJ27s. I found reports that it is necessary to swap the left hand inlet camshaft to get the old 1 peak / 720° (1 tooth on cam) signal for the old ECU. However, original Jaguar documentation states that the SC AJ27 engines still had the old 1 tooth camshaft (4 tooth cam on VVT engines only) so no need to swap over.

Could someone shed some light on the mysteries of an AJ26s to AJ27s swap?

 

Noticed the flexplate from the 26, I thought that you'd not changed it - oh. The 27 cams have 4 lobes, looking at a SC AJ27S head right now...not one.




Maybe time to knock them out and swap over, beats trying to reshim a 24 valve head.

 

Sean,

First reply and already a matchwinner it seems

I suspected that the AJ27s would have 4 lobes. So its definitely worth the trip down to the workshop and rip some valve covers off!

Just wondering - the (official looking) jag documents on the changes between AJ26s/27s must obviously be wrong then (see attached pic).

So i am correct in assuming that it's possible to change the lobe part of the cam only? Not really looking forward reshimming the thing... (or letting my mechanic do it who quite surprised me when he stated that the AJ-V8 had hydros...)

Many thanks

Andy

 

... here's the document.

PS: the cam with the timing piece on should be the inlet cam on the left bank to work with the AJ26s ECU, right?

 

You might try to swap the reluctors ONLY. They are a 'press-fit' in the camshaft. This would save resetting the valve lash.

Here is an old TSB for DTC 1396. It shows the reluctor and gap setting.

Good luck

bob gauff

 

Just checked - my AJ27s has the 4 lobe reluctor. So time to change that! Can i get it out without taking the camshaft out? I would try to loose the cam bearings and lift the rear end out and leave sprocket/ timing chain in place so i would not need to readjust timing.

 

No you can't....... I had one come out of its own accord, I could not figure out what was wrong with the car, as the engine turned sometimes it would pick up the reluctor and work and then die, I checked everything and all looked fine, it was only by shear fluke I was checking out the cam sensor I nudged the reluctor and it dropped out, it kind of fits inside the cam on a taper, this particular one was very loose, the customer was reluctant (forgive the pun) to change the cam so I whacked a few centre pops into the reluctor and hammered it back in.

Just FYI the AJ26 cams are solid, the AJ27 are hollow and a long drift through the sprocket bolt hole will allow you to knock it out

 

She runs!! Thanks guys!

My mechanic had quite a hard time swapping the reluctor as he needed to take the cam out and re-set the timing as you all said. Nonetheless she's running again. On the first few starts the car spewed out loads of black smoke and didn't run smoothly (cyl 5+8 not running properly). I think there still were loads of unburnt fuel in the cylinders.

This cleared after some time and now the big old cat rides again!

 

Cool

 

+1 feedback's always good - mods can add 'Fixed' to the thread title