A and B exhaust camshaft swap
 

Yes, you read that right.

So, a little background. Lightly abused 1998 XK8 Convertible, bought as a non-runner from a chap who had the top end rebuilt after a cam chain tensioner mishap by the owner before him, found two dead cylinders after the rebuild, and gave up.

I did a little digging and found that the A and B exhaust camshafts were installed on the wrong sides during the rebuild.

Any advice for the swap? It *seems* like I can lock the flywheel, remove the secondary cam chain tensioners, take the secondary cam chains of the sprockets, swap the cams, use the cam locking bar to set their timing, and reinstall the chains and tensioners.

Anything I'm missing?

CP
1998 XK8 Convertible
Marshall MI

I had a co-worker mechanic that worked with me at the dealer do the same thing on an AJ27 4.0 engine.
Don't remember if it was intake or exhaust cams but BENT VALVES was the result.
Lucky for him I had a worn NIKASIL/OVERHEATED engine with good valves so we swapped the bent ones and lapped them to the head.

We also had many shims to get the lash correct so CRISIS AVERTED.

Good luck.
Hope to valves dodged the pistons?

More fun - the cam caps were not reinstalled in the correct positions.

Assuming the plan for the exhaust cam swap works, can I replace the ones for the intake cams one at a time without removing the primary chain or tensioner?

Can the cam cap bolts be reused, assuming they were new for the rebuild? Or should I just replace them anyway?

Thanks in advance.

CP
1998 XK8 Convertible
Marshall, MI

@MotorMan When I first got it, I ran it for about 20 minutes without any mechanical noises, so I think the valves dodged the pistons, and I dodged a bullet. Compression tests on the two dead cylinders shows zero compression at TDC, but a leak down test on them is within normal range, so I think it is just timing.

CP

@motorcarman Wrong tag, sorry.

The cam caps go ZERO through NINE.

I had to correct an engine from another shop that put the caps ONE to ZERO.

I reuse the bolts all the time, no issues.

Time of death, 3:09pm
 

Whelp, it looks like it's the end of the road for this girl, at least in my hands. I scoped the cylinders, and the valves all looked good, but then......

https://cimg2.ibsrv.net/gimg/www.jag...ee7e482702.jpg

I'm guessing the mixed up exhaust cams prevented the exhaust gases from exiting the cylinder and melted/holed the piston. There's some slag on the cylinder walls as well. There is evidence of a small amount of valve/piston contact in another cylinder, but the valves looked visually OK:

https://cimg9.ibsrv.net/gimg/www.jag...2f14e7bab3.jpg

So, I'll either part it out, or try and sell it as a package with the spare AJ27 engine I have to someone with the desire and facilities to do an engine swap. It's a shame, because the rest of the car isn't bad, if a little worn inside.

Lesson learned? Don't start fixing the problem you *think* it has (low compression) before you find out the problem it *actually* has (swapped cams). I probably did that damage when I ran it last fall :(

On to the next one, older and wiser.

Oh - a follow-up to the cam cap issue: they are all correct, except for the 6 and 9 on the cam with the holed piston were reversed. I was reading the wrong numbers on the caps.

Incidentally, the cam in question looks like this, which seems weird:

https://cimg0.ibsrv.net/gimg/www.jag...3822d04185.jpg

Well, FWIW I've decided to rectify the cam issue and see if it runs. Talking with my Jag friends, there is consensus that the visible damage in the A3 cylinder is a) from the original timing chain mishap and b) not bad enough to prevent it running.

I'll post with how it goes when I get around to it.

I'd agree, since you noted that the valves now look OK, that they can't have caused the damage. I believe that the marks you see in the second pic. are machined when the pistons are made.

You can see them on the LHS in this pic:

https://cimg0.ibsrv.net/gimg/www.jag...a770de69a5.png

That is encouraging - thank you!

Well, I swapped the cams back, and she now fires up like a champ, and runs as smooth as butter. A bit smoky, which I am tracking down, but also this tappet-like sound - any of the boffins have suggestions? I can't locate the sound very well, it moves around like campfire smoke every time I move to where I think it is...

Video with sound

that sounds loud…get an extension or whatever else you can use as a dowel and see if any cylinders fail the test


https://youtu.be/BYWgZcyB0KQ?si=jphbB8olR0vL1VTJ

this is what wrong valve lash sounds like

I've located it with a stethoscope to the A bank, where the damaged piston is..

It sounds very top-endy, though, so I'm going to double-check the timing and also the valve clearances.

CP

Well, today I double-checked the tension on the exhaust cam chain (it was a little loose), and checked the valve clearances. A couple were less than optimal, but I wanted to see if the timing chain tension was the issue, so I re-tensioned the chain, re-torqued both sprocket bolts, and put it back together.

The tap is still there, and what's interesting is that I can hear the tappets separately when I rev it some, so it's not those.

I fear it is the damage in the piston at this point - unless there is something else I should try before throwing in the towel.

If it is bottom end, I need to decide if I want to drive it until it blows and have some fun out of it for my relatively paltry investment, or sell it as an engine rebuild project with very little else wrong with it. It fires right up, idles smoothly, throws no codes, and doesn't overheat.

It's all a shame, because there is so little else wrong with it :(

I have a 2000 XJ8L with a 2000 S-Type short block.
The heads and oil sumps were swapped to make an AJ27 engine from a damaged AJ28.
The AJ28 engine had a DROPPED VALVE SEAT and bent valves in #8.(I suspect an 'over-heat')
The piston has some dents on the crown but I took a chance and reassembled the engine as an AJ27.

The engine has been in my wife's daily driver for years and years. (50K miles?)

It has a noticeable 'piston-slap' from #8 upon cold startup but gets quiet/normal at operating temp.

I stopped worrying about the noise after a while and don't care anymore.

Runs and runs so I just leave it the way it is.

That's encouraging, although my tapping doesn't go away once it's warmed up...

I figure it can either sit for months waiting for a buyer, or I can drive it around a bit and see how it goes. I'm leaning towards sticking a plate on it and seeing what happens 🤷

It does need an alternator, though, so I won't be going far ..

Well, folks, she's a driver!

Scavenged the alternator from my AJ27 donor motor, replaced the upper and lower radiator hoses while I was at it, and took her for a blat along some twisties yesterday, on an unseasonably warm 63F day.

The tapping didn't get any worse during the drive, so I'm content to live with it for as long as it lasts. She revved freely, pulled hard with no additional noise or smoke, and drove at 60mph with no issues. Even the windshield washer worked!

Oil pressure gauge did suddenly drop to zero on the way back, but with full clean oil, and no accompanying noise, smell, smoke, or loss of power, and no oil in the coolant, I'm inclined to blame the sending unit rather than anything actually wrong with the motor. It *could* be starvation, but changing the sender first is a lot cheaper and easier than dropping the pan.

She's parked up for the winter now, but I'm so glad I got a run in first!