Hi everyone,

Starting a new thread for my rebuild project - 2015 Range Rover Supercharged, 63k miles.

The car has been battling a persistent misfire on cylinder 5 (sometimes cylinders 6–8 join in) during cold starts.

Long story short, the high-pressure fuel pump (HPFP) failed at some point. After replacing it along with all injectors, coils, and spark plugs, the issue persisted. I’ve done:

• Leak-down test – passed
• Head leaking test – clean
• Smoke test – no issues

Compression test showed 117 psi on cylinder 5 vs 125 psi on cylinder 1, and cylinder 5 pressure was building up slower than the others.

At this point, I decided to pull the engine and do a full rebuild - my first one, by the way.

I’m starting this thread since I’m sure I’ll have plenty of questions along the way.

Here’s the first one:

Do these camshafts look damaged or are they still serviceable?

There’s some visible wear and a few lines/spots.

 

From what I can see, I would say the camshafts are good. The head bearing surfaces could use a little bit of dressing up as the scratches do appear to be able to be felt with a fingernail. But, I would also say that because you have no scratches going to the edge, all should be good to rebuild as is. I would say to replace the caps for the camshafts more for assurance than anything. That will help minimize any total play that you may have also.

 

Thanks for your input. I’ve read in multiple places that the cylinder head and camshaft caps are machined together, so they’re not interchangeable.

 

Was the timing done when the fuel pump was done? I've seen some with bank 2 misfires on cold start and low compression when the cam timing isn't setup properly. The topix procedure is not the most clear. Probably doesn't have internal issues unless it was overheated.

 

Correct, they are bolted on and bored, so you cannot just swap them without machine work. They look fine to me based on all the engines i've opened up, if you have any head work done, be sure to set the clearances properly with the shims, many shops do not if they haven't dealt with these engines before. It's a bit tedious to assemble the cams, measure, then remove to replace shims and repeat, but getting it wrong will cause far more trouble.

 

The main timing was fine, no timing codes, and live data looked normal. The misfire has always been on cylinder 5, which is also the one with low compression (117 psi).

When I removed the valve covers, the driver’s side had noticeably more scratches on the camshafts. The timing still looked okay overall, though the driver’s side timing chain was slightly stretched, and the exhaust cam was off by about one degree. I was still able to fit the (Chinese) camshaft locking tool without issues.

If it were a timing or cam phaser issue, though, wouldn’t it cause misfires on multiple cylinders instead of just one?

 

Have some updates:

I removed the bank 2 head (the one with the misfire). The head gasket looks fine - suspiciously fresh, actually. Another interesting thing I noticed is that the exhaust gasket has a date stamp from 2022, which makes me think either the engine isn’t original or it’s been out before.

I also spotted a red marking with a date on the block - I’ll add a picture of that below.

I’m also attaching photos of the cylinder walls, rod bearings, pistons, and crankshaft.

Could someone please take a look and let me know how bad things look?

One more question - if I end up needing oversized pistons, does that mean I’ll have to go oversized on all cylinders, or can it be done individually?

 

It appears the engine has been overheated at some point, or antifreeze has been mixed with the engine oil.

It would be best to replace the engine, or at least the block.

Here is an AJ126 that was overheated causing head gasket failure. Note the slight scoring on cylinder 6 in the picture.

 

Another update:



I’ve removed both heads, all pistons, and the crankshaft.



All the pistons and cylinder bores look pretty much the same. There’s some wear on the crankshaft - a few scratches that I can barely feel with my fingernail.



In one of my earlier threads, I mentioned finding some shiny metal pieces in the oil filter of unknown origin. Interestingly, I found similar pieces inside each passenger side(the misfiring one) exhaust port - picture attached.



I thought they might’ve gotten trapped there when I removed the manifolds, but they look exactly like the ones I found in the filter. Now I’m wondering - could the block or something else be flaking or peeling, and those pieces ended up in the oil system?



And here’s a weird one - I found something that looks like a piece of a brush bristle stuck to one of the main bearings. I didn’t see any abnormal marks on the corresponding journal though.



Next step will be to bring the block, crankshaft, and heads to the machine shop to see if everything can be cleaned up and polished without going oversized.

 

That tag on the outside of the block is an overheat indicator, and sign of a previous rebuild. So this engine has been opened up at least once before. Hard to say what was done, as you aren't allowed to rebuild these according to the workshop manual. I hate to be one of those people but I think at this point the cheapest/safest way is to look for a good used engine.

 

I don’t have experience dealing with overheated engines, but I’m curious - what makes you so sure that this specific mark is from overheating? I’ve checked a few used engines online, and some of them have similar tags, which to me look like something added by a shop for warranty or tracking purposes.
Until a couple of days ago, I was planning to bring my engine to a machine shop, but after a closer inspection, I’m almost certain the pistons aren’t original. So at least on that part, you’re absolutely right - the engine has definitely been opened before.
Considering all the current damage, I’ve decided not to put more money into rebuilding it and instead put that toward a used low-mileage engine.
I found a 2014 Jaguar XJR engine with 46k miles for around $5k, which should arrive in about a month. Hopefully, it’s in good shape. Based on my research, I should be able to swap the oil pan, wiring, and sensors, and it should fit right in.

 

From my time replacing engines, those little round tags are just that, they have a material that will melt if the engine overheats, but not under normal temp ranges. Done for warranty tracking on used engines/cylinder heads. Doesn't mean it has already overheated, just means it has been rebuilt before or was sold as a used engine at some point. If it's still intact, it shows that it has not been overheated since it was applied, which is a good thing.