Help me diagnose a noisy XK top end! (video link)

XK-Engine
1

Hi all,

Could the experts please have a listen to the video I’ve included and weigh in on a cause?

It started only recently, occurs sporadically, only when the engine is hot and goes away as soon as it’s off idle. The valve lash is perfect and the car is running BEAUTIFULLY so you can appreciate how frustrating this is.

My best guess is a tappet bucket that has worn beyond tolerance and is bouncing in the bore. I have had the camshafts out 3 times this week trying to find the culprit without any luck.

Even some guidance on how to diagnose the correct bore and how to fix? I have a collection of buckets here and I am worried I may have swapped the wrong one in the last time I had the head off. Buggered if I know which one.

I’m thinking a micrometre set to find the smallest bucket and replacing with the largest one I can find but even that is flawed.

Thanks lads. Any thoughts appreciated.

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Best as I can tell that’s definitely the sound of a tappet, whether it be too loose, or a tappet bucket sleeve’s come up and the cam is hitting it. You’ll have to pull the cam covers to find out more.

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I hadn’t thought of the guide pulling loose. Will investigate when I get home thanks. Makes sense if it only starts when it’s hot.

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It definitely sounds like a tappet. You don’t need to take the cams out to (hopefully) find the single origin. Take the cam covers off, and with the cam lobe pointed up and away from the tappet/bucket, use your two thumb tips ‘rock’ each bucket in the guide. Rock them in the direction the cam would ‘force’ them as it goes around, as the guide wears the most from the buckets sliding up and down with pressure against the left and right sides of the guide. Do this on all the buckets, and I bet you’ll find the culprit. I suspect the only real cure is getting the head rebuilt if you find that the guide(s) are worn, since you will need to take the head off to get the guides serviced.

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Thanks kassaq that makes sense, I hadnt thhought of the direction they might wobble in.

6

Sounds like it needs hold down brackets. Can be done insitu, but be careful to collect all the swarf.

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Puzzling that it goes away off idle. That doesn’t seem consistent with it being a raised tappet guide.

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8

Not saying its definitely the priblem, but mbI had a similar problem with my Mk7, it varied quite a lot, wasn’t always there. I think they can slide down under gravity while the engine is still warm.

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It could be a tappet guide and it would be obvious when you pull the covers. It could be a very worn engine. Yes, tappet guides can slide up and down, the noise comes and goes, but it will leave marks on the guides and is very loud.

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Ok. I’ve pulled the covers again, fiddled/manoeuvred everything relevant and can’t find a bloody thing.

The buckets look great and aren’t loose, the cam is fine, the guides are stationary and haven’t moved. (The engine was sort of warm).

Tomorrow I’ll take the shafts out again and inspect every bucket.

Frustrating!

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Grab each guide with a pair of channel locks and ensure they wont move.

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I thought it was running fast. Does it really knock at half engine speed? If not it could be many external things….

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The noise might just be a bit pervasive - but - have you tried listening with a mechanic’s stethoscope? I have one and have had good success finding various types of noises. FWIW. Or the good old log shaft screwdriver?.

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Robert
Run the engine with no cam covers for a few seconds to at least find out what side.
I also suggest lifting the rear of the car to get the engine level so the oil does not collect. get some rags ready for oil splatter.
I would definitely do this before pulling the head. Just do one cam cover at a time if need be.

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