Hello
A car I am looking at… 1976 XJC 4.2. Any comments appreciated. Many thanks
Nick
I don’t know, mine doesn’t knock like that. It used to once, if it’s metallic (hard to judge) than it might be a tappet guide, if not it either is excessive tappet clearance or something serious.
Ideally you could feel for a stake down kit via the oil filler, and if you feel nothing try to take the (exhaust has the higher probability) valve cover off.
Is it rpm-related or at half the engine speed, then it would be cams and probably the tappet guide!
Then I’d negotiate the price down for that reason and carefully knock the guide back down, camshaft removed, set clearances while you’re at it.
Of course it could be something completely different, but it doesn’t sound right!
Hearing it again it might simply be valve clearance. If I’m not mistaken it gets less loud after more oil becomes available? It’s not ideal but maybe the seller has some documentation. In any case it would mean a bit of work, but doesn’t sound fatal.
Assuming that the compression test is in “bars” and not “psi”. 9 bars = 130psi, 8 bars = 116…not exactly sure what compression should be on a '76 4.2, but that sounds low.
Would also be concerned about the “knock”. JS
I’d assume the vertical mark at 14 was meant to show the correct compression, but that comes out to about 200 PSI which is obviously wrong.
Thanks both. I took the plunge anyway. The vendor is going to re-set the tappets. It runs pretty well, i’ll take the risk…
Sounds a little bit like it has dropped the lower chain tensioner rubber block and the tensioner piston is rubbing directly on the chain. Usually this sounds as though no 2 cylinder inlet valve has a problem.
Not to brag, but… this is my (9:1) engine.
Pressures are in bar, you don’t want more than I think 10% difference between cylinders. MartinScherz has one cylinder that’s significantly low and the engine still runs fine.
Yours is not exactly good but it might well be your valve clearances? Either way work will need to be done. But then you have a good engine and know it!
Oh. The motometer tester is great. Did you test with engine hot or cold, did you open the throttle fully while cranking? That’s how we tested.
Hello again.
Thanks everyone. Bought the car and engaged in some cautious driving.
Valves have been reset. Engine sounds a bit better to me now…? Yesterday after 30 miles or so.
https://photos.app.goo.gl/m3E7kNaCtWFhGJN96
https://photos.app.goo.gl/P13uqfAWbKACn4f17
Had been a bit concerned about low oil pressure readings (about 25) but given general view on unreliability of gauge probably auxiliary gauge reading is more accurate and is better? This was recorded at the garage before tappets reset.
https://photos.app.goo.gl/ddQZtRgFYKfWSMGNA
Fuel consumption seems on the high side at low teens but hard to tell so far, no “clean” runs and some short distances. Not exactly an economy choice anyway but think I got high teens on my previous XJC.
Thanks all!
Nick
Hi @nickhill
I came accross your thread and watched the videos of your engine sound.
Did it get better since 2018? Did you find the cause of that tapping noise?
Hello there,
Thanks for the follow-up. Since this time I’ve had a few adventures and the car is near (I hope) to completing an engine rebuild (new pistons, tappets, valves, rear seal, gaskets…) and bodywork restoration. So I will be able to report back in due course !
Nick