Hello, I have been trying to track down a fairly loud rattle on cold start.
Symptoms:
You can discount ‘lifters’ as the engine has solid cam adjusters so nothing pumps up with pressure on the valve train.
I would start by getting a mechanics stethoscope and probing the engine on start up. If you can record the sound and post it to YouTube with a link that might give us something to work on.
Just another thought, does the oil filter you have on the engine have a good anti drain back valve? It could be that the oil is draining out of the system while stopped?
Ok I thought as much about the lifters, I have a mechanics stethoscope, i have tried to pin it down a couple times with no luck but i will continue to try. I too wonder about the drain back valve in my oil filter, I believe i have a generic purlator filter, so I have a Bosch replacement sitting on the shelf that I have not tried yet, the spec sheet says the Bosch has an anit-drain back valve. It seems to me to be an oil problem, like the top end is not getting enough/any oil pressure for the first few seconds of a cold start. And the fact that it barely does it if i turn it off and restart points to this as the issue, i just dont know what is causing it. Maybe the oil pump is losing its prime?
That’s another possibility (does the anti drain back valve cover this?)
What grade of oil are you using?
I’m not sure if it does, just a guess. as for oil I am using Castrol 20W50 and I live in Southern California, so it should be perfect for my temp range.
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The mere lack of initial lubrication should not, in itself cause noises as described, William…
Unless standing for some time residual oil will persist throughout, and provide initial lubrication - as it does noiselessly for most (all?) of us with no specific issues.
In addition to the other good points raised; it may be piston slap - brief, until the pistons settle? Chain rattle due to a tensioner problem should be sort of detectable by location, using stethoscope - though the nature of noise propagation makes precise location difficult anywhere in a car…
The oil warning light is triggered at some 3 - 5 psi - which is adequate for bearing lubrication, but may be inadequate where higher pressures are needed. You could carefully time oil pressure build-up - just to see if there is any relation between the pressure and noise…
Piston slap is caused by wear/ovality of piston(s) - in early stages lasting briefly until heating reforms the piston(s). Questions arising here is whether piston(s) were properly oriented when installed - so when did you first notice the noise?
A compression test should be run, engine cold as usual, more as a routine - piston slap does not really interfere much with compression. It is fairly innocent, an irritant, up to a point…
Frank
xj6 85 Sov Europe (UK/NZ)
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My XJ6 is a Series 1. On occasion it might have gone a month without a drive and with all the oil back in the sump it perhaps clattered for a few seconds. In the finish I changed the oil filter head to a Series 3 unit and fitted a good quality anti drain back filter - now silent on starts, even with long durations between drives. I listen each morning to my neighbour’s 8 year old Honda rattle up to idle revs - he buys cheap filters with ineffectual or nonexistent anti drain back valves. Can’t be told. Paul
Interesting, I am not sure when this issue started, but it just did one day, the car sits a lot, it had been sent to a junkyard but we “saved” it. It seems to correspond to oil pressure, the second the oil pressure gauge reads above 40 psi it goes silent. I have looked up piston slap videos and do agree that it sounds similar but it goes away too fast I think. I am going to try to get my stethoscope down to where the bottom timing chain area to see if I can pin point it.
It sounds like big end bearings to me, I doubt that it’s an easy job to drop the sump.
I doubt it, Oil pressure is normal at idle and rises normally when the engine is revved. Which if I am not mistaken would not happen with worn crank bearings. generally, you would get much lower oil pressure when they are worn badly.
As promised a video clip of the sound. Pardon the slipping smog pump belt. you can hear at about 0:17 the sound stop abruptly and when I stop and restart the engine it doesn’t do it at all.
Google Drive link: https://photos.app.goo.gl/iLjJ8KVtbTJbYh58A
Perhaps it’s the bottom tensioner. If it’s not properly latching in the spiral ratchet (which accommodates chain wear) it may take a decent level of OP to take out the chain slack. I had this on my Mk2 - a previous repairer had not released the spring after fitting the tensioner meaning the slipper foot started from rock bottom at each engine start. I should, of course, be up the spiral per chain wear. I had significant chain noise until I remedied the problem with new chains and tensioner. FWIW. Paul.
I tend to agree with you, It seems to be the only logical answer with the symptoms that have been presented. The engine is not coming out any time soon so I will just have to live with it, it is a annoying noise but I don’t expect it to cause too much harm leaving it the way it is.
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I second that, William - whatever the cause it is very unlikely to need urgent action…
Frank
xj6 85 Sov Europe (UK/NZ)
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I bought the Mk2 at auction and it came with a “lower chain rattle” dated diagnosis in the provided sheaf of papers. That was some 5,000 miles and several years earlier than my purchase. The XJ6 is a much easier proposition for engine work than the Mk2. Even on a Mk2 all can be done with the engine in the car and in my case - the head remained on. Paul