The V8 Owners Forum -

Dear all,

a friend of mine has a Rover V8 that has started to develop a fault and we are trying to diagnose the cause.

The engine is a 1985 v8 with twin su carbs in a rover sd1. I dont know the mileage for sure, think it is about 150,000 ish.

When you start the engine from cold, it starts ok and settles down to a smooth idle. Oil pressure at idle (from the rover dash gauge) is 15 to 20 psi and then rises when throttle blipped.

However when the car has been left to idle for 15 to 20 mins the engine develops a knocking noise. See video below.



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If you rev the engine up, the noise doesnt go away, just increase with engine speed. If you leave the engine to cool down for about 5 mins and re start it, the noise is gone, until it warms up again.

We drained about 1/2 pint oil from the sump and found no evidence of metallic particles.

To me it sounds like something in the top end. It doesnt sound like main or big ends. I thought it could be a lazy tappet, but i cant understand why it would only do it when hot. Id have thought it would be the other way round, and then pump up when revs were lifted and oil pressure increases.

It could also be a little end bearing or piston slap, so as its warmed up the tolerances increase and with warm thin oil you get enough slack in a bearing to cause the knock.?

Basically does anyone have an idea what it might be and how to diagnose further before the engine has to come out and get pulled apart.

Im thinking oil flush, oil filter and oil change and try again.

Any help appreciated.

My guess is a leak at an exhaust manifold to head. For some reason sounds rather like heavy tappet. noise.

sounds like a tappet gone lazy, as oil heats up it thins out and leaks out the tappet, as the oil cools it gets thicker again and doesn't seep past the valve in the tappet.
what colour is the oil? and when was it last changed??

Oil was changed about a year ago, but this car is little used. I drained oil when it was cold (so I got the heavier scary looking particles if there were any) it wasn’t new looking and quite dark.

as you said earlier might pay to change oil and filter as its a cheaper option instead of pulling apart at present,

Maybe 20/50 thick stuff? Not sure what is in there at the moment.

don't start the dreaded rv8 oil debate lol
i run 20/50 fully synthetic in my 4.8 with crank driven oil pump with no problems

I’ve just read and interesting thread on another forum where someone has almost identical symptoms. As part of the diagnosis process he swapped the left and right bank complete rocker assemblies and the noise went. Might also try that even for a short term fix to confirm it’s not a small end.

You can proved if it is a tappet by removing the rocker covers and using a small feeler gauge with the engine running on each rocker, one by one. If it is a tappet, the noise will change. Best to use an old feeler gauge as it will get a bit chewed.