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I have just recently rebuilt my 998 2nd over-size pistons and rings, new bearings, with new followers, new lead free seats in the exhaust valves, and new rocker shaft. It has developed a tapping noise and I just can't find the cause.
It is present when at idle and goes away when the rev's pickup from idle.
I've removed the rocker gear and disassembled, checked and everything looks good. Because it's a new shaft, it has a second feed hole at post number two, so I drilled and tapped this out to insert a blanking bung same as post one to ensure it was not loosing oil pressure through the hole. No change to the noise.
Did a compression test (cold) and with the same amount of cranking, they were 180, 170, 170, 180 PSI.
The motor runs exceptionally well with great power and no missing what so ever.
I've checked with a stethoscope and still can't locate the source. Checked all auxiliaries, (generator, front pulley, fuel pump, water pump, distributor, carburettor, clutch/throw out bearing) and all ok. Front/back, each side with no louder at any point than the other. Clutch depressed makes no difference so not the primary gear.
I've reset the rocker clearances multiple times with no change.
I've ran the motor with the rocker cover off and ran a 2 thou feeler gauge under each rocker in turn with no change with the noise.
It has been doing it for about 2600km with no other changes in performance or noises.
Can anyone suggest anything else before I pull the head and check the valve seats as that's the only thing I can think of for the next step?
TIA.
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