engine knoch

engine knoch

Postby 8520stephen » Wed Sep 13, 2017 2:17 pm

can any one give me some help/advise with my p4 100
5000miles ago I had the engine completely rebuilt,since running it in I have noticed a loud knocking noise when under load and when the car is started from cold,this goes when it is warm ie after about 2 miles.
I have retarded the timing and have had some success when the car is warm/hot,but when started from cold the knocking is still there I have been advised that the distributor may be faulty. I have hade the car for 37 years so am reasonably familiar with how it should sound and this is not how a Rover should sound
Steve Crossley
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Re: engine knoch

Postby Phil - Nottingham » Mon Oct 09, 2017 8:39 am

Was the oil pump rebuilt and the pressure relief valve replaced in the side of the block. Dizzies can knock terrible when worn especially the 25D6 but yours should have the DMBZ6 which is better quality.

Swapping the dizzy for a known good one may be useful before buying a reconditioned one
P2/P4/P5/P5B/LR's - EXJ 8**/2**8MY & others
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Phil - Nottingham
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Re: engine knoch

Postby djm16 » Thu Oct 12, 2017 3:35 am

Knocking has to be coming from one end of the conrod or the other, ie big end or pinking.

It would be very disappointing if it was a big end knock, but check the oil pressure anyway.

Pinking under load would be either timing OR compression / octane mismatch. I had a 95 that was similar. I am guessing successive head skims raised the compression because it ran fine on 98 but not on 91 octane. The symptoms were similar, pinking under load, regardless of how retarded. If the engine got hot enough, you could also see where the piston crown made contact with the head (shiny area)!

I agree with Phil, a worn dizzy may also be a problem. Take off the distr cap. Turn the engine over to open the points, then waggle the rotor arm to and fro and see if the points open and close by more than a thou or two.
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