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SVRDefender90



Member Since: 24 Apr 2024
Location: Wiltshire
Posts: 4
United Kingdom 1990 Defender 90 V8 Petrol PU Auto Belize Green
Engine Knocking
I've just rebuilt a rover 3.9EFI V8 from scratch, it's in the defender and I'm turning the key for the first time but experiencing a deep heavy knocking when cranking.

During diagnosis I've unplugged injectors and fuel pump to be sure it's not hydro locking.
Compression test showed 160-175psi on all cylinders.
This isn't an oil pressure issue, all is well primed.
The engine was rotated by hand on the engine stand without issue.
The spark plugs have been checked incase they're impacting pistons but there's no contact.
If all spark plugs are removed (no compression), there is no knocking and it sounds perfect. The knock returns with just a single plug inserted into any cylinder and only on the compression stroke. Interestingly with 8 spark plugs inserted, it develops into a rhythmic triple knock, instead of a logical 8.

Any suggestions would be incredibly appreciated!
Post #1057576 16th Jan 2025 6:21pm
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blackwolf



Member Since: 03 Nov 2009
Location: South West England
Posts: 17495
United Kingdom 2007 Defender 110 Puma 2.4 DCPU Stornoway Grey
Big end?
Post #1057579 16th Jan 2025 7:14pm
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SVRDefender90



Member Since: 24 Apr 2024
Location: Wiltshire
Posts: 4
United Kingdom 1990 Defender 90 V8 Petrol PU Auto Belize Green
Re: Engine Knocking
blackwolf wrote:
Big end?


I wondered that but you'd think it would only show on the big end that has the issue, but I can put a plug or even a compression tester in any hole and get the knock.
The whole engine had a complete set of brand new bearings after the rotating assembly was balanced.
It had some new pistons machined which I was suspicious of, but the knock is too heavy for a piston slap on cranking I'd imagine.
Post #1057580 16th Jan 2025 7:18pm
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