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I have a low freq knocking, about 6 to 10 knocks, very loud on startup until oil pressure comes up. Knocking quiets down and engine runs well with no knocking but then returns at idle as oil pressure decreases after warmup, but not as loud as on initial startup. I replaced main crank and rod brgs, rebuilt oil pump, replaced timing gears and chain, all lifters and water pump. Compression on all cylinders is about the same and within normal specs. No improvement in level of knocking. Do I need to suspect a bad rod, pins or cam bearings?

  • Welcome to the site. Did you check the rod to crank journal clearances (Plastigauge or micrometer) when you put the new bearings in? Did you refurbish the crank at all (polish the journals)? Have you checked valve train clearances? Considering it quiets down after oil starts pumping, I'd leave the pins and cam bearings out of it. – Pᴀᴜʟsᴛᴇʀ2 Jun 9 '17 at 11:48
  • I'm an idiot and should probably have my tools locked up from me. When I found the crank to be in very good shape (could not feel imperfections with my finger nail) I bypassed the opportunity to measure the fit of the bearings with plastigage. Good thing my time is cheap. Now I will open it up and measure and then get the crank attended to, get the cam bearings in and take a close look at the rods themselves. I got in too much of a hurry to do the job right. Thank you both for your help. I'll let you all know how things look after a while. Great site by the way. Vern – vnulk Jun 9 '17 at 16:59
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If you still have knocking, it means that there is too much clearance somewhere. While you replaced the main crank and rod bearings - did you have the crankshaft ground and the new bearings matched the new sizes or did you just put new bearings around the old crank (not the best idea).

A possible different solution is to fit a small electric pump to build up the oil pressure before starting the engine, but finding the real cause and correcting that is better.

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