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Old 10-13-2020, 07:02 PM   #1
jack wingard
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Default Knocking on start up

On a cold start up there is a 30 second engine knock briefly. Where should I start to look?
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Old 10-13-2020, 07:44 PM   #2
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Default Re: Knocking on start up

Drop the pan and check for a worn rod or main bearing. They knock worse on start up until they get oil. Sometimes a worn/cracked piston will rattle for awhile until it warms up a little and expands.
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Old 10-13-2020, 07:48 PM   #3
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Default Re: Knocking on start up

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Originally Posted by jack wingard View Post
On a cold start up there is a 30 second engine knock briefly. Where should I start to look?
I'd start with a check of the main bearings, The rods get oil from the first revolution, not after 30 seconds which is about right for loose main bearings. Adjust them to 0.0015" and you'll be on your way for many more miles.
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Old 10-14-2020, 10:11 AM   #4
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Default Re: Knocking on start up

I once had a 302 engine that knocked like that for a few seconds. The fellow at the machine shop told me it was piston slap until the pistons warmed up and expanded. I dropped the pan, replaced all the rod shells with .001" undersize (oversize?) shells, knock went away.
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Old 10-14-2020, 10:36 AM   #5
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Default Re: Knocking on start up

I’m not a big fan of rushing in and taking things apart. If the engine runs good, isn’t smoking or using any oil, and is quite after 30 seconds?

I would do one thing first. Change the oil. Put in 20w-50 HD and one blue bottle of STP.

I have saved a couple of engines over the years from what some people felt needed a major overhaul, to many more happy miles. These cars are not as quite as your Ford Escape or your neighbor’s BMW.

Please no negative comments, this is just my opinion. Advice is free.

Enjoy.
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Old 10-14-2020, 10:49 AM   #6
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Default Re: Knocking on start up

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WHN 2X

I'll add to WHN, with the ignition key off, step on the starter for 10 - 15 seconds. Listen carefully as the engine sound will change as the oil from the pan is pumped up to bearings etc.. Then turn on ignition & start normally.

Diagnose from simple (cheap) to complex (expensive).
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Old 10-14-2020, 10:50 AM   #7
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Default Re: Knocking on start up

It's probably loose main bearings as Syncro909 says. I had an engine that did that, and leaked out the rear main like you wouldn't believe. It may be time for a complete rebuild.
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Old 10-14-2020, 11:20 AM   #8
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Default Re: Knocking on start up

A couple of years ago the engine in my Town Sedan started knocking at start up. I pulled the pan and found this lovely site. Not saying you lost a bearing but you may consider checking. All the "parts" were in the dipper tray so nothing showed in the oil.



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Old 10-14-2020, 04:45 PM   #9
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Default Re: Knocking on start up

WHN hit the nail on the head....rebuild an engine for what...to drive 400 miles a year?? Is this a daily driver.... up the oil viscosity, STP added and live with it for years and years I'll bet.
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Old 10-14-2020, 09:28 PM   #10
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Default Re: Knocking on start up

Its a simple matter to pull the pan and check it out. Should be done once in a while anyways. The bearings have wafer thin shims that you take out to tighten.
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Old 10-15-2020, 05:50 AM   #11
jack wingard
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Default Re: Knocking on start up

Thanks for all the advise. Over the winter I'll probably pull the pan and check things out.
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Old 10-19-2020, 11:52 PM   #12
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Default Re: Knocking on start up

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Originally Posted by eagle View Post
Its a simple matter to pull the pan and check it out. Should be done once in a while anyways. The bearings have wafer thin shims that you take out to tighten.
Exactly. We're not talking about rebuilding the engine, just adjust the shim stack to spec and off you go.
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