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Hi!
I've owned my 1981 K5 for 10 years (all stock and original except the paint)
the engine is getting tired, so I got one of the last OE replacements from my local dealer
p/n 19420194 this is as factory "stock" as they come for 350's.

My question is about oil I have not run the engine yet and need to follow the break sheet it came with as well as well.
My local Indy parts house I like to support has the following 10w-30 oils

AC Delco 10w-30 semi-syn (p/n 19419416)
Motorcraft 10w-30 semi-syn (forgot to write pn down)
Motorcraft 10w-30 diesel conventional
Total 10w-30 quartz 7000 semi-syn (p/n 220085)

Are these oils OK for flat tappet? I remember awhile back hot-rodders would say normal oil will chew up flat tappet cams and you need royal purple, redline, etc...
 

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‘01 Silverado 2500HD 8.1/Allison 5sp xcab long bed
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I had a flat tappet rebuild in my ‘95. I always ran VR racing oil (zinc rich) until it was no longer available. After that, I would run zinc additive with every change.
 

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I had a flat tappet rebuild in my ‘95. I always ran VR racing oil (zinc rich) until it was no longer available. After that, I would run zinc additive with every change.
Hi Cowboy, It's been years since I've been involved with engine break-ins but it seems I recall zinc rich for about 1500 miles. Is that right?
 

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‘01 Silverado 2500HD 8.1/Allison 5sp xcab long bed
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That sounds about right, but I never stopped using zinc rich oil.
 
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You'll wanna break in the cam with regular dino and ZDDP additive for 20 minutes between 2000 - 3000 RPM (or what your cam manual says) change the oil with the same combo and drive it for another 500 miles. Then you can switch to synthetic oil, or whatever you want. I'm running Mobil1 0W40 European full synthetic - it's higher in zinc and phosphorus than regular oils.
 
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