chevy 4.3 top end tap


Old 03-11-04, 12:14 AM
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chevy 4.3 top end tap

I have a 91 s10 blazer with an older 4.3 motor. Maybe a 87. I know that the push rods from my 91 motor were too short when I did the swap. The bottom end has 2000 miles on it now and has been bored .30 over with TRW flats. The top end is most likely over 100k. If I run it on the highway over 70mph or hard it starts to tap. It's not loud at all yet, but I can hear it. It will smoke if I pull away past half throttle, but not under slight throttle. No smoke during cruising. I figure the seals are bad and the valves or heads may be worn. These motors don't have valve guides do they? I plan on pulling the heads and putting new ones on. Just want to ask if my suspicions are correct. The lifters wouldn't make it tap would they? Should I worry about changing them too? I don't know if the guy that I bought the motor from changed them too. Anyway I can tell how worn they are?
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Old 03-11-04, 02:56 PM
Join Date: Apr 2002
Location: Pittsburgh,Pa
Posts: 2,417
Was this engine assembled complete with heads when you bought it?I've seen you posted other times about this engine something smells fishy to me.
Old 03-11-04, 03:57 PM
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It was assembled when I bought it. He told me the heads were not redone. When I pulled the pan to swap it for my 4x4 pan there was prelube in it. The bottem end had never seen fire. I looked in all the spark plug holes to check before I bought it. It's been bored. It didn't have valve covers when I bought it so I could see the heads weren't worked. It runs like it's been bored .30 over. I get 350 miles per tank of gas, I checked that twice. What's that, 20 mpg? Just has that tap after it gets warm and I run it hard. I figure new heads will fix that.

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