1985 Other Chevrolet Models Engine knocking

CHAOTICSLUMBER

MEMBER
1985 CHEVROLET
V8
2WD
AUTOMATIC
87,000 MILES

Hello and thanks in advance for your time.

I have an 85 Chevy C30, 2 wheel drive, V8 7.4L.

The engine is running great but it is having a deep sounding knock which is resonating through the drivers side tail pipe as a tick/tap (independent exhaust.) I changed the push rods and did a valve adjustment but to no avail. There is also an engine vibration (felt into the cab) at the beginning of acceleration in park.

I have am looking to narrow down the possibilities so I have some direction to go. I have heard rod/main bearings but with the sound only coming from one side of the exhaust has me doubting. I have also heard "Collapsed lifters" or a bent valve.

I am looking forward to any advice or direction you may offer. Thank you again.

3 Replies

HMAC300

MECHANIC
48,601 POSTS

Knocks/tips/taps noises like you describe are very hard to diagnose over the computer. Take it to a pro where he can run some tests on it to try to centralize it. You may have a burnt valve, making the sound through the exaust.

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Wednesday, November 25th, 2009 AT 3:31 PM

CHAOTICSLUMBER

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2 POSTS

Thanks for your reply HMAC300, sorry I did not reply sooner but I have been sick. Also, I have been out of work for a few months so I am trying not to take it to a shop and do the work myself to save money.

I put the truck up on ramps, drained the oil and removed the pan. I tested the rod bearings and they all passed, but then I noticed a little wear/rubbing on the #3 piston skirt and when I grab the skirt I can move it a little side to side. So I figured that it was Piston slap due to the piston and/or cylinder wear.

If that sounds about right as to the possible noise, is there a quick fix solution or at least a low cost one? This is work truck so even if I got work, I would not be able to go to work without this truck so I am trying to get it back up and running a.S.A.P.

Thanks again for any advice/direction you may be able to offer.

Todd

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Saturday, December 5th, 2009 AT 3:35 PM

HMAC300

MECHANIC
48,601 POSTS

From what i've read of your reply it sounds as if you may have a scuffed piston which will make noise like a tapping. YOu can still drive it but will eventually need fixing. Of coure the fixing will be exspensive as it's gonna be a bore cleanup as well as a new piston, so you are probably talking a rebuuild/overhaul.

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Monday, December 7th, 2009 AT 11:35 AM