knocking sound in engine- chevy C1500

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PKNZ
knocking sound in engine- chevy C1500

Post by PKNZ » Sun Jan 12, 2014 3:49 am

Hi
I was wondering if you could suggest how to diagnose a recent problem. I have a 93 chevy truck C1500 350 V8 with 4l60e 4stage auto 2wd. just got home from 150 mile trip (warm eng) and noticed when I stopped to park I could hear a dull light knocking from what sounds like the rear bottom end of engine. It is only there when the engine is in gear when I put into neutral it goes away. Started eng cold this morning no knock unless I put into gear D or Rv cant hear while driving only when idling in D eg when stopped at lights.engine has had oil change and service 3000 mls ago and have had no problems before this noise started.I have checked trans fluid hot in park levels to spec clean and no odour. No fault codes,and revs perfect with no knocks rattles or ticks. issue only apparent as described. Do I start to think bigend ,crank bearing (Ive heard that before) or could it be in the transmission I have recently thought I could hear a high pitch noise similar to a heater fan spinning coming from the fire wall area? Hoping you may shed some light on what to look for so I can determine if Im up for an eng rebuild or transmission. Truck has done 196k mls but dont know history of eng ie rebuild etc.No smoking or clicks from top end no oil leaks was running like a charm well serviced and looked after truck. would appreciate if you could suggest any process to determine cause

Many Thx
PK

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butch
Posts:90
Joined:Mon Dec 23, 2013 4:14 pm

Re: knocking sound in engine- chevy C1500

Post by butch » Tue Jan 14, 2014 4:48 pm

Your truck may have a cracked flywheel. They can act funny like your is. Sometimes they will knock only in gear at idle, then when you give it gas it will go away. Sometimes the opposite is true. It is also possible your truck has a lower end knock or piston slap. With any load on the engine, the noise can go away with a piston slap. Have never had a transmission make a knock noise like that.

Use a stethoscope to see if you can pinpoint the noise. You can also remove the flywheel inspection cover to see if it gets louder or even look for a crack in it.

PKNZ

Re: knocking sound in engine- chevy C1500

Post by PKNZ » Wed Jan 15, 2014 5:13 pm

Hi Butch,
Thank you for the reply it would seem as though the noise is centred somewhere around #6 Piston definietly lower end changed oil and filter as although only 3k since last done its been 14 mnths ago(just read service label) so may have been a bit thin. engine runs dead smooth with no engine mount shake at idle purrs like new revs to 5200rpm without issue and returns to smooth idle.The knock does appear intermittent, a lot quieter than before but still only in gear, no knock on cold start up and idle and nothing heard increasing slowly all the way thru the rev range so I assume its when its under load hence noise goes away my prior experience tells me if its piston slap its probably from old age like me and may keep going without any major concerns just not sure to ignore if it is the start of a journal bearing on the way out. Do you think it would be safe enough to wait and monitor before jumping in to a rebuild? I guess Im trying to reassure my self not to be overly concerned at this stage and your comments have probably ruled out the tranny as being the culprit. So thanks for the feedback thus far.

PK

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butch
Posts:90
Joined:Mon Dec 23, 2013 4:14 pm

Re: knocking sound in engine- chevy C1500

Post by butch » Fri Jan 17, 2014 6:10 pm

Your welcome. It does sound like you have a piston slap problem. The fact that it is not consistent kind of rules out a main bearing or rod bearing. They will knock every revolution of the engine no matter if under load or not.

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