Question about 1996 GMC Jimmy

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4.3 vortec engine , engine noise, knocking or tapping on top of engine, not when cold , but starts noise when it heats up, and gets louder as it gets hotter and hotter!!! Sounds like noise is in the center of engine!!!!

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  • Anonymous May 04, 2009

    i have a 98 v6 vortec it has allways had a timeing chain rattle at idle it is in a boat. it has 120 hrs run time. it seased i have it apart it spun a rod bearing closest to the oil pump i also found a badly damanged main 2nd from the front all other bearings look fine other than the bits of bearing material from the two that let go . the boat had 89 hrs i suspect maybe it has been run low on oil ie previous owner . also i found the drive gear on the cam that drives the balance shaft does not fit tight on the dowel. the hole in the gear is to big. i have two parts engines there the same thus cam timeing can be out. please help.

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The knocking or ticking is going to determine if it is in the top end, lifters, push-rod or rocker arm issue or the bottom end that would include pistons or bearings.
If it is a ticking noise, it will more than likely be a valve train issue.
If a knocking noise, piston or crankshaft related problem.

Attached is a web site that you can listen to a piston slap which is a known issue for your 4.3.
Listen to the noise and see if it sounds similar to your problem. A piston slap will generally sound as though it is coming from the central area of the engine.
Listen to the recording and let me know.
Regards,

Posted on Apr 19, 2009

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I just got a 2000 blazer with the 4.3L vortec (262) it sounds as if u r experiencing the same sound i was. i took it to a machnic because i thought it was the lifters. after having those replaced the sound was still there. i searched for months for answers and was finally tok it was the counter-balance shaft bushing. this was an annoying sound but i learned i could run it for a while with it like this. just make sure ur oil pressure is stable and put 1 quart of lucas oil and the rest a synthetic blend. let me know how it works.

Posted on May 04, 2009

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I wanted to add my recent experience to this thread...I recently purchased a 94 Silverado with the 4.3L balance shaft design. 139k miles and 180psi on all cylinders. Loud rattling noise just over 1K rpms. After tearing down motor.. inspected anything that would create this noise. Upon removal of intake and inspecting balance shaft.. I could grab shaft and rock it back and forth almost duplicating the noise. Then when timing chain was removed and balance shaft gears inspected.. the balance shaft drive gear behind cam sprocket had hollowed out bolt holes and dowel pin holes! After numerous new parts.. oil pump.. rod bearings.. balance shaft front bearing.. balance shaft gears.. timing chain/gears.. heads redone.. new push rods.. all new gaskets. it still makes the noise however its not as loud. There is a fix for the newer motors with a new timing chain tensioner kit but is not available for first gen years!. The new balance shaft gear was clearly tight on the dowel pin now and it made a difference but not completely. Read that.. GM indicated that this was not an issue.. well if the cam bolts broke from the cheap balance shaft gear metal banging away on them it will be an issue!.

Posted on Dec 06, 2014

  • 5 more comments 
  • bambam
    bambam Feb 20, 2015

    after driving this truck for about a month..I decided I cannot hande this rattling noise anymore! I am going to disable the shaft and install a different timing chain.

  • bambam
    bambam Feb 22, 2015

    update..removed balance shaft small gear..installed a single roller chain for A 99 4.3L and didnt feel any difference in idle vibration actually it was smooth! Noise is still present but 60% better..going to try new set of rocker arms before calling it quits! will do a motor for it later

  • bambam
    bambam Feb 22, 2015

    I ordered a double roller chain for the roller cam motors..IT WILL NOT FIT!! cam sprocket will grind into the block..you have to reuse the drive gear for the balance shaft.

  • bambam
    bambam Mar 04, 2015

    It appears that I had multiple noises inside this motor. I ordered new 1417-12 comps cam roller tip rockers..new rocker studs(make them adjustable) and permalocks by arp. I believe my remaining ticking noise is a worn rocker(s) arm. I have the nonadjustable style currently. I will update once I replace these items.

  • bambam
    bambam Mar 08, 2015

    replaced rockers and noise is still present..40mph..I am now leaning towards a piston issue..piston pin/side clearance etc.gm did a great job of installing second hand parts in these motors! other then cam/lifters..rest of valvetrain is junk..rod/main bearings look cheap..pistons arent quality made either.balance shaft design is useless. I felt slight difference in idle vibration after disabling shaft.I would suggest a high volume oil pump std for these motors! due to the wear in rocker arm lash and piston issues at a relatively low miles for motor.

  • bambam
    bambam Mar 08, 2015

    I wanted to add..I used a 99 single roller timing chain for this motor and it fit nice and tight! i originally replaced the stock chain with another and it clearly was junk. I noticed a big improvement from the roller chain.You cant use the chain tensioner on these motors either..wont fit unless you replace timing cover with newer version and then hope oil pan gasket fits too.

  • bambam
    bambam Mar 08, 2015

    it appears like my remaining engine noises are in lower end of motor..I am planning on replacing the short block (non-balance shaft) and retaining my top end.

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