95 S-10 4.3 TBI knocking to beat hell

Gmorning fellow wrenches, I have a 95 S-10 with the 4.3 TBI "balance shaft" V-6, 5 speed and have been strugling with a demon knock in the engine that just wont go away. Here is the history...got the truck cheap
with engine noise with the intention of doing a V-8 TBI swap, got anxious and yanked the engine and set aside and started collecting V-8 parts needed to do the job, as time went by and as girl friends came and gone it was 3 years before I got back to it and fuel prices shot up. Decided to just stuff the V-6 back in it freshened up of course, noticed this engine was replaced or rebuilt at some point with machine shop stamps on the rods and crank R.010-M.010 and pistons @.030. I had the heads redone, new oil pump and timing set, I pulled main caps on lower assembly and plastigauged them and are still in spec. all bearings are good! Didnt pull the pistons but didnt see any sign of cylinder scoring still had great cross hatching and little if any ridge up top and did a quick check for skirt play through out the stroke range on all cylinders and couldnt feel any noticable side play and the wrist pins looked good. Reassembled and installed with new clutch, filters, and hoses and all gaskets of course and repaired or replaced vacum lines as need. Went through the throttle body and cleaned up, installed new temp, oil, map and knock sensors. Fired up and set timing to 0 degrees with the ecm control wire unhooked from dist as per manual. Drove like a dream for a couple days back and forth to work on the highway and what not in town monitoring all vitals and all checks great with no noises, decided I needed to take on a long range test drive for about 100 miles before taking it on vacation and all went well untill I got back into town at the toll both, the same knocking noise came back, under load, accelerating or with the A/C on and the knock sensor is picking this up making the timing go bat shit just as did when I got the truck. I did notice upon freshening this motor up that the timing chain was realy stretched considering the amount of miles it was showing on the engine inside as far as ware and tare. I pulled the timing cover and bingo the chain was stretched again. I installed yet another new premium timing chain set as per instuctions with the balance shaft marks where they need to be per the manual and no the newly stetched chain did not jump teeth, fired up noise still there. Hooked up scanner/engine monitor no codes or check engine light and temps, oil pressure and air fuel ratios and fuel pressure are where they need to be as far as factory specs. Im at a total loss/mind f*ck on what it could be not to mention the cash layout, yikes I should have stuffed the small block in it and been money ahead! Any ideas before I shoot it?
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On Wed, 22 Nov 2006 08:11:13 -0600, snipped-for-privacy@webtv.net (GERALD FISK) wrote:
If you are dealing with spark knock, the generation of knock control you have is limited on how much it can control it because it cannot retard below base line timing like new ones can. Secounf you are 30 over which means that you are running a even higher effective compression ratio than stock and 87 octane is very marginal at best in that engine (though some amnt to believe otherwise. When I bought my 89 4x4 burb new it wanted to knock badly at times on 87 and the only way you could get it under control was to set timing at 2 to 4 degrees ATDC but it was a slug and drank gas like no tomoorow was coming. I soon gave up on 87 octane for it and swithed to using 93 octane in summer and sometimes 89 in winter abd advanced static timing rto 8BTDC to. It ran great and MPG improved a lot and it still runs great today after over 180K miles now. People that ride in it are amazed at how well it still runs and how responsive it is and I have never seen below 16 MPG average on it in the driving it does today and on trips it is usually around 18 MPG give or take. You can keep fighting it but if it is spark knock, stop using 87 and your trouble will go away and it will not realy cost you more to drive (likely less) because engine will operate more effecently and use less fuel. I never get a knock signal using 93 octane on mine even with advance timing so it always has full sprak advance. When I take it to Colorado for a few weeks every few years I set timing at 14 BTDC (a old trick) while there and it runs much better than it would even think about doing with stock timing and 87 octane.
----------------- TheSnoMan.com
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Umm....I will have to say no on the high octane for the simple reason that I run midgrade in that vehicle based off of the numbers we hammered out at the machine shop on the engine calculator program, it stated a minimum octane rating of 86 with a comp ratio of 8.7-1 but I run midgrade in everything just to stay consistent, cylinder head CC's and the CC's on the piston dish at TDC didn't justify feeding it any higher octane or even midgrade for that matter. I have done a few intake gasket replacements and timing chains on post 87 GM TBI V-8 and V-6 where distributor R&R is or may be necessary and have always set timing per book which usually states 0 degrees TDC with ECM control wire unplugged as per the book and have never had this rear up and bite me. To ensure that the computer ramps the advance and retard up and down as needed based off of load and temp with the ECM control wire hooked back up of course a little trick I learned to test knock sensor is to get engine to operating temp and to rap the side of the engine block 'carefully with a hammer' while running at idle or reved slightly and you will hear it stumble a bit and it can be seen on a timing light. The noise Im hearing is a distinct deep sounding knock but bearing to crank and rod tolerances are are still well below maximum allowed clearance. Just to make sure it was not sucking hot air all the time I bypassed the heat riser tube off of the air cleaner to exhaust manifold as well and it had no affect. I have the poor guys at the machine shop completely stumped as well as my self, it just doesnt make any sense why it ran perfect for a few days and then the noise came back after a long range test drive. I have parked it for the winter and figured screw it its getting what it really needs, a small block....have a good holiday gents.
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Just a thought from an amateur:
You said that the timing chain was surprisingly stretched when you overhauled the engine, and that the new chain got stretched as well. Combined with your thorough testing of main, piston, and wrist pin bearings, this leaves me wondering if you might have a problem in one of the heads, which is heard as a knock, and places excessive load on the timing chain.
I think I'd go at it with a stethoscope to work out *where* it knocks.
-tih
--
Don't ascribe to stupidity what can be adequately explained by ignorance.

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On Thu, 23 Nov 2006 15:46:07 +0100, Tom Ivar Helbekkmo

You know when you thing of this the only thing that can cause this is a binding dritributor, oil pump or cam bearings. ----------------- TheSnoMan.com
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On Thu, 23 Nov 2006 07:40:06 -0600, snipped-for-privacy@webtv.net (GERALD FISK) wrote:

I wish O could hear it to make sure it is spark knock or other source. (Does it knock with timing lset lead left disconnected?) Also do not beleive you shop program because that engine needs more than 86 octane if it is going to have any kind of timing advance in it. I have a old Jeep 360 V8 with 8 to1 CR and it will mostly run okay of 87 but that and a old tractor with 7 to 1 CR is all I use 87 in because 9 to1 and higher sufferes with it. You might check EGR function because it dilute incoming mixutre and make less oxygen availble and retards knock some (and power too). My 89 TBI 350 that I bought new runs so sweet with 91 to 93 octane aset at 8 BTDC I will NEVER go back to low octane fuel it it even if gas a $4 + a gallon because to do so would hurt its current performance and MPG. When I used stock timing and fuel when new it downshifted outof OD a lot of hills, want to knock at times and was a slug on hot days and a different animal than it is today. Also might consider pulling the pan to inspect bearings if disconnecting timing set lead does not change the knock and remove it. ----------------- TheSnoMan.com
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GERALD FISK wrote:

Bad balance shaft bearing?
--
Steve W.
Near Cooperstown, New York
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I'm beginning to wonder if I dont have a bad wrist pin in a spot I couldnt see on one of the front cylinders, and yea we ran a scope up and down the pan rails and on each cylinder at the head and its definitely not early spark or predetonation noise, the noise is most noticeable near the center and right of the timing cover. And the balance shaft bearings were good and the bore that the distributor sets into the block was kosher no wobble there and dist bushing were ok. Hehe if I keep over analyzing this thing it may be like getting M.I.T. involved here and who knows what the conclusion would be....laterz
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