A knock, maybe?

[JohnV]

Need some opinions. Got about 600 miles on my new engine. Runs great. Idles great. It's a stock 350 TBI in my 87 Silverado.

When you put a load on it going down the road it just sounds like it's knocking. When I say 'load' just mean when I accelerate, give it gas. I just feel if it was rods or lifters messed up it would knock when idling. The guy who put the engine in for me said he primed really well.

Anyway, just getting some opinions. I may not have explained it very well... Lol.

 

[Dutch Rutter]

Need some opinions. Got about 600 miles on my new engine. Runs great. Idles great. It's a stock 350 TBI in my 87 Silverado.

When you put a load on it going down the road it just sounds like it's knocking. When I say 'load' just mean when I accelerate, give it gas. I just feel if it was rods or lifters messed up it would knock when idling. The guy who put the engine in for me said he primed really well.

Anyway, just getting some opinions. I may not have explained it very well... Lol.

How's your timing and what octane of fuel are you running? An internal knock most of the time you will hear it even at idle.

This sounds more like a fuel or spark knock. More commonly known as pre detonation. And should be fixed soon. Check the timing and possible turn it down a few degrees.

A quick video might also help us to ID it.

 

[JohnV]

Thanks for your response. I've got the timing at zero. I have advanced it all the way to 10. I've tried different octanes of gas. Even put some non ethanol in it. Still does it. The sound or knock is annoying. The truck does run really well.

I've thought about retarding the timing a little?

You hear it more clear after the transmission shifts to second. When the exhaust gets quite ya know. Thought maybe an exhaust leak as well. Had it looked at the muffler shop, they said I didn't, so. Of course while I was there I got some new flowmaster mufflers 40 series.... Lol.

 

[Dutch Rutter]

@JohnV most fuel knocks will only be audible at WOT unless your timing is way too high. 0° should not ping, it also should not run very well with 0° advanced. With that low of timing it should be pretty sluggish.

With my sbc I have 14° advanced and I run premium pump. No knocking, but there is alot of other factors there, compression build up etc.

If it only sounds like a knock when ANY load is put on, an exhaust leak would make some sense. They usually sound different then a spark knock and VERY different then a internal knock.

The "you hear it more when the trans just shifts" part makes me ask if there are any tight clearances underneath the truck like exhaust hanger hitting a shackle or something along those lines. This most of the time would also be heard at idle.

I would also be looking at my flex plate, make sure there are no cracks or warps in it.

Hell, even look for loose bolts.

Seems like we're missing something. That video would be a big help. Until we get more info we're really just spit balling. I'm not very knowledgeable about TBI systems so somebody else would have to chime in if I missed anything.

 

[Dutch Rutter]

It's also worth mentioning, to help locate and isolate an internal type of knock, be it a lifter or anything else. Use a mechanic type stethoscope and hear around the block with it running at idle. A long handle screw driver or block of wood with your ear to the end of it also works well.

 

[1987 GMC Jimmy]

Same line of thinking. I’d pull the flexplate cover and check for backed out bolts between the plate and the TC. Also cracks in the flexplate. If you have a vacuum cleaner, you can wrap a rag around the hose, stuff it in the tailpipe where it seals good, and listen for a sucking sound around the manifold, collector, etc. If it’s a good-sized leak, you can feel the air being pulled in. It’ll get hot quick so don’t leave it on too long. Torque converter chatter wouldn’t happen in first or second. Misadjusted valves could be worth looking into. Do you have good oil pressure and ample oil? U Joints good? The timing set, particularly the chain, could conceivably make noise if it got sloppy that quick, but going beyond speculation, a video would help.

The serial data on the computer would also show knock counts via the knock sensor so that would be an invaluable clue in ascertaining that it may very well be detonation or some other engine problem that’s “loud” enough to be picked up. A few knocks here and there are perfectly normal, but if you have a knock count in the hundreds, that’s a problem. A mechanic’s stethoscope would also be a good tool to have.

Haha, great minds think alike.

 

[Rusty Nail]

I like flexplate too.

 

[HotRodPC]

Yep, Check the flexplate for certain. I once bought a Camaro WITH A ROD KNOCK. I was 90% certain it wasn't a rod knock. I even confident enough I felt I'd drive it the 45 miles home on the freeway. The guy thought I was nuts. I said, I'll just chance it to hold on. If it don't, the closer I get to the house, the cheaper the tow bill will be and hope it don't trash the block when it lets go. It never let go.

I replaced the cracked flexplate and the freeze plugs in the back of the block since they were staring at me and easy access at that time and sold the car for 3x what I paid for it. Bought it for $500, sold it for $1500.

 

[HotRodPC]

Who built the engine? Were the rods resized? Did whoever build it, plastiquage every bearing cap? That's why you measure EVERY journal. If you're confident in your build, then you know it's NOT a rod knock.

How about hot tank and vatting the block before the build? I know a guy who re built his cuz he chewed up a couple bearings running low on oil. I told him, send the block to the machine shop and get it cleaned out. He didn't do it since he didn't have the block bored. It was at about 100 miles or so, I started to hear a slight rod knock right off idle. I rode with him to the machine shop for a 2nd opinion. Machinist said, without doubt, it's a rod knock. Told the machinist the story of the build. Yep, you left metal shavings in the block. It's chewed up the new bearings already. Took it apart and sure enough. Every bearing was chewed on. Had to repolish the crank too and it was borderline whether it should be used or not so he got a different crank. The original crank has already been turned .010/.010 from the first screw up. He didn't want a .020/.020 crank in it.

 

[JohnV]

Thanks everyone!
As mentioned with timing, I have it on 0° according to the sticker is why. Seems as though the computer adjusts the timing anyway usually to about 12 or 14.

I bought the engine from advanced Auto. The guy who put it in basically just replaced the engine. I always premium gas 89 to 92. The "knock" definitely comes from around flexplate area.

I changed the oil today because I've already been about 500 miles on new engine. It was recommended I do that. I'm not necessarily mechanically efficient so to speak....lol. I done a video going down the road I'll try and post it. Lol... So we'll see.

 

[JohnV]

File too large...ugh

 

[Dutch Rutter]

File too large...ugh

Uploading to youtube and then posting a link is usually how I do videos.

 

[HotRodPC]

Thanks everyone!
As mentioned with timing, I have it on 0° according to the sticker is why. Seems as though the computer adjusts the timing anyway usually to about 12 or 14.

I bought the engine from advanced Auto. The guy who put it in basically just replaced the engine. I always premium gas 89 to 92. The "knock" definitely comes from around flexplate area.

I changed the oil today because I've already been about 500 miles on new engine. It was recommended I do that. I'm not necessarily mechanically efficient so to speak....lol. I done a video going down the road I'll try and post it. Lol... So we'll see.

So what did this oil look like? Was a grayish or have any shiney slivers in it? How about the oil filter? Did you look around the top of the oil filter and down in it for anything shiney? Let's hope you didn't, but changing the oil and reading the end of the drain plug, the oil and the filter and good tell tale signs. This is also why a magnetic drain plug is good to have too. A little gray is ok for a breaking in of engine, but shiney stuff and to much gray is NOT good. With only 500 miles on a new engine, it should very gold and clean. Personally, I'd have left it in for at least 1000 miles. Non Detergent Oil is hard to find these days but is the best oil for doing break ins if you have the Zinc additives. That's another question? Did you use break in cam lube added to the oil??? You might be wiping cam lobes and that'll cause some valve train noise.

 

[C10MixMaster]

Need some opinions. Got about 600 miles on my new engine. Runs great. Idles great. It's a stock 350 TBI in my 87 Silverado.

When you put a load on it going down the road it just sounds like it's knocking. When I say 'load' just mean when I accelerate, give it gas. I just feel if it was rods or lifters messed up it would knock when idling. The guy who put the engine in for me said he primed really well.

Anyway, just getting some opinions. I may not have explained it very well... Lol.

To the best of my recollection on an 87 with tbi you have to disconnect a wire to set the timing so the computer is not advancing or retarding it. if it was set with the wire connected your timing could be way off.

 

[HotRodPC]

To the best of my recollection on an 87 with tbi you have to disconnect a wire to set the timing so the computer is not advancing or retarding it. if it was set with the wire connected your timing could be way off.

Yep, cuz the computer will just chase your adjustment around. You disconnect the wire so you can set the INITIAL TIMING like for when the computer is NOT in closed loop operation before being warmed up completely, then the ECM starts tuning the timing.