454 knock - looking for suggestions

[Tremek]

Hi guys, in my intro thread I had posted about the 1977 GMC C25 Sierra Classic my dad had given me last fall; 77,000 miles and still on its original engine and transmission. The truck had sat more or less for the past 4 years, and as my buddy and I attempted to revive it this past week we unfortunately found it started with an ugly knock - click here for video and sound - so now I'm unsure where to take this thing.

It's a 77 RWD with a TH400 and 4:10 gears, heads are 781s (which I see are desirable in some circles) but it's choked by a weak cam and low compression not to mention whatever's making that knock is Not Good.

I'm torn as to what to do; in terms of diagnosing the knock, it was there both before and after a Rotella 10w30 oil change, so we pulled all the belts off the accessories, still there, used a stethoscope to try and isolate where we could hear it - seems like it's loudest top-front-center of the motor, maybe under the intake manifold with a bias to the passenger side.

So we then took the valve covers off (hence why the covers in the video are bright shiny paint) and adjusted valve lash, no change. Interestingly the knock is louder while in park than it is while in drive - you can hear in the video as it stalls against the converter that the knock itself somehow seems quieter.

We were trying to figure out what it could be - dead lifter, timing chain slap, or rod knock - but I feel like given how loud it is I'm leaning toward the latter. The truck still seemingly runs on all 8 cylinders and will go into gear and drive. Is there any chance it could be a broken flex plate or loose bolt or something? Were that the case, doesn't make sense to me that it's loudest from the front of the motor...

What do you guys think it is, what would you do, etc? If it's rod knock, would you guys try to save this motor, or stab in something else? Ultimately I'd like to drive the truck and use it for truck things but I also like HP, but of course need to balance HP with the reality of a happy wife and not spending $10k on this moneypit right now.

 

[84 M1008]

Just spitballin, sounds like a wrist pin to me.

 

[Obwonkonobe]

If you have the means, I'd tear it down and give it a BASIC rebuild, maybe toss in a new cam/lifters and defiantly bearings. If it runs good other than the knock I wouldn't touch anything else

 

[MrMarty51]

Pull one spark plug wire at a time, with the engine running.
If the knock goes away on one or two cylinders, those are the cylinders with the rods knocking.
If the knock gets louder, then, it is a piston or wrist pin problem.

 

[Craig 85]

I just had something similar happen to me. I adjusted the valves, pulled a plug wires one at a time and even the mechanical fuel pump. No luck. My truck has supposedly been off the road since 1998. I know it's been non-oped since 2007. The PO said he had replaced the original 454 with another. That engine sat for an extended period too. My knock started last fall right and you could hear it upon starting the engine. I noticed this winter (35-45 degree weather), the knock did not start until the engine oil started warming. This took up to 2 minutes.

I didn't want to tear half the engine apart to determine what the issue was since it's an unknown origin motor and I'm rebuilding the whole truck anyways. I bought a rebuilt 454 from GM (3ys/100K warranty) and I'm waiting for a shop to install it. They haven't pulled the engine yet, but I hope to find what the issue was when that happens.

 

[shiftpro]

Tremek you have a great block and heads...
FYI, the 781 heads with a little porting and oversized exhaust valves will support 700hp.

 

[4WDKC]

I just had something similar happen to me. I adjusted the valves, pulled a plug wires one at a time and even the mechanical fuel pump. No luck. My truck has supposedly been off the road since 1998. I know it's been non-oped since 2007. The PO said he had replaced the original 454 with another. That engine sat for an extended period too. My knock started last fall right and you could hear it upon starting the engine. I noticed this winter (35-45 degree weather), the knock did not start until the engine oil started warming. This took up to 2 minutes.

I didn't want to tear half the engine apart to determine what the issue was since it's an unknown origin motor and I'm rebuilding the whole truck anyways. I bought a rebuilt 454 from GM (3ys/100K warranty) and I'm waiting for a shop to install it. They haven't pulled the engine yet, but I hope to find what the issue was when that happens.

you said it didnt do it when the oil was cold? Make me wonder if the oil was just to thin and could be what the OP is experiencing since he put 10w30 in what probably has had 15w40 all its life..

 

[Tremek]

With my truck, my dad told me he had either Valvoline 5w-30 or 10w-30 run through it since he got the truck in 1983. With that said I don't know if older Valvoline had appropriate ZDDP additives or not; he claims he didn't add additives. With that said, for a while he kept records:

You must be registered for see images attach

To rule out any obvious issues with the flex plate we pulled the inspection cover and nothing stood out. So we started it again and I pulled the #2 spark plug (front passenger side) and the knock definitely changes in tone and gets quieter - so per the advice above, makes me think rod knock.

shiftpro: yeah would love to keep this truck numbers matching, I had read on the 781s that they're worth putting larger valves in for a street truck like this, so along with higher compression pistons and an appropriate cam this thing could make great power.

If I don't want to break the bank - but get this thing back on the road in a way that it should run well and be quick for the next 10 years as a 3rd car/truck - can you guys help me figure out the different paths?

Minimal effort to get back on the road:

• Pull oil pan, inspect crank & rod bearings - if crank is not scored, might be able to just get away with new rod bearings on one, or all rods?
• New cam & lifters - since I assume it has a hydraulic flat tappet cam, I could either go with the same style cam or a hydraulic roller cam - thoughts on either direction? Considering it's still hampered by the very low 7.9:1 (assumed) factory CR, are there any cams that can help it even as-is without changing the pistons & rotating assembly?
• Is the process from there to put in new 10w30 break-in oil w/ additive, run it per the break-in instructions and then drain that, and then another 10w30 + ZDDP additive change and, maybe, good to go at this point?

Versus Building it:

• Strip the motor & yank it
• Send the short block off to a machine shop to be inspected, and if good, then bored .060 over for a 496/502 setup?
• Also have the machine shop clean up the heads, and larger valves installed (is it 2.19s and 1.88s that I see frequently?)
• Rotating assembly: Do I need or want forged? FYI I'm also in Colorado so will always be approximately 20% down on power versus sea level...
• Fuel injection & intake manifold: I'm assuming by this point I shouldn't (or can't) keep the stock intake manifold; I'd frankly like to make this truck EFI for ease of starting and also if I drive into the mountains, not having to worry about jetting etc. If I want to go EFI, what intake do you guys recommend, what EFI systems do you guys like, and is MPFI worth pursuing?
• Cam: As I'd like to build it so I don't have to get back in here or worry about additives, I think I'd like to go hydraulic roller cam/lifters. Other than cost, any reason not to?
• Timing gear: Has to match cam yes?
• Headers: I imagine just about any LTs would help this beast breathe?
• Transmission: I'd really like to get an overdrive on the truck. A 4L80e is appealing for durability and making highway driving more tolerable. Thoughts here?

Overall as much as I'd like to drop $6k+ into the truck this month I probably shouldn't. Is there a happy medium you guys would chase? Thanks!

 

[HotRodPC]

Unless it's the sound to the camera, and audio to my computer, that doesn't sound like a rod knock at all to me. I'll have to listen to it a couple more times to be sure, but it just don't sound rod knockish IMO.

 

[HotRodPC]

On 2nd thought though, I guess I will go with rod knock or at least crank driven knock rather than valve train knock. Crank driven as in rod knock, wrist pin or cracked flexplate. Reason I'll change my mind isn't because of the tone of the sound that's likely thrown off by cam recording to my computer playing it back, but the speed of the knock/tick. It appears to be a fast knock/tick. Cam and Valvetrain spin half that of the crank so it was a valvetrain knock/tick it would be a slower knock/tick.

 

[idahovette]

I haven't ever done this, but can you pull the torque convertor bolts, slide the convertor back, and fire the engine to see if that makes any difference? Don't know if there is enough room for this to be done.

 

[4WDKC]

With my truck, my dad told me he had either Valvoline 5w-30 or 10w-30 run through it since he got the truck in 1983. With that said I don't know if older Valvoline had appropriate ZDDP additives or not; he claims he didn't add additives. With that said, for a while he kept records:

You must be registered for see images attach

To rule out any obvious issues with the flex plate we pulled the inspection cover and nothing stood out. So we started it again and I pulled the #2 spark plug (front passenger side) and the knock definitely changes in tone and gets quieter - so per the advice above, makes me think rod knock.

shiftpro: yeah would love to keep this truck numbers matching, I had read on the 781s that they're worth putting larger valves in for a street truck like this, so along with higher compression pistons and an appropriate cam this thing could make great power.

If I don't want to break the bank - but get this thing back on the road in a way that it should run well and be quick for the next 10 years as a 3rd car/truck - can you guys help me figure out the different paths?

Minimal effort to get back on the road:

• Pull oil pan, inspect crank & rod bearings - if crank is not scored, might be able to just get away with new rod bearings on one, or all rods?
• New cam & lifters - since I assume it has a hydraulic flat tappet cam, I could either go with the same style cam or a hydraulic roller cam - thoughts on either direction? Considering it's still hampered by the very low 7.9:1 (assumed) factory CR, are there any cams that can help it even as-is without changing the pistons & rotating assembly?
• Is the process from there to put in new 10w30 break-in oil w/ additive, run it per the break-in instructions and then drain that, and then another 10w30 + ZDDP additive change and, maybe, good to go at this point?

Versus Building it:

• Strip the motor & yank it
• Send the short block off to a machine shop to be inspected, and if good, then bored .060 over for a 496/502 setup?
• Also have the machine shop clean up the heads, and larger valves installed (is it 2.19s and 1.88s that I see frequently?)
• Rotating assembly: Do I need or want forged? FYI I'm also in Colorado so will always be approximately 20% down on power versus sea level...
• Fuel injection & intake manifold: I'm assuming by this point I shouldn't (or can't) keep the stock intake manifold; I'd frankly like to make this truck EFI for ease of starting and also if I drive into the mountains, not having to worry about jetting etc. If I want to go EFI, what intake do you guys recommend, what EFI systems do you guys like, and is MPFI worth pursuing?
• Cam: As I'd like to build it so I don't have to get back in here or worry about additives, I think I'd like to go hydraulic roller cam/lifters. Other than cost, any reason not to?
• Timing gear: Has to match cam yes?
• Headers: I imagine just about any LTs would help this beast breathe?
• Transmission: I'd really like to get an overdrive on the truck. A 4L80e is appealing for durability and making highway driving more tolerable. Thoughts here?

Overall as much as I'd like to drop $6k+ into the truck this month I probably shouldn't. Is there a happy medium you guys would chase? Thanks!

Back in the zinc was in oil by default it has been greatly reduced since flat tappet cams are no longer in production cars. Rotella supposedly has enough zinc in it, i use Valvoline VR1 racing oil is available in 10w30. If your going to build it and add efi just find a running vortec 454 96-01 and put your heads on it.

 

[crpntr78]

Yes, that can be done.

 

[crpntr78]

I haven't ever done this, but can you pull the torque convertor bolts, slide the convertor back, and fire the engine to see if that makes any difference? Don't know if there is enough room for this to be done.

Yes that can be done.

 

[Tremek]

Back in the zinc was in oil by default it has been greatly reduced since flat tappet cams are no longer in production cars. Rotella supposedly has enough zinc in it, i use Valvoline VR1 racing oil is available in 10w30. If your going to build it and add efi just find a running vortec 454 96-01 and put your heads on it.

So if I understand correctly mk IV heads can go on a Gen VI block, but not the other way around? What would the advantage be of taking my heads to the Gen VI truck? Also, why 96-01? Looks like the 4L80e started being behind the 454 in '91 if my searching is right?