Best Way to Get the Carbon Build-up Out of My Engine?

Rings are not sealingvproperly, indicated by wet/dry compression readings.

The "knocking" is hard to say if lower rod/crank or upper wrist pin, piston slap or valve train.

But, overall, not a good opinion of this engines soundness.

Bottom line.

Do you have funds to do a proper rebuild, or funds to find a new core?

Because, you can never run an engine into better condition, if it has problems.

Your engine is showing symptoms of problems.

 

I've got about $3k set aside for work I knew needed to be done this year. Don't think that'll be enough for a full rebuild though. I've kinda been expecting that this engine is gonna have to come apart to be honest. Not opposed at all to getting it done.

 

1. I have zero faith in "wet" compression testing. MAYBE when engines had gumption and sat up straight, (typical inline 6, inline 4, inline 8, etc.) the oil dropped into the spark plug hole could go around the rings to seal them. Once cylinder banks got lazy and leaned-over, (V-8, Slant 6 or Slant 4, etc.) all the oil would pool on the low side, you'd never be sure to get the high-side of the rings wet.

2. Merely adding incompressible oil to the combustion chamber would tend to increase the pressure readings unless there was a serious leak.

3. I have zero faith in recording "first hit" on the compression test versus subsequent "hits". You have no idea where the piston is in relation to the compression stroke. If that cylinder has just finished a compression stroke, it's got "power", "exhaust" and "intake" to build-up speed and inertia to provide a strong "initial hit". If the engine happens to stop where the cylinder under test is already into the compression stroke, the "first hit" is likely to be weak.

4. Almost nobody verifies their compression-tester pressure gauge for being accurate or repeatable. "Most" (not all) compression testers with a quick-coupler in the hose use an Industrial Interchange coupler and plug (Milton "M" style) I connect mine to my air compressor now and then, to verify that the gauges on the compression testers match each other, and the gauge on the air compressor regulator. This was important with quality gauges, now that Hazzard Fraught and lots of others are selling cheap junk tools, it's crucial.




5. Compression pressures vary with altitude and cranking speed, along with cam timing and about a dozen other less-important factors.

6. Used to be that GM specified both a standard for variation among cylinders (which was too generous) and a minimum "absolute" pressure of 100 psi. (which was too low, at least for non-high-altitude locations.) GM allowed the excess variation and the low pressure to minimize warranty claims, not to maximize power and efficiency. No idea what their current standards are.

7. Consider a cylinder-leakage test. Eliminates all problems with battery charge (cranking speed), oil in the cylinder, number of "hits", etc. A leakage test is terrific for finding WHAT is leaking--intake valve, exhaust valve, failed headgasket or cracked casting, or rings. 'Course, the cylinder-leakage testing comes with it's own issues.

 

So effectively beyond the dry compression test I'm not learning much of anything new besides how far oil can shoot out of my engine, gotcha lol. I think the results I've got might help give me a general impression, and since I'm thinking taking the top end apart is what's necessary anyways I can always leak test the valves and replace the head gasket after taking the heads off. My video definitely didn't capture how dirty that poor engine is, and it'll also be good to rule out as much as possible from the top end in regards to that knock, and while I'm there see about new rings. The real kicker is gonna be if the knock is in fact a rod bearing and the crankshaft is damaged. Otherwise I'm hoping I'll be able to handle all this without having to pull the engine since there is no room in the garage for that to happen. Barely have a foot on either end of the Riviera as is, and the other car hasn't run for 40 years unfortunately. I would much rather fix what is needed than rebuild the whole thing since I don't think I've got quite enough set aside for that, but if it's gotta happen then I'll figure something out.

 

I've used this method many times over the years . Even on engines that were not not running 100% . You would be surprised how well it works .

But not that much for the intake manifold . Valves and combustion chamber yes .

 

That random knocking sound is EXACTLY the same sound my ‘75 Electra made, it bothered me for the longest time, never did find out what exactly it was.
I towed a 5500 lb boat with the car, it wasn’t babied for sure, towed every weekend and numerous times up to North Bay Ontario, near 12000 lbs car and boat fuel, luggage, beer.
The noise/sound never got worse.
Oil pressure remained consistent
I’m thinking it was wrist pins, as the crank was machined, cylinders were honed, BUT, original pistons.
Cam was a mild RV type cam.
Valve train was silent.

 

That's reassuring then! Same as far as I can tell, the knocking doesn't get worse, oil pressure is still rock solid, no other indications that my engine is about to chuck metal. Once I get the top end apart I'll see what it's like, but I'm thinking I'll do what needs to be done for now and save more money for a full and solid rebuild later down the line. No sense putting more money than necessary into pistons and heads that I would probably want to replace anyways. Not ruling it out, but I'm glad to hear it's not just me with this issue. Thanks for the reply Mark!

 

Not while driving, only when I'm idling, and only really with the windows down. Otherwise it's hard to hear at all from inside the car.

 

GM has at least one bulletin on "carbon knock"; pour the water down the primary venturis, remove the combustion chamber carbon, see if the knock goes away. This is not a guaranteed fix, but it costs almost nothing except for two cents worth of tap-water, and your time, and perhaps an oil-change afterwards. Doesn't remove the carbon in the intake, but that's probably a minor issue that can be dealt-with now (or later) using the aerosol product I discussed earlier or some other product that trips your trigger. Then one oil change gets rid of all the nasty stuff.

You would be enormously better-off to find leaking valves or rings BEFORE disassembly. I don't know how you'd evaluate the ring seal AFTER you've ripped the head off. Easily accomplished with a cylinder leakdown tester that you're familiar with (Use the leakdown tester on a "Master Orifice" to calibrate your expectations, or perform some tests on known-good engines of approximately the same bore size as the one that's giving you trouble.)

If there are no leaking valves or excessively-leaking rings...why blow the time, money, effort, and enthusiasm on taking the top-end apart when you're not really fixing anything, and you don't have space to comfortably do the work anyway?

 

Spray not pour
Use a spray bottle

 

You could do that. Pack a lunch, you'll be there all day, and your hand will get cramps from pulling the trigger on the spray-bottle.

I drizzle a urine-stream of water back and forth between the primary venturis. If the RPM drops too much, I slow the flow. Starting RPM is 2000--2200-ish.

I figure that "if it's worth doing, it's worth over-doing", and "too much is just enough".

 

I used an old paint spray gun connected to my air compressor. Worked much easier. Sprayed a couple quarts then changed the oil. Helped clean it out a bit. May do it again.

 

Yeah after sleeping on it you're right. Like I said earlier there's no point putting a bunch of money and time into it if I'm wanting to rebuild later anyways, and based on the compression testing there doesn't seem to be any problem child cylinders. No use ripping the thing apart if pouring some water into it will do the trick anyways. Thank you for being the voice of reason Schurkey, I was too eager to rip into the engine I think. Still some things to do, my valve cover gaskets seem to want a replacement (quite sweaty looking around the top of the heads) and my thermostat housing is apparently leaking again after I replaced it last year. Will also need new plug wires since some of the new ones I put on 2 years ago decided to part ways with their metal contacts as I pulled them off for the compression test. I grabbed a couple pictures of the inside of the intake yesterday too.



This is the view from the secondary ports. The metal on the left must have been where I was picking at it after I took off the carb last time. Might be a bit much for Seafoam but worth a shot If I'm rebuilding anyways later there's gonna be a shiny new intake in the future.

 

Is there a chance that there is a flapper valve on the right side exhaust manifold between the manifold and pipe that is perhaps stuck shut?

 

I stuck it open after I got a new exhaust and could hear it opening and closing all the time getting on and off the throttle. Just took off the vacuum line and plugged it. If it's the heat riser valve you're talking about that is.

 

Yes. Just a thought.

 

EGR

 

Disconnected as far as I can tell, and probably has been for a long time

 

All is coming back together, except I'm not sure what to make of this. Rocker on the left side of cylinder 7 has a lot of lateral movement compared to every other one which doesn't move. Also missing a plastic piece covering a hole in the rocker arm.


Going to clean up the gasket remnants you can see up there no worries. Any ideas on the lateral movement?