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Changed intake Gaskets, Now the engine is angry! Help? :(
Hello everybody. First... thanks for checking this out and for those of you that have helpful info to share, I appreciate it. I've lurked here for a while, but I can't find answers or ideas to my current issue. I'm pretty "wordy", but I want to provide all the info I can, since I know how hard remote-diagnostics can be.
Vehicle: 1991 C4 Coupe - L98
tl;dr - Did intake gaskets, now engine sounds like I've got something metal on metal clacking going on in the top of the motor.
Okay, so first off, it's probably worth mentioning that I was a mechanic for several years, so this is not the first intake I've ever replaced (though it is my first chevy shortblock). I'm also human, so I suppose there's always that chance to error... because something has clearly gone amiss.
So I had a bad oil leak from the back of the motor along the "China Wall", I believe it's called. Minus the smoke from under the hood at stop lights, I'd been enjoying driving the car for the past month with only a couple minor issues. 1, at idle the check engine light (lean) would come on, but go away when I got moving. 2. Under about 2/3rds throttle the engine seemed to surge a little, I suspected a fuel problem because it wasn't really a missfire, and 3. It was consistently a little hard to start, always started, but just took excessive cranking, again, another reason to suspect fuel in my head. So I picked up an intake gasket kit, some new Bosch 3 L98 specific fuel injectors from a guy recommended on this forum, a new factory fuel pressure regulator diaphragm/spring, and a new o2 sensor. Last week... I started the work.
Due to a wedding, my day job, etc etc, I had to do the work in bursts. Anyway... long story short, I tore it all apart and cleaned everything up. Put in the new gaskets, used the "Right Stuff", as recommended, for the front and rear lower intake seals, put everything back together using the FSM, torqued everything down. There were no "extra bolts", everything seemed fine. Minus painting the runners and upper intake, everything went back together factory.
*Note* I marked the distributor before and after removal, in relation to the rotation part and the base, but did NOT mark the base to the engine. This was an error on my part. I used pictures I took during the process, and my original marks to line it back up when I went back together. I'm fairly certain it is at the least very close to what it was when I removed it.
Anyway... to wrap it up, changed the oil, filled the car with coolant, swapped out the fuel filter (which was super clogged), and the 02 sensor, then started the car. First, the car started the easiest it's ever started, but immediately I began hearing a loud, quick thunking/clacking noise from the top of the motor. I quickly shut the car off. Wondering if I was just too jumpy, I tried starting the car 2 other times, and each time the very loud, quick thunking/clacking returns. I can record a short video if that will help? It's bad enough I'm afraid to let it run long... it sounds like (to me, but I could totally be wrong here) like either I have something in a cylinder bouncing around, or something it holding a valve open and the piston is hitting it (though... if I understand, the SBC is not an interference motor?).
Generally speaking, I think I was very careful about disassembly and reassembly. Other than the short time I was cleaning off gasket material from the lower intake, I had all intake ports plugged with paper towel (picture below of the only time I didn't, before it was fully cleaned off).
Any ideas or things I can check? I do have a bore-scope... but I just don't want to tear the motor down if I'm just being paranoid, but I don't want to damage the engine enough that I have to have new valves and the head redone.
Last edited by Lunchcopter; Apr 5, 2018 at 12:15 PM.
If something is bouncing around in a cylinder many times it will leave witness marks on spark plug. You might pull them out. Are all the brackets tight and not rattling?
If something is bouncing around in a cylinder many times it will leave witness marks on spark plug. You might pull them out. Are all the brackets tight and not rattling?
Ooo... good thinking. Tonight when I get home and grab that short video, I'll pull the plugs and see how they are looking and let you know!
Yes, I'm very certain the brackets are tight. I went over every bolt multiple times to ensure proper torque specs and general tightness.
Before I start it, I'd pull the plugs and borescope the thing. If it clears that check, maybe run it for a bit WITHOUT the serpentine belt? If it still makes the noise, I'd guess the problem is internal. If not, maybe it is one of the accessories?
I imagine you didn't touch the lifter retaining plate or anything right? I'd also check timing and firing order just to be sure... I agree with aklim, pull the plugs and run without the belt to eliminate anything accessory related.
Before I start it, I'd pull the plugs and borescope the thing. If it clears that check, maybe run it for a bit WITHOUT the serpentine belt? If it still makes the noise, I'd guess the problem is internal. If not, maybe it is one of the accessories?
I can certainly try the serpentine belt thing, but if it's an accessory, it went horribly bad while sitting in my garage for a week, which I feel is probably unlikely, but no reason I can't check.
Originally Posted by 84 4+3
I imagine you didn't touch the lifter retaining plate or anything right? I'd also check timing and firing order just to be sure... I agree with aklim, pull the plugs and run without the belt to eliminate anything accessory related.
No, I didn't remove the valve covers, and other than setting the upper intake on some clean rags to scrub the dirt off the top and let it air-dry for several hours (5+), I didn't do anything else to the lower intake.
I'll need to pick up a timing light to check my timing (that'll be something I've not done in a long time!), and I'll double check my firing order.
Thank you both for the input! I'll pull the plugs and bore-scope the sucker before I fire it up. Here's to hoping I find the problem, and to hoping it didn't already bend something that's going to take a bunch more work!
I can certainly try the serpentine belt thing, but if it's an accessory, it went horribly bad while sitting in my garage for a week, which I feel is probably unlikely, but no reason I can't check.
No, I didn't remove the valve covers, and other than setting the upper intake on some clean rags to scrub the dirt off the top and let it air-dry for several hours (5+), I didn't do anything else to the lower intake.
I'll need to pick up a timing light to check my timing (that'll be something I've not done in a long time!), and I'll double check my firing order.
Thank you both for the input! I'll pull the plugs and bore-scope the sucker before I fire it up. Here's to hoping I find the problem, and to hoping it didn't already bend something that's going to take a bunch more work!
As said before pull plugs that can tell a Lot if things got that far in and with plugs out blow some Compressed air in leaving room for things inside to blow out. You may have Dislodged a piece of Carbon and it fell in, or you lost a bit of gasket down the Head.
So pull the plugs and hope for the best, a Compression test could show if things are 1/2 way into cylinder
As said before pull plugs that can tell a Lot if things got that far in and with plugs out blow some Compressed air in leaving room for things inside to blow out. You may have Dislodged a piece of Carbon and it fell in, or you lost a bit of gasket down the Head.
So pull the plugs and hope for the best, a Compression test could show if things are 1/2 way into cylinder
Okay... so while my borescope is a bit limited in it's articulation, I just completed pulling all the spark plugs one by one and I have no signs of damage to any of them. I also can't see any damage on the cylinder heads (other than I could probably use some cleaner ran through there a couple times to clean up the soot!). Here's pictures from each one in case you all see something I don't. I didn't photograph the spark plugs, but they all looked the same... light brown, normal gap, no scaring, no chips, no dents. So I guess my next move is either go back through them and compression test, or do we think it's time for me to fire it up and record a video for you all to see and hear it?
- Oh, and I double checked my firing order wiring and that was correct... I need a timing light and I can check my timing... but will one of these engines kick and rattle like crazy if it's just a little off? I don't know how far off it is, but compared to my pre-removal photos, it looks fairly close, but I have no concept of if like, a millimeter turn changes the timing a whole bunch or not.
I would spin it over a few times with the plugs out on the chance if something is there it might blow out spark plug hole. Only take about 15 sec. Just unplug pink wire from distributor cap first.
If it started easily the distributor is in correctly and the timing is close. If the Distributor cap not seated properly it will cause the rotor to hit the terminals inside the cap. I did that once. It's easy to tell, pull the cap and you can see the marks where it was making contact.
For those suggesting timing is off. If distributor is seated and and clamp it tight. Why would timing that was close cause engine noise? Just asking
If distributor is not seated all the was down and is up about 1/8 " or so above manifold. The distributor gear has not engaged oil pump driveshaft. Engine can start and oil pump would not pump oil properly. Gear would be spinning just above drive . If this is the case do not force distributor down! Light pressure while someone bumps engine the gear and shaft will eventually align and distributor will drop in. Balancer can be turned also but make sure is out of ignition.
If it started easily the distributor is in correctly and the timing is close. If the Distributor cap not seated properly it will cause the rotor to hit the terminals inside the cap. I did that once. It's easy to tell, pull the cap and you can see the marks where it was making contact.
In my personal experience retarded timing tends to start easier. It doesn't sound healthy but does tend to fire right off... The cap seating is a good idea.
Could a tool or piece of debris have fallen into the valley when the intake was off? The pushrods do move quite a bit and could cause a great deal of noise if something is in there..
Okay, so first off, it's probably worth mentioning that I was a mechanic for several years, so this is not the first intake I've ever replaced (though it is my first Chevy).
I marked the distributor before and after removal, in relation to the rotation part and the base, but did NOT mark the base to the engine. I'm fairly certain it is at the least very close to what it was when I removed it.
Originally Posted by Lunchcopter
I'll need to pick up a timing light to check my timing (that'll be something I've not done in a long time!),
Any time you remove the distributor from an engine, you NEED a timing light attached to the engine when you first attempt to start it! Ignition timing is extremely important to keep from damaging a newly assembled engine! Your experience as a mechanic should have taught you that.
Changed intake Gaskets, Now the engine is angry! Help? :(
