GT 40 Muffler Explosion

[Emil]

I looked around and couldn't find any other posts super similar, so here's how my weekend went:

Took the boat out on Havasu (2000 SAN) and it was running fine, except for a hesitation/sputter at speed. Has been sitting for a while so I thought maybe a little bad fuel/gummed injectors. Drove it a little longer and it died on me. This is where it gets interesting. I pressed the schrader valve on the fuel rail and found out there was air in the line, the fuel came out as a spray, with a little air hissing toward the end of releasing the pressure. I tightened all the fuel connections all the way back to the tank, but since the second schrader (the one on the FCC that represents the low pressure fuel pump) did NOT have air in it, I thought it must be coming from the rail or injectors.

I tried starting it again and as the title says, the muffler exploded. Top came right off and fiberglass pieces went everywhere. If anyone has any advice I would love to hear it. Going to try to straight pipe it tomorrow to see if it will start that way, and then begin diagnosing the air in the fuel.

Also, for context, I have always had a slight running rich problem, so I can understand how less-than-burnt fuel ended up in the exhaust.

[Emil]

Update:

I adjusted timing and it fired right up. So timing was obviously the issue, but since this happened in the middle of a run, does anyone have any idea how it could have un-timed itself? Mind you, I only mean ignition timing, the valve train is still timed, so the timing chain must not have jumped.

My current theory is a worn out distributor clamp, which allowed the distributor to turn and move itself out of time. I would appreciate any input on this!

[bturner]

Never heard of a warn clamp, loose clamp yes, but not warn clamp, no. With a high hour boat and bad maintenance, maybe a loose timing chain or one that has slipped a tooth but that would be rare on a marine 350 chevy as they should have metal gears and a steel timing chain. I would also expect to see other running issues with a loose chain as the timing would tend to change depending on load. Odd that it would just change if no one had touched it in in years but you never know.

This comes from the Brave Browser AI (god, have I really let myself get to this?)

Diagnosing Loose Timing Chain

Based on the provided search results, here’s a comprehensive guide on how to diagnose a loose timing chain: Symptoms:

1. Unusual noises: Listen for rattling, clattering, or slapping sounds coming from the engine, especially when idling or at low engine speeds. These noises can indicate a loose timing chain or chain guides.
2. Engine misfires: A stretched timing chain can cause valve timing issues, leading to misfires, rough running, and decreased engine performance.
3. Poor engine performance: A loose timing chain can affect valve timing, resulting in decreased power, rough idling, and poor acceleration.
4. Check Engine Light (CEL): A diagnostic trouble code (DTC) may be stored in the engine computer if the timing chain is loose or stretched.
5. Engine won’t start: If the timing chain breaks or jumps time, the engine may not have compression and won’t start.
6. Engine overheating: In rare cases, a loose timing chain may cause the water pump to malfunction, leading to engine overheating.

Diagnosis Steps:

1. Visual Inspection: Look for signs of wear or damage on the timing chain, guides, and tensioner components. Check for excessive slack or play in the chain.
2. Listen for Noises: Perform a thorough listen test while the engine is idling or at low speeds to identify unusual noises.
3. Scan Tool Analysis: Use a scan tool to read any stored DTCs and check for any engine performance issues.
4. Compression Test: Perform a compression test to identify any cylinders with low compression, which could indicate a timing chain issue.
5. Tensioner Check: Inspect the timing chain tensioner for proper operation and adjustability.
6. Chain Guide Inspection: Inspect the timing chain guides for wear, damage, or misalignment.
7. Chain Stretch Measurement: Use a specialized tool to measure the timing chain stretch, if available.

Common Causes:

1. Chain Wear: Over time, the timing chain stretches due to heat, vibration, and wear.
2. Tensioner Failure: The timing chain tensioner may fail to maintain proper tension, causing the chain to loosen.
3. Chain Guide Failure: The timing chain guides may break or wear out, allowing the chain to jump teeth or become loose.
4. Low Oil Levels: Insufficient oil levels can cause the timing chain tensioner to malfunction, leading to a loose chain.
5. Age and Mileage: Timing chains can fail due to age and mileage, even if properly maintained.

Conclusion:


A loose timing chain can cause significant engine damage if left unchecked. By recognizing the symptoms and following the diagnosis steps outlined above, you can identify and address the issue before it becomes catastrophic. Remember to always consult a qualified mechanic if you’re unsure about diagnosing or repairing a loose timing chain.

[Emil]

I'm still skeptical that the timing chain would have any issues. First because the compression is still perfectly fine. Second, because retiming just the ignition fixed the issue. If the valve train had jumped time, resetting the timing with the distributor should do *nearly* nothing I would think. On top of all that, the distributor and clamp both had shiny spots that were longer than where they should have contacted, which seems like they were rubbing loosely to me.

Maybe you're right and the clamp wasn't tight enough, but it was really tight when I pulled it out, and I doubt the bolt was bottoming. Would I be crazy to put a silicone/RTV/loctite between the clamp ant distributor (and the threads too I suppose)?

[jpwhit]

Would I be crazy to put a silicone/RTV/loctite between the clamp ant distributor (and the threads too I suppose)?

That would be a bad idea.

I doubt your issue is related to the timing chain for the reasons you stated in your original post. The issue wouldn't go away by resetting the ignition timing if the chain was causing the issue.

I'd suggest getting the timing set right, which it sound like it is, and then putting reference marks on everything associated with the distributor that could possibly move. That would include the body of the distributor to the clamp, clamp to engine, the rotor with engine at TDC to the distributor housing, the base plate in the distributor to the housing. There a fair number of places in a distributor where things can slip / move depending on how the distributor is designed and whether various parts are aligned by pins or press fits.

Once it's marked, first try twisting the distributor and the rotor by hand and see if anything moves. And if that's fine, then run it. If the problem returns, then check all your reference marks. At a minimum, you may prove nothing in the distributor moved and the problem lies elsewhere.

[Emil]

I love this idea, thanks!

I guess I'll just clean up the clamp and bolt then, and reinstall everything. I'll put some marks everywhere like you said, and then see if I can make it out to the lake (as soon as I get my new muffler from FAE)