Distributor gear broken

[SashaHens]

Hello all


In spring 2024 my PCM Excalibur 343 from 2009 received a new underblock, because previous underblock overheated and head gasket broke...

When I first started using the new engine everything was fine, except check engine was always lit after applying some throttle. PS the new engine had a proper run-in and frequent oil changes in the begining. The mechanic and myself checked the ECM with Diacom and no faults. Engine kept on going smooth through the season, except during fall 2024 I started noticing small engine hesitations at low speeds (20 mph)/low RPM (2000 rpm). Boat was taken out for the winter and had maintenance and this spring we started using it and stil the same hesitations and started to get worse, so hesitation became bigger. When the new engine was installed a lot of stuff was replaced (spark plugs iridium, coil, coil wire, distributor cap, rotor) so according to my mechanic the only culprit could be the sparkplug cables, so this spring I changed them as well, but still the same hesitation. It even became worse and i changed spark plugs, distributor cap, rotor, coil, every possible sensor , but no improvements. Then I checked my Cam retard and it was a +- 2 degrees, I moved it towards 15 degrees, advice given by the mechanic. Motor performed much better and just only still slightest of hesitation in low rpm's. last week I was going in the slalomcours at 34 mph and suddenly engine stops and wouldn't start anymore, when I cranked I could imediately notice that the timing was completely wrong, engine fighting itself.
So I took out my complete distributor and I discover that the teeth of the gear are completely worn down and some even missing on one side...



How could this happen? Is this a bad installation? Should a new distributor have been placed with the new engine?

[SilentSeven]

Was the crate engine from PCM or was it from a 3rd party?

I'm wondering if the distributor drive gear on the engine camshaft did not match distributor gear. Pretty much would have to be a 3rd party engine for a mismatch to occur. Best information I have is there only one model of distributor for the 343 engine.

[jpwhit]

The distributor drive gear has to be matched to the camshaft gear based on the type of lifters and the material used for the camshaft gear. Often if you reuse a distributor during an engine rebuild, you have to change the gear on the distributor to be compatible with the camshaft gear. I suspect this wasn't done on the rebuild.

The camshaft gear is definitely going to have to be replaced now. The other critical question was there other damage to the engine due to the metal bits circulating through the oil before being caught by the filter or settling in the oil pan.

[SashaHens]

Was the crate engine from PCM or was it from a 3rd party?

I'm wondering if the distributor drive gear on the engine camshaft did not match distributor gear. Pretty much would have to be a 3rd party engine for a mismatch to occur. Best information I have is there only one model of distributor for the 343 engine.

The crate engine is from mercury, I have al the documents in my glove compartment box, my mechanice is an official PCM dealer and he said this was a perfect fit.
If it is really a mismatch woudn't the teeth be worn down all around, now it is only on one side...

[SashaHens]

The distributor drive gear has to be matched to the camshaft gear based on the type of lifters and the material used for the camshaft gear. Often if you reuse a distributor during an engine rebuild, you have to change the gear on the distributor to be compatible with the camshaft gear. I suspect this wasn't done on the rebuild.

The camshaft gear is definitely going to have to be replaced now. The other critical question was there other damage to the engine due to the metal bits circulating through the oil before being caught by the filter or settling in the oil pan.

The gear wasn't changed, because this wasn't mentioned on the invoice. For sure we will have to do a good cleaning of the engine inside to remove all the metal fragments.

[SilentSeven]

Some better pictures would help. Also, can you confirm some details? I think you are saying that the 1/ the distributor gear is worn all the around and 2 / the gear is sheered on one side. You also confirming this is not a PCM crate engine, it's a 3rd party engine.

I think jpwhit has the best hypothesis. The replacement motor used a different cam gear material than the PCM engine leading to a material mismatch. The material mismatch caused the 360 degree gear wear. As the distributor gear wore, it got to a point where one side sheered off.

If this was my boat, I would also ask if the camshaft in the replacement engine is appropriate. The crate engine cam may not have the same profile as the PCM factory cam. If the old engine is still available, I might consider swapping the PCM cam back into the rebuilt block. The factory PCM ECU could have a tune optimized for the PCM camshaft. This is speculation only and you could likely contact PCM to confirm.

[SashaHens]

Some better pictures would help. Also, can you confirm some details? I think you are saying that the 1/ the distributor gear is worn all the around and 2 / the gear is sheered on one side. You also confirming this is not a PCM crate engine, it's a 3rd party engine.

I think jpwhit has the best hypothesis. The replacement motor used a different cam gear material than the PCM engine leading to a material mismatch. The material mismatch caused the 360 degree gear wear. As the distributor gear wore, it got to a point where one side sheered off.

If this was my boat, I would also ask if the camshaft in the replacement engine is appropriate. The crate engine cam may not have the same profile as the PCM factory cam. If the old engine is still available, I might consider swapping the PCM cam back into the rebuilt block. The factory PCM ECU could have a tune optimized for the PCM camshaft. This is speculation only and you could likely contact PCM to confirm.

Here you have some more pictures:



As you can see there is a side of the gear that shows barely any dammage, there is even 1 tooth that shows no damage and if you go the opposite side you see more wear, the are becoming like sharp knives until they are completely gone/broken of, so de the wear is not 360°

The crate engine is from Mercury but my mechanic said they use the same underblock engines...

My mechanic also came to check today and he was quite shocked when he saw this, he will contact Mercury and ask for explanation. In anyway eninge will be taken out and oil pan will be removed for cleaning and checking of the camshaft gear. We will also check if the oil pump is turning smoothly, because my mechanic suspects that this could be the culprit.

Will keep you updated, but if you have any other ideas, shoot

[SilentSeven]

Pictures didn't seem to post.

I'm assuming the Mercury engine is a re-manufactured short block. However I'm confused as to the supplier - "Mercury Marine" is a well known outboard and inboard engine manufacturer. Is Mercury Marine (MM) your short block supplier?

I don't believe MM has any relationship with Pleasure Craft Marine or PCM, the manufacturer of the Excalibur 343. It's quite possible that the both Mercury and PCM start with the same General Motors 350 CI / 5.7L block but I don't think it's safe to assume they equip it the same. A camshaft is one item that may be specced differently between suppliers.

I would challenge your mechanic a bit. I would ask him how he specifically confirmed the camshaft profile in the Mercury engine was identical to the camshaft installed in the PCM engine.

ChatGPT seems to confirm that MM and PCM both use GM sourced blocks but spec different cams.

GPT prompt I provided

For PCM and Mercury marine engines supplied by general motors, determine if they use the same engine camshaft

GPT response:

Mercury Marine (MerCruiser) and PCM both use camshafts tailored to their specific engine designs—even though many of their engines originate from GM blocks—so they do not share the same camshaft. Here's why:

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⚙️ Design and Application Differences

1. Cylinder Head & Valvetrain Differences
   • PCM builds inboard engines (e.g., 5.7 L, 6.0 L, 6.2 L) intended for direct-drive or V‑drive systems with emissions equipment.
   • MerCruiser marinizes similar GM blocks but adapts them for sterndrives, jets, or sterndrive setups with different heads and exhaust paths.
   • As Comp Cams explains, “Although they mostly use the same block, the cylinder heads are very different and require totally different camshafts… valve arrangement in the heads is different, and therefore the lobe placement on the camshafts must coincide with the head you are using.” (compcams.com)
2. Camshaft Profiles Tailored to Use
   • MerCruiser cams (e.g., for 5.7 L 350) are dual‑pattern hydraulic flat tappet or roller cams. Specs include ~200–212° duration @0.050″ lift, ~.440 lift, LSA ~110–112° (forums.iboats.com).
   • PCM cam specs aren’t typically published—but given their different valvetrain and calibration needs (e.g., catalyzed exhaust, throttle mapping tailored for wakeboarding), their cams would have distinct lift/duration and phasing.

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✅ Bottom Line

• They do not use the same camshaft—even if both are based on GM V8s, their cylinder heads, valvetrain geometry, and marine applications differ considerably.
• Each camshaft is custom-designed for the engine’s specific head and use-case (e.g., stern drive vs. inboard V‑drive, emissions tune vs. sports wake performance).

If you'd like, I can help find PCM cam spec data or compare a specific MerCruiser and PCM engine (like both 6.2 L) in detail—just let me know the models!