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Chrysler LM318 issuesparanoia

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bfiesta

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"1976 Silverton sedan w/twin C

"1976 Silverton sedan w/twin Chrysler LM318s. Had a compression check before I bought the boat and it check out GREAT. This is the first inboard boat I've owned. New (to me) 3 weeks. Went for a two hour cruise (our first), docked and shut down engines. Restarted engines about 10 minutes later and after about a minute heard a grinding sound and sounded like it was coming from the starboard engine. Shut it down and limped home on one engine. Oil & filters are new and full. No water. Coolant is new and full. Engine was rebuilt about 500 hours ago. Good maintenance history. Previous owner said the manifolds (log style) and risers (20 degree) were 'changed' (possibly just cleaned) two seasons ago. They look 'okay'.

Started the engine again a day later. I heard a rattle sound but not as loud. Possible impeller??? Valve rattle maybe? Shut it down immediately. Records show impellers were changed in 2004. Not a lot of time on them since.

Yesterday started the engine again. Faint rattle then sound went away. Ran engines for a good 20 minutes at idle and up too 2200 RPM. Seemed to run okay. No funky sounds. Looking at the sea strainer it appears that water is moving. After the 20 minute run-up the manifolds (both sides) were cool to the touch. However, the exhaust pipe immediately after the riser was HOT (could only hold my hand on it for a couple seconds, if that). Is this normal... for the exhaust pipe to be so hot and the manifold so cool?

Additionally, I pulled two spark plugs to check them out. They are fouled with black carbon. Not oily or gassy. Just carbon. The plugs and plug wires are brand new! Any thoughts on this?

I have a new distributor cap and rotor but haven't installed them yet.

Am I paranoid?"
 
".."Am I paranoid?" H

".."Am I paranoid?" Hey, even if you are, people could be following you!

No way the elbow should get that hot! You need to pull it and clean out the little holes in the back. (See photos.) But first, RUN to the store and buy an infrared temp gun and "shot" the entire exhaust system. The hot spot will jump right out at you.

Jeff

PS: Use a piece of 1/8 inch wire as your "drill" and flush with water when you're done. If it doesn't flow right out those little holes, drill some more.

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"Thanks for the info Jeff. Ho

"Thanks for the info Jeff. However, the risers are cool... it was the exauhst pipe immediately AFTER the elbow. Perhaps the volume of water isn't flowing out the exauhst pipe and it's backing up in the elbow? That is why the exaust pipe is so hot?

Could the rattle/grinding be just an impeller blade that finally flushed its self out the exauhst?

Any ideas on why the plugs would be fouled so quickly?

Again, thanks for the help and peace of mind."
 
"..."Could the rattle/grin

"..."Could the rattle/grinding be just an impeller blade that finally flushed its self out the exhaust?"

Could be. You need to pull it and run a hose through the riser and elbow to see what's happening.

..."Any ideas on why the plugs would be fouled so quickly?"

Carb flooding? Those old AFBs --I assume that's what you have?--are junk after 20 years, especially with ethanol gas. If so, I recommend new Edelbrock marine carbs--300 bucks on Amazon.com.

On the fouled plugs, I suggest you try the Fastjeff Balance Test:

Motor arm and idling, pull and replace one wire at a time from the distributor cap and note the rpm changes. If any don't do much, replace the wires (if they are old). I use big block 454 wires on mine that go OVER the manifolds instead of being jammed be ween the valve cover and manifold. That's an invitation to a short out.

Jeff"
 
Thanks again Jeff. Carbs are

Thanks again Jeff. Carbs are near the top of the to-do list. I assume the LM318 would use the Edelbrock Marine 600 CFM. Are they a direct bolt on? Please don't tell me I have to change manifolds!? :) Any tips for switching to these carbs?
 
"The Edelbrock marine carbs bo

"The Edelbrock marine carbs bolt on, but the flame arrestor is too small (at the neck), there's no vacuum fitting for the PCV valve (you have to drill and tap), and you'll need to wire up the electric choke. No biggee. Let me know when you need some advice.

Jeff"
 
"Jeff,
Took your advice and s

"Jeff,
Took your advice and shot both engines with an IR temp gun. Ran both engines for a good 20 minutes. Shot temps everywhere on the engines. My only 'hot' spot was the port exhaust pipe immediately after the elbow on the starboard engine. It was reading 180 degrees while everything else was reading half that temp.

Sounds like I'll be pulling that elbow tomorrow and checking it out. I am assuming that the elbow is junked up (like in your pic) and the water isn't flowing out the exhaust pipe as it should?

How often do you totally replace your risers and elbows? I was considering pulling and possibly replacing the whole lot.
Thanks."
 
Good man! (Ain't those

Good man! (Ain't those IR guns great!)

That 180 degrees is REALLY hot! I suspect your water flow through there is minimal.

One can get 20 years plus out of manifolds and risers in FRESH water; aout 5 years in salt. Hope yours is the former case!

Jeff
 
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