454 Exhaust Ports

[Danny Bailey]

A good friend of mine has another brand of boat with a single 454 engine. He pulled the exhaust manifolds off for inspection / replacement and found the machined surfaces on the heads where the gaskets go are rusted and chipping away. It looks like the exhaust port on the head side has been running red hot. The manifolds didn't look that bad. Anyone else had this problem with a 454?

[Paul]

It's possible that the carb is running too lean or ignition timing retarded. To check if the carb is running lean, pull out the spark plugs and look at the color of the electrode. White is lean, tan is good, dark is rich & wet or oily means oh sh**. I believe the ignition timing should be set at 8° BTDC at idel. A manual could confirm this. Also check that the centrifugal advance in the distributer is moving freely and that the springs are not damaged.

If all this checks out OK, then the heat may be comming from combustion blowing by the exhaust valves. A compression test would identify this problem. If so, then it's time for a valve job.

Hope This Helps

[prowlersfish]

Paul could be correct , or you may have normal condtion I have many
marine heads look that way . could you post or put a link to a photo ?

[JuiceClark]

Could be that little mist of exhaust moisture (blowback) when idling just before you shut if off.

The last 454 I had never was quite right. So I took it to a really good machine shop and they said there was exaggerated blowback because the valves were never exactly the right size to begin with! The moisture would just barely cause a little corrosion but then running it made the weakened surface all weird.

That's the chance you take with a rebuild.

Tony in Sw FL
1982 F-36

[Danny Bailey]

Thanks for the feedback. I'll try to get some photos and post them. More info: This is a 9 year old original engine (never rebuilt) with multi-port fuel injection hooked to a duo-prop outdrive. My friend told me last night he had read somewhere that 454's and 502's with an outdrive should be run without an exhaust bellows so the engine exhausts above the water and not through the prop. Sounds like the 'through the prop' route may be too small and restrictive for the bigger engines. This could be the reason for the heat damage on the exhaust ports.

[prowlersfish]

They have had a lot of isues with these sucking some water back at idel . it is due to valve overlap of the cam . C.C. had a lot proplems with this ( alot of bad engines) they were not they only ones . Merc. also has had some proplems with this . redoing how the exhust is run can help
so can taller risers.

[rossjo]

My 26 has a new 7.4L (454) Mercruiser engine, and a Brova-1 outdrive. It is Freshwater-cooled, and doesn't get hot.

Taller risers help keep water out, and there are also flapper valves (rubber and stainless on a stainless rod) that go in the top of the exhaust yokes, where they meet the risers via the rubber boots. I removed mine (which could be dangerous), as they typically burn out and get pushed down and through your outdrive (ruining seals, etc.) and restrict flow, which I didn't want to experience 60 mile offshore.

I also added the high performance exhaust bellows, that allow the exhast to blow out past the iopen reare-end of the boot connecting to the outdrive, so the exhaust gas doesn't have to go down through the prop.

Again - cam overlap is an issue (especially on the higher performance engines - like Magnums) ... as they can inhale some water at idle. Setting the ignition timing properly will help prevent this ...