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HotRodr56
10-18-2005, 10:15 AM
Ok motor guys. Engines are stock 454 mags. Last season the port engine destroyed the number 1 cylinder exhaust valve, left the stem, retainers, springs, rocker all intact just disintegrated the head of the valve. This in turn caused the cylinder wall to crack, allowed water to contaminate the oil and ruined the engine. I had the block sleeved, installed new parts including forged crank, 7/16 rods, forged pistons, new cam/lifters, had the heads checked and valves on #1 only replaced. This season engine ran fine, never pushed it hard, all was well until a couple of weeks ago. Repeat of first season engine meltdown except this time it is cylinder number 3. My best theory is the valves are fatigued from some past abuse and my plan is to replace them all, both heads, check spring pressures, and replace if needed. Engine will require a sleeve on #3 and a complete rebuild again. Please, if anyone knows why this has happened twice give me a clue. I do not want to make a career of rebuilding the port engine. I have pressure checked the exhaust risers for leaks and found none, so I can't figure out what makes the exhaust valves die like this. Last question is whether to replace all the valves with stainless or go with something better on the exhaust like inconel. I don't want to spend money on fancy parts I don't really need, but I SURE don't want to rebuild this engine any more. Thought? Theories? Help?

MOP
10-18-2005, 02:01 PM
Ok motor guys. Engines are stock 454 mags. Last season the port engine destroyed the number 1 cylinder exhaust valve, left the stem, retainers, springs, rocker all intact just disintegrated the head of the valve. This in turn caused the cylinder wall to crack, allowed water to contaminate the oil and ruined the engine. I had the block sleeved, installed new parts including forged crank, 7/16 rods, forged pistons, new cam/lifters, had the heads checked and valves on #1 only replaced. This season engine ran fine, never pushed it hard, all was well until a couple of weeks ago. Repeat of first season engine meltdown except this time it is cylinder number 3. My best theory is the valves are fatigued from some past abuse and my plan is to replace them all, both heads, check spring pressures, and replace if needed. Engine will require a sleeve on #3 and a complete rebuild again. Please, if anyone knows why this has happened twice give me a clue. I do not want to make a career of rebuilding the port engine. I have pressure checked the exhaust risers for leaks and found none, so I can't figure out what makes the exhaust valves die like this. Last question is whether to replace all the valves with stainless or go with something better on the exhaust like inconel. I don't want to spend money on fancy parts I don't really need, but I SURE don't want to rebuild this engine any more. Thought? Theories? Help?

It may not be caused by valve fatigue that seems a bit iffy, check you spark plug color you may have a fuel problem. That engine may be running on the lean side at higher RPM's but be fine at cruise speeds, could be tank supply or in the fuel system its self. The plugs should all look very much the same in color which should be on the dark side.

Below is a good chart, I like them to look like 10 or 11. With a marine app you are far better off being a little rich, lean is deadly with the high loads imposed on these engines.

Phil

http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html

mrfixxall
10-18-2005, 03:17 PM
i would check a lean condition,but it usually picks on more then one valve..your engine should already have inconal velves in it,,,check your block deck and head serface especially between the cylinders if its not true it can rob the othe rcylinder of its fuel mixture.....i would start looking for a new block i dont like to run with two sleeved cylinders side by side..are thease efi engines??? if so ck your injectors also i would rebuild both engines because usually the other enging may start developing problems also.........

joseph m. hahnl
10-18-2005, 05:31 PM
There was talk of manufacturing valves in two pieces and sonically welding the head onto the stem. I'm not sure if they actually did it but that maybe somthing to consider if they are stock valves. most exhaust valves are stainless steel .
I doubt they are inconel.but if it does, inconel being made of cobalt and nickel would tend to be very brittle and could shater.


joe

Ted Guldemond
10-18-2005, 07:07 PM
The most common reason I've seen for dropping a valve is too much play in the valve guides. In theory if the guides are sloppy each time the valve closes the valve head is just slightly off center. Not enough to not seat, but enough that there is continuous fatique at the valve stem neck.

HotRodr56
10-18-2005, 10:58 PM
Thanks for the feedback guys. More info on the engines, these are 1986 model single 4 barrel carbed engines and yes the port engine did appear very slightly on the lean side but not by much. So, I'm still not sure of this valve issue. Should I go back with all stainless intake and exhaust, go to inconel exhaust, replace all the valves, replace just the broken valve? I will have both heads completely checked and rebuilt with new guides at a minimum. Any more advice?

BUIZILLA
10-19-2005, 09:30 AM
vacuum leak at the intake gasket around #1-#3 ??