Exhaust valve or cylinder wall failure?
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Exhaust valve or cylinder wall failure?

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    Default Exhaust valve or cylinder wall failure?

    Obviously both, but would like opinions on which happened first. Ford 460 9.5:1 forged pistons, Draw thru with large PFM intercooler, running 9 psi boost, double AA impeller turning about 5300 RPM near full throttle (only about 6 psi at failure), turns about 5600 RPM at 9 psi full throttle, 21 ft Eliminator sport cruiser, run 91 octane in primaries and 116 leaded in secondaries, water jacketed log exhaust manifolds, roto-master turbos with wastegates. Timing at 30 deg advance maximum. Have measured AF at 11.5:1 at WOT. I think this is a fairly conservative setup and not turning super high revs. I'm leaning towards block failure due to the vertical and horizontal cracks. Leak sprayed a hot exhaust valve with cold lake water causing failure (broke right above head), but I'm certainly no expert in this area and definitely open to other thoughts. Thanks, Tim
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    how much is the cylinder over bored?

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    Only 0.030". Looks like there was at least 0.25" of wall thickness. I bought the short block with standard bore used prior to rebuilding it including machine shop work.
    Last edited by Turboelimtim; 06-18-2018 at 07:28 AM.

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    Aquacraft Eddie's Avatar
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    Im no expert at all but like you said maybe cold lake water got in,,have you checked the exhaust logs? this is what im afraid of with mine ,,i have no where your horsepower but im using logs that are at least 47 years old ,,,I think I would test the logs to see if they leak water and then go from there....or maybe a leak from the head????not to sure how that would be but im not familiar 460 stuff but just a thought …..
    Last edited by Eddie; 06-18-2018 at 07:33 AM.

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    I did not get the block decked. My machinist didn't think it was necessary. If you look at the head pic, and I'm no expert, it looks like water might have been getting past the gasket in multiple cylinders. Maybe that explains some of the discoloration on the intake valves. Also, some of the plugs had some rust on them. I did do a compression check prior to the outing and all were right at 180 psi.

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    I'am thinking a broken valve started it all.
    Last edited by bville; 06-18-2018 at 08:01 PM.

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    Quote Originally Posted by bville View Post
    I'am thinking a broken valve started it all.
    More like a stuck valve. i would need to see alot more.

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    only 30 deg of timing will cause a lot of heat on the exhaust valves that can weaken the metal.at what rpm was it fully advanced?also,11.5 afr is a little lean for a boosted engine on long hard runs,remember 11.5 is the average on one bank meaning some cylinders are richer and some are leaner.what head gasket were you useing?
    Last edited by buck28; 06-20-2018 at 07:02 AM.

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    Maybe I missed it, but what exhaust valves do you run? Inconel or Ferrea Super Duty would be good choices, anything else not so much with turbo heat.

    I think 11.5 AF should be "safe" if cylinders are fairly even, but I do not agree with 9.5-1 and 9 lbs boost. Find a chart and see what theoretical compression is with that combination.

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    Maybe this applies : 427 chev v-drive..had the heads done over some slightly lose guides
    Back togetherm put around for and hour...make a pass and at 5k the motor goes sour..instant key off..pull valve cover...wrecked roller rocker pushrod and slight bent intake valve.
    Sneak one head off, back to machine shop...they did repair and checked everything and i put it back together
    Did the exact same thing 2 more times....last time was almost catastrophic..bent valve stuck in guide, pulled the guide our and broke it....no idea how the valve didnt break it was bent in 3 different directions...done with that machine shop...i end up at Gary Kincaid Racing Engines.....he barely looks at it..."valve guide got hot...maybe air in the cooling system" Kinda check that on a regular basis...when i run on the trailer the dump water runs in a 5 gal bucket....bubbles..i would notice....so i tore the motor all apart....looked and looked....and put up with guff i got over reusing steel shim head gaskets...half dozen times....on the way back together i feel a litte spot in the upper cylinder wall..freekin crack....putting around with minimal load, no problem..load it uo and spin it and cylinder pressure pushes through the crack, gets trapped it the upper part of the head around the intake guide, it gets hot and even with .001 clearance it grabs the valve and even 550 lb spring pressure not enough to close it...Gary gave me a std bore 454 block, he honed it...i changed blocks, re used all the bearings and rings and head gaskets...back in the water in 2 days...never had any problems after that
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    Quote Originally Posted by ol guy View Post
    More like a stuck valve. i would need to see alot more.
    Are there some other pics I can post or check somethingto help? If so, what? If stuck, would the stem still (after cooled off) still be stuck in the guide (i.e. fused)? If so, that is likely what happened. What would cause a stuck valve? Just simply getting too hot? Should I run it without seals on the exhaust valves? What mechanism would causes the large vertical and horizontal cracks in the cylinder wall?
    Thanks for your help.

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    Quote Originally Posted by buck28 View Post
    only 30 deg of timing will cause a lot of heat on the exhaust valves that can weaken the metal.at what rpm was it fully advanced?also,11.5 afr is a little lean for a boosted engine on long hard runs,remember 11.5 is the average on one bank meaning some cylinders are richer and some are leaner.what head gasket were you useing?
    I actually thought 30 was a little aggressive for a boosted application. Full advance by 3000 RPM. No boost until 4000 RPM, then approximately linear from 0 to 9 between 4000 and 5500 RPM. Didn't, and don't normally run flat out for more than 30 seconds or so. Head gasket is a 0.040" copper.

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    Quote Originally Posted by obnoxious001 View Post
    Maybe I missed it, but what exhaust valves do you run? Inconel or Ferrea Super Duty would be good choices, anything else not so much with turbo heat.

    I think 11.5 AF should be "safe" if cylinders are fairly even, but I do not agree with 9.5-1 and 9 lbs boost. Find a chart and see what theoretical compression is with that combination.
    Stainless Steel. Ran these for years, albeit on 8.25:1, 13 psi, without issues. What do you mean by "I do not agree with 9.5-1 and 9 lbs boost"? I am using 91/116 ~50/50, but that is to prevent detonation. I don't see any signs of that. Effective CR is 15.2, old build (8.25,13 psi, same heads) eff. CR was 15.5. Thanks for your help.

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    Here is a thought. The hole burnt right above the exhaust valve in the engine tells me it leaned down big-time. Now a question did you find any parts of the tulip part of the valve? Question 2 your'e fuel system delivery--do you have a gauge and if so at 5K what is it at and were are you picking it up? If it is not right at the carb you may have a fuel delivery issue. Reason being if the tulip part of the valve was in the combustion chamber or in the cyclinder take a real good look at the the area were it came apart from the stem. Is it burned off or broke off? Alot of ??? but I have seen engines melt pistons and valves and you really need to figure out the cause before it causes more $.

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