HELP!!! seizied dohc.

[coupeownerBE]

Well this was my first 4.6.. its a 97 cobra with 87k on it.. everything looks great and stock on this car.. had my longtubes and h-pipe put on and went to the track just to play around a lil.. after my first pass it lost oil pressure at the very end of the track at low rpms and it died, while rolling, I tried to start it back up and it didnt turn over. tried popping the clutch and it wouldnt turn.. I tried turning the crank nut and it wouldnt turn.. so being hopefull I tried taking the belt loose and checking my pullies and all is good there.. still have all my oil.. everything looks great but no start.. help me out here. where do I start?

 

[NO BRAKES]

how much force were you able to put on the crank pulley? i had a car once that i couldnt get leverage on the crank and it wouldnt turn... but the power wire to the starter was corroded and broke off. maybe thats your problem.
but.... lack of lubrication is a big downer for mod motors. did your stock gauge show low pressure or was it a aftermarket gauge?
hopefully its just a bad connection on the starter

 

[joshjwc9]

Alternator still good? How about the battery? Start small with your searching, then work your way up. Next do a compression or leakdown if those turn out okay. First check the starter though like above.

 

[bwahl602]

if u lost oil pressure first then you may have locked it up

 

[trinity_gt]

If the oil pump gear(s) shattered, you'd lose oil pressure and if the bits are jammed up, they may be what's causing the apparent lock-up. Either way it's ugly.

You might want to pull the oil filter and cut it open to look for metal. If so, next up are the front cover, timing chains and then oil pump for a post-mortem.

 

[coupeownerBE]

The stock gauge showed no oil pressure then it died. I can hear the starter trying to turn it. Battery is good and the alternator should be fine. It doesn't seem to be a power issue. What about the oil pump are those known for problems and if so why didn't I get some kind of notice. No check engine light or low oil light.

 

[bhuff30]

If you can't turn the engine by hand, by popping the clutch or with the starter, you most likely siezed a bearing... or several. If you choose to repair that engine, you'll definately have to have that crank ground for undersized bearings (expensive), or try to find a used or rebuilt crank that is in spec. You would be best off doing a complete rebuild, with new rings and seals and freshened heads. Or... if you want to be ultra cheap, I guess you could find a 4.6 shortblock from the junk yard for 100$ (from a crown vic, lincoln or whatever) swap it in, clean the heads very well and call it done. But that'd be stupid because you already have a teksid aluminum block, and forged crank.

 

[coupeownerBE]

Guess she will be down for a bit....

 

[trinity_gt]

The stock gauge showed no oil pressure then it died. I can hear the starter trying to turn it. Battery is good and the alternator should be fine. It doesn't seem to be a power issue. What about the oil pump are those known for problems and if so why didn't I get some kind of notice. No check engine light or low oil light.

The oil pump is a gerotor-style pump mounted directly over the snout of the crankshaft. Its gear elements are made from powdered-metal and are pretty brittle. In stock form these aren't known, as far as I know, to be a common failure even given their brittle nature.

Hypothetically, if you ran an aftermarket underdrive pulley set with a damper that differed from the factory design significantly, you can increase the chances of torsional crankshaft vibrations shattering those oil pump gears. If your pulleys are stock then perhaps this isn't the failure at all or perhaps you've got the one-in-a-million gears that'd fail even with the stock damper in place.

If the gears did shatter, you'd not really have any notice. One second they're working properly the next they're shrapnel.

The loss of oil pressure suggests an oil pump failure. Since the oil pump resides over the crank snout it's possible that bits and pieces have jammed up in there locking the crank. It's a possible failure scenario. I suspect the engine's coming out so you might want to do some pre-pull digging (e.g. pull the timing cover, chains and oil pump off and have a look at it...) If you do this, don't try to verify the crank still turns with the pump out unless you put the timing chains and sprockets in place and re-time the cams to ensure you don't hurt any valves...

 

[coupeownerBE]

thanks guys...anyone got a running fox for trade..lol...

 

[GoBabyVroommm]

Oil pump that is what it sounds like.

 

[NO BRAKES]

thanks guys...anyone got a running fox for trade..lol...

ive got a spare mark viii motor if ya wanna do the swap