i know this is a f150 site but i have a 2001 crown vic with 4.6 police interceptor. it has a bent valve. do i need to replace the piston? is it a valve interference engine?

 

You wont know until you pull off the head. Maybe. How did the valve hit the piston? Never heard of a chain failing but I guess it not impossible. My kids first car was a pathfinder the timing belt failed and it rubbed out every single valve. The engine was good though. No piston damage to any of them. We just got new valves and put it back together and it ran great.

 

Well it sort of depends how hard the valve hit the piston. It really dosen't take much to bend one of the valves. Several things can allow a valve to hit a piston in a modular. Something stuck (debris) between the valve and valve seat which held the valve open long enough for the piston to smack it. A timing chain that slipped allowing the same senario. A valve stem that got bent from a upper valve train problem such as a follower that dislodged or broke, allowing the valve to stick in the guide and make contact with the piston. A collapsed lash adjuster that allowed the follower to lose control and start bouncing. A broken valve spring. This engine is not a freewheeling engine which would allow for piston to valve clearance if a timing chain broke or timing was compromised. When the first 4.6 prototypes came out they had "eyebrows" machined into the piston domes to allow clearance for the valves so it was originally designed to be freewheeling. Machining these eyebrows was cost prohibitive and was eliminated. Do you change the piston? If I were you and could see a considerable dent in the piston dome where the valve hit it then I would change the piston you don't want a cracked piston to destroy the entire engine. I have seen very small dents in piston domes that ran for many miles after the valve was changed and never caused a problem. I have seen other engines with the entire piston blown apart and laying in the oil pan from a valve hit. Just use some discretion when you make the call to change it or not. Maybe send a picture of the dome and get some input from others here. A small finger nail like dimple shouldn't cause a problem but it could also create a hot spot on the dome. Probably not a concern for an everyday driver but for racing application a whole different story. Good luck

 

i bought it with a miss. it is a 2001 crown vic police interceptor. it was an detective police car. i only payed $800 for the car. the timing chain tensioner and guide were bad. the timing chain was lose here is what i got when when we pulled the head off. do you think it could have bent the rod?

 

If your not planing on racing it or putting forced induction to it. I think I would just fix the head and run it.
It really doesn't look to bad.

Certainly not as bad as when I broke a brand new comp cams valve spring!
I'll never buy another product from them again!!
I ended up putting all new pistons in and had to have the head redone with no help from Comp!




Phil

 

Looks like it hit pretty hard. The problem I see is that when the valve hit the piston and bent you lose compression from the valve not seating so no igniton takes place. Now your injector is still shooting raw gas into the cyl. The gas will keep this piston/cyl cool and prevent any hot spots from friction. The piston is deformed from the valve hit, if you just replace the valve and try running this engine you will generate friction on the cyl wall when the hot piston expands. You will then score the cyl wall and generate enough heat to destroy the piston possibly causing engine failure. A very small nick you could get away with but this one is to severe. I would change the piston and go from there. Make sure the replacment piston is the correct grade, either a 1, 2 or 3 grade.They are usually all #2 grade but one or two may be a 1 or 3. The piston bore grade stamp for each cyl is on the right front of the block on a flat machined boss.(behind the front cover) Good luck.

 

I would just get a used engine. There is nothing special about the police engines.

 

^^^ Yep. The special thing about the police engines is the super high mileage. I wonder if a timing chain could strech to the point of skipping a tooth?

 

I've seen a piston look exactly like that at the local Ford performance shop. My friend didn't have a clue what happened to it.

 

it has 95,000 miles

 

95k on a PI is like 200k on a civilian vehicle. They idle extensively without putting miles on the clock.

 

Probably not, if it was a detectives car, they aren't normally run any harder than a civilian CV. Could be but not likely. I worked with 'em and they were like new at 95k.

 

i will let everyone know when we get it running. i think we are not going to replace the piston

 

You have the heads off already. Drop the pan and change the piston, 20 minute job.... It was hit hard enough to start scuffing the bore wall when it heats up. Then comes micro welding then piston failure. It may live but what if it dosen't? Cheap insurance in my book. Good luck

 

it runs!! im getting tags Tuesday. i will post pics when i get it home from my moms house