4.2 Valve Trouble
Thread Starter
|
New User
Joined: May 2003
Posts: 4
Likes: 0
4.2 Valve Trouble
Started with a leaking intake manifold gasket, found antifreeze in the cyl. Caused a loud knocking noise which I found to be the intake valve for the same cyl hitting the piston.
I have replaced the valve and spring thinking the valve was bent and the spring because I was there. The pushrod and rocker arm seem ok.
After the reassemble, the new valve continues to hit the piston.
I'm looking for what may be the cause???? The repair shop wants to replace the motor ($3900.00) I hope not to...
Any Ideas?
I have replaced the valve and spring thinking the valve was bent and the spring because I was there. The pushrod and rocker arm seem ok.
After the reassemble, the new valve continues to hit the piston.
I'm looking for what may be the cause???? The repair shop wants to replace the motor ($3900.00) I hope not to...
Any Ideas?
Last edited by DEFIORDA; May 22, 2003 at 03:24 PM.
Senior User
Joined: Apr 2003
Posts: 262
Likes: 0
From: Tucson
4.2 Valve Trouble
First off, don't pay $3900 for a new motor. I just recently replaced my 4.2 and it cost me a total of $2000 I think after all the parts and installation was complete.
My question is, how do you know that the valve is still hitting the piston? It's not like you can look from the outside and tell. Plus if that was the case, your motor wouldn't even run. A valve hitting the piston is something major that will destroy your engine.
My question is, how do you know that the valve is still hitting the piston? It's not like you can look from the outside and tell. Plus if that was the case, your motor wouldn't even run. A valve hitting the piston is something major that will destroy your engine.
Thread Starter
|
New User
Joined: May 2003
Posts: 4
Likes: 0
4.2 Valve Trouble
After I found the manifold leak and replace the gasket, I started the truck and found there to be a loud knocking noise. To identify what was causing the problem, I began looking at the valve train operation for signs. After I pulled the rocker arm for the intake valve on the cyl the noise stopped.
At this point I knew the problem was most likely a bent valve, I had swapped the push rod and rocker arm with another cyl.
When I pulled the head to replace the valve, the piston was clearly marked where the valve was hitting it.
After replacing the valve, same noise from the same intake valve for the same cyl. The motor does run with or without the rocker arm or spark plug. Although as you would suspect it does run rough missing parts.
I'm not looking forward to the third tear down to replace a lifter.
Looking for some ideas before I take that route.
At this point I knew the problem was most likely a bent valve, I had swapped the push rod and rocker arm with another cyl.
When I pulled the head to replace the valve, the piston was clearly marked where the valve was hitting it.
After replacing the valve, same noise from the same intake valve for the same cyl. The motor does run with or without the rocker arm or spark plug. Although as you would suspect it does run rough missing parts.
I'm not looking forward to the third tear down to replace a lifter.
Looking for some ideas before I take that route.
Senior User
Joined: Apr 2003
Posts: 262
Likes: 0
From: Tucson
4.2 Valve Trouble
it sounds like I know less about valve train operation than I thought I did 
As for solving your problem, it sounds like there is a defect in your motor that is causing the same valve to keep bending and hitting the piston. I guess check the rest of the engine and if worst comes to worst, get a new motor. 
As for solving your problem, it sounds like there is a defect in your motor that is causing the same valve to keep bending and hitting the piston. I guess check the rest of the engine and if worst comes to worst, get a new motor.
Postmaster
Joined: Mar 2003
Posts: 4,513
Likes: 0
From: La Tech University, La
4.2 Valve Trouble
If it was the timing chain chances are it would be more than just one piston. Granted there is a chance that the lobe shifted on the cam, It cold have ad low oil, (leaking gasket) the lifter locked onto the lobe and stretched the metal to one side, that could cuse a valve openeing early. umm... but I might say a bearing has too much play in it and is letting thepiston go up to far, or the rod has stretched.
Trending Topics
Senior User
Joined: Mar 2003
Posts: 116
Likes: 0
4.2 Valve Trouble
Yeah, I'm liking the rod bearing idea too... With coolant in the cylinder (non-compressable) piston, rod, or bearing damage is quite likely...
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
2027 Ford Super Duty Buyer's Guide (Every Model, Engine, & Package)
Brett Foote
Top 10 Ford Truck Tragedies
Joe Kucinski
AEV FXL Super Duty - the Super Duty Raptor Ford Doesn't Make
Brett Foote
Lobo Vs Lobo: Proof the F-150 Lobo Should Be Even Lower!
Michael S. Palmer
Ford's 2001 Explorer Sportsman Concept Looks For a New Home
Verdad Gallardo
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
2026 Shelby F-150 Off-Road: Better Than a Raptor R?
Brett Foote
2027 Super Duty Carhartt Package First Look: 12 Things You NEED to Know!
Michael S. Palmer
10 Most Surprising 2026 Ford Truck Features!
Joe Kucinski
New User
Joined: Mar 2003
Posts: 13
Likes: 0
4.2 Valve Trouble
Seems like rod slack might let piston hit valve except compression should be keeping piston down from head even more then normal . Sounds more like cam or lifter problem to me. I had 86 head work done once & mech told me it wouldn`t idle right after putting back together - had to change lifters as he said hyd lifters had expanded farther to make up for bent valve,new straight valves would be longer & that could make it hit piston. Hear you though , hate to tear down again.
Senior User
Joined: Feb 2003
Posts: 147
Likes: 0
From: Ardmore
4.2 Valve Trouble
When this piston hydrolocked from the coolant in the cylinder, you probably damaged the piston pin. The inertia of the piston moving up is more than enough to overcome compression. This lets the piston come up and hit the valve. When you had the head off, did you check the cylinder wall to see if it was scored? More than likely the damaged piston pin also damaged the cylinder.
Thread Starter
|
New User
Joined: May 2003
Posts: 4
Likes: 0
4.2 Valve Trouble
I was thinking piston problem, but thought I would hear a low knock or some noise it it had a problem. When I take the rocker arm off for the intake valve, the knock quits.
If the piston had excess movement, I should hear a low knock from the block.
If the piston had excess movement, I should hear a low knock from the block.
Postmaster
Joined: Mar 2003
Posts: 4,513
Likes: 0
From: La Tech University, La
4.2 Valve Trouble
Noit neccasirily, eeven if a bearing is elongated, it is still circular, and even at high speeds, the loose pin or rod or what not could actually be rotaing inside the connection never leaving the wall, possible ......you understand what I am trying to say.