A couple of months ago my truck started shaking while driving at about 50MPH. It just suddenly started shaking but if i rev the engine it doesn't shake as much. I stopped driving it immediately and haven't driving it since. I've changed the spark plugs/wires, both coil packs, EGR valve, EGR pipe, checked the timing and changed the belt, cleaned the MAF sensor, cleaned the IAC(?) and right now I'm checking the valve seats. Now the questions.

If I take the head off, do I need to have the block machined or can I get by with just installing a new gasket? I'm pretty sure I will have to have the head machined but I'm not sure about the block.

How expensive is it to get the seats replaced?

Can I get just the one that is bad replaced or should I do all of them?

Is there a chance that fixing the valve seats will cause the cylinders to have better compression and cause other problems with worn parts?

A lot of questions, I know. Any answers will be SOOO helpful. Thanks in advance

 

Have you done a compression test on all clyinders???

It would be best to have all the valve seats ground.

The head can be checked for any warpage.

How many miles on engine???

Let us know what the compression numbers are for each clyinder that will tell us alot.

If compression is low squirt a little oil in clyinder and test the compression again, this will help tell you if the valve seats are bad or if the piston rings are bad.

 

What Larry said.
I believe a bit more testing is needed before pulling the heads off. I can see how you would start to go to some of the bigger things, but unless you've got some time to burn. i wouldn't just tear into it yet.

However, to answer your questions, If you get the heads machined by a shop. They'll do just about everything, resurface the heads, new seats, the whole 9 yards. I'm sure if you talked to the guy he would tell you what all would be done.

IIRC, the going price is like $300

 

oops. I've already torn into it. I've got everything off but the head itself. the engine has 201k. I know one is bad for sure. I was going to check the valves once I pull off the head and if its not the valve seats I was going to assume it the piston rings. I really hope its not the rings.

 

Yea, Rings suck.

It seems like you've got your wits about you. so i'd just say start looking for a good machine shop.

 

lol I was afraid that you guys would say I should put it back together and test things first. I just spent 6 hours in 95 degree 47% humidity heat and I hope it wasn't for nothing.

 

Good luck man, my co worker is having the same problem with his 2003 3.0 Mazda Dual Sport.

 

I can't seem to get the head off. The book says not to pry but to beat it with a soft hammer. Some guys I've talked to say there is a special spot made for prying but I don't see it. I've beat that thing until my hands and arms hurt and it hasn't moved at all. Any pro-tips I should know?

Also the exhaust port on cylinder 4 has a tiny bit of rust and doesn't has the black look the others have. The link below has all the pictures I've been taking. feel free to look through and let me know if anything stands out.

https://plus.google.com/photos/10326...88234737755217