head question

[IDIBRONCO]

Technical question about a head. Background: a few months ago, I bought a 85 F250 with a 6.9 in it. I actually installed the engine in 1998 in the shop I used to work at. The engine was remanufactured by us. The machine shop we used didn't take any more material off of the heads than was necessary to ensure that they were flat. I had a head gasket go out in it after a couple of months of driving. The fire ring on the back cylinder on the passenger's side came apart. This isn't about why that happened. On the bottom side of the head, where the fire ring came apart, there is a groove that is .009" deep. I measured using my Starrett depth mic so I'm sure about the depth. My question is this, can I have the head surfaced and still have enough valve clearance? I know that the pistons protrude a few thousandths above the deck of the block and that's why I'm asking for opinions. I have no idea how much material might have been removed in 1998 by the machine shop. Just looking for opinions.

 

[racer30]

MMMM... without knowing the head's decked amount its going to be hard to be sure... One possible thought. Assemble the head on the engine with some puddy on the piston where the valves will hit it. lube the valve face with WD40 so it wont stick. only torque to about 30lbs so the gasket will be usable again. figure your clearance valve face to pistons by measuring the puddy minus what you think the gasket will compress. measure one of the old head gasket fire rings to help with your estimate of gasket compression... then find a machine shop that will cut .007 off so the imperfection is only .002 then build it....research head gaskets and find the thickest MFG gasket....Might help a bit...

 

[icanfixall]

Well this is a mess. You can very easily measure the head thickness with a 4 to 5 inch micrometer. You measure from the head deck to the valve cover gasket machined surface. Oem figures are 4.795 to 4.805. I have never figured out wht we need to stick to those figures. The heads are flat and the onlt thing that keeps the pistons from smacking the heads is the thickness of the head gasket. BTW the felpro compressed gasket thickness is about 72 thousands. The piston pops up as much as 31 thousands out of the cylinders. So with that measurement you have 41 thousands clearance between the head and the piston top but.. Thats not valve clearance either. Both valves are sunk in the head. No matter what thickness the heads are the valves must be the same sunk depth in the heads or seats. The intake iso.042 to 0.054 and the exhaust is 0.051 to 0.063. This is the amount they must be sunk or recessed into the seats below the deck heigth. Milling too much off the headscan possibily cause ratio problems or valve sticking out to far thru th springs but the springs can be shimmed for cloed pressure too. It becomes a problem when you have the valve stem too tall out of the keeper and grinding it down to fit causes a keeper problem. Also the lifter has a position the plunger needs to ride in. Can you mill off 9 thousands and be ok.. Maybe is the best answer I can offer knowing the little I know bout the milled head. Please measure the thickness of the head and post it..

 

[Torinojts]

My friend is in the same shoes. He had his heads milled .007. Installed the heads and now the pistons hit the valves with the lifters fully pumped up. I went over and we pulled the front cover back off. The timing marks are lined up (he had the cam out). Pistons pop out .030. He used felpro gaskets. Pulled heads back off. Measured heads and they measure at 4.787. The exh valve depth is .042-.046. Intakes are .035-.039. I am assuming this is the issue. So does he need new heads or can he have the seats ground down further and valve and spring hieghts reset??

 

[racer30]

The lifters should not be pumped up for install....You should be able to (bottom out the lifter) with your hand on the rocker at install with the tdc mark at 11:00. Then when the engine gets oil pressure the lifter will pump up to the correct height in just a few seconds after start up. If your lifters won't compress you need to remove them and clean out the varnish inside the lifter plunger bore. make sure you only take one apart at a time so you get them back together correctly. I have pics on my flickr page of a disassembled lifter. you will need to look for them. There was a guy on here a year ago that changed a cam without compressing his lifters and they hit the pistons until they bent a few push rods. The lifters are able to Adjust to any height in there working range of almost .350 I am not convinced shaving .07 will cause piston to valve interference. http://www.flickr.com/photos/racer30/

 

[Torinojts]

But don't you want to check clearance with a pumped up lifter or a solid lifter when checking VTP clearances. Just lick you would on a gas race engine? There is always a possibility you could have a lifter pump up correct?

 

[riotwarrior]

Sounds like a small calamity of horrors here.

Lets see, unknown measurements from the OP....we will wait for the report back on those!!!


Second to torinojts, sounds like the combination of head MILLED TOO MUCH and valves NOT DEEP ENOUGH have created an issue.

This by sounds of things has made it so the valves may be open when heads installed due to the stacking of clearances in a bad way!

Take and consider that being over on one measurement and under on another can have, and what we don't know is how high the pistons are above the deck surface which also has to be considered as well in this equation.

Without full disclosure we can only offer WAG not any type of realistic and accurate diagnosis.

Get us the info, we can help!

JM2CW

Al

 

[icanfixall]

Whats posted about the lifters "finding" there proper fill and working order is correct. So is them possibiliy having some varnish that limits them from working correctly too. 2 ways of fixing this. Clean the lifters or set the valves in the seats properly. Your specs of valve recession is way off. Personally I would do both but then you have no idea what fixed the problem. Its a lot of work to do one or the other and find out thats not fixing the problem. Personally I have never found the reason for a min max head thickness. If the valves are correctly recessed in the seats there will be no piton to valve contact no matter what the head thickness is.

 

[riotwarrior]

Whats posted about the lifters "finding" there proper fill and working order is correct. So is them possibiliy having some varnish that limits them from working correctly too. 2 ways of fixing this. Clean the lifters or set the valves in the seats properly. Your specs of valve recession is way off. Personally I would do both but then you have no idea what fixed the problem. Its a lot of work to do one or the other and find out thats not fixing the problem. Personally I have never found the reason for a min max head thickness. If the valves are correctly recessed in the seats there will be no piton to valve contact no matter what the head thickness is.

Gary, the min max thickness has quite a bit to do with valve train geometry actually. As well depth of valve does when head is within those specs.

Milling head surface brings that surface closer to rocker shaft mounting boss, this then changes how the valves and rocker arms and pushrods function. You could I suppose SHIM rocker stands, however I don't see this as a feasible method myself shorter pushrods would be!

We already have issues with guide wear for what ever reason, these specs affect where the rocker contacts the valve stem tip and how much thrust is put on it as well.

Now for me after seeing the guide I have, if I can ever get to where I can afford it, I'll have ROLLER rockers made cause that will eliminate the side-ward thrust imparted by rockers on valve stem once and for all.

I hope this makes sense I'd draw pictures but I suck at drawing I'm sure if you do some digging on the net you'll find info on what I mean!

It really comes down to geometry and if you mill enough off the heads you will need shorter pushrods to compensate for that removal of material.

JM2CW

Al

 

[Torinojts]

Double checked the piston out and they are .030 up. I should have been more clear. We check VTP clearance with zero lash. So I suppose we should find a different set of heads.