Rebuilding head

[zachdeagle16]

How many times can a head be rebuilt? and What do I need to do to make a non turbo head turbo other than swapping the cams?

 

[1fast97gsx]

How many times can a head be rebuilt?

It depends on the reason for the rebuilds and how worn parts are.

and What do I need to do to make a non turbo head turbo other than swapping the cams?

Bolt a turbo to it.

 

[BISHILVR]

You can rebuild the head as many times as you want, there is no limit but you have to check the amount removed from the surface of the head if you have it shaved every time that you rebuild it, which is'nt really neccessary. Too much aluminum removed from the head will leave it useless unless you plan to run a thicker head gasket with it to make up for the removal of aluminum from the surface. A turbo and a non turbo head are the same part number, there is no difference.

 

[zachdeagle16]

How can you tell how much aluminum is too much?

 

[zachdeagle16]

What the effects of having to much aluminum removed?

 

[BISHILVR]

Most machine shops will stamp into the bottom of the head (not on the gasket surface) the amount of aluminum that they removed from the head gasket surface in order to get the surface perfectly flat again. There is a certain amount of aluminum removal (shaving) that mitsubishi and other companys allow to be removed from the head and or the head gasket surface of the block, before the head or block is no longer considered usable. Removing too much surface metal from the head or block causes higher compression and cam timing to be off, since the head now sits closer to the crankshaft. The timing belt is made to a certain length and that length is depenant on the distance from the crank to the cam sprocket (cogs) to be accurate. When the head moves closer to the crank, from shaving the head or "decking" the block, that distance changes and wont allow you to set the timing belt marks dead on anymore. The nice thing is that companys make adjustable timing gears for that reason, we can use them to get timing spot on even with a block or head that has been shaved too far. Another item is a head gasket that is thicker than stock to make up for the removed metal and it will increase piston to head clearance to a safe level again. The head gaskets come in different thickness for different requirements.

 

[Scrymerr]

Is there any standard used to measure the 'thickness' of the head when it comes from the factory and then gauge how much material is left before the head is unusable?

 

[dets]

Is there any standard used to measure the 'thickness' of the head when it comes from the factory and then gauge how much material is left before the head is unusable?

well that sounds like a two part question.


The standard for measurement is usually a micrometer or any standard tool of measurement. Just compare current measures to factory spec.


The difficulty comes in understanding the relationship between the material removed and the new thermodynamic properties the head has.

When a head is decked, a good machine shop will stamp the bottom but some don't. Its important to keep an eye out for any cracks between the valve seats or any deformation at all.


FYI, i have yet to drop a valve or destroy a head on my rally car. Eventually i'll be tapping the rear and adding an additional coolant port just for exp. I'd like to see how low i can keep the temps.

 

[BISHILVR]

Is there any standard used to measure the 'thickness' of the head when it comes from the factory and then gauge how much material is left before the head is unusable?

A decent machine shop will have a machinists book that will give them the data to rebuild the head, including max material removal.

 

[Scrymerr]

A decent machine shop will have a machinists book that will give them the data to rebuild the head, including max material removal.

Well, how will a machinist know how much material has been previously removed? I have gotten plenty of heads machined that weren't marked with the amount of material removed or anything like that. I am curious as to whether or not there is some measurement that can be done on a brand new head that indicates the total amount of material on there, and then use that method of measuring on an old head to find out where said head is in relation to a new one. Does that make sense? I am planning on investing a bit of money into a head, and would rather do so on a head with some life left in it if you will.


Dan

 

[diambo4life]

Well, how will a machinist know how much material has been previously removed? I have gotten plenty of heads machined that weren't marked with the amount of material removed or anything like that. I am curious as to whether or not there is some measurement that can be done on a brand new head that indicates the total amount of material on there, and then use that method of measuring on an old head to find out where said head is in relation to a new one. Does that make sense? I am planning on investing a bit of money into a head, and would rather do so on a head with some life left in it if you will.


Dan

There are certain points on the cylinder head deck that indicate how much material you have until the head can no longer be resurfaced/reused. If you have a picture of the head's deck, I can show you exactly what I'm talking about.

 

[BISHILVR]

Yep, the machine shop will know. Take the head your interested in using to your good machine shop and let them check it out before you invest in it.

 

[pneumo]

Here's a good pic. See those circles in the upper right and lower left? Those tell you how much material has been removed. The inner part of the circle is deeper than the outer ring, so you measure how deep it is, and that tells you if the head still has enough material or not. I'm not a machinist, so I don't have any specs on the limit, but I do have a spare head that was resurfaced once, and the circles are between 0.85mm to 1.05mm deep. HTH.

 

[BoostedAWD91]

you can reuse the head plent of times as long as it is in good condition still. just have it checked for deck warpage, crackin in the head and valve seats.

 

[diambo4life]

Yes, but there's a limit to how many times it can be decked. As mentioned already, the points on the head arrowed in the pic below can indicate when you have reached the limit.

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When the depth of the inner circle gets to the same level/plane as the outside portion, the limit has been reached.

 

[zachdeagle16]

Thanks for all the replies that answeres my question.