To Shave heads or not?? Need help

I am redoing my heads on 87 mondial cab and want to know if I should shave heads just to "clean" surfaces up....I have read through many threads regarding shaving heads for increased compression, especially for turbo conversions, but I want to keep it stock and am wondering if just shaving heads as little as possible to clean surfaces is recommended.

The heads are not warped, I just had some bent valves. Thanks in advance!

 

Lets say that you cut the valve seats so the new valves seat well and don't leak.
The valves surface area cover a little more than 1/2 (4 valve heads) of the top of the combustion chamber.

So, if you had to recess the valve seats by (say) and average of 0.010" while cutting the new seats, you would want to shave the head by 1/2 that amount (0.005") in order to maintain the original compression.

The correct way to do this is to cc the heads if you are going to operate right on the edge of ping/detonation, otherwise the shave is to retain the compression you already have and to flatten the heads so the gasket seals perfectly.

 

Wouldn't cutting the valve seats and shaving the heads both increase compression? I would see both actions making the combustion chamber effectively smaller.
BT

 

The "official" policy oif FNA in this topic in TAHT era was that there was to be NO cutting of cylinder heads...re-surfacing as we call it here in machine shop/engine building land..

Their reasons are fairly starightforward: Liability is chiefly amogst them...if the head got "hot" enought to "bend it" so that .012" requires to be removed...there are compound sublties-many are carry overs from chain drive 128F/168/213/245/251 family engine issues-which are not quite as acute with belt engines.
Mainly are the issues of geometry changes from centerline of the CAMSHAFTS to the parting line, the change in chain angle(s) geometry and effects-albeit subtle-on camshaft timing...think about this carefully before responding...particularly with respect to SOHC, and lack of ability to move-individually-the lobe centers around...

The OTHER BIG deal was that with the advent of the 4 valve design were significant metals treatment changes done as the operational envelope changes now inherent in closed loop 3-way cat controlled engines.
The VALVE SEATS are stellite(a coating really), as are the 4-VALVEs, and the application of this material was....inconsistent, to be gentle..
however, it was adequate and extremely effective as a primary coating, to be able to guarantee suitability for fitness for use subsequent to a grinding procedeure, was not in the list of acceptable assumptions of liability...
In reality, and I quote: "you may "kiss" the seats, try and take no mre than 3-004" "..additionally, there is the issue of annealed alloy heads, there exists Brinnel figures on a 5mm ball for these heads...
"they" will never let this stuff out...
they rarely let it out then to the Dlr netwrk...
buy a head
buy an engine
buy a new car,
harsh, but it was the attitude 20+ years ago...

All which is vaguely ironic as the casting mnumbers, time stamps, and "clocking" bosses on the castings are identical for your heads and for 288/F-40(same head, essentially!), excepting for small details like their peanut plug's thread's inserts, and MINOR chamber machining...including the seats-which are also stellite...
FWIW...

 

Bill,

Seems to me that cutting the valve seats will make the chamber volume bigger, as the valves will sit deeper into the head, leaving more space in the combustion chamber. The increase would be very small, it would seem, but obviously measurable. Shaving the heads obviously would reduce the volume in the chamber, which is why it was recommended as an offset to the increase in volume from cutting the valve seats.

And aren't you proud of me for not making some stupid wise-crack about Yule Brenner, Vin Diesel or one of those guys??!!!! Shaved heads?? Get it???

 

p.s. I make no recommendation about whether either or both are a good idea, since I have no expertise or experience with doing either on a 3x8.

 

A light cleanup on a cylinder head surface is standard procedure with aluminum heads.

 

In the past I would have said "shave 'em!". Everybody around me used to do it and the extra compression was seen as welcome. However, as years progressed and I talked to more and more people, I noticed a lot of people do not even bother, especially the ones in the car fixing business. Some of them were the worst, in the case of a head gasket problem they did not even bother removing the head! They just drained the coolant, unbolted the head bolts, slid out the old head gasket and in with the new. Saves a lot of wrenching time not having to remove plenums, or perhaps even timing belts! And in a good percentage of the cases the customer will be happy with their fixed head gasket... argh.

Such bodging aside, the reasoning behind not skimming is that if the head wasn't removed because of a warpage, then the removal did not suddenly warp it and a quick cleanup job as you normally would on a gasket surface is sufficient. Seems very proper, and since I've done both skimmed and non-skimmed, and in both cases did not have issues, it seems right.

Yes it looks so nice after it's been machined, doesn't it. And it's lovely to remember that you put it all together that shiny. But once in, that shine doesn't last anyway, nobody sees it and apparently it doesn't make a difference in reliability afterwards at all! Your choice, really

 

I am proud of you, and I don't know why I was thinking that making the valve seat bigger (or recessed more) would push the valve into the combustion chamber. I've had some mental problems the past two days!

BT

 

It's springtime. The mind wanders to things more esoteric, like getting our sweet rides out on the road. All pure thought and reason is swept aside. Let's get out there and drive'm like we stole'm!!!

 

Wow.....thanks for all the input. It sounds like im going to have them lightly shaved to clean them.....less than .003 if shop can do it. Im going to go look at them and see what they look like first but I guess thats the consensus?