Itinerant Air-Cooled

I've decided to pull the trigger, and swap out my heads. Before everyone harangues me to do a complete rebuild, I'd like to say this engine runs very smoothly, decent power. When Colin looked at it 10 years ago, he thought the case had never been split apart, and swagged there was probably 50k miles on it. I've put on about 20k since. I hate to crack into a perfectly good running engine.

Only reason I'm swapping out the heads is I have a broken stud boss on the left head, and a helicoil in one of the sparkplug holes on the right head. Biggest reason is the broken stud boss....kinda loud and kinda stinky. Goal is to run it until it does need a full rebuild...hopefully another 30k miles.

This is what is on the list so far (some not related to engine work):

- two heads
- rubber fuel filler neck (mine has holes)
- push rod seals
- exhaust flanges
- exhaust manifold gasket
- steering dampener
- spark plugs (3 only have about 10k miles, the other is permanently seized to the helicoil)

I know I will need to cc the heads to get them close to what I have now, and I will also need to check, and adjust as necessary for crank end play. However, I figure I won't be able to order the crank shims until I pull the engine and now what size shims are in there now, and what I will have to order. I might do rings depending on what i find; primary goal is to maintain homeostasis but get rid of the exhaust leak.

What else should I put on my shopping list?

Consider adding:

• intake manifold gasket
  new valve adjustment screws (swivel-foot ones, since you're running solid lifters)
  maybe injector seals
  jeweller's or riffle files to remove the molding flash on the heads

If you buy new AMC heads, you will likely find that they already have the correct chamber volume, and that they will all be very close to one another, so close that you won't be able to measure the difference with a standard hobbyist cc-ing kit.

While you have the heads off, it would be a good idea to check the piston deck-height on each cylinder (to aid in your CR calculations) and also check that the cylinder-to-head seating surfaces are co-planar (ie. make sure that the pairs of cylinders are flat across their tops and that they present a single unified interface to the heads) If they are tilted or skewed in relation to each other, then there's little chance the heads will be able to seal effectively against them.

SlowLane wrote: check that the cylinder-to-head seating surfaces are co-planar
If they are tilted or skewed in relation to each other, then there's little chance the heads will be able to seal effectively against them.

And if they are not co-planar? Do we suggest that he tear down the engine and get the case milled?

I would personally bolt the heads up to 45 ft/lbs with a good coating of prussian blue on a set of sealing rings and see how they do under clamping torque . . . if they check out, then I would use sealing rings at final assembly, do the overnight 45 ft/lbs and retorque in the morning to 23-25 ft/lbs.
Colin

That Wandering Fellow wrote:And if they are not co-planar? Do we suggest that he tear down the engine and get the case milled?

My suggestion to check the cylinder tops was simply to give Mr. Troll an insight into things that might affect the application of his new heads. If he were to simply bolt them on without doing some forensic measurements first, the results might not be to his liking. And without said measurements, the reasons behind the poor results might be mis-attributed.

Okay, so in the real world there is no such thing as perfectly co-planar, just as there is no such thing as a perfectly smooth surface.

There will be, however, an acceptable level of co-planar-ness, beyond which it would make sense to mill the case. You have graciously provided a practical method for determining what that acceptable level would be, for your purposes.

As to your recommended sealing ring procedure, is the overnight sit @ 45 ft/lb intended to create a "set" in the sealing ring? Do you reckon that an aluminum (or copper?) sealing ring is any more likely to develop a "set" than just the bare aluminum head? Just curious where you got the 45 ft/lb value from? Is that intended to be the approximate equivalent clamping force to that experienced by a hot engine?

SlowLane wrote:is the overnight sit @ 45 ft/lb intended to create a "set" in the sealing ring? Do you reckon that an aluminum (or copper?) sealing ring is any more likely to develop a "set" than just the bare aluminum head? Just curious where you got the 45 ft/lb value from? Is that intended to be the approximate equivalent clamping force to that experienced by a hot engine?

It creates a set in everything, the case, the heads, the sealing rings. Yes, the 45 mimics a warmed up engine but to what degree I have no idea.

This came to me after discovering time and again that head torque always showed a drop after a period of time just sitting there. Then I read of re-torquing after time on my Lexus LS-400 engine camshafts which have such ridiculously close tolerances.

The mimicking a heat cycle is just pure horsesh*t conjecture, but I like it and I have never experienced a head leak.
Colin

I think you are stretching the head studs which then relax .

Bleyseng wrote:I think you are stretching the head studs which then relax .

I think you are crushing the aluminum-to-iron head sealing surfaces and sealing rings if used.
The whole reason they switched to necked thin head studs was to let them stretch and contract with the engine time and time again.
Colin