Cylinder Head Resurfacing

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My dad took the heads down to the guy who did our dyno runs so he could take a look at them and the pictures of our piston damage. He didn’t seem too concerned and recommended we resurface the heads and clean the high spots off the the piston.

He put the heads on the resurfacer and used a dial indicator to check for flatness.

 

They were off about 0.0015″ across the whole surface, so he reset the surfacer only to mill off the high spots. This removed about 90% of the damage from the heads. I’ll post a picture when I get them back.

2 thoughts on “Cylinder Head Resurfacing”

  1. Andrew

    Sorry for the bad luck. Odd that more than one cylinder was damaged by the single piece of debris.

    How do the cylinder walls look? Did they escape damage?

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  2. Jason

    When we mentioned this to the guy who ran the dyno shop, he said it wasn’t uncommon for debris to move from cylinder to cylinder, especially with a single plan manifold. As I understand it, here is how that can happen:

    When one cylinder is at the tail end of the exhaust stroke, both the intake and exhaust valves are open so that the inrush of a new fuel/air charge can help evacuate the old exhaust gases. If the engine is at idle, the throttle plates are closed, so the prior cylinder in the firing order is already 90º of rotation ahead of the one with both valves open and is sucking hard to get its fuel/air charge. With a dual plane (180º) manifold, it can only suck in the charge from the plenum below the throttle body because all other cylinders in the same plane of the manifold have closed valves. In a single plane (90º) manifold, it can actually reverse flow through the cylinder with both valves open and suck exhaust gases (and debris) back into the intake manifold.

    This is one of the reasons that single plane manifolds have a rougher idle (some exhaust gases moving from cylinder to cylinder), but it also explains how debris can move from cylinder to cylinder.

    Fortunately, the cylinder walls are fine. I was worried that I was going to have to replace that one piston and re-hone the bore.

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