Cylinder Head Tapered After Machining

Engine, Transmission and related drivetrain.
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abisel
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Cylinder Head Tapered After Machining

Post by abisel »

So what does one do when the thickness of the cylinder head has a slight taper front to back?

The head thickness difference between the front cam tower surface and the rear cam tower surface is .015. Is this enough to worry about since the timing chain cam sprocket and crank sprocket won't be parallel to each other? And the slight angle the cam makes to the rocker arms/ valve stems may require different size lash pads for each valve.

I suspect I should add the appropriate shim stock to each cam tower to eliminate the taper.
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okayfine
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Re: Cylinder Head Tapered After Machining

Post by okayfine »

Can be a sign that your head was surfaced on a sander versus a mill. I had a head rebuilt at a shop and it ended up tapered .050 front to back. That was not useable.

Was your head surfaced on the top? You talk about how the cam is angled, but are you just measuring the head thickness at points? If it's only been surfaced on the combustion side, it's still tapered, but the cam should still be aligned properly.
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abisel
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Re: Cylinder Head Tapered After Machining

Post by abisel »

The head was surfaced with a mill on both sides. First, .005 from the bottom then .015 from the top. The bottom surface was pretty flat, but the top was more like a banana. High in the middle 'cause the cam would bind up as soon as the front and rear towers were tightened. That is when we milled the top surface. I measured the head thickness at the cam tower surfaces.

Only .015 front to back is almost nothing, but I will get some shim stock to get the cam aligned.
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Byron510
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Re: Cylinder Head Tapered After Machining

Post by Byron510 »

At .015". This won't affect the timing chain sprocket alignment. As Julian noted above, if the top surface of the head was not machined, you can to valve geometry would be unaffected.
It can slightly affect the chamber volume, depends on what kind of a motor you are building (compression ratio).
All in all, you should be ok. Sloppy workmanship - yes, which is not good. But you'll be alright in most cases with this slight amount of taper.

Byron
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because the opposite never works.
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Byron510
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Re: Cylinder Head Tapered After Machining

Post by Byron510 »

We posted reaids at the same time;

Regarding the machining at the top of the head of they took 0.15" off, but got it 0.15" wrong, then there was likely more than 0.15 taken off.
However regarding geometry, the rocker pivots at one end on a ball, and the other end runs between a flat 5mm face perpendicular to the top of the vales stem. The angle produces by the tapered machining across the head would be so slight the the angle would be shared between the lash pad and rocker surface and the cam shaft wear pad against the camshaft itself. The oil between the two parts will help buffer this. Agreed it's not perfect, however from a machinists point of view I doubt that it's perfectly aligned from the factory judging by the wear patterns I have seen on engines that have never been rebuilt. It not ideal to add more incorrect geometry issues, butter I still feel you'll be fine running what you have if everything else checks out ok.
If you are using a new cam, then new rockers and lash pads are highly suggested. These parts always wear together and should always stay together.

Byron
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because the opposite never works.
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