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Tech Notes: |
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TECH
- FAQ's |
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Valve to Piston Clearances
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Valve to Piston Clearances |
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VERY IMPORTANT – Anytime a modification is made to a cylinder head
such as milling or decking, increase in valve size, larger camshaft or
valve train components, it is extremely important to check and establish
piston-to-valve clearance. The primary reason is to make sure that the
pistons and valves do not hit each other. Contact between a piston and
valve can cause extreme engine damage or complete engine failure.
Piston-to-valve clearance can be measured in several ways. A common
method, also know as the “Clay” method, can be performed and will be
discussed in detail for this newsletter. LC Engineering recommends a
minimum of 0.080” (eighty thousandths) for piston-to-valve clearance on
most applications.
With the cylinder head removed, spread modeling clay evenly across the top
of the #1 piston with the piston at TDC. Place the cylinder head; with
the #1 intake and exhaust rocker arm lash set at 0 (zero), on top of the
block using a crushed head gasket. Secure the head in place by tightening
the head bolts/studs so they are snug. It is not necessary to torque the
cylinder head down to the block since you will be removing it after this
next step.
Connect the timing chain to the upper sprocket with the cam set at the
correct timing. Now rotate the engine slowly clockwise, by hand, a
single revolution back to TDC. Loosen the head bolts/nuts and remove the
cylinder head from the block. You should now see some impressions in the
clay from the valves. Using an Exacto Knife, slice the clay from top to
bottom where the intake and exhaust valves left an indentation. With a
set of calipers or depth gauge, measure the thickness of the clay to
determine the correct piston-to-valve clearance number. Again, the number
should be no less than 0.080”.
PLEASE NOTE – It should be relatively easy to
rotate the engine clockwise with a ratchet attached to the crankshaft. If
you feel any interference, or the engine will not rotate any further,
STOP!! Any amount of force placed on the valves or piston will cause
damage. Most likely the pistons will need “notching” in order to continue
with assembly. Please contact our Technical Department for specific
information on how to proceed at 928-505-2501. |
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| Clay spread evenly
across top of piston before head is placed into position. |
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After rotation of the
engine, and removal of the head, you should see an indentation in
the clay. |
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Use a knife to slice
through the clay to establish an area to measure with. |
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| Clay Before |
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Clay After |
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Clay Cutting |
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Return to TECH NOTES Main Page |
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