Top-End Rebuild


Some specialized tools are needed if you really want to check all the engine component specifications.

Before we can cut the valve seats, the head needs to be cleaned, degreased and carbon deposits removed. The header pipe gasket will be pushed into the head and locked in with carbon. You might need a pick or similar to dislodge it. They are usually made of copper and are one-use only since they compress to make a good seal. A new gasket should be in the top-end rebuild gasket kit.

When the header pipe was removed the nut locked onto the stud, causing it to wind out of the head. Now is a good time to fix it back in place. Use high-strength Loctite as the low or medium type is broken down too easily with heat. Wind on two nuts to the stud and lock them together. This will allow you to tighten the stud into the head. Two spanners are then used to unlock the nuts so they can be removed from the stud.
The exhaust valve of high performance motorcycles is often made of harder material to withstand the high exhaust temperatures. Since exhaust gas is pushed out of the cylinder, the exhaust valve is sometimes smaller. Note, if the valve is seated on the entire face of the valve instead of approximately one-third of the face. This means it is worn and needs replacing. Check the manufacturers specifications for more detail.

It is always good practice to replace components back in their original position when reassembling the engine. The exhaust valves are not being replaced, so place each on on some cardboard and mark it accordingly. The titanium inlet valves are worn and will be replaced. The valve spring retainers and collets are also being replaced. The valve spring can lose some tension over time from heat and stress.

Cylinder heads on single cylinders rarely warp, but its good practice to check for any warping prior to reassembly. You need an accurate straight edge and a feeler gauge to check against the manufacturer's specifications. A steel ruler will not cut it as the accuracy of the reading is compromised. Once the straight edge is flat against the gasket surface, try inserting the minimum feeler gauge blade to see it the head is warped. Check in a few different angles.

The carbon in the exhaust port and cylinder head can be cleaned using a wire brush, but a much better way is to use a bead blaster. Don't use garnet blasting material as it is too harsh on the aluminum. Glass beads work well to bring the head back to near-new condition. After cleaning, the head needs a thorough blow out with compressed air to remove all the blasting media from the coolant channels as well as bolt threads.

Other parts that wear in the cylinder head are the valve guides. These are pressed into the head but can be replaced if worn. Once they wear, the valves tend to rock a little instead of traveling directly up and down. A small bore gauge is inserted into the guide and adjusted to find the widest section of the valve guide. A micrometer is needed for accurate measurement of the small bore gauge and the valve stem. Subtract the valve stem diameter from the guide internal diameter and that is your clearance.Tag: Top-End Top-End-Rebuild Maintenance Valves Mechanical Exhaust-System Bead Blaster Degrease Cleaning
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