Jabiru 3300 - Inlet and Exhaust Valve Seat Work

Introduction ...

This page contains photos of a Jabiru 3300A Solid Lifter engine having it's inlet and exhaust valve being ground and lapped in.



ALT text here

Image 1

On this particular engine all valve seats required regrinding. We use this Wolf valve seat grinder. It has a diamond tipped cutting tool which is used to cut a fresh grinding "face" on the cutting stone. In this image the top right arrow (of the enlarged image) points to the handle for adjusting the horizontal position of the cutting tip. The next arrow down points to the cutting tip itself. The next arrow down points to the stone drive point. We have a short bolt with rounded off corners that is placed in a hand drill. The bolt head is located where the arrow points and the hand drill is used to spin the shaft (slowly) with the cutting stone mounted on the end of it. The fourth arrow down points to the cutting stone itself. The bottom arrow points to the handle that controls the verticle postion of the grinding stone with reference to the cutting tip. Three cutting stones are required per valve. their cutting surface is set at 30, 45 and 60 degrees respectively. The 30 degrees and 60 degrees faces are ground first. Finally the 45 degress surface is ground to finish. The valve seat and valve will then require lapping in to provide a sealing surface. ...

View Larger Image ...


ALT text here

Image 3

To grind an accurate seat it is very important an accurate guide shaft is used. This valve guide shaft is one that Roger Lewis fabricated for me. The shaft has two diameters. The part of the shaft that locates in the valve stem guide is 7.05mm. The other end of the shaft is machined to fit inside the Wolf cutting stone drive shaft. Both ends of the guide shaft must be well lubricated and cutting oil must be generously and continuously applied to the face of the cutting stone during the cutting process ...

View Larger Image ...

ALT text here

Image 4

Having cleaned up the cylinder heads and removed any lead / carbon deposits we can locate the cutting stone tool on the guide shaft ...

View Larger Image ...

ALT text here

Image 5

Next offer up the hand drill to the cutting stone shaft. Some oil will help to preserve the condition of the drive bolt in the hand drill ...

View Larger Image ...

ALT text here

Image 6

Having generously oiled the face of the cutting stone. Select a slow speed range for the hand drill. Apply a firm but gentle force down the drive shaft onto the sutting stone face. Do not allow the stone to bounce or rotate too quickly. We want to get a clean ground surface. Keep lubricating the cutting stone throughout the process. The aim is to achieve a clean ground ring all the way around the valve seat will the mimimal loss of valve seat material. Cut the 30 degress and 60 degress surfaces first and finish with the 45 degrees surface. See the overhaul manual for more details ...

View Larger Image ...

ALT text here

Image 7

The next cylinder head job that needs doing is lapping the sealing surface on the inward facing mating surface of the cylinder head with it's associated cylinder barrel. The cylinder barrel and cylinder head are effectively a matching pair once they have been lapped together. A cylinder head that has been lapped in to a given barrel cannot be assumed to seal to another barrel. A small amount of lapping / grinding paste is applied to the mating surfaces. The cylinder barrel is placed in a padded vice and the cylinder head placed on top and gently rotated (by approximately 90 degrees back and forth) until you can visually confirm contact between the two surfaces all the way around. Do this in two steps. The first step involves using a medium grinding paste. The second step used a finer grade "finishing" grinding paste. Once you are satsfied that contact is made all around the mating surface then the surface can be cleaned. All residual grinding paste must be removed. Finally engineers blue can be used to verify the seal ...

View Larger Image ...


ALT text here

Image 9

The next job is to lap in the valves to their corresponding cylinder head valve seats. Again once a valve has been lapped in to a given valve seat it effectively becomes a matching pair. We use this reciprocating lapping tool with a low powered hand drill. Less power is more! Again start with medium coarse grinding paste if required and finish with fine grade paste ...

View Larger Image ...


ALT text here

Image 11

When you are satisfied there is a good seal verify this with engineers's blue and then make absolutley sure you remove all grinding paste from both the valve and the cylinder head ...

View Larger Image ...