- Measuring valve guide clearance
- Replace valve guides
To measure valve guide clearance:
Worn valve guides can cause the following complaints and defects:
- burnt valve discs;
- broken valve;
- rocker arm wear;
- increased oil consumption.
With a disassembled cylinder head, we want to measure the clearance of the valve in the valve guides with the above complaints. Not all manufacturers describe the maximum allowable clearance in the service documents. In that case, we can use the guideline values in the table below:
The following figure shows the measurement where the valve clearance of the exhaust valve is measured. The dial indicator is placed on a tripod and has thus been given a fixed position. We place the needle of the dial indicator with a pre-tension of at least 2 mm against the valve disc of the valve, which is slid about 10 mm from the cylinder head.
With moderate force we try to move the valve back and forth in the direction of the dial indicator. The dial indicator hand will move back and forth over a certain area of the dial as it moves. The stroke the pointer makes indicates the play.
Replace valve guides:
When we measure a clearance that is too large, we consult the technical data of the relevant engine to find out whether the valve guides can be replaced. If this is not necessary according to the factory regulations, a reputable overhaul company often knows what to do with it. Otherwise it would mean that the complete cylinder head would have to be replaced.
If it is possible to replace the valve guides, equipment will be required to remove the valve guides, ream the hole and install new valve guides. In most cases, the cylinder head must be heated to about 130 degrees Celsius and the valve guides must be pressed into the holes.
The two images below show the position of the valve guide in the cylinder head (left) and three different valve guides (right).