The valve guides are so named because they guide the stem of the valve during its motion. By properly locating the stem of the valve, the head and face of the valve are kept in proper relationship to the head. Occasionally, the valve guides will wear, causing poor valve sealing and poor engine performance. If this problem is suspected, check the sideways play of the valve within the guide.
If the play is minimal, it may not be necessary to replace the guides. A competent machine shop can knurl the guides. This process raises a spiral ridge on the inside of the guide, thereby eliminating the wobble and properly locating the valve. This is not a cure-all; it can only be done to correct minimal wear. Severe wear requires replacement of the valve guides.
REMOVAL & INSTALLATION
The use of the correct special tools or their equivalent is REQUIRED for this procedure.Gasoline Engines
See Figures 1 and 2
The valve guides on the B20 and B30 engines can be pressed out with Volvo special tool No. 2818 and a press. New guides are installed with special tool No. 2819 and a press. Substitution tools can be used for either of these operations, however, when installing the new guides, distance A in the illustration must equal 0.689 in. (17.5mm) for all B20 and B30 engines except the B20E and the B20F. For the B20E and B20F, distance A should equal 0.705 in. (18mm).
The valve guides on the B21 and the B27/B28/B280 are also pressed out with tool No. 2818. When removing the valve guides on the B27/B28/B280 engines, place the cylinder head on the press so that the guide (not the head) is vertical. This allows the guide to be pressed straight out and not at an angle to the press.
To fit new valve guides on the B21 and B23 engine, heat the head to approximately 140° F (60° C) in water and, using special tool No. 5027 for the intake valves and tool No. 5028 for the exhaust valves, press the valve guides in until the tool abuts the cylinder head.
The B230 head requires heating to 212° F (100° C); the installation tools are the same. If these tools are not available, press in the guides until the guide's height above the cylinder head surface, at the base of the guide, is 0.6061-0.6139 in. (15.4-15.6mm) for intake valve guides and 0.7051-0.7129 in. (17.9-18.1mm) for exhaust valve guides. When replacing the guides on the B230 engine, make sure the new guides have the same number of grooves at the end as the old guide. The number of grooves is an indication of the size of the guide.
B234 heads do not require heating but do require the guides to be installed under a minimum pressure of 2025 lbs. ((918.5 kg). The pressing operation is conducted in three steps with three different drifts of exact size. The final installation step leaves the top of the guide projecting above the head by 0.60 in. (15mm). The height is set by the installation tool.
After installing new guides, they must be reamed with a hand tool and the valves and seats must be ground (lapped).
On the B27/28 engines, the valve guides come in two oversizes. For oversize No. 1, the valve guide hole must be reamed out to 0.5195-0.5207 in. (13.20-13.23mm). For oversize No. 2, the hole must be reamed out to 0.5315-0.5326 in. (13.50-13.52mm). The grip in the cylinder head must be 0.0020-0.0037 in. (0.05-0.09mm).
After the holes have been reamed, press in the valve guides with special tool No. 5108 (for intake valves) and No. 5109 for exhaust. The correct pressing-in measurement for intake guides is 1.5551-1.5945 in. (39.5-40.5mm) and for exhaust guides 1.4370-1.4921 in. (36.5-37.9mm). After the guides are installed, ream them out to 0.3150-0.3158 in. (8.00-8.02mm) diameter.
The B28F and B280 heads require heating to about 300°F (149°C); it is generally outside the ability of the average home mechanic to safely deal with this level of heat. It is recommended that the head be taken to a machine shop for professional installation of new valve guides.
The valve seats on all engines are removable. Since the usual method of removing and installing valve seats includes either freezing or heating the valve seat or the cylinder head, this job should be performed by a competent machine shop or garage. The intake valve seats on the B28 engine are of a new design and should not be replaced with the old style seats.Diesel Engines
The valve guides are pressed out of the cold cylinder head toward the camshaft with an appropriate drift and press. To install a new guide, oil it lightly and press it into the cold cylinder head from the camshaft side. Press the guide in as far as it will go.
Once installed, the guide must be reamed out to the appropriate diameter.The valve seats can be refaced but cannot be replaced. Reface the exhaust seats by hand only: do not use a machine.