Checking and adjusting valve clearances (Mitsubishi Space Star)

Correct valve clearances are very important because they largely determine engine performance. If the valve clearances are too large, the engine will be noisy and the efficiency will be reduced because the valves open too late and close too early. More serious problems occur if the valve clearances are too small because the valves cannot close completely when the engine is hot, which can cause serious engine damage.

• Checking and adjusting valve clearances must be carried out on a cold engine.
• Remove the cylinder head cover.
• Check and adjust the valve drive clearances in the following sequence. Identify a cylinder with equally open intake and exhaust valves and check the valve clearances on the cylinder with closed intake and exhaust valves (Fig. 4.1).

• Using the crankshaft pulley mounting bolt, rotate the engine crankshaft sequentially by a quarter of a turn and take the following measurements.



• Use a metal feeler gauge to measure the clearance in the valve drive (Fig. 4.2). When measuring the clearance, the blade of the feeler gauge should move very tightly.

Nominal clearance (engine cold):

- when checking:

• inlet valve: 0.15-0.20 mm
• - exhaust valve: 0.35-0.45 mm

- when adjusting:

• inlet valve: 0.20 mm
• exhaust valve: 0.40 mm

• If the valve clearance is outside the nominal value, adjust it by selecting tappets of the required thickness, performing the following operations.
• Re-measure any valve clearances that are outside the specified range and record the actual valve clearance value.
• Using a micrometer, measure the distance (Fig. 4.3) from the end of the central pin to the front surface of the pusher.

• Calculate the thickness of the new tappet as follows:
• Thickness of tappet for adjustment = thickness of removed tappet (X) + (measured value - nominal clearance value)
• Select a plunger with a thickness that matches the required value. If a plunger of the required thickness is not available, use a plunger with a thickness closest to the calculated value.

Note

(1) Measure the tappet thickness with a micrometer only.

(2) Always use new tappets.

(3) The tappets have a thickness from 7.550 mm to 8.150 mm in 0.025 mm increments.

• Remove the camshaft and install the selected tappet.
• Clean and degrease the mating surfaces of the cylinder head and camshaft bearing caps. Use a suitable solvent for cleaning, and it is very important not to scratch the aluminum alloy from which the cylinder head is made.
• Lubricate and install the camshaft.
• Using a paint roller, apply Loctite 518 sealant to the mating surface of the camshaft bearing cap until it turns "reddish" and remove any excess paste that gets on the bearings.
• Install the camshaft support cover and screw in the cover and inner timing belt casing mounting bolts, after applying a locking compound (such as Loctite Frenfitanch) to the bolt threads.
• Tighten the camshaft support cover mounting bolts in the specified sequence.
• Install the cylinder head cover with a new gasket and tighten the cover mounting bolts in the specified sequence.
• Install the vacuum pump with a new gasket.
• Turn the camshaft one revolution and check that the valve clearances comply with the nominal values.
• Install the cylinder head cover.

[The article was taken from the website: mitsubishiman.ru]