MASCOT May 1992
SM 1500 - HIKER - H.R.G. SECTION
Derrick Bedwell
Well, Spring has brought a slight upsurge - certainly one car is being used on a daily basis. Once again the small demand for spares does not highlight any particular item. As promised last month, the article on camshafts, chains, clearances, etc. is continued. This likewise applies to 4ADs.
Camshaft ,Chain Tensioners - Both types are illustrated on the following pages, together with instructions for the SM 1500 engines. The text from the Singer Manual also covers clearances and timing. The second illustration shows the two most obvious differences between the two engines, i.e. the mechanical fuel pump and the oil filter on the Hunter engine.
SM 1500 Engines - Remember on these engines a slack or flaying chain, due to a broken tensioner spring, could rub through the camshaft oil feed pipe - with obvious results.
SM 1500 and 4AD
VALVE CLEARANCES.
A modified form of camshaft, Part No. C.11714, as fitted to the Hunter from Engine No. H.1501.Y, Is now supplied for all SM.1500 Service requirements and with this type the valve clearances must be set to.020" (.51 mm). (cold) Inlet and Exhaust.
A metal plate showing these clearance figures is supplied with the modified camshaft. In cases where replacement of the original pattern is involved and this plate should be permanently attached to the valve cover.
This modified camshaft can be identified by a groove which is machined around the outside diameter of the driving flange - See page B14.
VALVE TIMING.
From Engine No. D.730.S a mark is scribed on the rim of the driving flange of the camshaft which, when in line with the machined face of the pad at the butt face of No. 1 bearing cap of the camshaft, and with the mark 1 -4 on the flywheel set at top centre, indicates the inlet valves are opening at 10° B.T.D.C.
With engines bearing numbers prior to D.730.5 to position the camshaft with the inlet valve just opening at 10° B.T:D.C.
Proceed as follows :
Check and, if necessary, set the rocker clearances to .004" (.1 mm.) for the inlet valves and .006" (.15 mm.) for the .exhaust valves.
Rotate the engine slowly by means of the starting handle, and while doing so, endeavour to oscillate, with the forefinger and thumb, the collar of the inlet valve for No.1 Cylinder. As long as the valve is on its seat oscillation will be difficult, but immediately the valve commences to leave its seat oscillation will be comparatively easy.
Where this condition occurs is the exact opening position of the valve and for the timing to be correct, the mark 1/4 on the flywheel should at that point, be 10° or 15/16" (23.812 mm.) measured on the rim of the flywheel, before top centre.
These Instructions should be followed when positioning the camshaft prior to replacing the cylinder head or removing the primary chain and timing wheels as described on pages 89 and B21.
Any correction to the valve timing should be carried out as described under Method 2 on page 8.16.
NOTE. When positioning the camshaft always ensure that the electrode of the distributor rotor points to the segment in the cap connected to No. 4 Sparking Plug.
CAMSHAFT C HAIN TENSIONER ADJUSTMENT.
Secure from turning, with a fairly thin 7/16" spanner, the lock nut of the chain tensioner. and with the aid of a second 7/16" spanner remove the cover of the tensioner-the lock nut is the one nearest the cylinder head
Release the lock nut and. with a 3/16" spanner, screw "in" or "out" the threaded plug of the tensioner until the distance between the end of the cottered plunger and the end face of the threaded plug is 11/32". It is important that this dimension is not exceeded or reduced, as any such action will cause the chain to wear abnormally.
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