Cylinder head camshaft and valve gear wear Twin and Triple

The valves can be removed using a conventional valve spring compressor. Note where they are positioned, for they must be replaced in the same position. There is nothing fancy to be done. Conventional collets, springs collars and one spring (Triples) or twin springs (Twins) per valve are used. Late Twins and Triples have a rubber inlet valve oil seal fitted. If your machine has done any mileage at all, then automatically replace the valve springs.

Examine each valve very carefully for scoring on its stem, and stains there too, which might come from worn valve guides and/or stems. Look for pitting on the valve head. If the valve seat looks pitted too, then grinding may be the answer or replacement valves and/or seats. Exhaust valves last a shorter time than do inlets because they get hotter.

Once you have got to this stage and you are sure that both valves and seats are intact, then you should still grind them in. Use grinding paste, especially the coarse variety sparingly, and follow the instructions given on the carton. If you feel that you require new or re-cut seats and/or valve guides, then you must seek machineshop advice (seats and guides can be measured for wear — see the Specifications). Seats can only be re-cut a couple of times and then you will need a new seat inserting. This is a difficult, precise and costly business.

Check the camshaft sprocket for wear. It its worn then you must replace it but must also replace the camchain and tensioner roller.

The camshaft lobe surfaces must be perfectly smooth. Only very light scoring can be removed with a fine oil stone. Check the rim of the four ball bearings on which the camshafts rotate. If one is shaky, it makes good sense to replace all four.

NOTE: Very detailed checks for valves, seats and guides, other than wear limits in the Specifications, are not given because I want to stress the point of seeking a second professional opinion. If your engine is worn, the chances are that there will need to be more than one overhaul task. For example, it makes no sense in having re-cut valve seats without having checked out your guides, and vice versa. One further test you should undertake at this stage is to have the cylinder head joint checked for warping. Again this is a job for a specialist who has the proper facility. Engineer's Blue on a piece of glass won't do.

Assembly of the head is pretty straightforward and virtually a reverse process of the dismantling sequence.

Start with everything spotlessly clean. Have an oil can full of clean engine oil handy, and plenty of rag.

The 1000 and 1200 have identical cylinder heads, camshafts and valves. Early 1000s had cast iron combustion chamber caps, steel liners for the cam followers and inlet stubs with cylindrical rubber gaskets recessed in the cylinder head. For 1974 the second series head was used; with the exception of the present inlet stubs with flat insulation gaskets, unaltered since 1973. A little later the heads were modified so that the cam followers ran directly in the aluminium without liners. The combustion chambers were, of course, still using the cast iron cap. During 1975 all aluminium heads with pressed-in valve seats were used but back in early 1978 the cast iron cap heads were used again. These caps are sometimes called skulls.

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