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8. In my experience most Japanese engines, even quite old designs, will cope quite happily with unleaded petrol. However the hardened steels are tough to re-condition by hand, and traditional valve grinding methods don't usually make much of an impression on them. Before sending the head out for re-conditioning I decide to try the traditional method of valve grinding using a wooden stick fitted with a rubber sucker. With a little grinding paste smeared on the valve seat I can then rotate the valve by hand, lapping the valve head into its seat. |
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9. Lo and behold the traditional method works a treat, producing a splendid matt grey ring around the valve head and its matching seat. Two or three applications of grinding paste are sufficient to remove all traces of pitting, and I can finish off by carefully washing the valves and seats with petrol. However the ease with which I lapped in these valves makes me suspicious of running this engine on unleaded fuel, and I'll be recommending Lorenzo uses a fuel additive like Wynns Valve Guard when running the rebuilt engine. |
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10. The XS650 follows a traditional SOHC design and has four rocker arms held captive in the rocker cover. With the large diameter chromed plug removed the rocker pivot pin should simply slide out and allow the rocker to pull free. In practise the pivot pins are quite a tight fit in the rocker cover, but Yamaha have thoughtfully drilled and tapped each one so that an M6 screw can be wound in to help remove it. I found that by packing washers against the side of the casing I could progressively wind an M6 allen screw into each pin to withdraw it. |
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11. The rocker arms have the valve clearance adjuster at one end and the cam follower at the other. Each follower rides over its respective cam lobe whilst the engine is running, and is susceptible to wear, particularly if oil changes have been missed. Some slight scuffing is evident here but doesn't warrant the price of fitting a replacement. Heavy wear would mean replacement, and possibly a new camshaft to boot. Check the valve clearance adjusters too, these are prone to pitting on the XS650 motor and might need to be replaced. |
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12. To remove the ravages of corrosion and years of baked on dirt we have opted to have the head, rocker cover and barrels bead blasted. This is a specialist job and needs to be done with care. It's all to easy to get tiny amounts of grit into engine oilways, leading to horrors once the rebuilt engine is started up. I entrusted the parts to Paul Coward at Bikerworld, who once again carefully masked up all the vulnerable surfaces before producing a splendid finish. The next step is to thoroughly wash the parts in paraffin and blast everything clean and dry with a compressed air jet. To make doubly sure everything is spotlessly clean I then pop the bits in the dishwasher, making sure the wife is well out of the way first! |
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13. Before the valves go back in these valve stem seals need to be replaced. They just pop over the tops of the guides, and serve to stop excess oil running down the guides which would cause the engine to smoke on the over-run. Replace them every time they are disturbed. |
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14. Now the valves can be re-fitted in their original positions. The valve spring compressor allows me to hold the valve springs down whilst popping the split collets into place on the valve stem. A smear of grease holds them in place while I unwind the compressor and remove it. Don't forget the steel washers under the valve springs. |
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15. For purely cosmetic reasons I've cleaned up the crankcases and given them a coat of silver engine enamel. I'm reluctant to opt for bead blasting on such complex castings due to the risk of getting grit into the oilways. An hour spent with paraffin and steel wool before another application of the dishwasher gives a good enough surface to take the paint. Inside the top crankcase I noticed the legend "Paul 1991" scratched into the alloy, evidence of a previous re-build. I've now scratched "Rod 2002" alongside it! |
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16. Last month I commented that the engine can be stripped without splitting the camchain, and here's the evidence! Unfortunately the chain does loop around the rear slipper blade mount, so will have to be split if it is being replaced. The "soft link" can be easily found as then end plate is a lighter colour. |