Saturday, 23 July 2011

NX650 cylinder head

The only way out of the morass of worn parts is to spend money.

Repair options first: Phil Joy at Joy Engineering, Ware, no longer repairs cylinder heads as he did for many years. He suggested one person who might do the job, but then pointed out the scored central journal is not critical. That reminded me of a stripdown Honda UK did of a 1989 Dominator used by Performance Bikes. Nine months from new the central journal was scored, but it went as well as ever and there was no other engine damage.

This gave me hope, but we still had a cylinder head crack to deal with. I soon gave up looking for a second hand head. They aren't available, for obvious reasons, and used engines on eBay or from breakers sell around the £650 mark. Not a risk worth taking. They could have cracked heads too. New heads are £800-£1000 as far as I can tell.

The Cylinder Head Shop told me they could pop out the valve seats, grind the crack out, fill it with weld, remachine and then refit the seats for about £350. As a bonus, they would thicken the plug area to take a long reach plug. I sent it off. Six weeks and many calls later they hadn't started the job, so I got it sent back. They apologised and offered to get it done pronto, but I had lost all faith. The highly respected SRM Engineering reckoned a repair was not worth doing. Can you see daylight through the crack? No. Was it running OK when you got it? Yes. Well, you could always try putting it together and running it as is, they suggested.

I got a third opinion from Ducati bevel expert Tony Brancato, who I went to see on a job for Bike. Tony said he could repair it, but it would never be as good as a new. That settled it. I decided to replace the worn cam parts and re-use the old head. The cracks happen, apparently, due to overheating. I will make sure this engine never runs low on oil again.

Dave Silver Spares quoted £203 for a new camshaft. I found a cam billed on eBay (usa-motorcycles-inc) as an XR650/89 Dominator fitment in the USA for about £75 and went for that. Dave Silver supplied two followers and two sub-rockers for another £70 or so.

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