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Velocette TT winners
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I pulled the head off first. The piston had mark from the exhaust valve and when I stripped the head I found a bent exhaust valve and broken guide. The chamber was clean, like the bike had only been run a short while. The top of the piston and inlet valve were very clean but the exhaust valve had clearly not been seating[well it was bent]. The bore has very little wear, the bore was quite scuffed, I might get away with a hone, but the piston wanted replacing as it was also badly scuffed and the ring grooves were damaged. I checked the valve clearance before stripping the head, both valves had a lot of clearance, maybe 35-50 thou, both push rods were bent. One pushrod had a crack and the end fell out of it.


Figure 1. Piston rings, how mad are they..

The most bizzare thing so far is the rings, they look like they have had their ID resized with an angle grinder! "Nice restoration";-) I can only guess the rings were to wide and he only had an angle grinder at hand to cure them.


Figure 2. Broken valve guide.

In the pic it looks like there is a crack running away from the valve guide, I keep forgetting to check that[checked and it's a mark in the casting?], I think it's just a mark in the casting. The barrel had been shortened 0.152inch, I presume this was to raise the compression. The valves show some scoring to the stem, but didn't seem tight in the guides and as I didn't check valve to piston clearance I can't really say for definite why the valve got all friendly with the piston. Before speculating on anything you need to see the timing chest page.


Figure 3. Bent exhaust valve.

The exhaust valve is not grossly bent, it only had a small contact patch with the seat, but it managed enough compression to run! Conclusion thus far would have to be be the valve to piston clearance hadn't been checked[the barrel was shortened] and the valve played tag with the piston. The bore wear was negligible and would have possibly honed out but I fitted a new piston, I also opted for a secondhand barrel. The new barrel was bored to suite a Triumph Daytona piston, easy availability and the larger little end meaning I could bore the loose little end[little end had lot's of play]. The valve springs sat on a large washer perched on the step on one the guide and on one side the spring sat on a spacer sitting in the base of the spring cup. I replaced the springs and the spring seats.