STEP -BYSTEP
Engine strip and rebuild
1
On removing the head, Will found that the ‘seizure’ was simply one of the exhaust valves stuck open, otherwise the engine turned over smoothly. He’s got a good buy! 2
Bore, pistons and big-ends were good... sure, there was water in the gearbox, but that’s not unusual on 500s – it runs down the clutch cable if the grommet is missing. 3
A handy feature of these engines is a ‘cartridge’ gearbox that comes out in one piece without disturbing the gears – but little did we know all was not well here... 4
If an oil change ever reveals shiny flakes in the sump filter; stop riding – the big ends are breaking up and ready to seize. But there were no such problems here. 5
With the crankshaft out, the ‘sludge trap’ filter needs to be cleaned. Plug threads may be ‘caulked’ (threads locked by dot punch). Drill the burring away before removal. 6
It’s worth doing. Sludge comes from dirty oil; 1000-mile changes prevent this kind of build-up. There’s slight wear on the main journal but otherwise it’s in fine shape. 7
Rockerbox in Farnham had all the parts we needed. They’re engine builders, too, and only stock quality. Partsman Darrell clearly hated taking Will’s hard-earned cash! 8
Pete from Brit Steel Classics guided Will through the rebuild. Modus Engineering made a superb job of grinding the crank. And Will? Well, he supplied the Jaffa Cakes. 9
Pete and Will fitted new big-end shells and rebuilt the sludge trap as I bored the new bush to within reaming range of the crank diameter and fitted it to the crankcase.
10
Grease keeps swarf from oilways; it’s washed out later. This reaming requires minute cuts and constant swarf clearing to avoid the blades digging in. 11
Extension pilot aligns the reamer through the opposite bearing – but the pilot’s too big to fit, so I turned a larger-bore ‘dummy bearing’ from aluminium. 12
I also made a ‘go/not go’ gauge to check progress. Measured steps represent small increases in diameter – when the largest fits the bush, it’s spot on. 13
Over to the boys to assemble the crankcases; I was pleased – and relieved – at how smoothly the crank turned between my reamed bush and the new ballrace. 14
Only the unit 350/500 engines allow you to fit the cams after the crankcases are joined – but don’t forget to fit the engine breather disc/spring first. 15
The high gear bush extension had a wear groove from contact with the primary case oil seal; we pressed in a replacement which Will reamed to size. 16
Assembled, we couldn’t engage the gears properly. Pete noticed the selectors were reversed; ‘spot the difference’? There’s an extra bit on one fork. 17
I gave Will an indicator-type oil pressure release valve, worthwhile on these engines; low pressure means bottom-end trouble on the way. 18
While Pete fitted the timing gears, I showed Will how to grind valves. He said: “Great; feels like I’m finally fixing the bit that stopped the engine working!”
19
Worth checking each piston ring’s clearance with a feeler gauge; you want around four thou per inch of cylinder bore to avoid possible seizure.
20
Piston ring clamps keep the rings safely compressed while the barrel is lowered in place – but it’s still ideally a two man job. Use plenty of oil.
21
Pete showed Will how to fit the valve springs – a dab of grease on the valve collets keeps the first in place while you fit the second.
22
We’re fitting later-type pushrod tubes – they seal better. But you need to fit later tappet blocks or make seal-seating washers.
23
Paper rocker gaskets squeeze out – but using just ‘instant gasket’ can cause rocker/valve collar contact. See the shiny witness mark?
24
Pete finds that wire-reinforced gaskets shed strands into the oil, so he rates these copper gaskets (with RTV). But anneal and deburr them first...
25
Turn crank to level the pushrods and lower the box, lifting the rockers with the thumbs so you can feel them engaging with the pushrod ends.
26
Will’s smile says it all. I loved my first Triumph – they’re great, and thanks to Pete and Ferret I reckon Will’s got a bright future ahead!