Alan Dowds starts the engine rebuild on his ZRX.
It’s been a long time coming – but Alan Dowds has finally got all the components in place for his ZRX1100 turbo engine build.
the guys at Big CC Racing know all there is to know about putting bike engines together. It’s real-world, big-bhp work here though: these guys aren’t working for chi-chi WSB or Motogp teams, simply slamming in new factory parts straight from HRC or Yoshimura. Rather, they know how to get the very best from renovating and replacing parts in customers’ engines. Sean and Lynn understand what needs to go into an engine that will make hundreds of horsepower – it’s them who (literally) have to pick up the pieces if it all goes wrong on the dyno. So, while I’ve got a fair bit of experience rebuilding engines (albeit not for a while…), I’m sticking close to the experts for this build. Like a 16-year-old apprentice, I check every step, and let the grown-ups take over at crucial points. I’m keen to take on all the donkey work too: like schlepping the head and barrels across town to be lapped flat and true. Big CC uses Precision Lapping Ltd in Wokingham, and Mark there took me through the process. The firm has a series of enormous machines, which have gigantic rotating grinding stones, set up perfectly flat. Abrasive medium and oil are constantly flowed onto the stones, and lapping a flat surface onto a cylinder head or barrels merely involves holding the parts on the stone face as it spins. Mark’s experienced hand and eye tells him when the parts are flat – essential for a proper seal once the head and barrels are clamped together. Our ZRX parts are pretty good to start with, and don’t need much work. “We do loads of bike and car heads, and the bikes are generally very good,” said Gary. “They just need a little bit of cleaning up usually, whereas car heads are often very badly warped. That’s down to people not noticing cooling system problems until the car finally stops, and badly overheating the engine. You can end up lapping a car head for ages to get it flat.” With the head and barrels properly flat, I was back to the Big CC workshop, for more donkey work – cleaning and lapping the valves. One of Big CC’S Saturday helpers had stripped the head down for me, and cleaned the carbon off the valves and ports. He’d also marked each valve’s position, and noted down the clearance shims for each valve. They’ll all need rechecking after we grind them in, but it’s good to stick to where we began. The valves were pretty clean, but on closer inspection, the exhaust seating faces were in poor condition, with marking and pitting round the circumference. Hmmm. Step one was to get all the exhaust valves (and the worst of the intake valves) into the Big CC lathe, and clean them up with some emery paper. Thirty seconds or so of (careful!) pressure with a rolled-up piece of coarse aluminium oxide paper and the sealing faces were smooth and clean. Once they’re all shiny, with no dark pitting visible, it’s time to lap them into the heads. The aim is simple: we want a gas-tight seal
between the valve head and the valve seat in the combustion chamber. To do that, we locate each valve in its guide, and using a carborundum grinding paste on the seating faces, we rotate the valve back and forth, so the valve and seat form to each other’s shape, making a perfect fit, with a slightly rough finish that seals in the hot combustion gasses completely. I have memories of doing this using a stick with rubber suckers on the end, on my old GPZ550 back in the late 1980s. But even with Big CC’S clever oscillating device, which fits into a cordless drill, it’s a bit of a faff. Has to be done though, and I spend an hour or so grinding each of the 16 valves into place. Lynn has started the proper work though. He’s keen to get the bottom end together, to get the engine’s foundations laid down. He calls me over – there’s more apprentice work to do, scraping the last bits of sealant off the crankcase faces, and doing a final cleanup on the cases. Lynn points out the brown staining inside the crankcase, like a smoker’s fingertips. It comes from old, dirty oil being left in a motor for thousands of miles – nothing horrendous, but I’m glad to get it all scrubbed out in the parts washer. Much more worrying is the bits of nasty old orange Loctite sealant which are floating about the oilways and crevices of the cases. The legacy of idiocy is annoying – particularly on the balance shaft outer adjuster seal, where most of a £5 tube of
silicone has been used to (badly) repair a seal which cost us £2.97 plus VAT from Kawasaki. It’s all gone now though, and Lynn finishes the prep by giving each oilway and passageway a good blowing out with the air line. Now we’re ready to start. The first step of the bottom end is to get the rods onto the crank. We’ve got new bigend bearing shells in the same sizes as were in the engine. And we know from last month that our new billet forged con rods are well within spec size-wise for the job. But Lynn wants to check the clearances anyway, so we get the Plastigauge out. This sounds like a mad old job, but is actually pretty simple. Plastigauge is carefullyproduced threads of a plasticine-type material, in very precise sizes. You take a small length of it, and stick it onto the big-end bearing journal. Assemble the shells into the con rod, and bolt the con rod into place on the crankshaft, being very careful not to turn the rod on the crank. Torque the big end bolts to spec, and then gently take it all apart again. The Plastigauge is squashed flat between the bearing and the crank, and the width of the squashed section tells you how much clearance there is between the bearing shell and the journal. Our big ends are all well within spec – 0.050mm. Bingo! With the big end clearances checked, Lynn gets the rods fitted. A squirt of Lynn’s favourite engine building lube on each journal, each rod sat in place, and some special ARP fastener lube on the big end bolts. Then it’s torquey torquey time. Lynn shows us a special ARP bolt-stretching gauge which can be used to measure the bolt torque, instead of using a torque wrench setting. The bracket fits round the bolt, locating onto each end, and a dial gauge measures the tiny amount that the bolts lengthen when tightened up. Clever stuff. With the rods properly lubed and bolted into place, we turn to the crankcases. We’ve hooked out the old main bearing shells and fit the new ones, taking care to put the grooved and plain shells into the correct places (the grooved ones have a pressurised oil feed hole behind them). With a couple of the long cylinder head bolts threaded into the top crankcase to hold it up off the work bench, we slot the crank carefully into place. One oddity on the ZRX engine is the extra main bearing block that bolts into place next to the primary drive gear.
You need to torque this up now – once the bottom case is on, you can’t get at it… Next is the two gearbox shafts, with their gear clusters engaged in neutral position. The gearbox bearing shafts locate with a couple of semi-circular clips (which took a bit of finding in the parts box) – don’t forget these… The smaller bearings at the opposite ends also locate into the upper case. Now, it’s sealant time. The Kawasaki manual will give you the outline of where the silicone goo goes – there are certain places that don’t have it. Less is definitely more here – watching Lynn do this crucial task, I was aware I’d have been squirting loads of the stuff in here. Too much sealant will simply squeeze out, and end up possibly blocking oilways or the oil pump pickup later on. With the sealant carefully applied, Lynn gently located the crankcase lowers into place. We’d left the gearchange parts in place, so all we had to do was put the selector forks into the right position, and guide them into the appropriate guides on the gears. Slot the bottom case down, and a gentle tap into place. If it doesn’t go down easily, check there’s nothing out of place. We had one tricky dowel at the back of the cases, which took a bit of a knock to settle down. Once that’s done, get the crankcase lower bolts, and spin them into place, making sure you get them in the right order. A clever man would have made a nice cardboard template when taking the motor apart. I adopted trial and error. The important part is the big M8 bolts around the crankshaft. These are the chaps that will be subject to the most stress when the turbo’s trying to blast the Wiseco slugs into orbit, so give the bolts a once-over for any damaged threads or the like. Clean ’em up, and torque them up in order – this is stamped onto the lower crankcase, so no excuses. The smaller bolts are there to clamp the rest of the cases together, and keep them oil tight. Once they’re all torqued up, turn the cases over, and fit the small crankcase bolts into the top case, and torque them up. Bosh. That’s as far as we got in this session, and there is still loads to do! The next priority was to get the barrels up to Sean’s favourite reboring shop in Leeds, so they could be bored out to take the new Wiseco pistons. Our new bores will be 2mm oversize, taking capacity from 1052cc to 1109cc. Not quite up to the 1164cc of the later ZRX1200 – but halfway there. Once the barrels are back, we’ll get the pistons and block on, with an APE compression-reducing spacer plate on the bottom. Next, we’ll refit the valves, bolt the head on, dial in the cams, fit a stronger clutch (perhaps a lock-up unit), and refit the sump and all the oil pump gubbins. Starter motor, alternator, outer casings – and we’ll be done. Only a turbo installation and ground-up chassis rebuild to go after that…
Precision Lapping gets to work on Dowdsy’s ZRX motor. Before the clean up. Dull but necessary: Dowds gets the emery cloth on the valves. Lapping will ensure perfect fit. Surfaces will be perfectly honed. And after the clean up. All 16 of them. Laborious!
Valve seating wasn’t brilliant. Cleaning starts the old fashioned way. Grinding compound at the ready! Al laps the valves in the ZRX’S head. Oil-ways are blown clean. And applied. And old gasket and gunk removed.
And don’t skimp on the consumables! Torque nicely now! The Plastigauge goes on. Clearance checked with Plastigauge. Big CC’S lube of choice. Bearing shells going in. It’s all finally starting to come together isn’t it?