Alan Dowds starts the en­gine rebuild on his ZRX.

Classic Motorcycle Mechanics - - CONTENTS -

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…

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.

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!

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?

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