PROJECT BIKE

Har­ley en­gine gets at­ten­tion

Motorcycle News (UK) - - This Week - ped.baker@mo­tor­cy­cle­news.com PED BAKER DIY welder who also builds bi­cy­cles in his spare time HEIGHT 6in 4in WEIGHT 90kg

It’s taken a while, but Project Har­ley is mak­ing progress. After weigh­ing up the pros and cons of ei­ther re-sleev­ing the dam­aged front cylin­der and fit­ting new rings to the orig­i­nal pis­tons or buy­ing new over­sized pis­tons and re­bor­ing both cylin­ders, Har­ley-david­son tech­ni­cian Gavin Cupit sug­gested the re­bore route.

Krazy Horse in Bury St Ed­munds (01284 749645) sup­plied the S&S pis­tons plus base gas­kets and their ma­chine shop took care of the re­bore.

All post-1984 Har­ley en­gines fea­ture alu­minium cylin­ders fit­ted with steel lin­ers. On these mod­els, when the cylin­der head is torqued down, the cylin­ders dis­tort slightly. This dis­tor­tion must be mir­rored dur­ing the cylin­der ma­chin­ing pro­cesses. This is done with torque plates – steel plates with the cylin­der sand­wiched in­be­tween. All Har­ley-david­son Evo­lu­tion Big Twin, Evo­lu­tion Sport­ster and Twin Cam en­gine mod­els must have their bores ma­chined (and mea­sured) be­tween torque plates. If they’re bored without them, when the heads are torqued down the lin­ers will go bar­rel shaped. Pis­ton slap, poor com­pres­sion and oil con­sump­tion will fol­low.

The big bore 93 S&S stro­ker kit (raises ca­pac­ity from 1340cc to 1524cc) also re­quires some ma­chin­ing of the crankcases to al­low for the in­creased throw on the crank. After care­ful in­spec­tion, Gavin sus­pects the per­for­mance up­grades were made to the FXR from new, giv­ing the mod­i­fi­ca­tions a thumbs-up with no fur­ther work needed. With all the other parts in­spected and bear­ings and gas­kets or­dered, it’s just a case of re­mov­ing all the peel­ing chrome plate and cor­ro­sion from the cases and bolt­ing it all back to­gether.

In­side the ma­chined crank­case, ready for... ... the S&S crank with in­creased throw Torque plates repli­cate the ef­fects of en­gine torque

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