‘In­sid­ers say there are eight valves – a big deal on a pushrod, air­cooled Har­ley en­gine’

Motorcycle News (UK) - - This Week -

say the pushrod tubes on each cylin­der are par­al­lel, rather than con­verg­ing as they do on the cur­rent Twin Cam en­gine. That means there are sep­a­rate in­let and ex­haust camshafts – giv­ing a to­tal of three camshafts or pos­si­bly even four, all mounted in the block and gear driven from the camshaft.

Nor­mally, four-valve heads are associated with higher-revving, high­per­for­mance en­gines, usu­ally with dual over­head camshafts, while pushrods are linked to thud­ding mo­tors more in­ter­ested in torque, and usu­ally with only two valves per cylin­der.

How­ever, as en­gines be­come larger, the im­pe­tus for more valves also grows since they help get more gas in and out of the cylin­der more ef­fi­ciently and of­fer a bet­ter con­trol of that gas flow, in turn im­prov­ing the way the air-fuel mix burns. As well as im­prov­ing per­for­mance, that gives bet­ter emis­sions – and that’s a big deal, par­tic­u­larly on large, air-cooled en­gines. It’s not yet clear whether the wa­ter-cooled cylin­der head idea of the cur­rent ‘Twin Cooled’ twin cam en­gines is car­ried over to the Mil­wau­kee-eight.

The new en­gine’s ca­pac­ity is clearly 107 cu­bic inches – that’s 1753cc – and given that the en­gine is new there will be scope for much larger ver­sions for fu­ture mod­els. There’s al­ready talk of 117ci (1917cc) or 120ci (1966cc) ver­sions for CVO mod­els.

The en­gine will de­but in Har­ley’s top Tour­ing mod­els, but ex­pect it to spread to more bikes. The of­fi­cial un­veil­ing will come at the end of Au­gust, when Har­ley’s 2017 line-up is launched.

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