TUN­ING FOR SPEED

Real Classic - - 1954 Nimbus Type C -

RC read­ers with long me­mories will re­call Lasse Horskjær’s re­build of his own Nim­bus (RC123-126). Not long af­ter it was com­plete he set off on a trip from Copen­hagen to Cze­choslo­vakia, but in Ger­many things went wildly awry…

‘With­out warn­ing my Nim­bus sud­denly started to sound like a ma­chine gun. With the throt­tle part closed the sound al­most stopped, but it came back in full force with any ex­tra power. I wasn’t in any doubt. This sound could only be be­cause the big ends had lost their white metal bear­ings sur­faces. So very, very slowly I rode up­hill in first gear back to our ho­tel: end of ad­ven­ture!

‘Look­ing at the dip­stick, I found lots of oil, so the prob­lem wasn’t caused by lack of oil. I be­lieve long dis­tances on au­to­bahns had been too much for the old-fash­ioned white metal bear­ings. How­ever, when the Nim­bus had been run­ning it was very, very good; com­fort­able and re­spon­sive. So I de­cided to bite the bul­let and treat the mo­tor to a ma­jor over­haul (again-again), but dif­fer­ently this time.

‘Luck was with me. A ver­i­ta­ble Nim­bus guru, Niels Nielsen took in­ter­est in my project and al­lowed me to work in his work­shop, do­ing the rough stuff while he did the brainy jobs. By a mir­a­cle, he found one of the very last orig­i­nal Nim­bus crankshafts – brand new. He de­clared he had to “ruin it” right away, and grind all four jour­nals! Why’s that? Niels knows a very smart trick, used in the days where Nim­bus ma­chines were raced. He sub­sti­tuted the vul­ner­a­ble white metal bear­ings with Fiat 1200 Sport shell bear­ings which he reck­oned would suit my“press-on driv­ing style”.

‘So in went these mod­ern (1976!) half­shell bear­ings. Niels also talked me into new pis­ton rings, to­tal valve seat ren­o­va­tion, new valve springs, as well as eight new H-D stain­less valves, a new oil pump to­gether with a lot of other smaller im­prove­ments.

‘The end re­sult? A very, very lively Nim­bus, def­i­nitely with more power and a 100% clean pick-up from any speed. It now has an ab­so­lutely safe cruis­ing speed in the re­gion of 70mph. Top speed is over 85mph but that’s not to be used ex­cept in an “emer­gency”. The funny thing about my new mo­tor is that I don’t need to give it so much throt­tle as be­fore to hold a cer­tain ve­loc­ity. At half throt­tle the bike holds a con­stant speed of 60mph. Great!’

Lasse Horskjær’s Nim­bus; some­what mod­i­fied

Left: The con rods have been con­verted to take shell bear­ings to re­place the orig­i­nal white met­alling

Right: Neat and sim­ple; the en­gine from un­der­neath shows off the four con rods and two big main bear­ings

Right: H-D valves have re­placed the orig­i­nals

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