Mount­ing ex­cite­ment triples

The 500 en­gine mounts are ready to be welded onto the 400 frame. It’s all hap­pen­ing

Practical Sportsbikes (UK) - - On Our Bench - BSD: Miguel is tak­ing care of the ’box, Rad­i­cal Pre­ci­sion: en­gine mounts by our man Mick Reed, rad­i­cal­pre­ci­sio­ Bobles Bits: in­let spac­ers by Bob, look up him and his won­drous works on Face­book

You can’t rush a good resto. Nor can you hurry love, as The Supremes so tune­fully ad­vised us. The KH/H1 project has been slowly smoul­der­ing away as we ac­cu­mu­late both knowl­edge and parts – in that or­der. It’s now at the stage when the whole thing is ready to co­a­lesce into the smok­ing, snarling won­der-cy­cle we con­ceived as far back as Au­tumn 2017.

The Gary Clarke re­built crank­shaft sits wait­ing to be in­stalled along with a gear­box cur­rently hav­ing all the dogs on all the pin­ions un­der­cut. Even un­der en­thu­si­as­tic street rid­ing the stock ’box can jump out of gear. This is be­cause un­der heavy load, the en­gaged dogs are pulled away from each other. They are very slightly un­der­cut from the fac­tory, by 2-de­grees, but re­quire a steeper cut (5-de­gree) for hard rid­ing. Bent se­lec­tor forks can mimic the same prob­lem, and ours showed signs of hard use, but were not bent; the sec­ond to third gear fork was well-knack­ered, the other two worn but still OK for fu­ture ser­vice. We bought a very neatly re­man­u­fac­tured fork from Z1­

Miguel at BSD is un­der­cut­ting the dogs and su­perfin­ish­ing the en­tire cog-set. Su­perfin­ish­ing (vi­brat­ing the pin­ions in a big box of glass beads) re­duces con­tact fric­tion, al­lows the ’box to run cooler and makes it last longer. For out-and-out rac­ing some builders ma­chine three en­gage­ment dogs off to make it a three-dog ’box, this gives slightly faster shift­ing, but the pay­back is a lit­tle more lash in the trans­mis­sion, mak­ing the driv­e­line a bit slop­pier. We’ve stuck with six dogs.

The en­gine mounts were fab­ri­cated by Mick Reed at Rad­i­cal Pre­ci­sion. The sec­tions were laser-cut, the front lower mounts then form­folded and the bosses will be tack-welded be­fore

be­ing trued-up when we of­fer the en­gine into the frame with the out­put shaft and drive sprocket fit­ted into the cases to achieve a dead-true chain line. This will be the next stage be­fore we build the bot­tom end of the en­gine.

That will then be farmed-out to ace two-stroke man Bob Farn­ham for the port­ing and com­bus­tion cham­ber re­work­ing. He will also blend the spac­ers for the new 34mm Miku­nis (up from 28mm) and the in­let rub­bers for max­i­mum flow. Then, when he’s nailed the top-end to the bot­tom, we’ll be bolt­ing in a Zeel­tronic ig­ni­tion to fire the sparks at the new Wöss­ner pis­tons.

The H1F en­gine is rub­ber-mounted, not in a com­plex man­ner, in the sim­plest fash­ion pos­si­ble – big rub­ber slugs where the mounts are. When the rub­bers get worn (like ours) the en­gine shifts in the frame which is far from ideal for besthandling prac­tice, so our plan is to mould some new polyurethane bushes when we at­tack the rest of the chas­sis.

Mean­time EBC have come through with a set of fresh fi­bre plates and a heavy-duty clutch spring set to han­dle the new lev­els of power this en­gine will pro­duce. The first 1968 H1 pro­duced a claimed 60bhp, the B, C, D, E, F grad­u­ally less, and the fi­nal 500, the KH500 of 1976 made 52bhp. We’re look­ing for a rear wheel 60bhp, maybe a lit­tle more, but a good use­able spread of power with a fat midrange. We see no rea­son why this isn’t pos­si­ble with Bob’s magic and a good set of ex­pan­sion cham­bers.

So, it’ll be chas­sis next, while the en­gine goes to­gether. This chas­sis will be as stock as pos­si­ble. When we see just how much power we’ve got, we may have to think again. But for now, it’s get it all to­gether and go from there. We aim to be on the road by early sum­mer. And we can­not wait.


Cases in the frame, and sad cases in the frame

Laser-cut lower rear mount

The H1F 500cc crankcases sit­ting on top of the KH mounts that will be re­placed

Rear top mounts ready to bolt on for the dry build

Front lower en­gine mounts are sub­stan­tial items

Newspapers in English

Newspapers from UK

© PressReader. All rights reserved.