Classic Motorcycle Mechanics - - CONTENTS - cmm

Mark Hay­cock and you with two pages of tips.

Fil­ter Tip!

Q: Hi Mark, been in­ter­est­ing to read your stuff about oil fil­ters. I have a very tidy Yamaha XS500 my­self, a 1980 model and it has the spin-on con­ver­sion oil-fil­ter. When I got it, it had a Hi­flo HF303 in place and to change the fil­ter you had to take the side of the bike off to get to it, but if you use a Hi­flo HF204, this ba­si­cally is the same fil­ter but about one inch shorter. This means you can change the fil­ter with­out hav­ing to strip half the bike! Dave Cut­ler A: That is in­ter­est­ing, be­cause I see from the ap­pli­ca­tion list for the HF204 one of the many bikes it will fit is the Honda CB900F2. In other words it has the same di­men­sions as the Honda fil­ter I used and thus could re­place it. Great minds think alike! One thing I should point out is that this fil­ter has an M20 rather than M22 thread, so it will not act as a di­rect re­place­ment for the orig­i­nal Yamaha fil­ter.

1988 Honda BROS 400

Q: Hello from Dublin! I re­cently pur­chased a 1988 Honda Bros 400. The bike is a nice ex­am­ple and has sur­vived fairly well. I’m look­ing to do a tidy-up on her to make a good us­able mo­tor­bike. Firstly the paint: there is a rust patch around where the seat meets the tank and it has spread un­der the paint in places. I’ve been ad­vised to strip and re­paint the whole tank for best re­sults but she made it this far it seems a shame to get rid of the orig­i­nal paint job. Would it be pos­si­ble to touch up the area af­fected? I’ve been ad­vised against this but would like an opin­ion. The colour seems to be a me­tal­lic black; is it still avail­able? These bikes have an is­sue with the drive-gear strip­ping the splines off the shaft: mine hasn’t, but I’m won­der­ing as to the cause so as it can be avoided in the fu­ture. Some fo­rums suggest an in­cor­rect chain ten­sion. Last ques­tion, the switchgear has been badly bleached from the sun; are these generic part or spe­cific to the Bros? Bernard Mccann A: Is your paint black with blue me­tal­lic par­ti­cles? If so the colour is called Gran­ite Blue. You can con­firm this as some­where un­der the seat you should see a la­bel with the paint code PB184MU on it. I think you would be highly un­likely to get a touch-up spray or a brush-on tin but if you quote the Honda paint code you might be lucky. Oth­er­wise it will need a re­spray but some­one who knows what they are do­ing will make it look not just as good as, but bet­ter than new. Or you could take the op­por­tu­nity to change the colour to what­ever you want. There does ap­pear to be an is­sue with the splines on the gear­box out­put (counter) shaft which drive the sprocket. I have seen pic­tures of splines nearly worn out and find this very cu­ri­ous, as it seems to be a prob­lem which af­fects some bikes and not oth­ers. One cause might be that some shafts were in­cor­rectly, and hence in­suf­fi­ciently, hard­ened but the com­mon theme among own­ers is that the chain is of­ten run too tight. This is no doubt be­cause the de­sign of the rear sus­pen­sion is such that the chain ten­sion varies widely de­pend­ing on rear wheel po­si­tion. The rec­om­men­da­tion then is to set the ten­sion to be rather more slack than you would nor­mally ex­pect. The com­mon Honda sprocket mount­ing ar­range­ment us­ing a plate and two M6 bolts al­lows, by de­sign, the sprocket to move slightly on the splines in use (this is to al­low for slight mis­align­ment or sprocket de­for­ma­tion) and so the shaft needs to be well lubri­cated. The area by the sprocket is bound to be well lubri­cated if ad­e­quate chain lu­bri­ca­tion is car­ried out. I think the han­dle­bar switches were unique to the NT400/600 and they do not seem to be com­monly found, so you might be best ad­vised to stick with what you have.

Two-stroke tim­ing

Q: A two-stroke tim­ing query. Back in the early 70s when I was an ap­pren­tice bus me­chanic, I got to be a whizz, with my trusty DTI, at tim­ing up my mates’ points-equipped two-strokes (the im­prove­ment of 250 Kawasaki triples with three sets of points was as­tound­ing). The DTI made sure the pis­ton was in pre­cisely the cor­rect po­si­tion and a test lamp across the points made sure each set were open­ing at ex­actly the right time (though the im­prove­ment only lasted about a week). On mod­ern elec­tronic ig­ni­tions al­though the DTI bit is still the same, the elec­tri­cal bit seems to con­sist of lin­ing up a cou­ple of marks by eye. Given the pre­cise na­ture of elec­tron­ics, this method of set­ting the elec­tri­cal side seems a lit­tle hit and miss, espe­cially on any­thing highly-tuned. I mean, how do you know the marks are where they should be? Or what if the engine has been mod­i­fied? Still, see­ing as none other than Sir Stan of Stephens does it this way, it must in­deed be ac­cu­rate enough to do the job. John Ran­dall A: I think your con­clu­sion is cor­rect. Al­though it may be that the spec­i­fi­ca­tion is, say, 2.6mm as on the S1, what does that mean? Sim­ply that in Kawasaki’s tests when the engine was be­ing de­vel­oped 2.6mm turned out to be the best com­pro­mise be­tween a num­ber of dif­fer­ent fac­tors. The en­gines pro­duced at the fac­tory were not iden­ti­cal clones and there must be a range of di­men­sions and weights that will af­fect the way the engine runs, to a small ex­tent. It could well be that on a par­tic­u­lar engine 2.5mm would work a bit bet­ter but it is just eas­ier to set it to 2.6mm as that is a recog­nised com­pro­mise. And as you say, with points ig­ni­tion it does not take very long for the set­ting to change. So lin­ing up the marks is per­fectly ad­e­quate for nor­mal en­gines. For a tuned engine, the ex­per­i­men­tal process must be­gin again un­less of course rules of thumb are ap­plied.


Q: I’ve bought a tank for a Honda CB500 K on ebay: it’s in ex­cel­lent con­di­tion, re­ally solid but in­side the tank is rusty. It’s not flaky rust just pow­dery. Can you rec­om­mend a process for clean­ing in­side, or is there some­one who you can rec­om­mend? I’m hav­ing it re­sprayed at some point so a com­pany who can do both at the same time would be even bet­ter. Alan Evans A: I think you are wise in get­ting a pro­fes­sional to do the spray­ing as you can­not ex­pect to do that at home us­ing mod­ern durable paints which do need spe­cial­ist equip­ment to ap­ply them. Lin­ing the tank is a DIY job though, and I shall be look­ing at that in a sep­a­rate ar­ti­cle soon. Or, check our back is­sues for tank ex­per­tise from our own Steve Cooper in Fe­bru­ary 2014 and he told us how to re­move a tank liner in Au­gust 2017.

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