ASK THE EX­PERT

Yours Mini ques­tions an­swered by Keith Calver

Mini Magazine - - Contents -

Our tech ex­pert Keith Calver an­swers all your Mini tech­ni­cal queries.

BEAR­ING CHOICE

Q I’m strug­gling to get de­cent ball race wheel bear­ing kits. Is it pos­si­ble to swap the roller bear­ings in a drum hub for Timken ta­per rollers? If so, what would the torque fig­ure be? Toby

A Yes, you can sim­ply fit the Timken-type ta­per roller bear­ings to both ends of your car, pro­vid­ing it isn’t a re­ally early MkI. Up un­til around 1962 I think it was, the front wheel bear­ings were dif­fer­ent, with a smaller bore. Con­se­quently later ball race and Timken bear­ings would be some­what baggy on the drive flange shaft.

I used to do this mod years ago, us­ing Timken ta­per rollers ‘re­tired’ from my Mini Miglia in a cou­ple of my road Mi­nis owned at the time. Based on no more than my own ap­pli­ca­tion of gen­eral engi­neer­ing prac­tise, I used the drum brake torque set­tings. This is based on the fact that the ma­jor­ity of torque set­tings are de­vised for the fas­ten­ers and what they are fit­ted to rather than the other com­po­nents in the assem­bly. The torque set­tings given for the CV nuts on a Mini are more to do with the stretch and load of the CV nut, ta­per washer and thread on the end of the CV than the bear­ing/hub assem­bly. The bear­ings and as­so­ci­ated spac­ers are made from high strength, hard­ened steel so do not col­lapse fur­ther un­der greater torque pres­sure. I never had any prob­lems run­ning them like that.

As an aside, but per­ti­nent, I have heard way too many folk sug­gest that ta­per roller bear­ings are ‘ad­justable’ by sim­ply tight­en­ing the CV nut up more. They may be for cer­tain ap­pli­ca­tions that use shims to achieve a spe­cific amount of ‘play’ where a ‘fin­ger tight’ ap­proach is used in assem­bly, typ­i­cally on low-load ap­pli­ca­tions. But in ap­pli­ca­tions where high loads and specif­i­cally high torque set­tings are used to clamp the assem­bly to­gether, they are ex­tremely un­likely to be ‘ad­justable’ by in­creas­ing the clamp­ing load over that rec­om­mended. Again, the hard­ened high-grade steel com­po­nents of the bear­ing assem­bly will not crush down any fur­ther. All you are do­ing is over-stress­ing the threaded end of the CV joint. That can be dis­as­trous as it may cause the end of the CV to shear off, and the may­hem that im­plies.

STRAIGHT-CUT DROPS

Q I plan on hav­ing a gear­box re­built for my Mini May­fair, which will mainly be used for week­end fun and trips to shows. It’s go­ing to be 1330cc with a 276 cam and a Stage 3 head. I know a four-pin diff would be use­ful and I’m plan­ning to fit a cen­tre oil-pick

“The ques­tion then re­volves around whether you are des­per­ate for that dis­tinc­tive whine or not...”

up pipe, but should I fit straight­cut drop gears? A friend has a set for sale and I’m led to be­lieve they will help to cut trans­mis­sion power loss. Is the ex­tra cost worth it? Di­eter The straight-cut drop gears are the com­po­nents that give many a rac­ing Mini, and for those that want it on the street, that dis­tinc­tive whine in use – a noise that can be­come ex­tremely ir­ri­tat­ing on long runs. The ‘power’ gained is not in terms of tens of BHP; not even half that in re­al­ity. As a whole the dif­fer­ence be­tween a com­plete straight-cut trans­mis­sion assem­bly, from drop gears to fi­nal drive, only gains around 5-6bhp at best against a de­cently-built he­li­cal set-up. And ul­ti­mately the he­li­cal gears are far bet­ter qual­ity and there­fore longer last­ing and more re­li­able. So the ques­tion then re­volves around whether you are des­per­ate for that dis­tinc­tive whine or not.

CHEW­ING TYRES

Q I’ve got a ‘94 Mini May­fair and the tyres are wear­ing out on the in­ner edge. I’ve looked at the tie-rods and they ap­pear to be bent. Could this be caus­ing the prob­lem? What else might cause wear on the in­ner edges? Is the track­ing out? Ron­nie A Wear on the in­ner edges of tyres sug­gests it could be two causes – either ex­ces­sive neg­a­tive cam­ber or ex­ces­sive toe-out track­ing. The bent tierods will be giv­ing the ge­om­e­try in­creased caster an­gle, but this is not gen­er­ally the cause of the tyre wear you are ex­pe­ri­enc­ing. The bent tie-rods are not likely to be help­ing the sit­u­a­tion, or the car’s han­dling in terms of straight line run­ning. They should be re­placed as a mat­ter of course. Neg­a­tive cam­ber is where the top of the tyre, viewed head on, leans in to­wards the cen­tre­line of the car, caus­ing the tyre to run on its in­ner edge more. Toe out is where the lead­ing edges of the tyres are point­ing out­wards, away from the cen­tre­line of the car. Again, this causes the tyre con­tact patch to be more on the in­side edge. In both in­stances pre­ma­ture tyre wear on the in­ner edge is the re­sult.

The ques­tion is, which is it? With no fur­ther de­tails of the car given, I can only pre­sume the car is run­ning all stan­dard sus­pen­sion com­po­nents and ge­om­e­try. In which case the most likely cause is in­cor­rect track­ing, so get this checked and re-set. Ex­ces­sive neg­a­tive cam­ber on a stan­dard car is highly un­likely un­less the sus­pen­sion has lit­er­ally col­lapsed so it is sit­ting on its bump stops. The give-away here would be the tyre scrub­bing on the front wheel arches over ev­ery bump and dip in the road. There should be at least 1.75 inches be­tween the top of the arch and the top of the tyre.

Ta­per roller wheel bear­ings can be used in place of the ball bear­ing type.

Straight-cut drops can be noisy.

Too much toe-out can cause ex­ces­sive tyre wear.

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