DOWN ON POWER

Mini Magazine - - Tech -

Q I have a 1979 Mini Club­man, still fit­ted with its orig­i­nal 1098cc engine and gearbox. Both ap­pear to be in good con­di­tion, with the engine con­sum­ing lit­tle or no oil. How­ever, it seems to be work­ing ex­tremely hard at any­thing over 60mph. I’ve set the tim­ing as per the work­shop man­ual, and I think the fu­elling is right too. How­ever, it’s just wheezy and gut­less! I know it’s know a per­for­mance car, but I’ve driven loads of Minis over the years and even a 998 would make mince­meat of mine. A friend sug­gested it’s down to valve seat re­ces­sion, but surely it would smoke if that was so? Stephan

A Be­fore fit­ting any form of tun­ing up­grade, you need to make sure what you have is fit and healthy. First, get a leak-down test done, and if that looks good, get it set up on a rolling road with a Mini-savvy op­er­a­tor.

No to be con­fused with a com­pres­sion test, the leak­down test is used to de­ter­mine the health of each in­di­vid­ual cylin­der. This is done by set­ting each cylin­der in turn on its fir­ing stroke with the pis­ton at top dead cen­tre and both valves closed.

A tube with a threaded adap­tor at one end is screwed into the spark plug hole, while the other end has a cou­pling that at­taches to an air line so the cylin­der can be pres­surised with com­pressed air. The main sec­tion of the equip­ment is two gauges that show the air pres­sure be­ing ap­plied, and a sec­ond show­ing the amount of air be­ing leaked out by way of a per­cent­age. Up to 10 per cent leak­age is pretty good, 20 is okay and up to 30 is con­cern­ing. More than that, and you’ve got ma­jor is­sues.

It is not just the gauges that re­veal any prob­lems; air heard es­cap­ing can lead you to the spe­cific prob­lem. If heard com­ing out of the car­bu­ret­tor, it’s the in­let valves not seal­ing. Out of the ex­haust, it’s the ex­haust valves not seal­ing. If it’s out of the rocker cover and dip­stick tube, the rings are not seal­ing as they should.

Get­ting the car set up on a rolling road will op­ti­mise fu­elling and ig­ni­tion, and give a power out­put read­ing. Whilst rolling roads rarely pro­duce ac­tual and real per­for­mance read­ings, the fig­ures ob­tained can be di­rectly com­pared with other sim­i­lar units run up on it to give some idea of the health of the engine.

Be­fore head­ing off to the rolling road though, there are a cou­ple of things to check and sort. Make sure the ig­ni­tion sys­tem is in good health – so points, con­denser, ro­tor arm, dizzy cap, spark plugs and plug leads. Also check and set the valve clear­ances, as these can make a big dif­fer­ence too.

The other thing to check is the oil – fore­most the oil level. Some re­ports of en­gines that won’t rev and feel flat turned out to be be­cause of ex­ces­sive oil in the gearbox!

Check your engine is fit and healthy be­fore mak­ing up­grades.

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