RE­PLAC­ING THE BRO­KEN EX­HAUST MAN­I­FOLD

Land Rover Monthly - - Lrm Technical -

The man­i­fold to down­pipe flange should have four Bsf-thread studs in to which the down­pipe is se­cured. But in the past, those orig­i­nal studs must have cor­roded or stripped and some­one had sim­ply cut the studs off and drilled out the holes, fix­ing the ex­haust on us­ing reg­u­lar nuts and bolts. That’s annnoy­ing, but in the past when the car was worth £500, it was just what peo­ple did. To save dis­turb­ing the man­i­fold now, James tried us­ing some re­place­ment nuts and bolts, but you guessed it – when torquing them up, the drilled out (there­fore weak­ened) man­i­fold cracked.

The prob­lem with ex­haust fix­ings is the con­tin­ual heat they’re ex­posed to. In time, the studs and fix­ings be­come very tight and seized. Try to undo a man­i­fold to block fix­ing and you can be al­most cer­tain the stud into the block will sim­ply shear. If that hap­pens on one stud, the job can go from bad to worse, be­cause the oth­ers are likely to do the same and then you’ll have to deal with the en­gine block. That’s the rea­son me­chan­ics don’t like to dis­turb ex­haust man­i­folds un­less they re­ally have to.

The trick is to try some heat on the bolt us­ing a gas torch. The heat can ex­pand and loosen the thread and also break up cor­ro­sion in the process. Less cor­ro­sion means less force is needed to turn the nut, which means the force shouldn’t get high enough to shear the stud. James shows us how, with care, the bolts can be coaxed off with­out dam­ag­ing any­thing. 1 The man­i­fold flange holes had been drilled over­size to take bolts, weak­en­ing the flange. When this cor­ner broke off, a new man­i­fold was needed. 2 The 60-year-old man­i­fold fix­ings to the en­gine block are likely to shear if force is ap­plied. The trick is to put heat into them with a gas torch first. 3 With care, all our fix­ings came un­done and the man­i­fold is re­moved. Note the towel to keep crud from fall­ing into the ex­posed valve gear. 4 On re­mov­ing it, we see clear ev­i­dence that one man­i­fold gas­ket had failed. In re­al­ity, it would have had to come off to sort this any­way.

5 The en­gine mount­ing face is then cleaned up, and new ex­haust gas­kets are fit­ted. Easy to check ex­haust tap­pet clear­ances now, too.

6 The beau­ti­ful new Crad­docks man­i­fold goes on, us­ing new BSF nuts on the en­gine studs, and cor­rect brass nuts on the ex­haust down­pipe.

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