Tech Talk

The task of seal­ing joint faces falls to gas­ket ce­ment… doesn’t it?

Classic Dirtbike - - Contents - Words and pics Tim Brit­ton

All old bikes leak oil, it’s their charm… er no, they don’t have to, and with the help of Loc­tite we show you how top stop them drip­ping.

The whole hoary sub­ject of re­place­ment gas­kets, seal­ers and the like is one close to the heart of any reader of this magazine. Af­ter all, most of the mo­tor­cy­cles we use are at least 30 years old and the cases have been apart loads of times.

Gas­ket ce­ment is a prod­uct de­signed to hold a gas­ket in place be­fore be­ing fit­ted. Like many peo­ple, I’ve been guilty in the past of mis­us­ing the prod­ucts we glibly de­scribe as gas­ket goo, thankfully though I’ve not been as bad as the owner of an en­gine I was once asked to have a look at be­cause ‘…it stopped work­ing…’

One glance showed why – rib­bons of or­ange sil­i­cone ex­uded from ev­ery joint face on the en­gine and the sit­u­a­tion didn’t im­prove the deeper I went in. Ev­ery sin­gle oil-way and gallery was full of the stuff and the lad had ap­par­ently used two whole tubes of the goo to stop any oil leaks. A re­sult he had, in fact, achieved.

What he had missed was that in­stant gas­ket, gas­ket ce­ment or assem­bly sil­i­cone can only do its job prop­erly if the light­est smear is ap­plied to an al­ready flat joint­ing face. Ladling the stuff on with a trowel may well seal the joint but you can guar­an­tee if the ce­ment squeezes out of the side then it will squeeze out inside the en­gine too, where it can cause dam­age.

We’ve men­tioned many times how to make sure mat­ing faces are as flat as pos­si­ble in a home work­shop, by rub­bing them on an old mir­ror with a smear of fine grind­ing paste on it – but it doesn’t hurt to say it again. Nor does it hurt to say the grind­ing paste must be washed off thor­oughly, as you don’t want that get­ting inside your en­gine.

For the next bit of the feature we’re in­debted to Henkel Ltd for pro­vid­ing us with Loc­tite prod­ucts and in­struc­tions on how to use them to the best ad­van­tage.

As you can see, the en­gine we’re us­ing is just bare cases, so we can show things a lit­tle more clearly where the joint faces are.

The world of gas­kets and in­stant gas­kets has moved on a long way and thanks to peo­ple such as Henkel, with Loc­tite there is lit­tle rea­son why an older mo­tor­cy­cle shouldn’t be as oil-tight as a mod­ern one. Above: A se­lec­tion of en­gine cases typ­i­cal of thema­chines seen in CDB. From the left, the old cases fro­mour project IT, then the new project 3TA/5TA and our first project Ro­tax/canam

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