Keith Livingstone stripped his 1974 Triumph T120 to check up on an annoying rattle, but after heating the bottom end in the oven to part the cases he found oil had baked to form carbon in the small-ends.
“I realise I should have cleaned all the old oil off before putting the bottom end in the oven, but how can I remove it?”
I’d think the carbon was already there, Keith. It can build up when the bushes are worn, because the pin is no longer making a full contact. If it is just baked on from heating, probably the best way to remove it would be with a twisted ‘rope’ of wire wool or maybe a bit of fine emery paper wrapped around a wooden dowel – split the dowel down the middle and insert a folded strip of emery to make a lapping tool; go easy and use a bit of light oil. If you do decide to replace the small-ends, it’s best to press or pull them into the (hot) conrods using a shouldered tool made up to fit.
Ideally, you want a tube big enough to press the old bush into on one side and a stepped mandrel the other side to support the bush as it goes in. The tight fit should mean that, once fitted, the bush will need to be reamed or honed to size.
LEFT: Carbon on your small-end suggests wear.