Monday 13 April 2015

Nuts! - update

Updated 13th April

-JdK- One of the most annoying nuts on a Carroll OHC engine must be the nut holding the bevel on the camshaft. I may be 'teaching grandmother to suck eggs' but it took me two weeks to tighten this nut so here's the story.

The best way to assemble a Carroll cambox may be to first fit the bevel to the camshaft and tighten this nut. Then the camshaft can pushed through the bearing in the cambox, and spacer, cams and roller bearing fitted whereafter the nut on the other side of the camshaft can be tightened. The problem is that this is a left-hand nut. The camshaft is locked with a spanner using the nut at the bevel side but as this one is a right-hand nut, when one nut is tightened the other nut may come loose and vice-versa.

So the nut holding the bevel should be very tight. The 'square' at the end of the camshaft is easily damaged and cannot be used; further, the camshafts are made from unhardened steel like EN8 and can be easily twisted and damaged when you apply brute force.

The best way seems to be to just grip the bevel between two pieces of wood (shaped like in the photo above) in a vice. This looks brutal but the teeth on the bevel will be embedded in the wood and the torque will be spread over a large part of the bevel. It won't damage the bevel.

When doing this I found out the bevel needs to be gripped very tight in the vice otherwise the wood will splinter. I used good quality Meranti hardwood and a one-meter length of steel pipe to tighten up the vice. This was required because the nut needed 200 Nm torque (that is a lot!) before it was tight enough to allow the left-hand nut at the other side of the shaft to be torqued to 50 Nm. This is probably because the nut at the bevel side hardly moves once torqued up to around 40 Nm. It needs a really good pull with a very long spanner before it moves after that!

(Ian Bennett and Dr George also use this method and around 200 Nm to tighten this nut. Others suggest to just fit the cambox the engine, lock the crank and then tighten the nuts on the camshaft; that means putting a lot of torque on the teeth of the bevels. Perhaps the engine may withstand such abuse but it doesn't feel right to me.)

Update by Dr George on the 13th April: "I was inspired by this article and decided to upgrade my tired old lead jaws. Below is my new tool; it's two alloy plates with two thicknesses of roofing lead. It works perfectly!"