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TVR Tasmin, Valve Clearances

Another small job I wanted to take on whilst the car was in bits, was to check the valve clearances. I had no history of it being done, and its a fairly important thing to check on these engines, and not hard to do.

Valve clearance is the small gap that must exist between the rocker arm and the top of the valve stem. This gap allows for expansion of the parts as they heat up (mainly the valve), so that there isn’t either excessive space between the two (valve won’t open as far or as long, and will make a loud tapping noise) or too little (valve may not close, and can result in a burnt valve).

Some engines have the means to self adjust, usually via a hydraulic lifter (those things that make Mitsis go “tick tick tick”), but on these older engines (and even some modern engines, like Hondas) the clearances were a scheduled service item and needs to be checked and corrected.

On this engine it’s nice and easy to access with the intake piping out of the way. It’s just a matter of removing the valve covers, of which mine were leaking anyway.

It turns out that a few of the valve cover bolts weren’t even finger tight, so no wonder the oil was getting through the gasket!

With the covers off, you need to use a socket and ratchet to rotate the engine so that the crank timing mark lines up with TDC on the front pointer. If its correct, you should find that No 5 cylinder valves are “rocking” and this is when you measure No 1 cylinder clearances. “Rocking” is the term for when you watch the rockers on that cylinder and you will see the both are at the same height, but if you rock the crank one way, one rocker will push down slightly, and if you rock it the other way, the other rocker will push down.

Ford Cologne engines are a little special, so the layout isn’t quite what you expect. Take note of the layout of the intake and exhaust valves, they aren’t always in the same order.

The clearances should be as follows. These are done on a cold engine (about 20c ideally). The exhaust has a bigger clearance due to the additional heat the valve is subjected to.

When checked with a feeler gauge, there should be a slight drag on the blade, but not too tight, or too loose. You kinda just do it by feel and get to know what it should feel like

When one cylinder is done, check the list to see what rockers will be rocking next and turn the crank (in the direction of normal rotation) until those rockers rock, and check the clearances on the opposing cylinder in the list. Easy.

If any of them need adjusting, there will be a screw on the opposite end of the rocker, that either needs to be loosened or tightened to open or close the gap. Most cars have a locking nut to stop it rotating, but the Cologne doesn’t, so turning the screw will adjust it, and it self locks. Mine were very tight, so I used a six sided socket and rachet to turn them. A little goes a long way though, so sometimes even a slight tweak of the screw will be the difference between loose, and the right amount of drag.

Five of six cylinders had valves that were too tight to get the blade into, and one cylinder was loose as a goose. I don’t know what this means, hopefully it isn’t a sign of valve recession due to a lack of lead, but time will tell. It could also just be bad adjustment from a previous mechanic….

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