No adjustment

By: WebmasterAdmin

James Inchmore bought one of the more successful farms in the area after he immigrated to South Africa more than ten years ago. He never suspected his rather uncommon, and particularly British-sounding, surname would be the source of such mirth in the local community.

They had a field day dreaming up all kinds of suitable nicknames. The two nomenclatures that ended up sticking were Foot-long, for the old boy, and
Half-inch, for his diminutive son.

As soon as the family had settled in and Foot-long was making enough money to indulge in his passion, he began restoring old cars. His first project was an early VW Beetle that cost him a great deal of money to restore, but the task was made easier by his discovery that almost any Veedub part can be imported from China. The final result was a credit to his patience, and all went well for a number of years.

About a year ago, Foot-long brought the car to us because it started to lose performance and idle very unevenly. I asked Hennie to perform a compression test and he concluded that some of the exhaust valves were burnt.

When Hennie gave us the bad news I asked Foot-long whether the engine was in a good state of tune. He explained that all the settings that could cause valve burning were correct. The ignition timing was spot-on, the thermostat was working correctly, the oil cooler wasn’t blocked and, according to a Beetle expert, he was using the correct jets in the carburettor.

As he spoke, I got an inkling of what the cause of the burning might be, so I asked:

“Has the car been difficult to start before the bad idling started.”

“Yes, I often had to keep the starter going for more than 10 seconds”, he said.

“When did you last adjust the Beetle’s valve clearances?”

“They’re hydraulic; they don’t need to be adjusted,” he responded

“I think you‘ve been reading the wrong websites. The very last Beetles that rolled off the production line may have been fitted with hydraulic valves, but by far the majority were equipped with manual valve adjustment.”

“How does the valve clearance affect the valve temperature?”

“Over time the hammering action of valves tends to cause them to regress into their seats and, as a result, the valve clearances decrease. This, in turn, means that the valves stay open slightly longer than before. Valves can cool down only when they’re in contact with the seat so that the end result is an overheated valve.”

“How does hard-starting come into the picture?“

“If the valves stay open longer it affects the engine’s valve timing and reduces the pressure at the end of the compression stroke. This makes starting more difficult.”

I asked Hennie to check valve-clearances before removing the cylinder heads and he reported that my assumption had been correct. They were all too tight.

I must also mention that camshaft and follower wear, as well as bent pushrods or worn rocker arms can cause the valves to burn.

Hennie removed the cylinder heads and sent them to a specialist for refurbishment.

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