Post by GrumpyUnk on Aug 5, 2024 8:45:52 GMT -5
If you have heard many of the newish 4-cylinder turbo engines, a lot have mechanical valve lifters/followes. A well adjusted set will sound good, but if you have one or two that have excessive clearance, their noise will stand out and make the engine sound bad.
I guess the VW engineers back in the 1930's thought that having to work on the valve every 25-30,000 km was no big deal as the cylinder head about falls off the flat 4... kidding, but they are not difficult to pull. Perhaps a new exhaust valve with stellite surfaces might last longer. Exhaust valves generally burn when they cannot transfer heat to the valve seat. That can be clearance or in this case, less airflow over the head and higher seat temperature than the other 3.
Anyway, current engines can sound good if they are adjusted properly. I have heard some where it seems the builder didn't care, and they do not sound good to my ear.
The Chevrolet Vega had mechanical adjusters. The desired clearance was specified as .005-.010" or similar. To adjust when the clearance was out of range, you turned a screw head 1 revolution in either direction, which would add a chunk of clearance, or subtract same. You could not set the clearance to make the engine sound good as always there would be one or two that were at the large end of the range, and the others somewhat closer to the small end. The noise was always different so it sounded 'bad'. My take is they could have used finer threads on the wedge/screw so the adjustment difference from turn-to-turn was smaller, closing the range so the valve clearance could be closer between all the valves. I digress.
tom
The 139QMB I referred to above sounds good when started, but ride for a couple miles, and it sounds 'taoppy' more than I would expect. The valves are adjusted at the factory for almost silent operation. It seems the customers in the Far East do not like to hear valve clatter.
I guess the VW engineers back in the 1930's thought that having to work on the valve every 25-30,000 km was no big deal as the cylinder head about falls off the flat 4... kidding, but they are not difficult to pull. Perhaps a new exhaust valve with stellite surfaces might last longer. Exhaust valves generally burn when they cannot transfer heat to the valve seat. That can be clearance or in this case, less airflow over the head and higher seat temperature than the other 3.
Anyway, current engines can sound good if they are adjusted properly. I have heard some where it seems the builder didn't care, and they do not sound good to my ear.
The Chevrolet Vega had mechanical adjusters. The desired clearance was specified as .005-.010" or similar. To adjust when the clearance was out of range, you turned a screw head 1 revolution in either direction, which would add a chunk of clearance, or subtract same. You could not set the clearance to make the engine sound good as always there would be one or two that were at the large end of the range, and the others somewhat closer to the small end. The noise was always different so it sounded 'bad'. My take is they could have used finer threads on the wedge/screw so the adjustment difference from turn-to-turn was smaller, closing the range so the valve clearance could be closer between all the valves. I digress.
tom
The 139QMB I referred to above sounds good when started, but ride for a couple miles, and it sounds 'taoppy' more than I would expect. The valves are adjusted at the factory for almost silent operation. It seems the customers in the Far East do not like to hear valve clatter.
