Recently faced with another mystery. The client arrived on a far from yet “killed” VAZ 2109 with a banal, at first glance, complaint: the engine “undermines”. The reason was found in a matter of minutes: the candle of the first cylinder did not look very good, and it could not stand the test at the stand. Replaced - but with a new motor shook. We rehabilitated the candle posthumously: it clearly fell victim to another defect.
Compression in the first cylinder barely reached 8 kgf / cm2, although in others it was close to 13. With the addition of oil, it did not increase much - which means we will deal with the valves.
They removed the head. The exhaust valve is broken - the track on the working chamfer slid to one side, the same on the saddle. Layers of soot leave no room for doubt: here it is, the cause of leaks. Guide sleeve end - hole, even by eye, ellipse. Okay - we replaced the valve and the sleeve, milled the saddle, ground it. The satisfied customer departed … But not even a month had passed before a familiar figure appeared on the threshold: the motor was troit again!
Immediately started by checking compression. And again in the first cylinder the familiar 8 kgf / cm2. Next is a repetition of what has already been completed: the valve, seat and sleeve are broken, as if we had not done any repairs. Maybe summed up the quality of parts? In our century, this is a common thing, and we - already by complaint, "at the expense of the company" - replaced them with imported ones.
… I could not believe my own eyes when the client again came to us with the same complaint! It turned out that some underlying cause was ruining the details. Now the glands were studied meticulously as never before - and now I looked inside the glass of the pusher of the ill-fated valve. What nonsense! The valve trail is offset from the axis of the pusher so that the valve end works only part of the area. The rest of the pushers are in order.
What was going on? It is likely that a variable force displaced from the axis of the valve causes the latter to swing in the bore of the sleeve and breaks it, and the distortion of the valve in the seat increases. How to get rid of this?
You can replace the substandard head, but it will cost dearly, eight thousand. They offered the customer a sparing option. In the factory, a hole in the pusher guide was machined on a jig boring machine - strictly aligned with the valve sleeve, a repair sleeve was pressed into this socket - and it was already bored under the pusher. The saddle in the head, badly worn, had to be replaced. Repair is troublesome, but still several times cheaper than replacing the head.