QuestionThis is a follow up to a question I had asked on 12/20/06 -
titled "mechanical mystery". I have a 1986 Hyundai Excel GL with engine ID # G4AJG137803, an engine displacement of 1468cc. As mentioned previously, I had heard something break with a loud clashing noise as I was idling the car on my driveway. I had shut the engine off immediately. What I found was a broken exhaust rocker shaft that had completely broken in half where the bolt is on the #3 cylinder rocker-shaft. Also found that the #2 cylinder jet-valve had broken on the stem with 7/8 of an inch of the bottom portion of the jet-valve missing. I don't see how it can fall into the cylinder, since there is an obstruction at the bottom of the cylinder head. Yet the engine still gets stuck whenever the #2 piston reaches top dead center, as I rotate the engine at the crankshaft pulley center nut clockwise & counterclockwise. Have checked all connecting rods for spun bearings, nothing binding behind the crankshaft pulley, and the front wheels were off the ground with the transmission in neutral. I have also checked the height of the valve springs to see if the missing piece of the jet-valve could be lodged between the valve seat & valve face. No such luck. Looks like I'll have to take the cylinder head off. What do you think. Have also done some checking on remanufactured cylinder heads. Another question: Can a cylinder head from a 1495cc engine fit on my car, since there is only a 27cc difference between the two engines? I did show the broken exhaust rocker shaft to a reputable machine shop, and they told me the reason it broke was because the walls where rocker shaft bolts go through, were thin on the outside, and seem to have been drilled at a slight angle.
Thanks in advance for any insight you can give me on this, I sure would hate taking the cylinder head off, especially when the weather is cold outside.
AnswerUsually, the cause of the rocker shaft breaking is due to the loosening of one of the end rocker shaft bolts. I've seen this numerous times. Sometimes it's just loose and needs to be tightened. Other times, it breaks and needs to be replaced. And sometimes, the threads where the loose bolt was are damaged and need to be repaired.
Jet valve failures were also fairly frequent on this engine. They tended to get carboned up and stuck or the valve end would burn off from not seating properly. I've heard of cases where a jet valve broke or burned and the valve stem somehow got into the cylinder and caused damage to the engine, but I've never seen one. Like you, I don't understand how the valve would get into the cylinder past the plug in the head. Bottom line, I think you'll need to pull the head and have a look if you can't see anything through the spark plug hole.
