Hey all, just like the subject says, I have a crankshaft that can rotate 350 degrees and stops. This is on a 1997 Sunfire 2.4L twin cam manual and I was replacing the water pump on it and let the chain slip while turning it so the timing was way off. In the process of getting everything lined back up, the cams rotate 360 in whichever direction without binding at any point which I found strange unless this is a non-interference engine. However the crankshaft cannot return to TDC, it can rotate freely in either direction to anywhere but TDC without binding until it gets close.
I took the intake cam off thinking I was going to have a problem with the valves or something and after I found nothing wrong, I started thinking a bit more and realized there was no way it was a valve anyway. How can the cams each rotate to a thousand different combinations and the crank freely up until that last 10 degrees and it be a valve in the way. So is it possible something on the crank is binding due to the chain slipping? How did it happen if nothing else but the water pump is driven by the chain? Any help would be appreciated, I was hoping to have the car running by the end of the weekend but it is not looking good, thanks.
Sounds like its hitting a valve to me.
pull both cams out and then try to spin the crank a full rotation, with no valves open everything should spin good
Bob Guptill wrote:pull both cams out and then try to spin the crank a full rotation, with no valves open everything should spin good
If he already bent one pulling the cams wont accomplish much. Set the crank at 90* BTDC, line up the cams correct and then rotate the crank to TDC. Set chain, pull alignment pins and try to rotate crank. If you are trying to rotate the crank with the chain off you will have piston to valve contact. The 2.4 is an interference engine.
Okay, pulled the exhaust cam and found a busted 'lifter?' or what would you call the cup between the cam and spring? Also, looking at the spring height, 7 out of the 8 on that side look the same height and the last one is actually higher. How is it higher unless the other 7 are bent or this 1 is pushed up into the valve seat partially busted or something? The one that is higher is not the one that busted it's lifter either, same cylinder though. Oh and the crankshaft still does not turn completely so at least one of the valves is bent or I busted something else. The issues I found already are on cylinder 4 though, is that on it's compression or exhaust stroke when cylinder 1 is at TDC? I guess exhaust would make sense at this point. The head will be coming off tomorrow to access the damage, just ran out of time tonight, thanks for the replies.
cylinder 1 and 4 are companions, when cylinder 1 is on tdc for compression 4 is on tdc for exhaust
but at tdc on exhaust both valves intake and exhaust are open due to the valve overlap built into the cams
mitdr774 wrote:Bob Guptill wrote:pull both cams out and then try to spin the crank a full rotation, with no valves open everything should spin good
If he already bent one pulling the cams wont accomplish much. Set the crank at 90* BTDC, line up the cams correct and then rotate the crank to TDC. Set chain, pull alignment pins and try to rotate crank. If you are trying to rotate the crank with the chain off you will have piston to valve contact. The 2.4 is an interference engine.
Bleave it or not, I had a cam butten break in the cam shaft when the engine was runing...... I pulled the head, and all was good...
atleast I had a new GM HG laying around..
Chris
'02 Z-24 Supercharged
13.7 @102.45 MPH Third Place, 2007 GMSC Bash SOLD AS OF 01MAR08
