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Car Forum / GMC Cars / February 20051996 grand am quad 4
I am working on my sisters quad 4. It wouldn't start and compression was low between #2 & #3 cylinder. Oil mixed with water. I have taken of the head but the gasket is not blown. There are marks in the head and on top of the pistons. She had a water pump installed by a garage a few months ago and I think that when they removed the timing chain they put the cams out 180. Not positive but my manual says the cam dowel pins should be on the bottom at TDC and they are at the top. This car has classic signs of head gasket failure yet the gasket isn't blown, I can see any cracks, could it be worn down? Would the cam being out cause these marks in the pistons and head? I will have to have the head machined but do I have to replace the marked pistons? Thanks Sorry guys I can't type...should read I have taken off the head. and I can't see and cracks in the head, cylinder walls or block. > I am working on my sisters quad 4. It wouldn't start and compression was > low between #2 & #3 cylinder. Oil mixed with water. I have taken of the head [quoted text clipped - 15 lines] > > Thanks > She had a water pump installed by a garage a few months ago and I > think that when they removed the timing chain they put the cams out > 180. Not positive but my manual says the cam dowel pins should be on > the bottom at TDC and they are at the top. It isn't possible to have the cams out 180 degrees. Think about it, cams turn at 1/2 crank speed....so if you rotate the crank one more rotation, where will the cams be? And on the Quad 4, there are locating holes in the cam sprockets that should line up with holes in the timing cover housing...this is the only reliable way to time these engines. Ian Thanks Ian, You're right I shouldn't have said out 180. The pins are shown at the bottom in my manual but the end up at the top at top dead center..I assume that my manual is wrong I take it that slack in the chain would cause the marks on the piston and head surface. > > She had a water pump installed by a garage a few months ago and I > > think that when they removed the timing chain they put the cams out [quoted text clipped - 9 lines] > > Ian besides, if the cam timing was that far off on this engine you would have had bent valves to deal with. > Thanks Ian, > [quoted text clipped - 18 lines] > > > > Ian > You're right I shouldn't have said out 180. The pins are shown at the > bottom in my manual but the end up at the top at top dead center..I > assume that my manual is wrong Not necessarily, you may reading the manual wrong. They probably mean the "locating" pin is at the bottom on both sprockets. It's really just a hole in the sprocket that lines up with hole in the front cover. Here is a picture of the cams correctly timed with the GM locating pins installed in the cams. You can see that the dowel pins in the cams are at the top, but the locating pin/holes are towards the bottom. http://members.shaw.ca/ianrmac/Images/DSC01277.JPG > I take it that slack in the chain would cause the marks on the piston > and head surface. No, I've seen engines that have been running with the chain tensioner in the retracted position, and I haven't seen any of that type of damage. You have to be out a bit more then that to start to have interference damage. Ian Thanks Ian for the picture. That is how it is at top dead centre. Do you have any idea as to what could cause the pistions to be hitting and do I have to replace them? > > You're right I shouldn't have said out 180. The pins are shown at the > > bottom in my manual but the end up at the top at top dead center..I [quoted text clipped - 20 lines] > > Ian How deep are the gouges in the piston heads? Is there any slack in the wrist pins? How much carbon was in the combustion chambers in the heads. > Thanks Ian for the picture. That is how it is at top dead centre. > [quoted text clipped - 25 lines] >> >> Ian There wasn't much carbon (two and three had anti-freeze). I haven't even checked pistons other then looking at the top of them and wiping the carbon away. I will take some shots of the head and pistons and link them tommorow. Most gouges were on two and four with some on three. > How deep are the gouges in the piston heads? Is there any slack in the > wrist pins? How much carbon was in the combustion chambers in the heads. [quoted text clipped - 28 lines] > >> > >> Ian Either the head gasket or the head itself had to be compromised to allow antifreeze into the cylinders (discounting cracked block). The head on my 1989 Quad 4 had many small cracks around the spark plug area when I disassembled it for the second time.. I would advise that you have the head Magnafluxed before you reassemble it, just to make sure it's not cracked. Mike >There wasn't much carbon (two and three had anti-freeze). I haven't even >checked pistons other then looking at the top of them and wiping the carbon [quoted text clipped - 36 lines] >> >> >> >> Ian |
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