Hi all - I'm a shade tree mechanic, and this is my first time removing a head to replace a head gasket. I have the head off, but am not sure how to tell if I have cracked the block.

98 Blazer 4x4, 4.3 vortec - water for coolant, and we had a winter freeze in VA. Radiator turned to an icecube, and as I drove it down the road, it started to overheat (near red line). Waited till it cooled, and drove it home, pulling over twice as it started to near red line again. After this, a freeze plug needed to be replaced, and the truck started spewing steam out of the tail pipe - burning coolant.

During the tear down, when I removed the bottom head bolts closest to passenger firewall, water POURED from each. The head gasket wasn't happy about coming off, but doesn't really show any major signs of failure.

So now I have the engine apart, ready to put a new head gasket on - but how do I know if it was just the head gasket, or if I cracked the block? I know to check the head for warping, or have it machined - I just don't want to put it all back together and have missed something obvious. The piston on the suspect cylinder it at the top, so I can't just look down the hole and see if the wall has a crack.

BTW: Before I tore her apart, she was running good as ever, despite the clouds of smoke from the exhaust. Would a cracked block have made the truck run bad?

Thanks in advance!

 

Oil in Antifreeze
Engine antifreeze that has oil mixed in it is a classic sign of a cracked engine block and/or a blown head gasket, both of which can allow circulating engine antifreeze to mix with circulating engine oil. The engine block contains the small passageways through which oil and antifreeze circulate throughout a vehicle's engine. If an engine block crack develops in close proximity to these passageways, circulating engine oil can mix with, and pollute, circulating engine antifreeze. This condition can normally be verified when the engine radiator cap is removed and the condition of the engine antifreeze is inspected.

Antifreeze in Oil
Just as a cracked engine block can allow engine oil to mix with circulating antifreeze, the opposite can scenario can also occur: antifreeze can mix with circulating engine oil. This type of a situation only happens when an engine block has a severe enough or deep enough crack that allows the antifreeze to enter the engine oil passageways. Normally, antifreeze-contaminated oil produces a funny smell and/or visible smoke emanating from a vehicle's exhaust pipe, or cloudy, milky-colored oil that can be visually spotted on the engine dipstick during a routine oil inspection.


Low Engine Compression
Engine compression, which is the end result of engine combustion, is housed within the engine cylinders, which are located within the main engine block. A cracked engine block can result in low engine compression if the crack is severe enough and/or deep enough within the engine block to pierce any one of the engine cylinders. At this point, normal engine combustion pressure is disrupted, which in turn, lowers engine compression and results in poor engine performance.

Engine Smoke
Engine smoke is often times seen in vehicles with cracked engine blocks. Smoke emanating from within an engine is normally caused by a severely cracked engine block; a crack severe enough to allow engine combustion and engine exhaust gases, which normally present as black and/or bluish gray colored smoke, to flow directly out of the cracked portion of the engine block. These types of severe engine block fractures normally create severe engine performance problems, in addition to visible smoke.

Visual Crack in Block
Many times, a routine vehicle engine inspection will uncover a cracked engine block. If an engine is clean enough and free from excess dirt and/or grime, a visual engine inspection, which is often times performed during a routine engine tune-up or engine service, can spot engine block cracks that are severe enough to cause significant fracturing of the engine block casing material. Normally, large engine block cracks cause obvious engine mechanical symptoms, but in rare cases where no engine mechanical symptoms are produced, large engine block cracks can be spotted visually during routine engine maintenance.

Engine Overheating
Engine overheating can occur if a cracked engine block is severe enough to allow engine antifreeze to leak out of the engine, which causes engine temperatures to rise, and the engine to overheat. Engine antifreeze circulates deep within an engine block, in and around the main engine combustion chambers. Therefore, only severe engine block cracks, cracks that extend deep enough inside of an engine to expose the passageways through which antifreeze circulates, would cause engine overheating.

 

Is there a reason you can't turn the engine by hand so you can look down #6 cylinder? I'm a shade tree mechanic myself, but I'm missing why you can't do that.

 

I've never done that before. Also worried that if I do, I'll throw off the timing, since I marked it before removing the distributor. If I can turn it by hand, how do I do that? Is setting the timing just a crap shoot when I put it all back together?

Thanks

 

As long as you haven't removed the timing chain, you're not going to screw-up the timing. You will have some extra steps to install the distributor, but it's pretty straight forward. To turn the crank by hand:

1. Remove the spark plugs on the head you didn't remove (its much harder to turn the crank with the spark plugs installed due to the compression).

2. Using a socket and ratchet/breaker bar (1/2 drive would be best), you turn the crankshaft balancer bolt inside the crankshaft pulley at the front of the engine clockwise (as if you were tightening the bolt). This will turn the crank. Depending on what stage to which you have the engine broken down, it may be easier attacking this from the bottom of your engine as opposed to the top. Just be sure to keep the socket situated squarely on the bolt as you turn the crank so you don't round it off and/or bust your knuckles.


Basically to insure the distributor is installed correctly there's two ways you could do it:

If you marked the distributor, you could mark exactly where the timing mark on the crank pulley is. Then just insure you rotate the pulley past that mark twice, ending exactly in the same spot on the second revolution. It takes two revolutions of the pulley for every one revolution of the distributor (compression stroke and exhaust stroke). If you go past the mark on the second turn, do not back up and go counter-clockwise. Do two more revolutions clockwise. If you line everything back up correctly, the crank will be in exactly the same position as it is now as if you hadn't turn anything.

The other method that is used when you are starting from scratch with no marks (so you can use this if you lose count on the turns):

1. Insure #1 piston is at Top Dead Center on the COMPRESSION stroke. That's one of the most common mistakes is that someone may install the distributor at TDC on the exhaust stroke. There are various way to determine you are on the compression stroke. But insure you end on the timing marks. Once again, do not back up counter-clockwise to fall on the timing marks. If you have a compression gauge, that is probably the best method.

2. If you look at the bottom of the distributor you will see where the shaft engages with the oil pump. You will put a large screwdriver in the distributor hole to turn the oil pump shaft so it will align with the distributor shaft when you drop it is. You goal is drop the distributor in so the rotor points at the tiny "6" son the distributor. Since the gears turns a bit when you put the distributor in, you will want to move the rotor to the left of the "6". Then when the distributor falls in place, the rotor will turn to the "6" as the gears mesh.

If, when you start your engine, you get a DTC code of P1345, you are probably at least one tooth off on your distributor.

 

Want to know if it's cracked? Pull the block out & take the heads to a machine shop.... Have them manuflux heads and block! that will tell ya....otherwise it's kind of a leap of faith, unless u want to just put it back together and hope????

 

This is what I was going to suggest also.Other than that severe whiteish blue smoke coming from the exhaust would be a sign of a cracked head or block.

 

I had this problem myself. PO said the block was cracked. Freeze plugs also blew from freezing. However after doing compression test found a cracked head. Tore down gasket was blown and after inspection found a crack in the head. Put it all back together with new Felpro gaskets ( Don' use any other gasket no matter what) fired it up and ran like a top. For about 5 minutes. Steam began rolling out exhaust so tore it down again pulled opposite head. No sign of gasket failure but that head had also froze and cracked. The prior compression check on that bank showed good. I guess heat seperated and expanded the crack. Running good now. On another note I blew two freeze plugs. One was not bad but the other was behind the motor mount right side. Nasty job. Don't even attempt without a lift in my opinion. Guess what I am saying if your freeze plugs blew you should be OK but since you have it down replace BOTH heads. I got mine for $75 each. Make sure you get the roller rocker heads. I think they had a design change right in those years so check that out. This is not to say the block is good. Only one way to find that out and if your going through all that trouble might as well get another motor.