About 6 weeks ago, I purchased a new cylinder head for my 1995.5 Isuzu Rodeo because I was having combustion blow-back problems that heated the exhaust manifold to a bright red color. I replaced the exhaust manifold because it was cracked in three places. During the process of removing the old head, I discovered that the root of my problem was that the keyways on the harmonic balancer and the crankshaft timing pulley were quite worn allowing the pulleys to move a little around the shaft. Luckily the keyway on the crankshaft was not damaged.
I replaced both the harmonic balancer and the crankshaft pulley. After reassembling the engine, I could not get it to start (but it had compression), and I assumed that it was a distributor adjustment problem. I also recalled that I had not checked the valve clearances. In the process of checking and setting the valve clearance I noticed that the timing belt was off about 6 or eight teeth. I reset the timing belt and set the valves and reassembled the engine.
It would not crank, and for some reason, now there was no compression on any cylinder. When I turned the starter, it just whined, as if there were no spark plugs installed. At this point, I was at a loss. I rechecked the timing belt, and it was off about 15 degrees on the crankshaft. At this point I suspected that the belt was defective and replaced it. The engine still wouldn't start and did not have compression on any cylinder. I took the valve cover off, and turned the crank shaft until the number one cylinder valves were closed. I created a pressure gauge fitting that screwed into the spark plug threads, and used an air compressor to test the compression. The cylinder got up to about 100 psi, the same as the compressor regulator and it put quite a lot of force on the wrench that I was using to hold the crankshaft stationary. I repeated this on each cylinder and confirmed that the valves were sealing and each cylinder had compression when the valves were closed. In fact the number 3 cylinder created so much force, it broke loose the crankshaft bolt torqued to 88 ft-lb.
The next thing I thought was that perhaps the original timing belt had slipped more than it appeared, and when I reset it, I had done so with the camshaft rotated 180 degrees from the proper mark. So, I removed the timing belt and rotated the camshaft 180 degrees and reassembled everything. The engine still won't crank, and there isn't compression on any cylinder.
My only idea now is that the shaft key for the camshaft pulley wheel is broken or worn allowing the pulley wheel to slip and causing the camshaft to be out of time with the crankshaft. But, I'm getting tired of removing and replacing the timing belt, so I don't want to test this theory if there is a better way I can spend my time to troubleshoot and resolve this problem.