I will preface this by asking that no rude comments towards the owner of this vehicle be made. This post is intended to educate.
A customer brought in their 1999 Tacoma Pre-runner with a 3.4 V6 engine. they had just bought it and knew the initial condition of the engine was questionable. The timing belt was broken and there was no way to check the condition of the engine at that point. The purchaser was also told that the truck had sat up for 4 years since the belt broke.
It was towed to our shop and left with us to inspect and check the condition of the engine. Using a HAND TOOL, the crankshaft was checked and free movement was noticed. The camshafts were also checked for freedom of movement, and all of them checked clear. The problem was noted when the water pump pulley was seized up, as well as the idler pulley for the timing belt. It is my belief that the water pump seized, causing the belt to break. However since 4 years has lapsed, there was no way to tell for sure, and no belt burns were noticed on the water pump due to the rust.
Thanks to a previous vehicle recently being in here for a new timing belt and water pump kit, I had a spare backup belt, water pump, and pulley set. I set the crankshaft and camshafts to the correct timing mark, and installed the donor parts. Since this engine is a zero-clearance engine, the only way to safely get the crankshaft and camshafts lined up properly was to be VERY slow and careful when rotating the parts. The first step is to get the crankshaft to TDC of the #1 compression stroke. Once there I backed off the crankshaft about 30 degrees. This allows the camshafts to safely rotate without any of the pistons striking an open valve. After the crankshaft was set and backed off, I rotated the cams to their proper timing mark, and returned the crankshaft to the proper position. I then installed the water pump, pulleys, and belt. (Note that these photos are from a different truck, and are just visually indicating a properly set up timing belt)
If you notice on the single cam pulley photo, it is stamped as right or left pulley. You CAN install them incorrectly, so watch how they come off and go back on. The "L" or left pulley goes on the left cylinder head, NOT on the left side as you look at the engine!
Since we are concerned about the engine already being damaged, we hand rotated the engine and I noticed at 4 different points that there appeared to be minimal, but definite contact of valve and piston. This was further diagnosed with a cylinder leakdown test showing that the left head had 2 cylinders that would not hold any pressure. Time for the heads to come off.
Removed the valve covers, and you can see what 4 years of oil sitting inside and engine can do. It did not look pretty. Once I removed the heads I noted that on the left head, 3 different valves in 2 different cylinder heads were stuck open. The appearance was that they were bent, however further inspection showed that they were stuck in their bore. Either way, the heads needed removal, as you could also see a large amount of carbon buildup on the pistons. This carbon was so dense that the chunks almost appeared to be a broken piece of the engine. The photos do not show up very well however. After the heads were removed, the oil pan comes next. This REALLY shows how bad oil can get when sitting for an extended period of time. 4 years is a long time. The oil itself was actually SOLID, and would not even move when the pan was stood on it's side, or even when INVERTED!
The good news was that the cylinder walls were free of scoring, and still were in good condition.
The next pictures show what happens after 4 days of vat soaking, and two vats of fresh fluid will do to said cylinder heads. We are currently waiting on parts, and we will do what we can to show a step by step assembly of the heads, and the timing. For those who are curious, even though the engine say for 4 years, it appears that the oil in the crankshaft journals had drained down into the pan, thus not clogging up the crank bearings or rod bearings. At this time, due to the cost, the customer has decided to take the chance and just clean what we can, instead of totally disassembling the engine and rebuilding.