I changed the timing belts about 3,000 miles ago, and since then the engine had a vibration at about 3,200 RPM. My truck also developed a large oil leak the past few weeks and I decided to find out why today. I thought I might find the problem with the vibration as well. I went to the self serve car wash, and cleaned the engine. When I got home I noticed oil leaking from what appeared to be the front crankshaft seal. A trip to NAPA and a seal was purchased. A few weeks ago I noticed a sound like a belt slipping or a bearing going bad. A few days ago the sound went away. I now know why the sound went away and the reason for the vibration and oil leak. I pulled the top cover, and much to my surprise I found this:
It seems that the reason for the oil leak is because the upper silent shaft gear had come loose. It was just sitting there, bolt and all. The gear spacer is the sealing surface and it had moved forward causing the leak. I think that it is a miracle from God that the bolt or gear did not get wadded up between the belt and another gear. When I removed the lower cover the gear and bolt fell out. Upon inspection I found that the flat spot on the gear was worn off and the gear was just slipping on the shaft (the reason for the noise and vibration). After a while, it must have loosened the bolt and fell off.
Left gear is an extra one I had from another engine, Right is the rounded out one (notice the flat gone).
The incredible part is that the gear was the only damaged part. The belt, silent shaft, spacer, bolt and washer were all fine. I put the parts back on and the engine runs smooth and quiet now! It could have been a disaster if any one of those parts fell down any further. I thank God it was an easy repair and cost only my time. I returned the seal to NAPA, as it would have been a big job to replace it (found that it was not leaking).