We were doing a head gasket swap on a 2015 Prius following the steps in the video we found online. We neglected to lock down the camshafts in position before removing the cam housing. (A case of I thought you did it...) When the housing bolts were removed, the valve spring pressure caused the camshafts to turn slightly. On an engine without VVT, I would have no problem just turning them to the correct position and installing the chain. I have rebuilt countless engines in my career but never tore into one with VVT. I am hoping that one of the knowledgeable technicians on this forum can give me some guidance as to the best way to correct this error. I am thinking that if I put the timing chain on the sprockets with the timing marks aligned and the sprockets in the correct positions while the housing is on the bench, then locking the camshafts in place, I should be OK when it is reinstalled. But that is a theory, and I don't want to find out the hard way that it's wrong. If someone could lend some advice, I would appreciate it. Thanks in advance. Thundertruck
Never done anything like this, but, this video is apparently the go-to: And this you might have seen, but if not: Also, priuschat member @NutzAboutBolts has a 3-part series of videos on head gasket replacement, videos 30a through 30c, linked here: Nutz About Bolts Prius Maintenance Videos | PriusChat About 13 minutes into 30c he starts installing the timing chain.
Update: (in case anyone else makes the same mistake.) I turned both camshafts to the proper position while on the bench and locked them down with the 3 layers of paper shop towel as described in the video. Then installed the camshaft housing assembly and cam chain with the proper timing marks on the chain and sprockets aligned. After installing the chain guides, timing cover, and chain tensioner, I double checked the timing mark alignment. (You can see the crankshaft marks through the seal opening before installing the balancer, it's just not real easy to get yourself in the right position.) Then I used the balancer bolt to rotate the crankshaft slowly to be sure that there was no valve to piston clearance problem. (Turn it clockwise when facing the balancer from the passenger side wheel well.) After about 8 or 10 complete rotations of the chain, the timing marks were again on the right positions on the sprockets. I did notice that the chain between the camshaft sprockets would get very loose at times while the engine was being rotated even though the tensioner was installed. This is because the tensioner has only spring pressure on the chain until the engine starts and creates oil pressure. The engine oil pressure takes out the final amount of slack in the chain once the engine is started. Confident that everything was assembled correctly, we finished the engine assembly and started it. Everything worked perfectly. Thank you, Mendel, for taking the time to lend your advice and for the links to the videos and other information you provided.
