Do i need a special tool to hold camshaft sprockets in place?

[miloe79]

Hello everyone..
I have 95 SR with a 3.5L engine. Long story short, the timing was off by a few teeth, I hire a "mechanic" and he bailed on me half way thrugh the job, now I'm left with an engine thats all taken apart and up to me to put back together, so here it goes...After setting the crankshaft to TDC, I am trying to time, or rotate my camshafts so that the timing mark on them stays align with the marks on the engine block, but the camshaft sprokets "spring" to specific positions, and thus they jump pass the place where I would need to keep them to have them align properly (I hope Im explaining this right). I was told by some mechanics that I for sure would need to get some type of Tool that would hold the Camshafts in that proper place and prevent it from jumping, so that I could put the timing belt on and everything still being aligned correctly. I was hoping the mechanics weren't just saying all this just to get my business and prevent me from doing a good job of timing it myself :-/ So with this being said: QUESTION 1: Do I REALLY need a Camshaft Holding tool? I dont know much about the internal workings, but I was thinking maybe these cams jump to a specific position for a good reason, and by forcing it to stay between the Index Marks on the engine housing I was damaging something because it just didn't feel right. ANYONE KNOW WHATS GOING ON HERE? Because what do I know? Im just learning. I also called Autozone to see if I could rent a tool from them that holds the Cams in place, but they said that they dont carry one :-/ and QUESTION 2: Why do the camshafts "jump" like that anyway? Why do they not just turn in a smooth manner? What is happening internally when this springing action is going on? to compare the Camshaft Sprockets to clock faces, instead of them turning smoothly like a second hand, They jump from 10 clock directly to 2 o clock (when rotating clockwise). Then from 2 o clock to 6 o clock (or something like that). Is all this normal? It this good or bad? If someone can provide me with a link to some illustrations that can help me see all of this clearer I would very much appreciate that as well. PLEASE SIMPLE EXPLANATIONS as IM NO EXPERT

 

[BOPOH]

there are few very informative youtube videos on how to secure timing belt to DOHC cams with zip-ties. Cams jumping is simply because valves are open either fully or partially(spring compressed) that's why you see sprockets turning different. One last thing, if it was confirmed that timing was off by a few teeth you might need to replace valves and possibly heads and pistons. I've read somewhere that 6g74 can jump 6 teeth without any really damage but maybe it's on SOHC only, you have DOHC. Good luck

 

[Howah]

I normally just use a wrenchs on the cam gear bolts to hold the cams at the timing mark while putting on the belt. My 3.5dohc skipped 3 or so tooth and it needed a pair of exhaust valves and guides on cylinder 3.

 

[BEG]

When replacing the timing belt, it's not super-critical that the cams be on TDC the whole time. The valve spring pressure is going to want to force the cams off TDC. Just go about the timing belt replacement and hold them at TDC individually when it's time to route the new belt over them.

 

[miloe79]

Thanks guys! I really appreciate the help, i guess the only thing left to do is to install the timing belt, and cross my fingers that I didn't bent any valves. The mechanic did a compression test, and said everything seem to be fine.... We'll see..