Cam chain lamentations

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Over the years I`ve worked on everthing from chainsaws to Caterpillar tractors. I like to consider myself a somewhat sophisticated driveway mech, but I`m just about licked by a `92 Nissan Sentra! In the course of replacing a cracked cylinder head, I did the cam chains, guides, tensioners, etc. Studied the manuals and aligned all the timing marks. The mistake I made was in not installing the lower cam chain tensioner before rotating the engine to double check my marks. I think the lower chain jumped a tooth and the marks haven`t lined up since. The valves don`t contact the pistons and the distributor drive seems to line up, but the marks on the cam gears, idler and chains don`t. I pondered someway to compensate the upper chain to make up for what I think is a now one tooth retarded setting on the lower chain, i.e. advance the top chain one tooth. After all, the engine doesn`t know where the marks are, but I can`t decide whether to advance at the idler or the cams. I think I`m just gonna have to start over. This car has very little space to work and the oil pan must come off (again), along with water pump, etc. I will try to do this without head removal, although most manuals recommend it. Any ideas on correction insitu involving the upper cam chain or cams would be appreciated! This is a DOHC arrangement with a lower chain turning an idler gear which moves an upper chain turning the cams.
 
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Make sure it hasn't got a ''hunting tooth'' - the marks won't line up for a 100 turns or so....not like a cam belt. Otherwise just change the top chain for the cams,it must be easier.Is it the SR20?
 

Cornbread

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Hello Silk, I wondered if they should line up every other crank rotation like a belt or not. I`ll play with it some more, maybe put the dizzy in and see about ign timing as well. It is the GA16DE, little cousin to the SR20. Sounds like you have had some experience with these engines.
 

JTK

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Wish I could help with this Nissan 4cyl. We owned a 1993 and 2001 Sentra. Loved them. Chain driven overhead cams sure do sound nice, but gawd help ya if you need to do top end work. Dude on another board supposedly burned a valve due to a faulty fuel injector on a 2007 GM Ecotec 2.2L. GM's warrantying it (10y/100K), but the book says something like 16hrs labor for the work! Ecotecs are a chain driven DOHC. Joel
 

Cornbread

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I think (hope) Silk is on the right track. I`m going to hand turn it some more and see if the marks come back into alignment. Yep, cam timing is very interesting, but can make you scratch your head at times (no pun intended)!
 
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If doing it properly is out of the question, and all else fails, you could try slots in the cam gear to rotate it into position. Then pin it if necessary. The second gear will automatically be right. People have used slotted or new holes in gears for years, or offset keys.
 

Cornbread

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True. I`ll tear it back down if I need to. At least I`m not trying to beat a flat rate. The "hunting tooth" possibility gives a glimmer of hope!
 
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 Originally Posted By: Cornbread
It is the GA16DE, little cousin to the SR20.
I have a GA16DE in my NX Coupe.I don't remember any problems with cam timing on them.Some may have variable cam timing....there is provision for it,but I've never seen a GA16 with it fitted.
 

Cornbread

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My GA16 has a rudimentary variable cam timing device on the intake cam. I think it is a centrifugal mechanism integral with the chain sprocket, but has nothing to do with initial set up. I rotated the engine a few times last night. The dist. drive, TDC mark on crank pulley, and cam lobes on #1 cyl. look right every time. Yet to see the marks on the chains and sprockets line up again though. I think if I were even one tooth off something would be evident. I think if I kept rotating the engine enough the marks would eventually get back to initial alignment.
 
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With some variable cam timing systems, you have to manually rotate the cam into it's rest position to check the timing. When the car is off, it could be anywhere. You can't trust a return spring, if there is one.
 
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On the Taurus SHO motors both the one that uses a chain and the other that uses a belt once the engine is turned over the marks don't line up again.
 

JTK

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Right on SHOZ, but the marks have to line up under the right combination of events, # of rotations; #1 at TDC, etc... Joel
 
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 Originally Posted By: JTK
but the book says something like 16hrs labor for the work!
16 hours?????? That's a HUGE job! That's getting into "Engine R&R" territory. Which I'm assuming is necessary for it to pay that much. Taking the engine out for head removal? Man, that's just ridiculous.
 

JTK

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 Originally Posted By: AcuraTech
 Originally Posted By: JTK
but the book says something like 16hrs labor for the work!
16 hours?????? That's a HUGE job! That's getting into "Engine R&R" territory.
I'm just going off the 2007 Saturn Ion owner's post on that. No verification. Joel
 

Cornbread

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Silk, you were spot on. Never could line up the marks again, but all other timing parameters were good. I completed the assembly and she fired right up and ran great! Without your input and that of others I would have torn it all back down again. Many thanks for everyone`s help and taking the time to reply.
 
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