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Discussion Starter #1
I pulled my ga16de motor from my 97' 200 sx to do an upper and lower timing chain replacement...along with a few other things.... While turning the lower pulley to find top dead center I managed to skip teeth on the timing chains idler gear. I heard the clicking noise but did not realize what was happening until it was to late. I have no idea how many times the timing chain clicked through the idler gear. So I need a second opinion as to how to proceed next...

I was thinking of placing the bottom pulley to top dead center (key on crank 12 o'clock) then check distributor to make sure I am firing on plug #1






And then this is where I need advise...since the marks on the chain mean nothing any more I was thinking of placing the intake cam so the pin that holds the sprocket is at the 12 o'clock position and the exhaust cam sprocket so the pin is just below the 9 o'clock position... that would put the timing marks at about 2 o'clock on the intake side and about 10 o'clock on the exhaust side... does this sound reasonable ? Any help would be appreciated.



 

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Take the chains, sprockets, etc. off and start over. Get a manual that shows the correct chain/sprocket orientation before you go second guessing and slapping stuff back together. The marks on the chains and the sprockets mean everything. You might get away with one tooth off (although the engine will run like crap), but two teeth off and you're looking at getting the valves reworked and quite possibly dropping in a few new pistons.
I don't remember the correct orientation off the top of my head and I'm not going to go looking for it. I've been there myself, screwed up, and cost myself triple the work and double the cost by not paying attention.
 

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Do what jdg said. Line those marks up right, here is a pic:

And here is what the mating mark might look like on the lower gear:


When you are done with that you can recheck your work using the distibuter, here is a pic:

I'm not too sure how it works, but if the rotor is facing the opposite way as the picture above, turn the crankshaft one more revolution and then check again, because it takes two revolutions for the piston to make a full cycle. The real purpose of the pic above is to make sure the #1 piston is at TDC and not the opposite. Just lining up the TDC mark on the crank isn't enough.
 

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Discussion Starter #4
Thanks b13er,
The pictures are very helpful...what Iam struggling with is the idler gear is no longer in the correct position, there fore the timing marks on the chain don't line up with the gears timing marks. So when the bottom crank is at top dead center the cams are not..
So where do the cams end up at top dead center?
 

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There's 2 marks on your cams, one on each cam. They line up with the marked teeth as shown in the previous post. If I had to throw a clock position at it, 9:30 on the intake, 1:00 on the exhaust.

On a side note, looking at your pictures, your idler gear is about shot, as mine was when I had my "issues". Looks like there's chunks missing, teeth are worn down, etc. Mine wasn't nearly as bad and I replaced it anyways. Could be one of the reasons your chains slipped...well, between that and not having any oil pressure behind the tensioner.

And note ahead of time for you...if you replace the idler gear, you'll have to pull the timing cover. A few people have gotten away with taking a dremel to it in a few places to make clearance for the chains and the gear to come out, but I surely wouldn't recommend that method.
 

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Discussion Starter #6
Jdg, thank you for your help...I just needed the re-assurance before I moved forward...in my timing chain kit with gears,tensioner a etc...there were two items I can't seem to find on my engine. Can someone enlighten me as to where they go?


 

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Those are the upper and lower guides (similar to that long curved guide for the lower chain). They were deleted, by the factory, from later year engines, and deleted, by some sort of update, from most later year engines, I want to say '95-up. I think you can see the original implementation in the pictures for the '95 models.
In your first post, the 4th picture, one of those guides fits between the inner 2 bolts of the cam's end caps near the intake/exhaust sprockets. Don't remember where the other one goes.
They deleted them because they wore out a lot quicker than the upper chain tensioner and made a lot of noise as well...even though they're a piece of cake to change out.
 

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Discussion Starter #8
Thanks for the clarification.... Left over parts seems to be a normal thing in my projects. Tim Allen has a comedy routine where he puts together a BBQ and had left over parts, sends his wife over to light it for the first time only to have it erupt with flames...turns out one of those left over parts was the gas regulator. Uh oh.
Thanks for your help.
 

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yeah, as jdg said, that idler gear is shot. that's why you got that huge slack in the upper chain. Mine was worse with teeth missing on the cam sprockets. Skipped a tooth and lucky enough not to have valves hit the pistons.
 

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I now fully understand the severity and complexity of your dilemma.

I'm guess you understand that rotating the camshafts independently of the crankshaft (and vise versa) can bend your valves. So whatever you do, make sure you know what you're doing. You might have already bent them with the teeth slipping incident. As JDG said, more than a couple teeth off and you might have bent a valve.

I think the safest thing you can do is this:

1. uninstall the cams, which should ensure you don't bend any valves (right guys?) in the next step.

2. set the crank to tdc

3. uninstall the spark plugs and use a coat hanger to feel down there and make sure piston #1 is at TDC (as high as it can go). If it isn't, rotate the crank another revolution until it gets to TDC again, this time piston #1 should definitely be as high as it can go.

4. once that is done install the exhaust cam so the mating mark is in-between 1 and 2 o-clock. Install the intake cam so that it's mating mark is in-between 10 and 11 o-clock. The smaller gear on the idler should have it's mating mark between 4 and 5 o clock, and the bigger gear on the idler has it's mating mark at about 1 o-clock.

It should be just like the pictures I posted above, excluding the top half of the second photo: it shows the mating marks at 12 and and 6 o-clock, which isn't what it's going to look like when you've done everything correct, it will be 1 o-clock on the bigger idler gear, and the crank gear will be between 7 and 8 o-clock (like the bottom half of that photo).
 

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That's the route I'd take to make sure nothing else is jacked up...pull both cams and do a leakdown check of each cylinder, which will ensure (for the most part anyways) that there aren't any bent valves. Gotta be careful pulling the cams as well. Keep the caps in order, undo the bolts evenly and in the pattern shown in the book.
You could put everything back together, chains, sprockets, and all that, then run a compression check. Might save a bunch of time if there aren't any bent valves, but would surely waste all that time if there was a bent valve. If you turned the crank by hand with the chains off, I don't think you could spin a piston past a valve without using a big breaker bar.
I know...I've done it...a few years ago when I got that intermediate sprocket with 26 teeth instead of 25 teeth (or maybe it was the other way around, regardless, I had the wrong part). I could turn the crank twice, and on the third time around, I'd hit a valve because the cams would be out of sync due to the wrong number of teeth. Took me awhile to figure that one out... I can't find that post where I documented all of that either... Damn you search engine!!!

I made a quicky video of my "pre-screwup" fixes to my 1.6L awhile back. You can see I don't have either of those guides as well. Also, look at my intermediate sprocket. I swapped mine because of 3 chipped teeth and not much wear otherwise. Your sprocket is, well, shot...
Short story made long, I started off just swapping out the upper tensioner, found the intermediate sprocket bad, busted that ridge on the exhaust cam, got that all fixed (or so I thought), took it out for a drive, worked good.
Took it out the next day, got 15 miles, and the motor quit again. Got it back home and found the chains had slipped off due to me not tightening down the lower front guide bolts. Near as I can figure, I was in the process of installing the lower front guide when the wife came out to give me the phone for a call and I forgot to tighten down those bolts. They worked loose after a few miles and found their way into the lower gears, caused the chain to jump off, wrecked a few thing, smacked #3 exhaust valves into the piston.
Had to pull the head, get the valves replaced, have the head reworked, swap out all of the timing components again, and so on.
 

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"1. uninstall the cams, which should ensure you don't bend any valves (right guys?) in the next step.

2. set the crank to tdc

3. uninstall the spark plugs and use a coat hanger to feel down there and make sure piston #1 is at TDC (as high as it can go). If it isn't, rotate the crank another revolution until it gets to TDC again, this time piston #1 should definitely be as high as it can go."

If you don't have the cams installed and set the crank to TDC, it doesn't matter if you are at TDC #1 or TDC #4 as they are the same thing; remember the crank turns 2 revolutions for every turn of the camshafts. In other words, if the crank is at TDC #1, both #1 and #4 pistons will be at the top of their stroke and #2 and #3 will be at the bottom of their stroke. Having a valve touch a piston while you are turning the crank by hand will likely not bend the valve, nor will having the cam gear jump while attempting to install a timing chain. I would leave the cams installed and just remove the spark plugs and turn the crank and cams slowly while trying to get them in-synch.
 

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smj999smj,
jdg just mentioned he did hit a valve, and the FSM has a big caution saying: after removing timing chain, do not turn the crankshaft and camshaft separately or valves will strike pistons". If your chain was slipping on the idler gear while turning the crank, it's the equivalency of having no chain at all and doing exactly what the FSM says not to do. At least jdg said you would need a breaker bar to bend a valve, but then that is just theory. Maybe the valve he ran in to was as extended as it could be, and maybe it's easier to bend a valve that's halfway opened. Or were you just saying you can't bend a valve with no camshaft installed?

Thanks for the info about the #1 and #4 piston and the two revolutions thing. I just know the FSM says to make sure piston 1 is at TDC when doing the whole timing chain thing. I'm sure it's so you can reference the distributor and make sure it's pointing at the number 1 cylinder once you're done with the job. I guess they just chose 1, but if you felt like it you could choose 4, and then make sure the distributor is pointing at 4 when you're done.

jdg,
Holy crap I forgot you need to organize the caps, good thing someone remembered, but then again this guy should at least own and have read the timing chain section in the Haynes manual, which also informs you of this. He is also going to need the torque specs and the tightening sequence for the cams.
 

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Here it is in a nutshell:

Considering the FSM wrote that, we can conclude a ga16de is what is referred to as an interference engine (http://en.wikipedia.org/wiki/Interference_engine).

Let's say he skipped 4 teeth. Everything might be ok right now, but if he keeps turning that crank there will probably be trouble. Considering he doesn't know how many teeth he skipped, he can't exactly undo what he did. So the safest solution would be taking the cams off, before he brakes something. But something might be broken right now, so a leakdown test would also be a smart idea. Fix all the problems while the engine is out.

-------------------------------------------------

Story:

A friend of mines timing chain broke on their ford focus last month. The mechanic put a new timing chain on, and it worked for a week and then a valve started clanking real loud. I feared that a valve got bent because the mechanic mentioned that it was an interference engine. I'm sure the mechanic never even bothered to do a compression check.
 

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Let's say he skipped 4 teeth. Everything might be ok right now, but if he keeps turning that crank there will probably be trouble.
Nah, if he's turning it by hand (e.g. ratchet & breaker bar), he won't bend/break anything. I tried :eek: with a decent sized breaker bar too. Just stopped dead when the piston and valve said hello. Then I pulled my head outta my ass and figured out what the deal was (e.g. wrong number of teeth on the intermediate sprocket).
Unless the guy has forearms like Popeye or something...
 

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I suppose mainly because a compression check is dynamic, and a leak down check is a static check.
An engine spinning on a starter at a decent rate can build up a fair amount of pressure quickly, but bleed down just as fast. Maybe that spinning engine wouldn't give it enough time to bleed down before it started building pressure back up again.
And, with a leak down check, if you've got bad rings vs rotten valves/seats/eat, you'd be able to listen to the engine (somewhat anyways) and figure out generally if you got either or (e.g. bad rings would leak into the block, bad valves would leak out the intake or the exhaust).
meh...personal preference. Leak down check and compression checks are free(-ish). Tearing down an engine twice sucks balls.
 

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Discussion Starter #18
Thanks guys for all of your input...just to clarify when I skipped teeth on the idler gear I was turning the crank by hand. The upper tensioner was shredded, see pic...so I replaced it...however the sound of a rattling chain didn't go away so i knew I needed to rebuild the entire thing, cover with oil pump, water pump gears chain etc...I pulled the engine, removed the cover, I proceeded to place the motor to tdc and thats when i screwed up ....the rest was explained in my first post...so this weekend I will put the two cams back to where tdc should be then remove the old sprockets and chain...then place the bottom crank to tdc, remove its gear...then reinstall all sprockets with timing marks placed accordingly and line up the timing chain off color links to the timing marks. Will post pics when I'm done..

 

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And to further clarify, hopefully you pulled the pin out of the new upper tensioner after putting it in right?

And to further furthermore clarify, are you going to swap that intermediate gear?
 

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I didn't say to install the cams at TDC #4....what I tried to explain is that if you had the crank at 0 degrees TDC, the #1 piston (as well as the #4 piston) will both be at the top of their stroke...and will still be at the top of the stroke if you turn the crank one revolution. As far as the service manual, I'm aware of the warning. I'm just give you my 16 years of experience as a Nissan tech working on Nissan engines. Now I'm not talking about whipping the crank around as fast as you can with the chain removed, but just turning the crank slowly by hand and stopping if you feel resistance. If he just jumped a few teeth, he's not going to be turning the crank or cam a whole lot, anyway.
 
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