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1G Another Timing Belt Question, Dhoh!

Posted by Mech Addict, Aug 2, 2020

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  1. Mech Addict

    Mech Addict Proven Member

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    OK, I know there is a lot of information on timing belt tech. I thought I was following it, but now realize I am trying to reassemble my belt, but with the bottom end all aligned, my cams appear 180 degrees out. I failed to notice that the cam gear buttons were pointing at 6 oclock, instead of 12 o'clock when I disassembled it. Seems like I should have rotated the crank another 3 revs prior to taking it all apart. Fortunately I've now realized it, as I'm more carefully starting the assemble process. Unfortunately, my time machine is not working, and I can't go back and do it right the first time.

    So, I have the crank and oil pump sprocket indicators aligned with their pointers. Balance belt reinstalled on and tensioned with the balance gear arrow aligned to the notch. My cam gears are set with the two marks aligned right in line with the head, but the gear buttons pointing down. Since this is an interference engine, how do I rotate the cams 180 degrees?? Seems like it will get stuck when the valves encounter the pistons.

    Then the more I thought about it, I can't understand how much difference it would make. The signal for the engine computer for fuel and start comes off the cam, not the lower assembly. The only thing that has me nervous is that it seems there is some 3 degree offset in the cam gear button position when the cam gear marks are aligned, and if it is 180 degrees off, then the 3 degrees is going the wrong way.

    Any suggestions on how to get it aligned properly (I mean actual physical steps) from this point. Also curious as to why it matters, given the cam position sensor design.
     

    Street Build 532  6

    1990 Mitsubishi Eclipse GSX
    awd · manual · 1G DSM
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  2. Mech Addict

    Mech Addict Proven Member

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    I meant to write "fuel and spark", not "fuel and start". I just realized that could sound confusing.
     

    Street Build 532  6

    1990 Mitsubishi Eclipse GSX
    awd · manual · 1G DSM
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  3. 406_Talon

    406_Talon Supporting Member

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    I did my first head gasket a while ago and I thought about this situation in a panic while eating dinner one night. Luckily mine was correct when I sprinted out to the garage to check. I would think that if the cams were out of phase the balance shafts would need to be as well? That makes my head hurt... Anyway, My idea was if you bring the crank to 90 past TDC all 4 pistons should be down in the bore sufficiently to allow the valves to move past with no interference, unless you have a monster cam. Or you could rotate the crank as you turn the cams to keep the pistons out of the way, like the belt would. Last option, you could pop the cam caps, flip the cams over, and pop them back on. I like that one now that I think about it.
     

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  4. pauleyman

    pauleyman DSM Wiseman

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    Crank at tdc number 1 and 4 are at the top. All you have to do is move the crank away from tdc a little bit, take the belt off, then move the cams to correct position. Move the crank back to tdc and reinstall the belt making sure oil pump/ balance shafts are in phase etc. Technically you could button up a motor with the cams down and nothing would happen except you just set the balance shafts out of phase. The car would physically run. Cams are supposed to be down as you pointed out. Every three turns they are down then three more they are up.
    Again if the crank is not at tdc mark nor 180 from tdc then no pistons are at the top. Just a little bit before or after tdc is plenty. Think about it and it makes sense and you won't be nervous.
     

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  5. Mech Addict

    Mech Addict Proven Member

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    OK, makes sense. Thanks for calming me down. I was able to rotate the crank off TDC. spine the cams 180, and get it all lined up again. Belt is now on. I definitely did not want to pop the valve cover and have to go that route, though it initially occurred to me. (who knows what other surprises await?) The whole timing belt change was prompted by a leaking water pump, which I may have caused when changing out a leaking power steering pump (combination of previous owner running only water in the car, and my overzealous belt tightening). While I do like working on the car, I was not wanting to go further down the rabbit hole on this particular repair. I did replace all the usual recommended parts with the T-belt change using OEM parts (and all accessory belts too; history uncertain...).

    Still can't wrap my head around why the out of phase cams would be a problem, though. I believe the balancers would be in phase with the crank as long as all the marks lined up, and the screwdriver in the balance chamber plug was inserted OK. Seems like I've read about this before, but couldn't find the proper search to read it again. I totally get it if the spark or fuel timing was fixed to the crank. Then the fuel and spark would be on the wrong stroke (the stroke being a combination of valve and crank phase). But with the ECU reading the CAS, which is only spun by the intake cam....
    Yeah, my head hurts too. Perhaps time for some barley pop!
    Thanks for the replies-
     

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  6. pauleyman

    pauleyman DSM Wiseman

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    You're overthinking this. Everything is relative to the crank. Cams turn half crankshaft rpm. If memory serves front bs is double and rear is triple. You could count revolutions. It may be possible but its kind of not worth messing with. Ive tried to explain this over the years as people get all bent out of shape as to whether crank is tdc on power or exhaust etc etc especially on a new head install. Bottom line is it doesn't matter. Tdc is tdc. Everything else happens relative to that one crank position. Its physically possible to install a timing belt with no marks lined up it would just be stupid difficult.
     

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  7. Mech Addict

    Mech Addict Proven Member

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    I stopped overthinking it this morning, and put it all the way the FSM and VFAQ describes (and using the helpful tips from previous responses). I should have followed the instructions more closely, paid attention to the cam dowels, and it would not have happened. Turned out very easy to fix the mistake. In my post I was simply musing about the mechanical aspects of how the engine operates, because it fascinates me, and I assume some others, too. I agree that the bottom end does not move differently on power or intake stroke in typical four stroke reciprocating piston engines. That was kind of my point. It is the valves, spark, and sometimes fuel (for port injection) that defines which stroke is happening.
     

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  8. luv2rallye

    luv2rallye DSM Wiseman

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  9. pauleyman

    pauleyman DSM Wiseman

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  10. 406_Talon

    406_Talon Supporting Member

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    So hypothetically, if a guy were to do this, not notice, and start the car what would happen? Bent valves? Or just lots of vibration from out of phase bs?
     

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  11. pauleyman

    pauleyman DSM Wiseman

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    Likely out of phase balance shafts. I didn't count revolutions on the shafts. For sure you would not bend valves. Not possible. The engine naturally sits this way all on its own every few revolutions.
     

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  12. Mech Addict

    Mech Addict Proven Member

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    When you say "do this", you're referring to setting the timing with the cams 180 degrees out of sync? I don't feel like I have the answer, but I have been hypothesizing that it might run just fine. My little thought-experiment goes like this:
    You start with an engine that runs fine, it's been set up per the factory method with dowels at 12 o'clock
    You take off the covers, and rotate the crank until the lower marks are aligned to their pointers, but the cams are 180 degrees off, so the dowels are pointing to 6 o'clock. But stock cam gears have little timing alignment marks 180 degrees apart (so they can serve as intake or exhaust, interchangeably). In theory, you should rotate the crank another 3 revolutions, which would put the bottom end back in alignment, but moves the cams 180 degrees from where they were, which would be cam gear marks aligned and dowels at 12 o'clock. Only you don't, because like me, you're an idiot (not you, of course, a hypothetical "you"), didn't look at the manual procedure close enough, and left it at 6 o'clock.
    You proceed to remove the tensioner, belts, etc., keeping it in this position (still cams 180 degrees off), and then you put the everything back together. As pauleyman noted, all the marks are simply a convenience, so you don't have to count all the teeth and confirm the relative positions of all the parts in some other, incredibly convoluted way. But in my example, you still have the opposing cam gear reference marks to line up.
    Now because the engine was running fine, properly timed, and you have reassembled it with all alignment marks as you left it, why wouldn't it run fine again. I think this is where I ended up on this past Saturday morning. But having done plenty of other kinds of damage during routine repair on my own accord, I decided to ask for help, and then follow the advice given. (I have a problem, but at least I can admit it).
    That's essentially where I'm at with this. Of course with aftermarket cam sprockets, especially adjustable ones, this might not even be possible, as they may only have one timing mark, not two. But how would it be different to the engine if you got everything out of position during the procedure, and then simply set it back to all reference marks aligned, but cams 180 degrees off? I don't see it, but I've been known to miss the obvious.
     

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  13. Mech Addict

    Mech Addict Proven Member

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    I was under the impression that the screwdriver in the balance plug hole ensured that the balance shaft was correctly positioned. It only has to time with the crank, not the cams, Yes?
     

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  14. pauleyman

    pauleyman DSM Wiseman

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    Yes that's true. But lets say the shafts are ok but you install cams 180 out. Will the shafts still be in phase if you rotate to where crank and cams are now aligned? I don't know. For the front shaft I would say yes this is probably true. For the rear shaft I'm not sure. I would say no otherwise it wouldn't matter which way we had cams. Remember the front is directly driven but the rear isn't.
     

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