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Do I have China cam sprockets and chain? How to verify cam timing? - Hardtuned.net

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Do I have China cam sprockets and chain? How to verify cam timing? 

6 replies to this topic

#1 trexxs

  • Joined:09-November 17
  • Location:Australia QLD
  • Car:180sx

Posted 09 November 2017 - 02:57 AM

https://imgur.com/a/BAHTG

Well I went and replaced my timing chain tensioner on my vct sr20det today without putting the engine on TDC first as I didn't think the chain would jump when releasing the tensioner with the factory method.

Nek minnit, not too sure if it did jump or not, or if it was just the sound of the tensioner releasing (sounded like a loud crack)
but I went and put the engine on TDC to verify cam timing and what I saw got me confused.

Cylinder 1 was at TDC compression stroke, cam lobes pointed out, exhaust cam dowel at 12 o'clock

BUT

the mark on the exhaust cam sprocket is at about 11 o'clock, before the dowel, instead of being located after the dowel at about 1 o'clock as all other sr20det's have it.
To make matters worse the timing chain does not have any coloured links on it.

So after 2 hours of research I couldn't find a single answer to this predicament.

How else would I be able to check cam timing apart front pulling shit out and counting the links from the crank gear?

Maybe I should just whack on the valve cover and try and start it, see what happens.

Any help would be appreciated,

Cheers

#2 pmod

  • Joined:13-May 10
  • Location:Australia NSW
  • Car:Fruity 180sx

Posted 09 November 2017 - 08:36 AM

Having fiddled with the timing chain myself plenty of times, I'll save you some effort and share my experiences fixing other people's mistakes.

Some answers to your questions:
  • No, you should not start the engine because that looks miles off. I count 8 links divot-to-divot (16 rollers), when it should be 20, but for all I know you're not at TDC on the compression stroke.
  • Those look like OEM sprockets, but even if they were china spec, they must still have the same number of teeth if the engine was running fine.
  • The coloured links are purely for initial assembly, and won't help you once the car has been running, because the links move position. Think about it; the spacing is 20 > 48 > 56. There is no way the coloured links would return to the save spot every time the car is set to TDC.
  • When you mess around with the chain tensioner or fiddle with the cams, you should ziptie the chain to at least one sprocket. In the case of what you did, I'd ziptie it to both so you know it physically cannot rotate out of position.
  • When setting the car to TDC, remove spark plug number 1 and drop a long screwdriver down the hole, such that it's sitting on the top of the piston. Rotate the crank with a 1/2" ratchet until it's at the right timing mark, observing the movement of the screwdriver. There are two positions of the crank at that timing mark, because the crank rotates twice for every one rotation of the sprocket, so watching the screwdriver bob up and down makes everything more obvious.
Given your situation, this is what you must do to un-fuck your potentially-fucked timing.
  • Download the S14 SR20DET FSM and review the process to set it to TDC, as well as the link spacing and divot positioning. This is the information I pulled from a past thread and it's pretty much as I remember it being, however YOU MUST CHECK THE FSM AND CONFIRM THIS FOR YOURSELF. If you break anything, you want to be the sole person responsible, so verify everything for yourself. Don't trust the Internet when it comes to assembly settings, trust Nissan.

    Intake dot at 11:30 exhaust dot at 1:30
    11 full links between the 2 dots
    Both in and ex front lobes should point away from each other
  • Confirm that the crank is sitting at the right timing mark, which it really should be, then drop a screwdriver down plug #1 and confirm that the piston is also at the right point. If it is not, DO NOT ROTATE THE CRANK ANY MORE. IF YOUR TIMING IS OFF BY 3 LINKS, KISS YOUR VALVES GOODBYE. I REPEAT, IF YOUR CRANK IS ON THE WRONG HALF OF THE STROKE, DO NOT ROTATE IT RIGHT NOW.
In the event that your crank at the TDC timing mark is actually out by 180 degrees, then do the following to correct it:
  • Remove the chain tensioner and remove the cam caps using the exact order and method outlined in the FSM. It's not hard, but failure to do this properly could result in cracking the head. Do it by the book and you won't break anything.
  • Ziptie the timing chain to some screwdrivers so that it can't fall into the timing case once the cams have been removed, then remove the cams.
  • If your crank wasn't on the correct rotation for TDC, you can now reposition it by holding the chain up to maintaining tension, then rotating it into position using the timing mark and a screwdriver in the spark plug hole as a reference. With the cams out the valves are up, so there's absolutely no risk of damage. When you're happy with the position, put the cams in place, set the divot position to align with the 11:30/1:30 positions, then install the cam caps exactly as explained in the FSM.
  • You have now manually set the crank into TDC, and can now continue with the proceess.
Once you've established the crank is at TDC, amend set the sprockets and chain in place:
  • Remove the chain tensioner and rotate the cams and set the timing marks to align with the 11:30/1:30 positions, then apply the chain (shuffling the links along them as needed). Shift the chain around until you have 11 links (22 rollers) from divot to divot, and don't freak out if the divots are between links, because that's how it can be on a running engine. When you're satisfied with them, ziptie the chain to the sprockets and install the chain tensioner. If it becomes obvious that one side of the chain has way more tension than the other, remove the tensioner, shuffle the chain along as many links as needed, then reinstall the tensioner. When all seems well, count your divot-to-divot links again to ensure they're correct. Obviously you'll have to remove and add more zipties as needed.
  • Get some meth and wipe down the rollers/links at the divots, then colour them in using a permanent marker. This won't be of much use, it's just so you can see where they end up every two rotations.
  • Don't install the rocker cover or CAS, because you haven't finished yet.
  • Rotate the crank two full rotations to set it back into TDC, checking for any feeling or sounds of impact in the head (i.e. the valves hitting the pistons). Take it slow and you should be able to advert disaster if you messed up. Count the links total number of links as you go, just to make sure the chain is correct, which it should be.
  • Once back into TDC, count the links divot-to-divot and confirm that it's correct. Repeat this a couple of times to ensure that every time you set it to TDC, the number of links between the divots doesn't change and that the chain tension either side appears equal.
  • Install your CAS to the position you hopefully marked, button everything up, pray to Zeus and test the car.


#3 pmod

  • Joined:13-May 10
  • Location:Australia NSW
  • Car:Fruity 180sx

Posted 09 November 2017 - 08:54 AM

Seems I didn't read your post properly, as you have already rotated the engine to TDC from a non-TDC state with a chain you suspected might have jumped some teeth. Not something I would have done, but ok.

Given your situation, you simply need to set the sprockets in place like I said in steps 1-6, inspect it divot-to-divot and hope you haven't already bent your valves. What's done is done, but your best shot at recovery is to manually set the sprockets to match the crank at TDC, then fit the chain and install the tensioner like I outlined. Counting the links to the crank is great if you don't have the oil pan and sump installed, I've done it myself, but if the chain tension is equal both sides and the number of links at the top stays the same after 3+ rotations to TDC, it should be fine.

If you feel the pressing need to count links to the crank, the way I've done it is to remove the oil pan (and possibly sump, can't remember), paint a link on the chain from the gap under the timing case, count the difference of the mark you painted to the crank sprocket divot, mark the links at the top, then rotate the crank and count everything out. It's just adding assembly marks at the end of the day, and I'd not bother on an installed engine, I would just count the top links and see how it runs. It can survive being off by one tooth, and if it is, the engine will run like shit. Two teeth and you'll probably bend valves.

#4 trexxs

  • Joined:09-November 17
  • Location:Australia QLD
  • Car:180sx

Posted 09 November 2017 - 11:24 AM

Hey mate, thanks for the response.

However, the issue right now is that the cam sprocket marks CANNOT be used to verify cam timing.

Why? Because on all exhaust cam sprockets, as depicted in the fsm as well as various other images and general consensus of the marks, the timing mark is located AFTER the exhaust cam dowel.

My exhaust sprocket mark is BEFORE the dowel.

Meaning when the exhaust cam dowel is at 12 o'clock, the mark should normally be at the 1:30 position, however, mine will NEVER be in that position and will always be at the 11 o'clock position unless the exhaust cam is advanced forward, which we obviously don't want.

Therefore the guideline to verifying cam timing by counting links between sprocket marks cannot be used to verify the timing,as far as I'm aware.

Now if the crank is set at tdc timing mark, piston no. 1 will be at tdc regardless of cam position. So the engine right now is in fact at tdc, however, valve timing may be an issue as none of my sprockets had holes in them to zip tie the chain when releasing the tensioner.

The only things I can verify now is the general direction the cylinder 1 cam lobes are facing, which are correct, and the mark on the CAS, which is correct. But these are not concrete evidence of correct valve timing.



#5 pmod

  • Joined:13-May 10
  • Location:Australia NSW
  • Car:Fruity 180sx

Posted 09 November 2017 - 02:59 PM

Looking up some pictures, you might have a point; I forgot that the S14 exhaust sprocket has holes in the same as the S13 sprockets. So, you could be right about the exhaust gear being an aftermarket part.

In that case, you really have two options:

1. Compare your exhaust gear to an oem-spec unit, mark the correct timing dot relative to the dowel, reposition it as needed, then count the chain links out. If you know anyone with a VCT SR20 that has stock cams, this should be an easy thing to achieve, because you can compare the two timing dots based on the lobe position. Set a lobe on the exhaust cam of both engines to be barely touching one rocker, then make up a little cardboard/wooden jig that slots over the rocker cover studs, marking the position of the divot on the good sprocket. Transfer that mark to the China sprocket, drill a mark and then get on with the job. Even something like wooden mount with a coathanger bolted onto it would work; bolt on the wood and bend the wire to mark the position. Remove and test fit a few times to confirm it's accurate, then transfer it to your engine and mark the dot.

2. Replace the exhaust gear with a used or new [genuine] one, then count it out.

It's a bit crude, but if the engine was running fine it shouldn't be a major issue if you double-check everything, and you have both the dowels and the cam lobes to use as a point of reference.

#6 trexxs

  • Joined:09-November 17
  • Location:Australia QLD
  • Car:180sx

Posted 09 November 2017 - 06:41 PM

Good point! I didn't even consider getting another sprocket to compare. I actually have a couple lying around from engines I've stripped but they've been stashed at my mates place for a while so it never crossed my mind.

I'll go dig em up

Cheers!

#7 trexxs

  • Joined:09-November 17
  • Location:Australia QLD
  • Car:180sx

Posted 09 November 2017 - 10:04 PM

Problem sorted. My friend brought over the spare exhaust cam sprocket and from matching the mark onto the teeth of my existing sprocket I found that the exhaust cam was retarded by one teeth.

My method of fixing this was to take out the tensioner and turn the crank counter-clockwise to slacken the chain on the exhaust side. Then I simply lifted the chain over the exhaust sprocket by one teeth.
To avoid a repeat of the chain skipping a teeth again when releasing the tensioner, I simply turned the crank clockwise until the chain was tight between the sprockets and between the exhaust cam sprocket and crank gear, leaving the tensioner side chain at full slack.
Now I really should've known this crucial step as I have done a fair few timing belts as a current apprentice. However the reasoning was never explained to me and I just assumed that it was to make sure the non tensioner side timing was correct. WRONG, well not entirely, as I have learnt from my mistake.

The main reason is to prevent any movement of the cams or slippage of the belts when releasing or setting the tensioner. While it's not a critical step as mistimed cams can easily be corrected when full access is available, however this becomes a critical step when there is only limited access and you want to avoid removing the cams, something that is not mentioned in the fsm.

Now if you had shitty China cam sprockets like mine that lacked any holes to zip tie the chain, tensioning the non tensioner side chain and allowing the tensioner side to slacken is a must before releasing the tensioner with the fsm method. In fact, if you only had small and thin zip ties to tie the chain, it's a better idea to just forgo the zip ties and use the method above to prevent any zip ties breaking and falling into the crank case, and skipping a teeth in the end anyway.

Happy wrenching!





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