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Discussion Starter · #1 ·
Hi, I am new here. I just got greedy and purchased a 2005 Tiburon GT (V6) that had "rough idle after timing belt change". The car ran lousily, idled rough; turning on the A/C made it almost stall. I knew I was purchasing a project, and I got it cheap. The bozo(s) later disclosed the original timing belt broke off.

I thought the timing was off by a single tooth but it turned into a larger project. First, the RH cam sprocket (closer to the firewall) was installed backwards(front side facing the engine), wobbling wildly. So I opened the head cover, and turned the cam sprocket right side up. But to my astonishment, the RH cam sprocket is off by 180 degrees.

Before I get a ton of RTFM replies, let me assure I understand how the timing marks line up. The crank turns twice for each cam revolution. So I understand that the TDC means the crankshaft pulley is lined up, and the marks on both cam sprockets should line up against the marks on the head cover. In my case, the LH (close to the bumper) lines up, and the RH is off by 180 degrees. To my amazement, the compression is fine - about 170-180PSI on each of the 6 cylinders. So the previous owner either got lucky or the valves were repaired.

I know I cannot simply rotate the RH camshaft by 180 degrees - I would hit the valves against the cylinders. Indeed, when I take the timing belt off and (slowly and carefully) try to rotate the RH cam by a few degrees, I encounter resistance: first by the lobes pushing against springs, then by valves hitting the top of the cylinder. So I see two options:
1. Remove the RH cams (lift them from their seats); verify the chain linking them is correct (it appears so), then turning them by 1/2 rotation and putting it all back together. Or,
2. Is there a way to (gently and carefully) "walk" the cam by turning the crank by a few degrees, while maintaining the timing belt against LH cam, and turning the RH cam by hand a little "faster", thus making up the 180 degree advancement I need? My thinking is that if I get to a spot where the cylinders are off the top spot, it would give me enough clearance to open the valves.

I have never dealt with a V6, so I cannot even imagine the geometry of such a move. Do you think it is possible? I am reluctant to touch the camshaft bearing caps, and would like to avoid it if possible. But I'll do it if my option #2 is too crazy or risky (or impossible).

Thank you for your advice. I like this community; there is a ton of useful info here.
Dudlo
 

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I don't believe you can walk the cam due to the interference. Infact you may have already bent valves as a result. You can certainly try by moving the crank back and forth with very low effort as you turn the cam... but I would personally pull the valve cover and reseat the cams in the correct position. Would also be a good idea to check the chain driven gears to ensure they are in time too. Who knows what else they screwed up.
 

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Discussion Starter · #3 · (Edited)
Thank you for your response. I ended us "sitting" (not walking) the cam, and I'll explain how. But first a message for the future reader: YOU MOST LIKELY DO NOT NEED TO (and should not) DO THIS! The procedure below was to correct a botched timing belt replacement. Ignore this if you are dealing with an "off by one tooth" timing belt situation.

I realized there was no chance of moving the camshaft alone without hitting the pistons. But if I could find a spot where none of the valves were opened, I could move the rest of the engine (crank and the other camshaft) to "catch up" with the one that was off by 180 degrees. It became clear that TDC was not the right spot - the cylinder #5 exhaust valves were fully opened. However, I found that at the 180 degree offset from TDC, the RH cam lined up perfectly - no cam lobes (on RH side) were engaged, so all valves were closed. This is what I did:
  • got the engine to the TDC position: crank lined up, LH cam (side close to the bumper) lined up, RH cam off by 180 degrees
  • marked the exact spot of the 180 degrees off on both cam sprockets - off by 24 teeth (made it easier to line up later)
  • made the RH cam sprocket spin freely: removed the belt, removed the cam sprocket, and inserted a washer that blocked the shaft key (on the camshaft) from being inserted into the keyway (hole) on the sprocket. Attached the sprocket, and hand tightened. Now the RH sprocket could turn/spin without the camshaft moving at all. I did all this because it would be impossible to correctly turn the crank and LH camshaft without the belt fully on (most likely the belt would jump without the tension on it).
  • put back the timing belt
  • turned the crank one turn: the LH camshaft moved by half a turn (in sync with the crank). The RH sprocket turned but the RH camshaft did not (I locked the camshaft using a 24mm open box wrench).
  • ended up in position where both camshafts were 180 degrees off the TDC. Now they were synced!
  • removed the belt, RH sprocket, and "special free-spining" washer, reinstalled the sprocket, tightened to 90Nm, put the belt back up
  • turned the crank to TDC, verified that everything was lined up. Released the tensioner; turned the engine by hand and using the starter. Both sprockets were on the mark; the chains were correctly linked (their arrows pointing outwards). There was no cylinder to valve contact/resistance.

It took a lot of head scratching but I think it was less work than popping the cams. More, I feel better about not disturbing the cams unnecessarily. I'll continue next weekend - I ordered seals, gaskets... Plus the "craftsmen" before me used about a pound of goop on the gaskets, so I'll have to remove all that junk. I am still amazed the engine ran at all (with only 3 cylinders firing). I cannot believe there was no valve damage (compression is fine). I'll report back when I put everything back up.

dudlo
 

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Thanks for the follow up. It really helps future readers! I replied to this thread previously with a lot of doubt that the valves survived the last timing belt job. Out of abundance of caution I would have removed the cams because it's not a very difficult procedure. But I am pleasantly surprised that it worked out for you and that you were able to workout a solution the way you did. You are already ahead of 99% of Tiburon owners with the knowledge you bring!
 

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Discussion Starter · #5 ·
chase,
Thank you. I'd withhold the praise until I put everything back together. I am not all that positive that it'll run. You are correct that popping the cams would not be bad; I just prefer to not disturb things if I can avoid it.
One thing for sure: it feels great to have feedback and advice. Thank you for keeping the forum alive and useful.
 

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Discussion Starter · #6 ·
I owe a follow-up here. I have not put everything together; just enough to start up the engine with head covers, "plenum" back, exposed timing belt. It ran better. Quickly settled for target idle speed (before it would always idle at some 1200RPM). So I am declaring victory. Thank you for all your advice.
 
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