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TB skipped during tensioner tightening rotation…

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Please help with any input. I think I’ll likely ship the car at this point but wondering if there another way to remedy this. I had everything all lined up and installed…had the crank pulley with blue line on top, tightened the tensioner pulley. I then proceeded to rotate the pulley when suddenly the crank pulley skipped couple of teeth with subsequent loose belt going toward the front exhaust pulley. I’ve done other timing belts and felt so confident but this happens at the very end..I’m guessing maybe I didn’t take all the slack off the belt before I did the final tensioner tightening. I’m pretty far from TDC and don’t want to force anything at this point and just tow the car to a shop. Unless you think there’s a simple way to remedy this. I just don’t see how anyhow but doesn’t hurt to ask the prime experts while I kick myself.

It wasn’t even a money thing. I just like wrenching…
 
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The NSX timing belt is DIFFICULT. Regardless of the money, I find that I am the best mechanic I know because I can take all the time to get it done correctly...because, as you say, money is not an issue.

I went around with Kaz one time way back when my TB went limp as I was doing my final checks when the crank was in the middle of the 4-stroke cycle (the crank goes around 2x for every cam rotation). I suspect that might be you too.

Use a clean wood rod (I use a chopstick) to ensure TDC in piston #1 to gauge the travel up and down. There is also a slight possibility that your harmonic balancer has slipped and not showing TDC properly.

At this point to be safe you should back off all the tappet valve adjustments so there is no possibility of the valves hitting the pistons. So you can index the crank and cams.

(not recommended: You might be able to hand rotate the entire crank+cams so you can reindex despite the two teeth belt slip. Though, If you feel ANY resistance...stop!!!)

Kaz has some close-ups of the indexing of the cams (http://www.nsxcb.co.uk/entry.php?1956-Eng-Refresh-LMA-Brake-OH-etc-24&bt=2796). From personal experience: you need straight edges and mirrors to eliminate any parallax errors.


Kaz was nice enough to make this video for us showing TB tension:
good: https://www.youtube.com/watch?v=AR-YZ1YqnoU
bad: https://www.youtube.com/watch?v=Cj8jwBshvCk

if you need tools: I am in Tauranga. PM for email.
 
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I was thinking back to what I missed and it’s a sheer stupidity on my part, I did leave the car in gear and didn’t have it in neutral. That probably contributed to this mess…
 
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I was thinking back to what I missed and it’s a sheer stupidity on my part, I did leave the car in gear and didn’t have it in neutral. That probably contributed to this mess…

Look dont beat yourself up , if it was timed and tensioned correctly being in gear would not cause it to jump . You would only be able to turn it till the car started move , you did install the belt with the white mark (tdc) lined up , remove slack in belt .Then tighten tension bolt ,turn clockwise till the blue mark comes up , loosen and retighten tension bolt ,yes?. Becareful with the timing belt pdf because Gary is wrong on the tension adjustment ( he tells you to turn crank one complete turn past white and then to blue . Follow the service manual,good luck.
 
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I haven’t read thru the c30 procedure in a while, but remember vividly changing the belt on a c27 (not identical) but the step where the new belt is installed, and the tensioner takes up the slack, then tightened before hand rotating the engine CCW, is to make sure any extra slack is on the tensioner side, then the extra slack taken up by loosening the tensioner hold down. I have repaired (reworked) several Honda engines which were serviced by mechanics who failed to align marks and who assembled the engines 1 tooth off, and would think (hope) the c30 has enough clearance that being 2 teeth jumped would run without damage.
You can do it!
 
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Dood, you are almost there...you can do it!

If only the crank moved two teeth and the cams didn't move...I personally would move the crank back counterclockwise, re-index, and set/tension the timing belt. Then verify the indexing after TWO rotations with the crank.



>Gary is wrong on the tension adjustment

Yes, there is where I got a hold of Kaz to verify what was going wrong and he was kind enough to make the videos and help me out. That was over 10 years ago and all was well until the next timing belt change.

I now have a JDM NSX and the tensioner is humming loudly...so lucky me I get to do another TB.
 
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If only the crank moved two teeth and the cams didn't move...I personally would move the crank back counterclockwise, re-index, and set/tension the timing belt. Then verify the indexing after TWO rotations with the crank.

I was thinking the same thing. Even if you did have some cam movement I would be inclined to try the 'release belt tension, reposition and re-index'. Of course this will all depend on how many teeth you jumped. If you jumped an undetermined number of teeth, then I would be inclined to follow Drew's original recommendation of backing off all the valve adjustments so that you know all the valves are (should be) closed. I would then add that it might be prudent to get a spark plug air hose adapter so that you can pressurize the individual cylinders with compressed air and listen for air escaping into the exhaust or intake manifold (a budget leak down test) which could be a sign of bent valve. There is no point in going through the timing belt installation if you have a valve problem. With luck, you are OK.

"tightened the tensioner pulley. I then proceeded to rotate the pulley when suddenly the crank pulley skipped couple of teeth "

I am a little unclear about that statement. Did you attempt to rotate the TB by rotating the tensioner pulley? If the crank was 'locked' because the transmission was in gear and you attempted to rotate the engine using the tensioner pulley (not sure how you would even do that) I can see that could cause a tooth hop on the crank pulley. I would have to double check the tensioner geometry; but, if you attempted to rotate the tensioner pulley I think you might actually unload the tensioner spring causing loss of tension. If you attempted to rotate the belt using the crank pulley it should have been quite obvious that the engine was in gear. That should also have not generated a tooth hop because having the transmission in gear would not generate any abnormal tension on the TB - if you are rotating via the crank pulley. If you rotated the crank pulley and you generated a tooth hop I would be looking for some other problem than having the transmission in gear.
 
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Did you attempt to rotate the TB by rotating the tensioner pulley? If the crank was 'locked' because the transmission was in gear and you attempted to rotate the engine using the tensioner pulley (not sure how you would even do that) I can see that could cause a tooth hop on the crank pulley.

Without the crank tool, I have broken loose the crank screw by putting an MT car in gear and between gear-train advantage and twist in the crankshaft, I was amazed at how much the front pulley (and crank) will rotate. It will jump back to position if torque is removed too!
 
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Without the crank tool, I have broken loose the crank screw by putting an MT car in gear and between gear-train advantage and twist in the crankshaft, I was amazed at how much the front pulley (and crank) will rotate. It will jump back to position if torque is removed too!

Because of the play in the drive train and the flex in the tire sidewall, I agree that you can move the front crank pulley while it is in gear. My point was that if you are doing this, it should be quite obvious that the transmission is in gear ( too much resistance to rotation). The transmission being in gear is also not the cause of the problem since the tension being applied to the belt by rotation of the crank pulley is normal (if you are rotating the crank pulley).
 
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Because of the play in the drive train and the flex in the tire sidewall, I agree that you can move the front crank pulley while it is in gear. My point was that if you are doing this, it should be quite obvious that the transmission is in gear ( too much resistance to rotation). The transmission being in gear is also not the cause of the problem since the tension being applied to the belt by rotation of the crank pulley is normal (if you are rotating the crank pulley).

👍👍
 
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Thanks for all the input. I got spooked and ended up arranging the car to be towed to a reputable NSX shop. I’ve done my Z’s VG timing belt 3x, VR4 once and I thought those cars were difficult enough and felt so confident with the NSX. It was all so easy until the tensioning part. Cams even had slots to hold in place! Unless the other ones where I relied on carefully rotating and lining up the cam pulleys with gear locks or cam lockers. I must say the tensioning system on the NSX is quite tricky compared to the two other cars I worked on from the era. Spring vs slide bolt tension mechanism with correct tension adjusted based on belt deflection distance from horizontal plane. I was spinning the crank pulley from blue mark on top and the belt skipped only when I tried to spin the crank pulley to reverify my marks. Not sure if that was necessary…it’s a bit of a blur now since I’ve been just sad and mad about the whole deal. At least the shop mechanic seemed very understanding and was reassuring about bailing me out.
 
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Thanks for all the input. I got spooked and ended up arranging the car to be towed to a reputable NSX shop. I’ve done my Z’s VG timing belt 3x, VR4 once and I thought those cars were difficult enough and felt so confident with the NSX. It was all so easy until the tensioning part. Cams even had slots to hold in place! Unless the other ones where I relied on carefully rotating and lining up the cam pulleys with gear locks or cam lockers. I must say the tensioning system on the NSX is quite tricky compared to the two other cars I worked on from the era. Spring vs slide bolt tension mechanism with correct tension adjusted based on belt deflection distance from horizontal plane. I was spinning the crank pulley from blue mark on top and the belt skipped only when I tried to spin the crank pulley to reverify my marks. Not sure if that was necessary…it’s a bit of a blur now since I’ve been just sad and mad about the whole deal. At least the shop mechanic seemed very understanding and was reassuring about bailing me out.

It’s all good. Nothing is worse than worrying about if you did the job right, missed a torque spec, etc. I very infrequently turn a wrench anymore, and always think about the muscle memory that I’ve lost over the last 30 years.
 
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Car finally got to GT Japanese auto. Great things I read about on prime and reviews seem spot on so far. Had race ramps which worked perfect for the tow truck. I was watching the whole thing on my ring camera which was fun.

Kun the master mechanic has been super so far. Taking really awesome care of my car. Way better than I ever imagined a shop would do. I always had trust issues with random mechanics but my mind is completely at ease even before he finishes the job. You can just tell with the way he communicates that he knows the platform inside out and respects the customer car like his own. I’ll post pics as they come to me and update here. Like I told him, my days of working on the NSX is likely over with a shop like his.

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That looks like spectacular service. Just from the prep along it looks like someone who really takes car of the cars they are working on. Looking forward to more info and you getting back on the road!
 
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There were some gaskets missing on the timing cover per mechanic and waiting on those backordered gaskets. Last timing belt was done by an Acura dealer. Maybe they were displaced or inadvertently not installed. Anyway, I miss driving the car and the weathers been perfect too. I’m having them do the oil pan gasket and few other things while she’s there.
 
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There were some gaskets missing on the timing cover per mechanic and waiting on those backordered gaskets. Last timing belt was done by an Acura dealer. Maybe they were displaced or inadvertently not installed. Anyway, I miss driving the car and the weathers been perfect too. I’m having them do the oil pan gasket and few other things while she’s there.

Those gaskets are rubber as I recall. In a pinch (due to a long back order) RTV would / could work.

Things like missing gaskets are what bother me about taking the car to any service shop, even dealers.

Has the mechanic completed the timing belt indexing and reinstallation?
 
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Picked up the car couple of days ago and drove it home 3 hours away. All is good again and it was an amazing drive back home. Car was gone for 2 weeks due to timing cover gasket backorder. Kun at GT auto gave the car clean bill of health and lined up everything as it should with no damage to report. He said the key was that I didn’t try to start the car or do anything beyond where I was. I had him do the entire fluid flush, oil pan gasket, alignment and the works while she was there. I can trust these guys and that’s always why I always tried to do DIY because I’ve been suckered before. He mentioned how he’s worked on so many NSXs that he knows where every bolt goes. Made me feel great that every time he sent progress pics, there was another NSX. Lol.

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after my 5th 90k service of 23 years of ownership

Glad to hear it all went back smoothly. Per OldGuy, it's hard to bend a valve without a starter motor to help you.

Because of having opportunities for misalignment from factory markings, and they are a bit of a challenge to see because of all the different angles, and making sure no pistons were on at the top of it's stroke...before loosening the tensioner, I have always marked the belt to the crank and cam gears. Then I mimic these markings on the new belt, literally counting every teeth (my OCD; measure 5 times then cut once), then properly reinstall the new belt and hand crank and listen for unusual noises and skipped teeth at TDC.

If there were skipped teeth, I would reverse rotate, then repeat this process. I have never had to repeat this process as these procedures never failed me.

I've had my share of bent valves many years ago because of improper techniques and because of that, I've landed on this procedure. Needless to say, this information is useless with a snapped timing belt.


FWIW: I also own the Honda crank pulley tool (used it the first four times I did my NSX timing belt); but with the Milwaukie 1/2" impact paired to a 12HD battery, I have never looked back.
 
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