Tension in TB

[duncan]

Advice, words of wisdom requested.
I’m in the middle of doing a major service.
TB replaced;
Cams pinned, old belt marked with dots against cam gears, teeth on belt counted and transferred to new TB. New TB fitted, cams un-pinned, crank rotated and TB tensioned against blue mark on pulley. All happy.

End covers on, engine remounted, re-check on valves, and rear cam cover on.
About to fit front cam cover and slack now apparent in TB between Inlet and Exhaust cams on the front bank. TB no longer drum tight/ tappable.
So, all unhappy and HELP!

Is this slack normal, when the crank is aligned with the blue mark this is described as ‘maximum tension’, presumably therefore all other positions are at a lesser tension, is what I observed a manifestation of this.
Trying to think of a good reason not to re-expose TB and repeat the process.
Duncan

[goldnsx]

You'd better recheck the tension for sure before waking up in the middle of the night...

Just one elementary question: did you remove the (ignition) plugs while tensioning the TB?

The best references you can find are the videos of our master Kaz found here: https://www.youtube.com/user/kzukna1/videos esp. this one: https://www.youtube.com/watch?v=T3Ym3hj61ko but check all 6 videos.

Or you might do a video as well and show us. :)

Good luck!

[duncan]

Hi, the sleepless night was last night!
Plugs were out when I tensioned the TB, plugs were in when I observed the slack.

[goldnsx]

The reference point is with plugs OUT, regardless what it is with plugs IN. I'd expect that the slack or tension gets distributed all around the TB with the engine running due to the additional force to overcome the compression in each cylinder. Still, if the tension is set properly with the plugs OUT and the right procedure described by the SM or Kaz it should be fine. Others might chime in as well.

I've asked about the plugs because there was at least one guy in the US who tensioned the TB with the plugs IN which is a definite no-go.

[Kaz-kzukNA1]

Year model?
If very early 91 model, don't use the hole (where you insert the 5mm pin punch) at the FRONT EXH cam holder plate as the timing reference.
In fact, you should use only the arrow on the oil pump cover (for crank shaft/piston position), markings at the front/back face of each cam pulleys and the marker on the TB silver metal cover plate.
Pin punch purpose is more of restricting the cam shaft movement when there is no TB installed or when you are in the middle of installing the TB and not for the final timing check purpose although it will provide some level of backup.

Using your old TB as a reference is also hit and miss.
On several engines in Japan and UK, I already saw number of engines with wrong timing enough for me not to trust the exiting timing alignment.

Kaz

[britlude]

Silly question time.... When you fit the new belt, you rotate the engine a few times check the marks line up then rotate the crank forward to the blue mark and release/tighten the tensioner, letting it do it's thing to set the tension......

Now, why would that process be any different with the timing covers on?? they did make the tensioning bolt accessable from the outside covers after all..... Just thinking out loud (as much as you can in a forum post) and haven't got my manual to hand to double check!

[duncan]

Thanks for the quick responses.
Mystery “solved” - TB re-exposed and no tension in the belt, tensioning pulley fully torque in it’s slackest position!
Pleased that something was found and without the engine going bang.
When I originally tensioned the belt, I did it with the lower cover in place so as to line the blue mark against the two V notches in the lower cover, obviously didn’t tension.
I think the belt may have jumped, so next stages(?)
- back all the tappets off, remove TB, establish cam timing against pins at TDC, (TDC = cast arrow in oil pump cover and centre of keyway?), remount belt, tension without lower cover in place, reset valve clearances.
Thoughts anyone.
Hopefully I’ll sleep tonight!

[britlude]

Glad you've found the cause... dry run the tensioner procedure without the belt on, just to make sure everything is doing what it should and not binding anywhere, the tensioner pinging over with the spring ....

[goldnsx]

When I originally tensioned the belt, I did it with the lower cover in place so as to line the blue mark against the two V notches in the lower cover, obviously didn’t tension.
I think the belt may have jumped, so next stages(?)
You're way better off by counting the teeth on the front cams to find the magic spot of 9 teeth like shown in the video of Kaz.

You definitly should check if the timing is still correct. If you left the plugs out while turning the engine I don't think it jumped. You would have noticed it while turning the engine. Backing all tappets off is safer to check the timing. But for the tensioner procedure I'm not sure if you can do it correctly with non-acting valves. The 9 teeth rule depends on active valves, that's my strong suspicion.

One last hint: in OT, when you set the tension and torque the tensioner bolt, you should mark the position of the tensioner pulley against the screw. At 9 teeth you release the tensioner screw a little bit but just enough that it can readjust. It's good if the marked position of the tensioner pulley doesn't move at all or just a tiny bit (less than 1 mm). Torque it down 43 Nm. Recheck timing and tension of the TB, compare to Kaz's videos and call it a day.

Good luck and no (more?) nightmares about it. :)

[Kaz-kzukNA1]

From your old post, I think your NSX is not early 91 model.
If that is the case, you can use the pin punch method (hole on each cam holder plate) to lock all four cam shafts at #1 TDC while the TB is removed and when installing it.
However, please don't rely on it for the timing purpose regardless of the year model.

If early 91 model, never use the pin punch method for timing purpose especially when installing the TB.
The Front exh cam won't line up square against the hole on the cam plate even when at #1 TDC.

Again, don't rely on the pin punch method for the timing check because the hole on the intake camshaft is not deep enough for the purpose and depending on the diameter of the pin punch, the camshaft timing can be off by 1 tooth.

As you have already 'practiced' the removal/installation of the TB and not removing the camshafts, you don't need to back off the valve clearance adjuster if you can lock all four cam shafts while removing the TB.

In fact, at #1 TDC, all valves at the Front bank (#4, 5, 6cyl) are closed so both cam shafts are free from any pressure from all cam lobes that it is very unlikely to accidentally rotate the cam shafts even without the TB.
Thus, no need to back off the valve clearance adjuster on this bank.

You need to be bit careful with the Rear bank because both cam shafts are under pressure from the cam lobes that both wants to spin on their own in advanced direction when removing the TB if no pin punches were used.

However, while #1cyl piston is at the TDC (minimum clearance against the valves), the piston at the #2cyl is at 2/3 of the intake stage and the one at the #3cyl is at 1/3 of the exh stage so some safety clearance between the valve and the piston head.
Just make sure to keep both pin punches inserted at the rear bank until you are about to slip the TB on to the rear exh cam pulley by advancing the pulley by 1/2 tooth.

Unfortunately, the workshop manual is not 100% clear on how far the slack of TB should be removed.

Already saw so many engines with super loose TB tension in Japan and UK not just because of the TB stretch with age but mainly caused by the improper TB tension adjusting process.
It will result in at least 1/2 tooth (but not full 1 tooth) offset at the rear bank cam alignment.



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The TB tensioner operates between the TB drive pulley and the rear bank exh cam pulley (slack no.6) assuming that all other slack (at no.1, 2, 3, 4, 5) are completely removed before starting the actual tension adjustment.

Removing the slack doesn't have to be at TDC (although the workshop manual kind of states that it has to be at #1 TDC) because you are meant to be removing the TB slack all the way around (no.1 - 6).
It doesn't matter where the crank/cam sits while removing the slack.

You can't achieve this by just turning the engine several times.

The problem with the workshop manual is that depending on how much slack you can remove at no.6 (between the TB drive pulley and the rear bank exh cam pulley), the entire TB would 'relax' at different rate as soon as you start rotating the crank for 9 cam teeth.
For the clarification, this is true even if you removed all of the TB slack while at #1 TDC (as per the manual).


I will share how the slack was removed and tension adjusted at the factory and please remember, only a few selected engineers were allowed to build your NSX engines.

After installing the TB per the manual, keep the TB lower cover removed.

Remove any pin punches (if in use) and never let the crank to rotate in anti-clockwise direction during the following process.

Lock the crank with the adaptor.
You can keep the timing at #1 TDC but not a MUST condition for the following process.

While locking the crank, use pulley holder in anti-clockwise direction at the front exh cam pulley to remove the slack at location no.1.

While locking the crank and holding the front exh cam pulley under tension (anti-clockwise force), use another pulley holder to remove the slack from location no.2 following the anti-clockwise method as above.

Repeat the same process for location no.3, 4 and 5 while locking the crank and the pulley at the previous process.

Now when it comes to removing the slack at no.6, you want to be able to access the TB tensioner body.
While locking the crank and applying anti-clockwise force at the rear bank exh cam pulley, loosen the tensioner bolt but no more than 180deg and push the tensioner body towards the front bank as far as possible.
The spring will assist you in doing so but if the tensioner holder bolt is too loose allowing the tensioner body to sit with some angle, you can't remove all the slack.
Tighten the tension adjuster holder bolt for now and still keep the crank locked.
Almost impossible to achieve the same level of tension as other places (no.1 - 5) but at least, try to imagine that you are aiming to remove any slack and even generate some tension at no.6.

Now gently tap on each location no.1, 2, 3, 4, 5, 6.
You should feel stiff tension at no.1 - 5 and slightly less tension at no.6 but no slack.

Now set the timing at #1TDC (rotate crank in clockwise direction only and never reverse it even if you past the #1 TDC).
If you started the slack removal process at #1 TDC, just double check that you are still at #1 TDC.

Mark the front bank intake cam pulley 9 teeth past #1 TDC.
It will be just about 1+1/2 teeth after #4 TDC marker.
This is where the blue marker on the crank pulley would line up at the marker on the TB lower cover if installed.

Now loosen the tensioner bolt but only for 180deg.
Let the spring to adjust the tension and don't touch the tensioner body this time.

Tighten the tensioner bolt to the spec.

Unlike other engines with automatic TB tension adjuster, NSX engine relies on this initial tension adjustment until the next TB service so it's very important to adjust it properly.

Otherwise, the loose TB will cause noise at cold winter fire up until the engine gets hot because it will keep hitting the TB rear mid cover and if too much tension applied, it will cause whine noise.

[Kaz-kzukNA1]

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Not sure you have seen these photos so I'm going to post them in a hope to assist you.

I can't provide exact weight force data against the TB but when the TB tension is properly adjusted and if applied very gentle pressure with just one finger while at #1 TDC, you will see 10mm movement from rest point in both ways like these photos.

Good luck.


Kaz

[duncan]

Thanks for the comments and support.
For my clarity: tensioning (whether blue mark or 9 teeth) is with set valve clearances so a tension against valve springs only, the plugs out so no compression from the cylinder.

[ozon02]

Thank you Kaz that you shared your practical knowledge. These information could be found reading the blog but here are dispelled my" doubts with 5 mm pin punches". I am during the Engine Refresh (according to your recommendations) which I Barn find in Germany.

sorry for english i use a translator

[goldnsx]

Thanks for all the additional info!

One question: is the +-10mm slack at 6 right after removing the slack at 1-5 or after that?


and please remember, only a few selected engineers were allowed to build your NSX engines.
If I imagine the average mechanic in Europe handling that procedure who might sees an NSX every 5 years or less...at least there are no known/heard of fatal failures. So there is some safety margin in there as well.

[Kaz-kzukNA1]

The measurement is always taken after the tension adjuster bolt locked with 9 cam teeth method and crank turned several times.
After this, set at #1TDC and while keeping the crank locked, measurement taken.


Kaz