Gap or Gap and Frequency Tension, or Gap Frequency and Gap again?

Hi

I went thru the same conundrum.
Too much information, some of which overlaps and some contradicts.

To me the issue, is that any adjustment you make the to the tensioner pulley needs time and 2 rotations of the belt to allow itself to equalise across the entire belt.
I found that adjusting the tensioner altered the relative timing of the cams by a tiny amount.
Also if the timing of one cam was out, you may have half a tooth of the belt not sitting in the pulley nicely.
So an iterative process took place.
But in the end I found the frequency and the hole sort of lined up within tolerances.


I view the frequency and tensioner gap as complimentary if everything is ok, the hole will sort of line up and you will get the frequency. If one or other is out then something is wrong.


FatBillyBob on the 348 forum, offered a solution that I found to be very good.

Lock the cams in place with some cardboard under the caps.
Slacken the pulley bolts a little - you will not be able to move them by hand but they will move.
Adjust the pulley to get the correct gap - now go and have a coffee.
When you come back you will find the pulleys have moved slightly to equalise the tension.
Lock up the pulley bolts.
Rotate the belt twice or more.
Check the tension, gap and timing marks.

I was able to get everything spot on this way.

 

I'm not a pro, and I have done this exactly 2 times. There are some very respectable mechanics that may respond with the correct answer. Here's my 0.02:

I believe the initial measurement with the 2mm gap is a starting point. I wondered why I was checking this gap to begin with and here are my theories:

1- Assuming the retaining pin is inserted correctly, the retaining pin will slip out within some tolerance slight shaft movement. The measurement helps place it correctly within this small tolerance.

2- it is possible to have the pin in on an angle if it is not passing through the posterior hole (I'm using the terminology anterior hole - shaft - posterior hole). In this case the 2mm gap is a check.

3- its possible to pull out the pin, and have the hydraulic piston take a minute to settle and be to tight or loose, and this gap would be an easy check.

4- if the gap is persistently off, maybe this reflects a problem in the tensioner requiring replacement - e.g. if the gap collapses after multiple attempts to set it properly fail.

None the less I used it as a starting point. Then had to make a slight adjustment using a frequency meter as outlined in the WSM. From my experience the ending gap should be pretty close to the 2mm after tensioned.

If you think about it you will have to give up on either frequency, or the gap. Otherwise you will find yourself in an endless loop.

check and set gap
check and set tension
recheck and reset gap
recheck and reset tension
repeat forever...


Although I respect Angus I don't think there is a need to remove a cam bearing cap and lock the cams for this routine timing belt change.

 

@360+Volt
Fully agree with you if you are happy with your cam timing.

In my case the inlet cam was 'off' and when corrected the belt was halfish a tooth out. So I had to either accept the error or do something to get it right.



But if I may, in a related matter ask a question that is sort of connected.
When putting back all the ancillary belts, there are 2 idler bearings.
One at the bottom for the AC belt and one in the middle that i think was the water pump belt.

It doesn't seem clear to me from the WSM whether these items should just kiss the belt, float close to but not touching the belt or some other answer.
I spoke to a few people who have more experience and there was a consistent answer, but the issue was that it's just not stated clearly in the WSM. (at which point someone will now point to the exact sentence in the WSM where it's stated)

 

I agree with the ambiguity of accessory belt idler bearing adjustment. I ended up using what I thought was was common sense and set mine to be close but not in contact with the belt. I felt this bearing wasn't very robust, and probably was engineered to prevent excessive belt deflection.

Well I was wrong, either a respected pro posted, or I found it buried in the WSM (can't remember which) that the idler should contact the belt. I'll try to find the reference for u. I haven't changed mine yet, due for belts this year, and will verify this is correct, and set accordingly.


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Angus, Its in the section for AC Compressor control belt. page 28 in section A3.04

 

@Kevin, yes that is what i meant.


@360, your right.
For the benefit of others it says....

"Bring the nut (3) into contact with the belt and lock the fastening nut".

Well the first 'nut' is clearly a typo and should read 'bearing'.
So that's one item ticked-off my "like to know" list.

 

Kevin; Did you change the tensioners as well? Or just belts and bearings?

I imagine changing the tensioners might also be a "fault source" when it comes to getting all items to recommended specs..?

 

Yes, that's how I interpreted the picture also.


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Kevin, what tension tool are you using ? I may try a belt job myself and setting
the belt tension, and tool, is the main thing holding me back.

 

I use ianalyzer for my iPhone. Works perfectly with the built in microphone.

Being an anal man of science (and religion) I borrowed a Ducati frequency meter from a friend to verify it. some folks have used the Ducati tester as a less expensive option for the Ferrari $$££ meter. The smart phone app worked perfectly. If u think about it it's just measuring a vibrating frequency, and as long as the device will pick it up even a guitar tuner should work.

I suggest testing the belts before removing them, and practicing on the accessory belts.


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Its kind of reassuring to see others with the same conundrum I've faced. I am interested to find out if any one else has found the right bank ( cyl 1-4) to set up perfectly with all three parameters achieved but the left bank not so? Further I wonder if any one else feels that the left bank tension should be set with no 5 act tdc compression .........the wsm instruction starts by reference to cyl 5 for setting tension on the left bank. I found that with the engine at no 1 tdc I could not get consistent results for the left bank whereas I did when positioning at no 5 tdc for left bank tension only. I hypothesise that with cyl 1 at tdc the cams on the left bank interact more with the valve springs an induce a minimal slack in the top run between the cam pulleys of the left bank.
All thoughts welcome.

 

The way I interpreted the WSM is as follows:

1. You use the frequency to set the preload tension with the eccentric tensioner pulley (with the hydraulic tensioner fixed with the pin).
2. You release the hydraulic tensioner for the dynamic tension which should result in the "gap"

Looking carefully at the rocker arm, there are actually 3 steps, and NONE of them correspond to the figure in the WSM from above!

For anyone interested, my belt change is posted here:
https://www.ferrarichat.com/forum/posts/148206418/