360 Another thread about setting belt tension

Interesting dilemma.

I went through the same thing myself, just did my first cam belt change last week and had the same issues with tension that you did. Looking at your pictures, it does appear that your tensioners are compressed a bit more than mine. I am not sure what the significance of that is if everything else is okay.

Ferrari spec notes frequency between 190 and 210, a gap on the tensioner's between 1.9 and 2.3 mm and the pin to slide freely through the hole. Given that the only variable you can address is belt tension, it is sometimes not possible to get all 3 variables to match up. After much back-and-forth, I elected to focus mostly on getting the pin to move freely and the frequency within spec, while ignoring the gap. That being said, once I got my belts tensioned to right around 200 Hz total, the pin moved relatively freely, but the gaps were slightly below the 1.9 mm recommendation. My tensioners, however, were not compressed all the way down like it appears yours are.

A few hints that I found along the way,

1) top dead center is critical. The belt tension varies throughout the cycle because of the valve springs. Therefore, if you not testing the tension at exactly top dead center, it will not be consistent. It took me a long time to figure out this rather obvious thing. I used the chopstick in cylinder 1 technique along with a video borescope to confirm TDC

2) the belts settle a bit. Once I got the tension where I thought it was perfect (after many attempts), I used the starter to turn the motor over a number of revolutions and left it overnight. The next day, the tension was way off. I dialed it back in and it stayed perfect. I had a similar issue with the accessory belts. I got the tensions perfect and then the next day they were way too low. Had to retension them. They have been fine ever since.

3) YouTube videos make the job look much easier than it actually is. My biggest struggle was with keeping everything in line after I tensioned the belts. I would put the belt on with everything lined up perfectly and when I tension the belts everything would be off by 1 tooth. Ultimately this resulted in me doing the job twice. I had everything done, buttoned up and car seem to be running okay. I noticed a check engine light came on and error code suggested cam position sensor. I took everything back apart and realized that both sides were off by 1 tooth. My solution was to overcorrect by 1 tooth on each side, turned the engine back to top dead center, put the belt on and then tension it. This got everything to finally lined up perfect. I wish I knew this before I got started, it would have saved me days of frustration. Lesson learned.

All that being said, I am glad I did this job but it was a lot more tedious and difficult than I expected. Now that I have gotten my first belt change out of the way, I think I could do it much more efficiently a second time. Fortunately it will be a few years before I need to do this again.
Image Unavailable, Please Login

 

If it's off by one tooth, you did not do it correctly. You left too much belt slack between the crank pulley and the first cam pulley when you fit the belt on.

 

Yup, that's what I figured, but everytime I put the belt on the same thing would happen. It would line up perfectly, but when I tensioned, it would shift by one tooth. My solution was to overcorrect by one tooth and lock the pulleys, take the belt off and put the engine back at TDC, then replace and tension the belt. Worked perfectly for me.

 

I had a major brain fart on my last belt change because I did the same thing you did, even though I had done it before...I think I even made a thread before calling myself an idiot on that very thread.

This is the problem with "watching Youtube videos" rather than using the WSM. Most of those videos are garbage and even the good ones still miss a few things. You need use the frequency check as just a check, the main thing you are looking for is the 1.9-2.3mm space on the belt tensioner, with the pin moving freely. Also make sure you are measuring in the right area, you have to look at the image closely because it's misleading. If these conditions are satisfied, then after 2 rotations then your belts should be in spec for frequency measurements. Your tensioners are completely compressed. That ain't right.

Image Unavailable, Please Login

It would not be off by 1 tooth because you tensioned the belts. It's extremely easy to add a tooth at the top, in between the pulleys.

I have mentioned the "chopstick" thing hundreds of times on this forum. Dumbest thing on earth when doing a critical timing process on a damn Ferrari motor. I like Scott, but this stinks up his credibility and that video needs to be removed before someone grenades their engine.

STOP WATCHING YOUTUBE VIDEOS AND FOLLOW THE DAMN WSM.

 

The very last step is to pull the pins. The pins were pulled while you are still adjusting the pulley which should not happen. The pins stay in through the entire process and that pin should move freely the entire time.

 

I saw the same thing. I suppose my question is what is the highest priority? My gap is about 1.3 mm but my tension is perfect based on frequency. the pin still slides, but there is slight friction. I figure the belt will still stretch slightly, so the gap may widen over time. Did I over tignten it or is it just right?


What is the highest priority? Tensioner gap or belt frequency?

 

No I would absolutely not ignore it. That's basically the check that let's you know that everything is set correctly. If everything is correct, it will be within spec.

 

No priorities, they will both be within spec if done correctly. The tensioner will do it's job and extend as the belt stretches, but this has to be the starting point.

 

You have actually read the factory shop manual and have deduced that the proper point of measurement is at the wide point of the gap on the left side?
How can that be? The picture in the shop manual is very clear. The narrow point is the correct point of measurement. I have been replacing belts on 360s as a routine part of my job since the cars were introduced in 1999. I have never once encountered a car whose belts were correctly adjusted by a quality, job specific electronic belt tensiometer that the gap size, pin hole alignment and tensionometer reading were not within specification.

 

Impossible to tell but the final setting picture is too tight. If a substantial gap in a cold condition is not present, when hot it will bottom out the tensioner, it cannot compensate for engine expansion making the belt too tight and the tensioner will rattle.

 

FWIW, I am also not a pro, but my takeaway from the WSM and all other resources is that the gap specc’d is in between the tensioner body and pulley arm. This is not the notch that is cast into the pulley arm. There should be no contact between the two parts other than the tensioner shaft itself. Your pictures are showing the pulley arm resting on the tensioner, ie, fully compressed.
Here’s a picture of my engine after tensioning. All 3 parameters were in spec. Note the gap between the pulley arm and tensioner body.
Also, what tensioner bearings did you use?
Image Unavailable, Please Login

 

The WSM states that the measurement should be taken in between the pawl on the arm that comes in contact with the tensioner piston and the body of the tensioner, basically you are measuring how far the piston on the tensioner is extended. I believe there are minor differences in how those swing arms are cast, so measuring them to a tenth of a millimeter would not be accurate. This is mine, brand new tensioners/bearings/belts...this is NOT at TDC, but you can see there is a gap between the right part of the arm and the tensioner. In the OP's pictures, the first one is definitely collapsed, but the second possibly has a gap that is not easy to photograph.

Image Unavailable, Please Login

 

I've asked that question a couple of years ago when I did my belts, but since there was no answer let me ask again. Without going into details (I may or may not have done it perfectly, but I used a frequency meter etc and the car has been running fine), I've been driving without the belt covers and without the cover to engine compartment so I could be watching the belts while driving.

I was surprised that the long part of the belts was flapping quite a bit as the engine RPM was changing under load. Hard to measure exactly while driving but like 0.5 inch up and 0.5 inch down.

Is it OK that the belts flap like that, or is there a problem with the tentioners and/or the belts are not tight enough? Thank you.

 

I know I talk crap about the infamous "chopstick" vid, but a little after the 1 hr, 1 minute mark you can see the motor running without the timing covers. There is a bit of movement on the long side, but all I can tell you is that if you followed the WSM to a T and everything is in spec, you should be good.