308 cam belt tensioner spring

In all likelihood, never. The only purpose of the tensioner spring is to put initial tension on the belt. Once the bearing is in place and properly tensioned, you lock it down and it doesn't move until the next time you change the belts. After you lock the bearing, the spring does no more work. It just sits there. And if the spring ever failed, you can probably tension the belt manually. Can't imagine you'd be replacing the spring.

 

Actually,I did replace the tensioner springs this May. The car is 25 years old and I figured that the springs could be a bit tired. The springs are what sets the correct tension on the belts. The new springs were a bit longer than the old ones and did have a bit more pressure. I'm not sure that the difference was that significant. But the low cost of the springs was cheap piece of mind. Of course, after I replaced the tensioner bearings, springs and the timing belts, one of the cam belt drive pulley outer bearings failed, and I lost 16 valves. Sooooo, I'd worry more about the drive pulley outer bearings than the tensioner springs! Still I think replacing the springs makes sense.

 

What a nightmare!!!
Is it possible that the longer spring put too much tension on the belt?

 

I have run into a number of the short springs that apply too much tension to the belts. Setting the belt tension by the spring only is much akin to lining up the cam marks with the caps....its a starting point

 

"What a nightmare!!!
Is it possible that the longer spring put too much tension on the belt?"

"I have run into a number of the short springs that apply too much tension to the belts. Setting the belt tension by the spring only is much akin to lining up the cam marks with the caps....its a starting point"

As to the first comment, I don't think that the slight increase in tension was the cause. Those bearings are sealed and don't last forever. "Rifleman" has noted that he's seeing more bad ones lately, and speculates that 25-30 years may be their limit. Just bad luck.

As to the second comment, I'm unaware of any, Ferrari approved, method of setting timing belt tension, other than the spring pressure.

 

Your scaring me!!!!

 

Ferrari's methods for any service work is vauge to say the least. I would trust Dave's advise. But some further description of belt tightness would be appreciated. Hundreds of us have just let the spring go, turn the engine around a few times and called it good.

 

I only have experience on my 348, but read 2 things in the 348 workshop manual re: belt tensioners. First is that it says to watch the tensioner as you rotate the engine, and tighten the tensioner when it's at it's greatest extension. The second is that if the tension is too low, measured with a Staeger tensionometer, to stretch the spring to increase it.

As you turn the engine, you can see the tensioner moving back and forth. So on mine, I made sure it was as far out as possible before tightening the tensioner bolt down. AFA stretching the spring, not sure how well this works, but I think by inference, you could collapse the spring to reduce tension. AAR, I don't have a Staeger, so I just locked the tensioner down without doing anything with the spring. I"m sure I'll have the car in 4-5yrs or so when I'm due for my next major, so we'll see how I did.

 

Thats kinda my point. I don't know anyone that has a tensionometer, and most of us have done the belt replacement just using the spring to set the tension. Some of the posts I've read by the pro's suggest that the spring is not completly dependable and find sometimes the belt too loose or too tight. I'm just trying to get a handle on what too loose or too tight actually is. I got my engine turned over to the point where the belts were the tightest, and tried the twist test. I was able to twist the belt a little bit over 45 degrees but not 90 degrees. From what I have read that is what is suggested. I too will just have to wait and see.

 

did my spring with the engine rebuild in june ......the chance of the spring sh#tting itselfs mill to one ..........25 years static in one position and for the price of 2 springs may as well change them............. happy new year to you all from down unda!!

 

+1 here at my shop Dave

 

$110 for 2 coil metal wires? Sheez, I would just leave mine alone.

 

The cost was NOTHING like that from Dennis McCaan.

 

Gentlemen, please see your points that I emphasized above.

To the pros who do this everyday, you're strongly suggesting to do it properly, but you're alluding us as to what those specified values are.

As Mr. "Glassman" pointed out, is twisting the belt 45 degrees a correct amount? As "ria" posted - and we know this too as we all have the 308 workshop manual - there is no specified tension to achieve, let the spring do the work (and as Mr. Helms pointed out, cleaned parts that move freely will have less chance of influencing an incorrect tension).

FWIW: The last time I did my belts was seven years ago (oh the horror! ) and performed the manual's method. I will be doing this again after I wrap up my suspension rebuild I'm in the midst of now. In those seven years, they've stayed on the engine.

So, is this topic much ado about nothing?...

 

Adam, On that I have no doubt, I know you.

The pro's in this field can leave nothing to chance. Those that don't bother to take the time or are not willing to make the investment in the equipment to assure perfection on every job done.... they are giving the marque the reputation it now has regarding reliability. With 75% of my current work load pertaining to fixing what others have created its an irritant to me and is the reasoning behind the question "How good do you want it?".

Peter, """ but you're alluding us as to what those specified values are.""" I assume you forgot the word "NOT" in your question. I have a number of answers to your question. First, no I am not as even if I did they would have no meaning what so ever to you as you do not have the equipment to verify it against a number I would give you. Second, someone else is doing the job not me, I'm am in the business to fix these cars, not pass along every bit of proprietary data I have earned over the course of 36 years doing it. I would venture a guess that even if I posted the numbers I use, most reading this wouldn't run out and spend $thousands to purchase the proper equipment, they didn't before they started the job, why now? Because someone said You don't need it.
"""cleaned parts that move freely will have less chance of influencing an incorrect tension""" Keep reading my reply, the next sentence lays this statement to rest.
"""So, is this topic much ado about nothing?... """ So it would seem as your belts have not fallen off the car?! Personally my standards are set a bit higher than that. I have to know I am not causing damage to other components that are influenced by the belt tension. Anyone that has done this job with BOTH eyes open knows the 1/4 belt tensions tighter by the spring than the 5/8 on most of the early 8 cylinder cars...which is right and why does this happen? If you don't have answers to that question, well....I will wait for the answers. Heck, I have no idea what tension turning a belt 45 degrees represents...I have never done it.

Choose to believe what I have stated as fact or not, nothing I can do about it. I come here to learn about new issues owners are seeing and learn about what their thoughts are regarding expectations of the marque. I consider it a great area to learn about these things and there is a wealth of information here for folks to use to keep the cars running in a cost effective manner. I hold tech sessions at my shop to keep the local club members informed as to how they can save money and what they can do themselves with little to no risk with the tools on hand. I like the idea of saving money and support it and teach it where I can. I am tens of thousands of dollars into making parts to fix known issues on these cars where there isn't a valid alternative with little to no chance of ever making my investment back, if my motives for posting are coming into question this alone should dispel that myth.

I stated "thousands have been done by this method" which is dead accurate. I also stated that these settings are getting a bit more critical as the cars age which again is dead accurate. When I see a trend regarding failures there is reason behind it and my job is to do a complete failure analysis and understand it so I am not subjecting my customers to any undo risk.

Blindly trusting the spring method has its risks, I have much data to support that statement and folks can choose to believe it or not. If I get one person to take a second look at the belt tension and question if its right or not then I consider my time posting here well spent. I will follow that by saying every "much ado about nothing" reply regarding something I have stated has me cutting back on beating my head against the wall.....it no longer feels good when I stop. Much easier for me to just read than type.

Dave

 

I really should learn to play the Lottery! Replaced 2 springs in the last 4 years with broken coils.

 

Last major I did, I wondered about this tension thing. Being an engineer, I like numbers on things. How tight should the belt be? I want a number and a way to measure it accurately. I cleaned and lubed the tensioner spring assemblies, then used the spring tensioner method because that was all I had. One thing I'm curious about when using a specified tension on the belt: how do you know where to set the engine to take the measurement, and where do you measure it? The tension in the belt varies as you rotate the engine, and you get different numbers depending on where you measure it as well.

Birdman

 

Exactly. Numerous reading have to be taken at various stopping points before one can see an average or even duplicated readings. We gave up on this method many years ago and now take the sum of multiple reads at specific points in the belt run, different on each model, and consider this the best and most accurate method. Doing it this way, slack in every area is taken into account. One needs a pocket calculator at hand to do the 348's. Even when this is all said and done we still "feel" the slack and decide if its OK or we recheck it all over again.

Lord Kelvin: "If you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind" My folks had the full quote framed and hung on the bathroom wall (go figure) when I was a kid and it has stuck with me ever since.

 

Dave tells us the way:

A Sonic Tension Meter is the tool, as he says, they're a tad pricey:
http://www.alliedbearings.com/new_prod/gates/belttension_testers.pdf

But somewhat understandably won't tell us the numbers:

Even having the numbers wouldn't be sufficient, you need the meas't conditions as well:

I have a Gates 505C sonic tension meter, and am starting to collect data as I do majors.

 

I don't think so. This is a very important area of question by most owners. Personally, I read these threads with great interest. And any information Dave Helms and others are willing to share is greatly appreciated. These guy's make their living doing this, and to share any knowledge with us free of charge is gracious.
I live in an area that makes it prohibited to send my cars to a certified tech. I am interested in any and all information I can gather.

 

Well I just did mine (348) and I hated the idea of setting the tension using the 'default spring load' method. Like Dave said, there are so many variables that can affect the final tension value (room temperature at install time is another one). As our cars get older the window of acceptable tension range becomes narrower due to years or wear. I had to use this method because its the only one I can afford. I priced a staeger tensiometer (very hard to find) and it is over $900. Even if I did buy one what are the chances I would use it correctly (ie.: that meeting at the Ferrari factory on 'Proper use of the Steager for a Ferrari engine'). I know the tension on the new belt is greater than the belt that came off - I am assuming part of this is due belt wear but wether or not it is the whole reason I don't know. I have accepted that it might not be right and only time will tell the whole story.

The problem is, unless you have years and years of experience, you lack baseline. Its like trying to prove the existance of god.

 

Ria's question has, obviously, stirred up a hornet's nest. I have to agree that if you want it done right (minimum risk of a belt system failure) take it to someone like Dave. But, if you are able to own a Ferrari, only because you can do your own work, and don't want (can't) to invest in a $1000. ++++ Sonic tension gage, then the tension spring method presents the next best thing. Doing your own work on this type of car can be very risky, even with the Chat line input. That is a risk an owner, like myself, must (and does) accept.