Problems with timing belts too tight?

Phil,
sounds like you need the manual. The kind Mr Jenkins can "loan" you one at http://www.ferrari.stevejenkins.com/books/. I'd expect this would answer a lot of your concerns & make you feel a little less anxious if you feel like stripping-down the whole car into tiny pieces!

Good luck.

 

i am no expert on the 328 ( carb 308 guy) but it seems to me that the waterpump is more prone to damage than the tensioners and tensioner bearings. i would not run the car until you can get a tensionmeter. there is a thread somewhere that mentions the deflection travel in a properly tensioned belt. 1/4 to 1/2 inch is normal for most normal belts on normal cars. the ferrari belts are more exact . the manual should be a big help to you.

 

My experience here is based on doing the majors on my TR, not sure if your belt system is the same....but I think it is. I believe that the tensioner load is preset at the factory and automatically "decides" how much tension the belt will have. From reading your post it seems that you did everything right. Normal procedure after installing the belt is to turn the engine over while watching the tensioner...it will move around slightly....and then tighten the tensioner down when it's at the "most extended" point. If you force the tensioner tighter by pushing on it....then the belt is too tight. It's usually a good idea to replace the tensioner bearings when you do the belts.

 

I am in a similar quandry, having worked on numerous car engines in the past, to deep strip level, and knowing I am more than capable of doing the engine out part of cambelt change on my 348. My only concern is that of not having a tensionmeter as specified in the manual. I did the cambelt change on my old Porsche 928 (engine in so much less hassle) many years ago but in that case I was able to borrow the correct tensionmeter from the Porsche training school, Reading, UK.

For my 348 I have all the required documentation, a new belt and tensioners, standard tools, torque wrenches, garage space etc but no Ferrari contact or supplier to obtain or borrow such a tensionmeter.

I really want to do my own work as I have painstakingly refurbished many items on my car that I am confident from past experience WOULD get damaged even in some minor way by A N Other person during their removal and refitment! It would also enable me to refurbish many other areas that need attention during the work to get to the cambelt change.

I am currently undecided if I go the 'pay up £1500 and at least I get the book stamped but live with the inevitable hassle of correcting the detailing afterwards, or do it myself and get the tension to where I feel it is likely to be right and just take it in to get the 'lower level of disturbance' service done outsourced.

 

Your technique sounds fine. The way I was taught by Verell to do it is to rotate the crank and watch the tensioner. It will move a little back and forth as the tension goes up and down due to the varying force on the belt from the cams. Find the point where the tensioner is providing the most tension judging from it pushing in the most on the belt. That's where you tighten it. Always be sure that the spring in the tensioner is lubed and working right. (When you change the belts, you should always pull the tensioner assembly off and clean/lube. Very easy.) Beyond that, let the tensioner decide how much tension. Then tighten it down. Those belts do not stretch much, if at all. They have a kevlar-like fiber in them. When it wears out, it breaks. Not much stretching going on. The teeth on the belt are pretty big. It needs to be pretty loose to jump a tooth.

One things Ferrari is very clear about is that you do not re-tension the belts. If you over tension them and need to do it again, get new belts. (They're only $20, no big deal). If you come back for service later and they are loose for some reason. Do not re-tension them. Replace!

Birdman

 

Birdman is 100% correct. Applying a slight torque to the crank in the direction of rotation will allow the tensioner to work as intended, applying the proper tension. Then, just lock it down.

The belts will "wear in" and develop a little slack, which is normal. Don't be concerned - the slack will not continue to increase.

An old trick was told to me by a mechanic from FAF. To check for proper tension grab the belt with your fingertips between the longest span and gently twist it - if it twists 90 degrees or less, you're in fine shape.

For what it's worth, time seems to be a bigger factor than mileage. One of my customers let his girlfriend drive his 308QV year-round and when I changed the belts after 2 years/ 30,000+ miles, they still looked like new.

I do recall a 308 upgrade somewhere in the 80s. They changed the belt fiber material from polyester to Kevlar as I recall. The older belts have green printing while the upgraded ones have white.

Bob Z.

 

Jonathan, nice writeup.

Just a couple of minor clarification/elaborations:

The only time you can re-tension is during initial installation if you find that you've got it too tight or loose. Once you've taken it for a drive, you shouldn't retension.

My rule of thumb is that ideally you should be able to twist the belt about 45 degrees w/your fingers. Much less than that & it's too tight, 90 or more & it's too loose.

I once amazed when I saw a Mondial QV with the long section of the cam belt between the drive gear & intake cam gear vibrating back & fourth for almost an inch as the engine was running! You could twist the front bank's cam belt to almost 135 degrees!! As far as the owner could determine from limited records, it had been running that way for many years & well beyond the recommended service interval! That bank's cam timing was still correct when we pulled the cover & checked it! Sure wouldn't have wanted to try tracking that car where down shifts, etc. would be suddenly changing the engine's speed tho.

Ferrari does not specify using any tension gauge for, or give specs for tension on, the cam belts.

As for tensioning the water pump, A/C, etc. belts, I've been looking for the recommended Gates 150 tensioner for years & have never found a picture of one, much less one for sale. Apparently it's long been superceded by something else. If anyone has one, I'd appreciate their posting a picture.

 

It is possible to overtension belts but you didn't do it so don't worry. The method Birdman described is the factory method and works very well.

Belt tension on those is not super critical. As Verell mentioned I have also seen them so loose it was scary and the car had been doing just fine for who knows how long.

Ferrari has adopted an electronic ultra sonic method for tensioning all belts now and the tools are really slick but they are expensive no matter where you source them. From comercial suppliers they can be had for $7-800.
The neat thing about them is that I can use it by strumming the belt with my finger, you can retest the same belt by hitting it with a wrench and Birdman can do it with some other tool or method and we will all get the same reading. Any one who uses measuring equipment of any kind will tell you the most important feature is repeatability. On many new cars, at least the Ferrari's careful, consistant belt tension adjustment is very important.

 

The Gates Sonic Tension meter #505C is similar, but at $1000 still too price for non-commercial use. Would love to have one tho!The Gates double-barrel mechanical tester is more affordable at $54, but requires clearence to get to the belts that I don't think is available.

So I guess I'll continue using the twist test.

Talking about loose belts but not skipping teeth, I've seen two different 308s (1 was mine!) where drive gear was jumping around almost 1/8" in all directions, & rattling like you wouldn't believe. I turned white when I saw it & nearly killed myself getting to the ign switch. Happened at end of the 1st drive of the season!

The other car was JWise's. It started getting noisey over mile from my house with the drive gear jumping around a similar amount when we pulled the wheel liner to look at it.

Was quickly obvious that one of the outer timing drive bearings had severely disentigrated. Half the balls were broken in half and some were completely missing.

I think we were lucky that we weren't pushing our cars at all when it happened.