Timing belt install

As we have discussed at length, changing the belt doesn't, CAN NOT, change timing more that that associated with the difference in length of the tensioned portion of the belt, which is, AT MOST, a fraction of the manufacturing tolerance in belt length. Typically this means +/- 1/2 degree of less change provided the belts are installed correctly, tooth A into gap A, tooth B into gap B, etc. Timing belts are precision components.

 

Well, speaking for myself, I'm not talking about moving anything to an "unknown position" All I said was you can back the crank off to allow the belt tooth alignment and then put it back on it's mark which will take all of the slack out between the cam sprocket and the drive sprocket. It's really not a big deal.

 

As already said, no movement to unknown positions is involved. The end result is identical to the previous belt.

The reason for vernier pulleys is for initial engine build. For sure, go ahead and degree the cams for maximum accuracy, in case Ferrari did it wrong, but we are discussing a belt change here, not engine blueprinting. Precise timing adjustment, even if worthwhile at all, would be something only done once, and not at belt change intervals.

To add to that, precise timing would change with engine temperature and belt hours from install, so being too exact, even once, achieves very little.

 

The only thing I would add is that if it's the first time you've done it on your car I wouldn't just assume that the last guy who did it got it right because, as was mentioned, it could be a tooth or two off and it's still going to run and you might not know it. So, for myself at least, when I do mine (which is going to be soon since I'm about to do head gaskets) I want to make sure it's all lined up right.

 

+1000. This always kills me. " You must degree the cams to make sure the last person that degreed the cams didn't mess up the timing." WTF?!?!?!?!?! You mean degreeing the cams causes them to be out of time? Then WTF would I degree them? The logic of it is so simply circular it makes me laugh out loud. Let the hate commence.

 

Paging Rifledriver! Cleanup needed in bay 1. Meanwhile, millsj is probably out test driving the 328 while we rumble here. Proves that timing belt threads can be dangerous.

 

I'm going to assume it only jumped only a partial rotation (say, 10-60 degrees), and that you rotated it "backwards" back to it's proper position. IE, if it jumped clockwise, you corrected by rotating counter-clockwise.

If all the above is true, you're fine. Proceed with the tensioning once you're ready, and just be careful to note if turning the crank is running into resistance. If so, you've got valve contact (so STOP). If smoothly turning, breath easy.

Tip: it's easier to turn the crank if you take out all the plugs.

 

I was working on 308's and owned a 308 when they were new in the late 70's. How many of these cars are on their 3rd or 4th owner or even more? How many belt changes have been done? How many have been done with nail polish while eating a sandwich over your motor? How many have had heads off? I don't understand the refusal to just do the job to a high standard every time the belts come off? Are you guys being paid by the hour or something?

 

This is normal.

 

I can answer that question, for myself. I've done one belt change on my car, and I didn't pull the covers off and adjust all the valves. Why? First off, I didn't how to do that yet... It's certainly more involved. I knew I could change only the belts and not screw anything up. The valves? I was pretty sure I was going to mess something up if I tried that. Secondly, it was important to me to at least know that the belts were new and tensioned correctly.

The complete procedure is certainly important. But also important is the belt itself. And it's better to at least change that using cam marks, than to not do it at all.

 

Coming from the Alfa Romeo world I'll have to say that I'm a bit baffled with all of this nail polish fuss. Why don't you guys just put the engine at #1 TDC, line up all the hash marks and go from there? Don't move the cams they have off center lobes under spring pressure, keep them locked. If you are at #1 TDC #1,4, 5 and 8 are all the way at the top.and # 2,3 6 and 7 are all the way at the bottom because it's a flat plane crank. So any moderate turn of the crank in either direction is just going to turn the top cylinders down. The only way to crash pistons in to valves is if you are a complete idiot.

 

Changing the vernier adjustment just to be able to slip on the untensioned belt is not doing things to a high standard. I had to re-read this but it seems to be what you are suggesting. Have you actually done this on a 308?

There is certainly a case to be made that its worth checking once that someone previously has not got the timing out. But thats all. Once thats ascertained there is nothing whatsoever to be gained in degreeing when changing a belt. Furthermore this does not relate to the original question as this does not make getting the belt on any easier, its a whole different procedure.

 

Um, it's a 90 degree V8 with a flat plane crank. 1,4 are at TDC. 2,3 are a BDC. 5,6,7,8 are at 90 degrees crank rotation and all are less than 1/2 stroke up the cylinders.
Incidentally, this is why, when assembling a flat plane crank engine you should rotate the crank to 45* before TDC. Then the heads can be put on w/o worrying about the position of the cams as no valves will hit the pistons. Then the cams can be rotated to align the marks and the crank rotated 45* forward to TDC once the marks are aligned and the cams locked.

View attachment 2528153

 

Again circular logic.. Cams must be degreed because the last time they were degreed, they got out of time. If that is true, then don't degree the cams ever. Or just keep degreeing them until the end of time to make sure the last time they were degreed (by you the person checking the last person's work) they didn't get out of time. ROFLMAO. When does this logic end?

 

You have to understand. FBB and a few other, particularly on the 355 forum, think that everyone who works on these cars is an incompetent. Which, as you point out, is circular because if the last guy was incompetent and got it wrong, how can I possibly get it right, since I too must be incompetent, in which case the next owner, who will also be incompetent will have to retime the car to correct my error, thus making another error in setting the cam timing. It is truly amazing that any of these 308s some now 42 years old, run at all. The only conclusion is that all these cars are running around just fine with incorrect timing. Thus, accurate timing doesn't really matter and is unnecessary.

 

ROFLMAO

 

Thanks for the pictures John, cleared up my brain fart.

 

"Opinions expressed here are strictly my own.
The right answers come when you do your own homework. "

That bit at least is right.

The engine has marks on the crank & marks on the cams, use them. Make a note of where they are before you start changing the belts & as long as they are in the same place when you finish then the engine is timed the same way as it was before you started. If it changes it can only be by a whole tooth on the belt which is a huge amount and very visible.

The belts do not stretch in use - or at least if they do its by nothing like even half a tooth. So unless you want to alter the cam timing from where it was before then you do not EVER start messing with the cam timing pins just to get a new belt on.​

If a new belt won't go on its because something is not quite lined up which is probably because something moved a little during disassembly. It happens all the time, its nothing to panic about & as has been indicated, the trick is to undo the whole tensioner assembly, put the belt on & clamp it over the long run & then wiggle the tensioner assembly into place.

As Andy also said, if you need to wiggle the crank a little then you do it - it will be blindingly obvious if the thing is a then tooth out somewhere - I seem to manage to achieve that at least half the time I change the front belt!

As has also been recorded hereabouts in the past , 1 tooth out will not cause an interference issue, it will just run like crap. Its not difficult to spot if you've done it and its not difficult to sort it out before you run the motor.

Deja vu on this discussion (!)

 

OMG that is the stupidest thing I have ever heard! The process is so simple just read the WSM. And Andy yes I have done this on 308's sine they were new in the 70's. I have rebuilt Ferrari motors and gearboxes too. in the 70's and 80's I apprenticed with 2 former FNA mechanics who went on their own. You guys are really barking up the wrong tree. Doing it the wrong way with commitee agreement with John who has never done it does not make it the right way. Good bye...

 

You’re so smart. Just ask yourself. Why don’t you try responding with logic and facts rather than your resume.

 

It was taught to me by a factory trained Ferrari mechanic who worked on these cars when new and who also later ran an indy shop. 'nough said.

 

I agree that:

You cannot "accidentally" change the timing if you have marked the position of the cams and crank before starting work. As noted, the slight moving of a cam to get the belt teeth to engage is inconsequential.

IF you have never verified the cam timing, IMO, it is a good practice to do that the first time YOU do the belts in your car. I say that more in a educational, How-to sense, rather than a fear that some previous mech somehow got the timing off by a tooth. OTOH...

Being off by one tooth is a LOT and is easily seen. Assuming the cams/crank position was marked to start with, it's impossible to accidentally mis-time. Well, OK, I guess "impossible" is impossible. Let's just say it would very difficult NOT to notice that.

Worrying about timing "changes" with engine hot or cold or slight variations in belts is for folks like F1 engine builders, not us! What's important to us is belt change interval discussions!