Quick timing belt change question

Will the cam lock for the 308 QV engine work for a timing belt change on a 328?

 

Yes,QV and 328 are identical. What cam lock are you using or do have?

 

Mike,

My friend Paul has one that we've used to do timing belts on his QV engine. Made of nylon if I recall correctly. That's why I was asking, since he has one that we have used successfully on his engine.

Thanks,
Steve

 

Recently another Fchatter and I did his belts. We ditched any of the tools in place of using the rubber mounts from the AC compressor and a bolt. Simply put one rubber mount on the top of the two cam gears (they're triangular shaped and its intuitive as to which way to insert it between the cam gears), and the other on the bottom. Hold them together with a bolt and nut and you are done. Cheap, simple, and in stock if you have an AC compressor on your car.

 

Do you have a pic you can post?

 

http://www.youtube.com/watch?v=BQhfcdQf1QA

 

Why is everyone so paranoid about locking cam gears in place?

On my 2V car, the only one that might move a little bit is the 5-8 Exhaust bank and I can't get the new belt on unless I slip it back in the right direction. Also, I checked and before I removed the old belts all the marks were lined up perfect so if I do put it on wrong, it will not line up and I now I'm off a tooth.

Are the QV cars just more prone to moving around a bit?

 

> Are the QV cars just more prone to moving around a bit?

Should be less.

Thanks for a good post. We tend to raise these engines/cars to religious levels when in fact, they're just hardware. Mark 'em, change the belts and put 'em back in service.

 

It's helpful anytime you change a belt/chain on a car to put the engine at TDC first. That way, if something does move, you have a reference. However, much of the time this is not done and mechanics just remove the old belt/chain and put the new one on in the present position of the pulleys/gears position.

Setting the tension on a cam belt is very important, of course, and it's worth noting that belt tension on any car with a mechanical tension device is set at the tightest portion of the belt travel. In other words, you rotate the engine and new belt to the point that has the least amount of deflection and adjust the tension at that point. If you adjust the tension at the loosest point, for example, you risk shearing teeth or, at minimum, wearing out the belt long before it's time.

 

It's not about the valves and the tension it takes to open them. Belts/chains are not true and neither are pulleys. You could remove the valves completely and just spin the engine/belts/cams and you would see that at some point in the rotation the belt is tighter than other points in the rotation. If you tighten the tension at the belts loosest point, it then becomes too tight at it's tightest point. All belts, chains on any device are adjusted this way - you rotate to find the tightest position and adjust the tension. This includes fan belts, water pump belts, motorcycle drive chains, etc. Putting the tension on the loosest point just wears the belt/chain out faster and overly stresses the bearings involved.

So basically, after installing a new belt/chain you rotate the parts, checking the deflection at the same spot in the run but every 1/8 turn or thereabouts. When you find the rotation point where there is the least deflection of the belt/chain at the adjustment measuring position, you set the tension to whatever deflection or other tension spec is applicable.

 

I'm not so sure. If you set (lock) the tensioners at the least deflection, won't the belt become (excessively) loose at the point of the most deflection?

 

This works just fine - and, by way its function, can be used with very little lateral tension. Less than is used with tapered blocks and a bolt.

As to belt tension, there is one designed-in tension spec which reflects the nature and physical properties of the drive system (chain or belt). It's a waste of time to get hung up on what point in the rotation there's more/less tension on the belt. Set it to the spec with the thing at TDC (or pick your own darn point) and be done with it.
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that looks like good way to hold em thanks as belt replace in due in 2010 for mine

 

This is what I've used for my QV and should work for the 328 as well.
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Could you please elaborate on: "As to belt tension, there is one designed-in tension spec which reflects the nature and physical properties of the drive system (chain or belt)."

Thank you.

 

Yes.

And you get erratic valve timing also with too loose of a belt.

The valve spring pressure wants to accelerate the cam(s) forward in certain areas or rotation, just as the springs want to retard movement in other areas of rotation. Setting the tension with the belt at maximum deflection sets the tension at valve opening and keeps the cam from over running the crank during valve closing.



Doug

 

Next time the car is apart

But actually, now that I have seen the C-clamp method, it is superior to what any of us are doing.

 

I'm guessing here, but it seems to me that on each cam of a DOHC 4 or 8 cyl. car you have four lobes (or lobe pairs for you QV guys). I'll speculate that they are evenly spaced across the circle, so one lobe every 90*. So if the cam is fully opening a valve it will probably stay put, but if it is on a ramp it will want to snap down that ramp until another lobe is stopped by its valve spring. So I would expect a maximum of 45* of rotation from valve springs. And I would expect that there are four areas of high tension (ramping open a valve) and four of low tension (valve spring pushing the cam along). It is probably very sine wave looking, depending on your cam profile. OK, so you have this tension sine wave operating on the belt from one cam and a nearly identical operation, at some phase offset also operating on the belt. I think the reality is that there are points where the cams are pushing the belt in the same direction, points where they are pushing in opposite directions. Depending on what side of the cams you are measuring tension on you will see the action of the valve springs tugging or pushing the belt unless you have landed in a valley between lobes or at the peak of a lobe. On the 2V apparently you are there at #1TDC on three cams.

I've never tried it, but on a pushrod V8 where one cam is opening and closing everything can you easily turn it because all of the valve actions try to cancel each other out? I'll have to ask the muscle car guys I know. I'll bet the cam drive stress on a DOHC motor is under multiples more stress than a cam-in-block V8.

 

Yup, exactly right. And when the whole thing is rotating at 1,000 or 7,000 rpm the spring-loaded tensioner is doing a good job of ensuring the belt has a reasonably decent and consistent tension at roughly the designed spec such that slack and/or harmonic vibrations don't build up and cause the belt to skip a tooth or two.

 

I'm not trying to be picky but, to be precise, the tensioner (when in use) is not "spring loaded", as it is clamped down after adjustment. The spring only sets the original, static, tension on the belt, after that, the spring has no function. The idler/tensioner pulley rotates but its centerline never moves. It cannot control the tension variances.

"RIFLEMAN": Imagine this: You're on a desert island, in combat conditions, with ONLY a metric socket set and, if you wish, a pry bar. How would you set the belt tension?
(This should be very illuminating)

 

Of course, on these engines, there is no need to fool with determining the tight/loose point because the factory setup "automatically sets" the tension when following the service instructions.

 

Are you guys not relying on the belt tensioner anymore?

 

Fred, you're absolutely correct. I wasn't being clear. What you said - ie. the tensioner sets a spec tension regardless of where in the rotation the belt/camshafts are. Yes, at some points it'll be a little tighter, at some points looser, but overall, when the thing is turning 7,000 rpm the tension is in the spec range and does a good job of ensuring no skipped teeth. It's generally other things that cause belt failure (not tension) such as oil or road debris invasion, contamination, aged/deteriorated belts, seized cam bearings, overrevving, etc....

 

I knew you knew, I just wasn't sure about others.

Here's what scares me, do you tighten the tensioner at its max extension, its min extension or in beween the two? When I first got my 308 QV Mondial, I replaced the belts and tensioner pulleys. I set the tensioners at max extension. About a month later, a drive pulley outer bearing let go and 16 valves went with it! Maybe max extension is too much? This is why I want "Rifledriver" to address my (above) desert island, combat conditions, scenero.

 

Why not just follow the service manual - page B 40/41 of the 328 manual describes the procedure - by rotating the engine two full turns by hand with socket/breaker bar with the lock nut on the tensioner loose and then, keeping tension on the belts with the socket/breaker bar, tighten the tensioner nut. This automatically ensures that you have set the tension at the belt's tightest point.

This is the way any belt/chain is tensioned, whether it is done completely manually or "semi-auromatically" as in this case.