Why I don't like timing belts ...

Of course this also means that when Ferrari releases their version, it will be one more complicated system, which will forever break down and cost big $$$ to fix, that we will have to suffer with on our F-cars!!!

 

The bigger question is why belts on interference engines?

Belts strip more often than chains break! If a chain breaks on a non-interference engine, most damage will be minimal. Not so with a belt; bent valves etc.

 

I have to wonder if this will be potentially riskier than a belt...more electronics plus pneumatically actuated valves. I'll stick with belts but I'd rather have a chain. Just think what would happen if a crucial relay dropped out while you were driving.

 

Not to worry, an easily built in fail safe would be to have the valves default to their closed position in the event of a failure and to have the circuit cut electrical power to the fuel injector, thus effectively "disabling" the affected cylinder(s) --- and sparing any components from mechanical damage

 

I disagree because it would be more complicated than the current system. The system is mechanical, electrical , and pneumatic. A pneumatic valve has to open in order to release pressure for the valve to close. If it doesn't, kablamo. If it delays a few microseconds due to a valve sticking, kablamo. Nothing is truly failsafe. At least what we currently have can be readily serviced by car owners.

 

No it can't.

A belt that has run for 15 minutes look pretty much the same as one that has run for years. That is the problem.

Assuming of course you do not have oil leak issues.
Pete

 

Another altenative is gear driven camshafts...a bit noisey but worth it.

 

400I chain wears out by 50Km and is a very expensive replacement. Belts seem kinda of nice.

 

I am also a belt-hater. The noise argument is simply bollox, especially older engines are easily noisier than their chain. It's just cheaper to make an engine with belts, and a great way to regularly get your clients back for that oh-so important belt replacement. It's a win-win, but for the manufacturer, not you.

The pinnacle of ridiculous is found in the F-cars needing an engine-out job to replace them - and this every three years on some. That's just plain failure of design in my view.
50k on a 400i chain? That's also a failure of design, if true. A chain should easily last 150-200k, if the tensioner is properly engineered.

 

I do not understand what the hold up is, Ford has been doing it since 1964 427 SOHC. anyone with the ambition and access to a machine shop could reporoduce what Ford designed and built.
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Alfa Romeo and others have been doing chains up to double overhead cams since the 1920's ...

Pete

 

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For a Testarossa 12

 

Idler pulley on the tight side of the chain? Hmmm that is unusual ...

Or does a 308 engine run anti clockwise?
Pete

 

It runs in the normal direction. The owner has quite a fair number of km.'s on it without problem.

 

Glad, but it is a design mistake that is putting more load than necessary on the idler pulley bearings. You will never (?) see this done by a manufacturer.

Pity cause so easily could have been on the right side ... and thus will make other engineers doubt the implementation.
Pete

 

I'm not an engineer so I can't make much of an argument one way or another on that point. What I can say is the guy that did this works for the racing division of Sachs in Germany and is heavily involved in clutches and dampers for three of the current F1 teams. Don't think he got that job because he does things in a haphazard fashion. He's a pretty smart guy.

PS. and he "rallyes" a 1750 so he can't be too bad a bloke, right? ;-)

 

Yep and everything can be designed around so I'm sure there was a reason ...

Absolutely

Pete

 

The crankshaft rotates in the "normal" direction, clockwise; but the lower cam chain drive sprockets rotate in the opposite, or counterclockwise direction. The tensioners are on the slack side of the chain

 

Unhu

Last month I changed a set of timing gears on a 2005 Kioti Diesel tractor with only 225 hours on it when the oil pump driven off the same crank gear went bad stripped its gear teeth and the debris ate scattered gear teeth throughout the system--And it still ran with normal noise after the scrunch when it all went bad and the oil light came on. Quick kill and tow it back to the barn with the '49 International.

Mondial 2V timing belt and tensioner change is easier and parts cost for Mondial 2V belts and tensioners is about the same as the gears etc. was to fix the tractor.

 

Arh thanks!!!!!!, that makes perfect sense and I thought it was weird that an engineer would get this wrong ... and they haven't.

All is right with the world .
Pete

 

Seems to me that when the engine revs up it produces the greatest load on the belt. However, when the engine speed increases, the belts streach a small amount relieving the tension on the idler and the belt running across it. Belt needs to have a great deal of wrap on the exhaust cam drive wheel to ensure it does not skip a notch. On the intake cam drive wheel the belt is pulled into the wheel due to the tension of the belt so less wrap is necessary. With the exhaust cam drive this is not the case hence the large amount of wrap on the exhaust cam drive. To maintain the wrap, the idler is positions as such. But, again, the tension in the belt if far less on the slack side where the idler is located, and this is due to the streach of the belt under load even at constant engine speed.

Another way of doing it without so much of a wrap is by driving only one cam. That cam then has a small chain that drives the other. Ford does this with its turbocharged Taurus. With this drive there is less reverse bending on the idler.

 

Huh? The "slack" side? There is no slack side. There is a section of the belt where the tensioner is located, but it ain't slack there. The tension on the belt is uniform across all sections - from drive pulley to cam pulley to cam pulley to tensioner and back to drive pulley. Yes, the tensioner may have a small amount of throw on it due to a very small amount of stretch, but it's movement is more determined by belt slapping than by stretch. But again, the tension is uniform across all the sections.

 

Just curious... is there a way to change the 355 set-up to chain and, would you want to?

 

Slack means less tension, not completely loose. Just look at a bicycle chain on a child's bike. When he pedals, the portion of chain on the top is taught. The bottom portion is 'slack'. Now suppose the bike was really old and would go backwards if you pedaled backwards. The part of the chain on top will now be 'slack' with the portion of on the bottom having much more tension.

If there is no unbalanced force in the belt, no work can be done. You're implying that it takes no work to turn the cams. I doubt that. Tension only equalizes when the engine is not running. The tensioners are locked on this engine.

Look at the AC belt on the 328. It has an idler to keep it from slapping. Why does it want to slap. It's because it has less tension when the AC is on. When the engine is not running, the tension is equal everywhere on the belt. When the belt is driving the AC compressor, the tension is not equal.