Internal belt must be involved to change. A chain can be broken and wound into the engine hooked onto the back of the old chain, can't be done with a belt. I have changed many Benz chains-which can/do break- this way. Some Benz chains do last forever, esp. those in diesel engines. Chain drives tend to be more compact and eliminate the seals on the cams, a potential leak and a definite increase in cost. I see a trend back to chains after a coupla decades of belts.
In reply to iceracer: Does nascar use gears or a chain? Stock drive is a chain, might be Morse or roller.
Chas_H wrote: Internal belt must be involved to change. A chain can be broken and wound into the engine hooked onto the back of the old chain, can't be done with a belt.
That's how you do Mercedes because their design does not have a removable chain case. Every other timing chain engine in the world allows you to remove the chain as an assembly.
With respect to NASCAR, I would be very, very susprised if they used a gear drive. Belt drive is in vogue because of the aforementioned harmonic-killing properties. Geardrives have the exact opposite, they introduce a lot of noise into the cam, which translates into valvetrain issues and distributor/oil pump issues on engines that have those. Geardrives are mainly useful for impressing people when you lump and whine your way into the burger stand parking lot.
Knurled wrote:Chas_H wrote: Internal belt must be involved to change. A chain can be broken and wound into the engine hooked onto the back of the old chain, can't be done with a belt.That's how you do Mercedes because their design does not have a removable chain case. Every other timing chain engine in the world allows you to remove the chain as an assembly. With respect to NASCAR, I would be very, very susprised if they used a gear drive. Belt drive is in vogue because of the aforementioned harmonic-killing properties. Geardrives have the exact opposite, they introduce a lot of noise into the cam, which translates into valvetrain issues and distributor/oil pump issues on engines that have those. Geardrives are mainly useful for impressing people when you lump and whine your way into the burger stand parking lot.
In my experience there are few engines that cannot be done by feeding in a new chain, which is the easiest way to do it. The big concern with feeding in a new chain is retracting the chain tensioner. In some engines the front of the engine must be removed to access the chain tensioner. This is much more work than breaking the chain. Some engine do use a gear drive for the cam. Volvos and some British 4s, also RR/Bentley V8s. And lets not forget the good old VW flat 4. Many diesel engines use a gear train to drive the camshaft, as do F1 engines. I think considerations other than harmonics are the reason for using a timing chain rather than gears.
Never owned a belt driven engine and likely never will.
Chas_H wrote: In my experience there are few engines that cannot be done by feeding in a new chain, which is the easiest way to do it.
It doesn't change the guides or tensioner, which are the parts that generally go bad.
Some engine do use a gear drive for the cam. Volvos and some British 4s, also RR/Bentley V8s. And lets not forget the good old VW flat 4. Many diesel engines use a gear train to drive the camshaft, as do F1 engines.
None of those are 9000+rpm pushrod V8 engines.
Knurled wrote:Some engine do use a gear drive for the cam. Volvos and some British 4s, also RR/Bentley V8s. And lets not forget the good old VW flat 4. Many diesel engines use a gear train to drive the camshaft, as do F1 engines.None of those are 9000+rpm pushrod V8 engines.
You lost me there. I'm not making any claims for gear vs chain. I asked if nascar used one or the other.
But I think the reasons for using what ever they do are not grounded in harmonics, but rather in the rules.
Can't figure out how to copy a link on my kindle but an article in circle track magazine says most nascar teams use gears while some have found an advantage with chains.
My thought with the pushrods is that in a stock application, you don't need to do anything for 200k miles most of the time. If you do lose a chain, you don't have to open up the top of the motor to mess with them.
OHC with a chain requires tensioners, guides, etc. More parts to fail/replace. The chain has to go so far that you get more stretch, flop, what ever.
Belts need much of the same attention depending upon application
Part of my issue is the most OHC motors are transverse, making repairs that much harder regardless of drive type.
Sadly finding a pushrod motor or a car with an engine pointing the right way to tough these days. You're buying a truck or sportscar. A few oddites stand out, but there isn't much in the bargain basement these days in the salt states.
In response to Nascar style engines. Here is what they use, or something similar. I will repeat this once more: Belt drives reduce engine harmonics. Pretty important when you spin at 9,000 rpm for hours on end. I spend enough time in the race shops and engine shops, I know this crap. Gear drives are too harsh. All the vibration from the crank goes right to the cam and gears.
http://www.jesel.com/innovation/belt-drives.html
http://www.cvproducts.com/Products/Engine/Belt%20Drives/
I'm going to have to go with Gearheadotaku on this one. For a stock DD, I'll take the push rod engines with chain drives any day. Maintenance = zero. I've never had one fail, including the one in my work van that's pushing 350K.
Then again I've never had a OHC belt or chain fail either and I put almost 200K on the 5.4 in my conversion van before I sold it.
Gear drive FTMFW!
That's why I love my Ford 300 sixes..
They don't need to make noise unless you're one of those clowns who actually -likes- gear drive noise.
Belts have just as much additional maintenance as chains. They need tensioners and idlers as well as belts.
Don't forget the "Well ma'am, since we're in this far, it's only another $xxx.xx to install a new (insert part here, usually a water pump) and it would cost twice as much to go back in and do it later" that gets generated for the service department.
Don't forget, in those race engines, chains have a lower top speed they can be run at.
Belts don't have as much mass and aren't as likely to try to separate themselves from the components they're driving.
This is partly why you don't see chain-driven blowers nowadays.
Trans_Maro wrote: . Don't forget the "Well ma'am, since we're in this far, it's only another $xxx.xx to install a new (insert part here, usually a water pump) and it would cost twice as much to go back in and do it later" that gets generated for the service department.
Water pumps run off the timing belt are a pet peeve of mine. Run the water pump off the fan belt and if it fails, you pull over and can usually just unbolt the pump and swap another one on. If a timing belt driven water pump seizes, it takes the timing belt with it, and if you've designed an interference engine (which for some reason often seems to get paired with timing belt driven water pumps), the cylinder head assembly and pistons too. The whole thing seems to be designing in an extra, unnecessary weak point into the motor because someone didn't do a proper failure mode and effects analysis.
In reply to MadScientistMatt:
True. Replacing the water pump is considered by most to be part of a timing belt change in a TDI. None of the three I've replaced in my car so far really looked like it needed replacement, but I've learned not to trust German water pumps... Plus, the coolant should be changed every 100K anyway... so it's just one of those "may as well..." kind of things.
Trans_Maro wrote: Gear drive FTMFW! That's why I love my Ford 300 sixes.. They don't need to make noise unless you're one of those clowns who actually -likes- gear drive noise. Belts have just as much additional maintenance as chains. They need tensioners and idlers as well as belts. Don't forget the "Well ma'am, since we're in this far, it's only another $xxx.xx to install a new (insert part here, usually a water pump) and it would cost twice as much to go back in and do it later" that gets generated for the service department.
I inquired at the Toyota dealer about a timing belt change on our Sienna last year, and they quoted me a price of $xxx.xx. I asked if that included the water pump. They said it wasn't recommended to replace that part. I asked if it were driven by the timing belt, ad they said yes. I said well why not do it while you are in there? They changed the quote by maybe $100 so I just had them do it as it seemed dumb not to. Maybe my dealer is on the up and up, but they didn't think it was necessary. Either that or they wanted it to fail later, and get paid even more.
It depends on the car for me...
I have owned a few billion cars with chains. I have repaired a few billion cars with belts. That's an exaggeration, but you get the point.
Most belts are relatively reliable if you change them every 60k. Most belts are also a pretty massive undertaking. It doesn't matter to me if its the easiest belt change on the planet, its still required maintenance. If its a VW beetle, you couldn't PAY me enough money to own one of those and have to do my own belt changes. If its a Mitsu anything, you couldn't pay me enough to own one with their leaky oil-pressure tensioners that leak and never provide enough tension. Anyone who has watched a Mitsubishi DOHC run at 4000 rpm with the cover off has probably run for cover in fear of dying from the impending shrapnel.
I would, however, consider owning a non-interference belt engine.
On the flipside, you couldn't pay me to own a 4.0L ford with a timing chain. The guides are crap and replacing them (even in the labor guides) requires removing the engine. R&R engine for an Explorer is something like 15 hours. R&R timing chain/guides is listed at something like 18.8 hours.
I'll keep my timing chains. My wife had a Tercel with 400k+ on the ticker. I think I changed the spark plugs a few times. I have a chevy pickup with a 350. It has no tensioners, just a chain. I changed the chain at 350k because it started to make some noise.
I have worked in, managed, and owned several shops. I got so tired of replacing heads on VWs, Mitsubishis, and Mazdas that I vowed to avoid them at all costs. Even the mere thought of adding that complex maintenance work to an otherwise bulletproof vehicle seems like a massive Achilles heel.
Re: water pumps. Most chain engines drive the water pump with the chain, too...
Knurled wrote: Re: water pumps. Most chain engines drive the water pump with the chain, too...
Really?
I've never seen one.
That being said, the newest thing I own is a 1996 Ford.
ncjay wrote:
Or when you spin to 14,000+ 
Trans_Maro wrote: Really? I've never seen one. That being said, the newest thing I own is a 1996 Ford.
The new breed of Ford Duratecs, the Quad 4 and Ecotec, and plenty of Chryslers run the water pump off of the chain. And the LT1, if we want to get technical about it 
I suspect that we'll see more and more of it. Less belt driven accessories means simpler engine compartments and easier packaging and less NVH. There are generally only two belt driven accessories anymore, the alternator and A/C compressor... and a hybrid design requires neither of those, either.
Practically speaking, I see nothing wrong with driving the water pump from the timing belt. With a couple exceptions, tou usually have to take the belt off to change the water pump no matter what's driving it
I thought belts were a good idea until I was introduced to the interference head.
honestly, if you replace the belt when you are supposed to, belts are just as reliable as pushrods or chains. Especially modern belts.
When fiat introduced the timing belt to the general public with the 124, many of those engines met an untimely end (sorry) because people thought they were being ripped off for being told they needed to replace a "fan belt" at 20,000 miles
In reply to Knurled:
Cool, now I know..
I don't see the problem either.
My 850 Volvo drove the water pump from the timing belt and it was reasonably easy to change both.
Shawn
It depends on the application.
For a race engine, timing belt for sure. It's lighter, can rev higher without issues, and even if it is maintenance intensive, all racing engines are.
For a DD, timing chain for sure. It's maintenance free, and very reliable. While I know they can fail, it has never happen to me or anyone I know. And I'll take a "it might fail if you put cheap oil in it" over a "you HAVE to do this 2-3 hours, 200-400$ job every xxx miles" every time.
As for timing gears, on a racing engine, the harmonic problems is a none issue. Harmonics are a problem when the frequency of your engine matches the natural frequency of your gear set. In a racing engine, the frequency (RPM) of the engine is constantly varying, so you only momentarily pass at the natural frequency, so there is no time for harmonics to be a problem. You get problems with harmonics when you run at a constant RPM (like on an airplane engine, or while you are cruising). And any harmonics is easily taken care of with a torsional damper.
With that said, most timing gear setup are very complicated, heavy and expensive for the little gain they have over a chain or belt.
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