Leon R
Veteran Member
- Joined
- Mar 20, 2000
- Location
- b.c. Canada
Whatever happened to the research that was being tossed around here on the forum about developing a timing chain to replace the belt? That must have been about 8 mths ago.
Timing belt mods
- Thread starter Leon R
- Start date
M
mickey
Guest
The more you think about it the more you realize what a daunting technical problem it would be. First of all, timing chains require guide rails and tensioners that are totally different from the belt design. You'd need to design and manufacture a timing cover that would be completely sealed and impervious to hot oil since the chain would require constant lubrication. Etc.
A more realistic idea, though still very complex, would be a gear drive. I think the biggest reason VW didn't do that is the noise. If you've ever been around a Dodge Cummins pickup you know what I mean! You can reduce the noise somewhat by using helical gears instead of straight-cut, but they're still pretty nasty. And, again, you'd need a sealed timing cover and a lubrication system.
Unless you happen to own a high tech machine shop such a system would be economically beyond the reach of an individual TDI owner. Desiging and manufacturing a conversion kit would mean a HUGE investment in R&D and tooling, so you'd need to have hundreds of TDI owners signed up ahead of time.
Realistically, it ain't gonna happen.
-mickey
A more realistic idea, though still very complex, would be a gear drive. I think the biggest reason VW didn't do that is the noise. If you've ever been around a Dodge Cummins pickup you know what I mean! You can reduce the noise somewhat by using helical gears instead of straight-cut, but they're still pretty nasty. And, again, you'd need a sealed timing cover and a lubrication system.
Unless you happen to own a high tech machine shop such a system would be economically beyond the reach of an individual TDI owner. Desiging and manufacturing a conversion kit would mean a HUGE investment in R&D and tooling, so you'd need to have hundreds of TDI owners signed up ahead of time.
Realistically, it ain't gonna happen.
-mickey
NYTDI
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- Joined
- Mar 23, 2001
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- 1999.5 Golf TDI AUTOMATIC trans. GLS w/PLX package silver/black cloth
If I understand the belt longevity problem on the TDI it has to do with the fact that the injection pump puts a lot of strain/load on the belt. Couldn't the pump be driven some other way that would load the engine not the belt? Electric motor, hydraulic pump or PTO from the crank/transmission.
car54
theGAME
The pump is driven by the timing belt because it must remain in perfect time. Its just not a simple fuel pump like you would find on a gas engine, If it was driven some other way, It wouldnt be in perfect time with the engine. that would cause problems.
It seems to me the majority of timing belt problems seem to be with shops that dont know what the h3ll they are doing...
It seems to me the majority of timing belt problems seem to be with shops that dont know what the h3ll they are doing...
NYTDI
Veteran Member
- Joined
- Mar 23, 2001
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- Mid - Hudson
- TDI
- 1999.5 Golf TDI AUTOMATIC trans. GLS w/PLX package silver/black cloth
If we have crank triggered ignitions why not crank triggered pumps that are driven by other than the belt directly. Forgive me if I'm a bit uninformed, I'm a gasser new to TDI's.
Drivbiwire
Zehntes Jahr der Veteran
- Joined
- Oct 13, 1998
- Location
- Boise, Idaho
- TDI
- 2013 Passat TDI, Newmar Ventana 8.3L ISC 3945, 2016 E250 BT, 2000 Jetta TDI
Do ignition system need to develope 19,000 PSI? ahhh no..
A gasoline engine is simple, throttle body opens allowing air to enter at a controlled rate, the ECU senses the volume of air and mixes 1 part of gas for every 14 parts of air, the gas mixes around a bit with the air as it makes it's way past the valves, the engine sucks it in compresses it a bit, an electronic signal moving at the speed of light fires a spark and boom you have ignition.
A diesel process is a bit easier and a bit more complex, I suppose it's better to say that you can't compare the two.
A diesel has no throttle body, therefore it is always sucking in all the air it can all the time. To better that one more we are going to add a turbo to really ram the air into the intake. Now we have a pump that is precisely timed in relation to the crankshaft. As the air is rammed into the cylinder it fills with a massive volume of air and is then compressed at ratios that boggle the mind. most new diesels are around 18:1 compression ratios, and some older ones go as high as 24:1. The reason is when you compress air it heats. We are going to do one better we are going to take pressurized air (around 17psi) and comress it in a cylinder with a 19.5:1 comression ratio, can you say HOT? Well because the crank is only at TDC for a very short period of time we need to act quickly to take advantage of the highly compressed air at TDC and to allow the slow burning diesel fuel enough time to burn to reduce emissions. Because there is no spark to ignite the fuel we have to rely entirely on the high temperature air in the cylinder to act as our spark plug. We cannot just spray in the fuel before TDC because as the piston compresses the fuel will start to burn too early and push the piston in the wrong direction. If we spray it in too late igniton may not occur at all. I think it's safe to say that the window of ideal injection time occurs from 20degrees before TDC and 5 degrees after TDC.
What controls Diesel RPM? Well, you need to think of a blow torch. Increase the amount of fuel to the flame and what happens? the flame gets bigger. Decrease it and the flame get's smaller. If you increase the fuel too high you get soot because the there is not enough air around the flame to burn all the fuel your dumping in. If you lower the fuel too much the flame goes out.
A diesel is very similar. We add just enough fuel to make the engine run at the rpm we want. If the engine runs faster we take away the fuel, if it runs too slow we add fuel, just like the blow torch we only add what we need.
With that in mind since we are only adding just enough fuel, we need to inject this fuel within a very short peiod of time. Since this period of time is so small given the rpm of the engine we need to be very accurate to ensure that the fuel is injected at the perfect time.
Because we need to deliver a substantial quantity of fuel in a very short period of time the fuel must be pressurized at very high pressures to get it all into the cylinder for combustion to occur at the correct time. This means we need to have pressures anywhere from 14,000-29,000 PSI and keep it in perfect time with the rotation of the crankshaft. In order to do this VW uses a special heavily reinforced belt that has teeth to keep the pump and cam in perfect time with the crankshaft. Other manufacturers use push rods, gears, chains or even the upcoming PD sytem that has no pump at all but rather injector pumps driven off of the camshft rather than an additional pump.
The timing belt is a very accurate and reliable method of running a camshaft and injection pump. The belt does not wear out the pulleys, it lasts a long time, it does not require lubtication, it's quiet, light, simple, and inexpensive.
The question keeps popping up why the belt failures? simple mechanic error! You just don't throw a belt on a car and send it on it's way. There are small adjustments that must be made when installing a different belt, notice I said different? Yes even though it is new the fact remains that there are now two belts alike. So when installing the new belt youneed to reset the cam so that it is in perfect time with the crank, and readjust the injection timing. What happens is because of the low experience levels of most mechanics with timing belts they do not understand or know how to identify some of the catastrophic pitfalls that lie within the timing belt setup.
Alignment and tension are everything with a rubber timing belt. If the belt is too loose it skips, too tight it stretches, if it's not aligned properly it shaves itself too bits! As proof of the durability of a belt I have seen belts with over 116,000 miles and that was on a TDI! it was not the prettiest belt but it hung in there.
The belt issue is blown out of proportion in my opinion. I see why VW did it this way and there are good reasons. I know other manufacturers do things other ways but there engines are all years behind the VW diesels in technology and power per liter.
Hope this helps clarify, if not my hands are too tired to type anymore....
DB
A diesel is
A gasoline engine is simple, throttle body opens allowing air to enter at a controlled rate, the ECU senses the volume of air and mixes 1 part of gas for every 14 parts of air, the gas mixes around a bit with the air as it makes it's way past the valves, the engine sucks it in compresses it a bit, an electronic signal moving at the speed of light fires a spark and boom you have ignition.
A diesel process is a bit easier and a bit more complex, I suppose it's better to say that you can't compare the two.
A diesel has no throttle body, therefore it is always sucking in all the air it can all the time. To better that one more we are going to add a turbo to really ram the air into the intake. Now we have a pump that is precisely timed in relation to the crankshaft. As the air is rammed into the cylinder it fills with a massive volume of air and is then compressed at ratios that boggle the mind. most new diesels are around 18:1 compression ratios, and some older ones go as high as 24:1. The reason is when you compress air it heats. We are going to do one better we are going to take pressurized air (around 17psi) and comress it in a cylinder with a 19.5:1 comression ratio, can you say HOT? Well because the crank is only at TDC for a very short period of time we need to act quickly to take advantage of the highly compressed air at TDC and to allow the slow burning diesel fuel enough time to burn to reduce emissions. Because there is no spark to ignite the fuel we have to rely entirely on the high temperature air in the cylinder to act as our spark plug. We cannot just spray in the fuel before TDC because as the piston compresses the fuel will start to burn too early and push the piston in the wrong direction. If we spray it in too late igniton may not occur at all. I think it's safe to say that the window of ideal injection time occurs from 20degrees before TDC and 5 degrees after TDC.
What controls Diesel RPM? Well, you need to think of a blow torch. Increase the amount of fuel to the flame and what happens? the flame gets bigger. Decrease it and the flame get's smaller. If you increase the fuel too high you get soot because the there is not enough air around the flame to burn all the fuel your dumping in. If you lower the fuel too much the flame goes out.
A diesel is very similar. We add just enough fuel to make the engine run at the rpm we want. If the engine runs faster we take away the fuel, if it runs too slow we add fuel, just like the blow torch we only add what we need.
With that in mind since we are only adding just enough fuel, we need to inject this fuel within a very short peiod of time. Since this period of time is so small given the rpm of the engine we need to be very accurate to ensure that the fuel is injected at the perfect time.
Because we need to deliver a substantial quantity of fuel in a very short period of time the fuel must be pressurized at very high pressures to get it all into the cylinder for combustion to occur at the correct time. This means we need to have pressures anywhere from 14,000-29,000 PSI and keep it in perfect time with the rotation of the crankshaft. In order to do this VW uses a special heavily reinforced belt that has teeth to keep the pump and cam in perfect time with the crankshaft. Other manufacturers use push rods, gears, chains or even the upcoming PD sytem that has no pump at all but rather injector pumps driven off of the camshft rather than an additional pump.
The timing belt is a very accurate and reliable method of running a camshaft and injection pump. The belt does not wear out the pulleys, it lasts a long time, it does not require lubtication, it's quiet, light, simple, and inexpensive.
The question keeps popping up why the belt failures? simple mechanic error! You just don't throw a belt on a car and send it on it's way. There are small adjustments that must be made when installing a different belt, notice I said different? Yes even though it is new the fact remains that there are now two belts alike. So when installing the new belt youneed to reset the cam so that it is in perfect time with the crank, and readjust the injection timing. What happens is because of the low experience levels of most mechanics with timing belts they do not understand or know how to identify some of the catastrophic pitfalls that lie within the timing belt setup.
Alignment and tension are everything with a rubber timing belt. If the belt is too loose it skips, too tight it stretches, if it's not aligned properly it shaves itself too bits! As proof of the durability of a belt I have seen belts with over 116,000 miles and that was on a TDI! it was not the prettiest belt but it hung in there.
The belt issue is blown out of proportion in my opinion. I see why VW did it this way and there are good reasons. I know other manufacturers do things other ways but there engines are all years behind the VW diesels in technology and power per liter.
Hope this helps clarify, if not my hands are too tired to type anymore....
DB
A diesel is
golfstream
Top Post Dawg
Damn, I enjoyed reading that!
Thank you, DB.
Mel
Mel
M
mickey
Guest
European TDIs are all going to the Pumpe Deuse ("Pump Nozzle") design, which uses extra cam lobes to directly activate plunger-type injectors, thus eliminating the need for any kind of high pressure injector pump. That still doens't help the belt situation, though, since the cam is driven by the belt. Only by eliminating the belt from the fuel pressurization process entirely will the situation be resolved. (And even then you'd have to replace the belt every 90K anyway.)
A pump mounted on the end of the crankshaft would be nice, but would require at least a couple of gears because the pump would need to turn at 1/2 crank speed. And it would be too bulky sticking out the end of the engine.
It's a difficult problem to overcome. VW's mistake was in making the assumption that TDI buyers wouldn't tolerate a slight increase in noise from a chain or gear drive. Mercedes has been using chains almost exclusively in their engines for decades, gas and diesel, and I don't hear too many people complaining about what noisy cars they are. But you STILL need to change the chains every 150K or so. There's no escape!
Unfortuanately, we're stuck with 'em the way they are. The best suggestion I can make is to learn to change them yourself. With the proper tools and some experience it can be a two hour job and cost well under $100.
-mickey
A pump mounted on the end of the crankshaft would be nice, but would require at least a couple of gears because the pump would need to turn at 1/2 crank speed. And it would be too bulky sticking out the end of the engine.
It's a difficult problem to overcome. VW's mistake was in making the assumption that TDI buyers wouldn't tolerate a slight increase in noise from a chain or gear drive. Mercedes has been using chains almost exclusively in their engines for decades, gas and diesel, and I don't hear too many people complaining about what noisy cars they are. But you STILL need to change the chains every 150K or so. There's no escape!
Unfortuanately, we're stuck with 'em the way they are. The best suggestion I can make is to learn to change them yourself. With the proper tools and some experience it can be a two hour job and cost well under $100.
-mickey
NYTDI
Veteran Member
- Joined
- Mar 23, 2001
- Location
- Mid - Hudson
- TDI
- 1999.5 Golf TDI AUTOMATIC trans. GLS w/PLX package silver/black cloth
DBW & Mickey - thanks (once again) for the enlightenment, I'll see if I can come up with some more simplistic scenarios to entertain/frustrate you. And of course we have to work with what we have been given
The TB change on the TDI dosen't sound like a job a first timer should do w/o an experinced eye to point out the potential problems, pitfalls, and allowable shortcuts. I've done a few gas belts but obviously a bit more is involved here.
The TB change on the TDI dosen't sound like a job a first timer should do w/o an experinced eye to point out the potential problems, pitfalls, and allowable shortcuts. I've done a few gas belts but obviously a bit more is involved here.
Harvieux
Vendor , w/Business number
Hello DBW, I would love to hear the reason why VW dosen't engineer the TDI not to ruin the heads upon timing belt failure. BTW, I am presenting my local stealership with some of your past posts regarding timing belt changes,fair labor chages,and fuel pump timing procedures. Hope you don't mind! I am showing them their inadequacies so I can get a better performance and price but best of all to let them know I'll be watching and they are on notice. Later.
Drivbiwire
Zehntes Jahr der Veteran
- Joined
- Oct 13, 1998
- Location
- Boise, Idaho
- TDI
- 2013 Passat TDI, Newmar Ventana 8.3L ISC 3945, 2016 E250 BT, 2000 Jetta TDI
The reason a TDI cannot be designed to have no damage when a belt fails is because there is no large combustion chamber like a gasoline engine has. The valves are flush with the cylinder head face and all the air that is compressed is forced into the piston bowl that represents about 30% of the piston crown surface area.
When a belt fails VW did the best they could and designed the valves to fail in a very specific manner, it's the best they could do given the tight confines of a diesel engine combustion chamber.
If a timing belt fails the head can be repaired but it is usually cheaper to buy a new one due to associated labor costs. I priced a new head not too long ago for an A3 at $850.00 brand new (no core charge for the old head). That included a complete head without injectors. That is not that bad. If you want a reman its almost $975, I have to believe it is because of availability.
I don't mind if anyone copies my posts, after all it is a public forum, what am I gonna do say no?
All the info here is for the benefit of those who participate and enjoy the TDI engine whether they own one or not. Make copies and let your dealer read them, put them in the spotlight and make it known your an educated consumer.
DB
[ April 03, 2001: Message edited by: Drivbiwire ]
When a belt fails VW did the best they could and designed the valves to fail in a very specific manner, it's the best they could do given the tight confines of a diesel engine combustion chamber.
If a timing belt fails the head can be repaired but it is usually cheaper to buy a new one due to associated labor costs. I priced a new head not too long ago for an A3 at $850.00 brand new (no core charge for the old head). That included a complete head without injectors. That is not that bad. If you want a reman its almost $975, I have to believe it is because of availability.
I don't mind if anyone copies my posts, after all it is a public forum, what am I gonna do say no?
All the info here is for the benefit of those who participate and enjoy the TDI engine whether they own one or not. Make copies and let your dealer read them, put them in the spotlight and make it known your an educated consumer.
DB
[ April 03, 2001: Message edited by: Drivbiwire ]
M
mickey
Guest
NYTDI: When someone stops asking they stop learning. Ask away!
-mickey
p.s. All diesels are valve-benders, as far as I know. There is no place for the valves to hide. A direct injection diesel like a TDI has ZERO clearance above the piston!
-mickey
p.s. All diesels are valve-benders, as far as I know. There is no place for the valves to hide. A direct injection diesel like a TDI has ZERO clearance above the piston!
NYTDI
Veteran Member
- Joined
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- Location
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- TDI
- 1999.5 Golf TDI AUTOMATIC trans. GLS w/PLX package silver/black cloth
OK mickey - I know I'm repeating here a bit -but why not drive the pump off the crank directly? The old mechanical fuel pumps had the lever arm off the crank design. Couldn't an improved/redesigned version of a crank driven pump end all the belt and pump timing issues? Is it an issue of compact design/packaging or achieving adequate pressure?
Mike Piles
Veteran Member
I worked for International Harvester the Bosch injector pumps where gear driven. The gears were probably goood for the life of the engine.
M
mickey
Guest
You'd have to add an idler gear to drive the pump with the crank or the pump would turn the wrong direction.
-mickey
p.s. VW uses timing belts for the same reasons most other engine manufacturers use them: They're cheap, lightweight and quiet. Gears would be none of the above.
[ April 05, 2001: Message edited by: mickey ]
-mickey
p.s. VW uses timing belts for the same reasons most other engine manufacturers use them: They're cheap, lightweight and quiet. Gears would be none of the above.
[ April 05, 2001: Message edited by: mickey ]
Mike Piles
Veteran Member
<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>Originally posted by mickey:
You'd have to add an idler gear to drive the pump with the crank or the pump would turn the wrong direction.
-mickey
p.s. VW uses timing belts for the same reasons most other engine manufacturers use them: They're cheap, lightweight and quiet. Gears would be none of the above.
[ April 05, 2001: Message edited by: mickey ]<HR></BLOCKQUOTE>
Durable would be my primary concern even if more expensive and noisy. I guess that after youv'e been exposed to a six banger Detroit Diesel from an armored personnel carier runing full bore with a 10 inch exhaust pipe no muffler, na little noise doesn't mean much.
You'd have to add an idler gear to drive the pump with the crank or the pump would turn the wrong direction.
-mickey
p.s. VW uses timing belts for the same reasons most other engine manufacturers use them: They're cheap, lightweight and quiet. Gears would be none of the above.
[ April 05, 2001: Message edited by: mickey ]<HR></BLOCKQUOTE>
Durable would be my primary concern even if more expensive and noisy. I guess that after youv'e been exposed to a six banger Detroit Diesel from an armored personnel carier runing full bore with a 10 inch exhaust pipe no muffler, na little noise doesn't mean much.