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Ford engine design question.


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Does anyone know the correct answer as to why several Ford engines do not use a key way on crank and camshafts? Ford has been doing this for several years, but mainly with Chain driven engines. Now new model timing belt driven engines are this way.

I have heard everything from its cheaper to make, to its to make us buy special tools. Does anyone actually know the exact reason.

 

I currently have a 1.6 eco boost that has belt valves because the fead belt tensioner failed and twisted the belt around the balancer causing sudden stop of the balancer. The rotational force caused the timing sprockets to slip out of time damaging engine. A key way on crank and cams would have prevented this.

So I'm very interested in hearing what a engineer has to say about it.

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From an engine timing perspective it isn't necessary to key the crankshaft pulley if the crankshaft is set to TDC using a crank position screw on the side of the block and the camshaft position plate locking the cams to the correct time. You could say by machining a key-way on the crank that the crank nose is weaker for the same diameter. Also how often do this kind of failure happen? However it is also the kind of manufacturing cheapness that is pervasive on almost all passenger car engines out there, not just Ford, where engineers are required by the bosses to fight for the last penny of component and assembly cost. It's a very different mindset in the heavy-duty engine world.

Edited by Inselaffe
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Less accessory drive/load on the nose of the Cranks?

 

Camshaft drive load is less with roller followers and lighter spring loads on 4V engines.

 

Does anyone know if they align and use a taper on the Crank/Cams - is this is correct?

Edited by jpd80
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From an engine timing perspective it isn't necessary to key the crankshaft pulley if the crankshaft is set to TDC using a crank position screw on the side of the block and the camshaft position plate locking the cams to the correct time. You could say by machining a key-way on the crank that the crank nose is weaker for the same diameter. Also how often do this kind of failure happen? However it is also the kind of manufacturing cheapness that is pervasive on almost all passenger car engines out there, not just Ford, where engineers are required by the bosses to fight for the last penny of component and assembly cost. It's a very different mindset in the heavy-duty engine world.

So far I have seen 2 1.6L do this. One was a NA Fiesta and now this ecoboost escape. Seems we are having belt tensioner failures on these engines.

 

I don't have a issue timing up a engine with a peg in block and a cam locking tool. However to make sure cams are correct and install bar at back of head, requires removal of DI injectors, vacuum pump, HP fuel pump. It's really a large job. All of this could be avoided if the pulleys were locked into place with something other than being pinched together.

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Less accessory drive/load on the nose of the Cranks?

 

Camshaft drive load is less with roller followers and lighter spring loads on 4V engines.now

 

Does anyone know if they align and use a taper on the Crank/Cams - is this is correct?

The 1.6 uses damb not followers. The lift is very high but low duration. The lobe comes to a sharp point. I'm sure that's the squeeze all the power out of little engines.

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Hmm sounds like the 1.6L engine could turn out to be a problem child. Do you happen to know if its replacement, the 1.5L is lacking a keyway also?

I have not looked yet, but I suspect it's the same way. The 2.3/2.5 has been same way for a long time. However those use a chain instead of belt. That seems to make a difference.

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Right, machining keyways into the crankshaft, camshafts, damper, and their respective sprockets is not free. These keyways are typically only a short radius away from centerline. Therefore, high accuracy (tight tolerances) are necessary in order to have good timing accuracy. The keyway also is a significant source of stress concentration which can lead to fatigue failure.

 

Removing the keyways makes it easier to have high timing accuracy at lower cost or even better accuracy for maybe the same cost. I don't know the real cost to benefit analysis. On the I4 Duratecs, the crankshaft timing pin tool contacts on the outside of the crank counterweight which is a much farther radius out from centerline than the outside diameter of the crank snout. The slots across the backs of the cams are carryover from the old Zetec engines, so that isn't anything new. Even uses the same timing tool. It's about the best of an alignment method you can get on the camshaft without having some part have a large radius which takes up space. The full length slot (2x radius length) is better than a keyway (1x radius length) assuming the radii are equal.

 

Sure, there is more risk of the timing slipping. In fact, they did have issues with the timing slipping at the crank of some of the first I4 prototypes. That is why the very thin friction shims were added to both sides of the crankshaft sprocket. These provide a 2 or more times multiplier of the coefficient of friction between the surfaces. If you do any bolted joint design, you will know how much of a huge help this would be in keeping surfaces in shear from slipping. If you google ESK friction shim, you will find the Ford I4 engine crank and crank sprocket setup. Ford is not the only OE using friction shims in the powertrain.

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I can understand using the peg and bar at back of cams for accurate timing. However, a more robust way of keeping the sprockets in time should be used to keep a $200 repair of a belt tensioner/pulley issue turning into a $3k head replacement. Btw the basic idea of slots in the cams does date way back. However, the tools may be similar but they are not the same as the old. The peg is different size/shape and so is the bar.

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So far I have seen 2 1.6L do this. One was a NA Fiesta and now this ecoboost escape. Seems we are having belt tensioner failures on these engines.

 

I don't have a issue timing up a engine with a peg in block and a cam locking tool. However to make sure cams are correct and install bar at back of head, requires removal of DI injectors, vacuum pump, HP fuel pump. It's really a large job. All of this could be avoided if the pulleys were locked into place with something other than being pinched together.

 

Definitely much more of a pain to remove the cam cover with all the DI stuff. The primary problem seems to be the FEAD belt tensioner though, they need to find out why it is failing. As procyon says a keyway introduces a stress riser on the crankshaft nose and may have knock on issues in terms of durability especially now that turbo versions are putting more torsional energy into the crank damper. The 2.0 has no keyway and 2 diamond face shims to reduce the potential of slip, maybe that could be applied here.

 

Hmm sounds like the 1.6L engine could turn out to be a problem child. Do you happen to know if its replacement, the 1.5L is lacking a keyway also?

 

Its got to be remembered that the Sigma engine has been in production for nearly 20 years now and is in millions of vehicles around the world that have performed admirably.

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But has it been in production with the same levels of boost that it's now experiencing in the EB application? Putting a turbo on an engine changes the stresses on it dramatically, both physically and thermally.

 

I would put a lot of money on that those relevant within Ford know this. The timing slippage and valve crashing is secondary (& tertiary) failure issues, the FEAD belt tensioner appears to be the primary failure and that needs to be sorted, there are probably similar tensioner failures that don't cause timing slip and trash the valvetrain. Are the occurrences of this subsequent failure enough to justify probably very expensive corrective actions, only Ford knows. Personally I'm used to dealing with ~$30000 engines made in the tens of thousands rather than ~$3000 engines made in the hundreds of thousands, so my default would be make sure it can't slip.

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I recall an engineer telling me years ago that the key on a shaft is only supposed to be an alignment tool for assembly; the fit of the gear on the shaft is supposed to be what keeps the gear in place. If they can assemble it without the key for alignment, then there's no longer an engineering reason to keep it (and the related costs).

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As others have said, any time you eliminate a machined feature you reduce cost and can get more parts per hour. With the accuracy and repeatability of current machining centers and cutters, interference fits are about the least expensive way to go. (Although Ford does not seem to like them on the large / heavy production machinery they buy.)

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Less machining=less money. Also manufacturing tolerances can be looser on the gears. Its still a f***ing stupid idea.

 

... The timing slippage and valve crashing is secondary (& tertiary) failure issues, ...

 

I recall an engineer telling me years ago that the key on a shaft is only supposed to be an alignment tool for assembly; the fit of the gear on the shaft is supposed to be what keeps the gear in place.

I hope Ford learned the lessons that Yamaha missed on the SHO V8 ! A large percentage of those had gear slippage that resulted in valves and pistons "meeting in the middle".

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