Cutting corners on automotive engines 9

[enginesrus]

Like the crankshaft snout that has no keyway cut into it, and requires a nice tight bolt to push on the harmonic balancer to keep the timing gear from rotating and throwing the valve actuating system out of time.
And best of all the bolt has a right hand thread (clock wise to tighten) and that end of the crankshaft turns the same direction, so you have not only dynamic movement from engine and firing pulses, but also any belt driven accessories like alternator, power steering pump and what ever else is belt driven tending to loosen that bolt. I personally don't think you would ever find such idiocy on an aircraft.

 

[SnTMan]

Well, you might on a $20,000 aircraft

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[GregLocock]

That's a gutsy decision, saves maybe $3 a car.

Cheers

Greg Locock


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[Comcokid]

Yea. Like the 2300 cc engine used in the Pinto/Bobcats. Became a standard engine by the oil additive industry as a test bed for a long time. But every new engine a test organization would buy, they immediately tore-down and cleaned. Seems they wouldn't bother to clean the metal shavings leftover from machining the rocker arm shafts before assembling the engines. Rocker arm shafts were hollow and were sometimes full of turnings. Otherwise, a well designed engine. If it didn't cause problems within the warranty period, they didn't care.

Learned that from by brother-n-Law who worked as a Chem E in the lube testing industry a long time.

 

[Lou Scannon]

If you mean the Lima 2.3, what rocker arm shafts? This is an SOHC engine with cam followers pivoting on individual lash adjusters; no shafts in sight above the block other than the camshaft. Perhaps that's what you meant. Now if they left shavings inside of it, the first place they would escape and with high probability do catastrophic damage, is the cam lobes.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[TugboatEng]

ERUs, those keyless cam drive systems use diamond faced washers to lock the assembly together.

Besides, keys are absolutely awful for power transmission. Our preferred power transmission manufacturer for tugboats did away with keys decades ago. Keyless shafting is FAR superior in both strength and service ease.

 

[BrianPetersen]

Keys and keyways get smashed up if they are relied upon to transmit cyclic or vibratory loads, and camshafts and crankshafts most certainly have cyclic and vibratory loads. The only use for a key is to encourage installation of the components at the correct phase angle.

VW diesel engines have had the cam sprocket on a taper on the camshaft for decades. No keyway. You're supposed to use a locking tool (a piece of steel the right thickness) to lock the camshaft in place when tightening the center bolt. I put many hundreds of thousands of kilometers on a couple of those, and it was never an issue.

Right-hand threads on the center bolt is also not an issue. The bolt isn't being relied upon to transmit any of the torque, and if the part is being held on by taperlock or by special high-friction washers, there is no fretting or relative motion between the bolt and whatever it's holding place ... unlike what would happen if it were a slip-fit with a keyway ...

Of course it relies upon the correct parts being used, and the correct washers being used, and the correct center bolt being used, and the correct tightening procedure and torque being used.

 

[TugboatEng]

Of course it relies upon the correct parts being used, and the correct washers being used, and the correct center bolt being used, and the correct tightening procedure and torque being used.

Which of course, the average mechanic will not do to cut a few corners.

 

[enginesrus]

I never said a single key was a great idea, but no key of any sort is not a good idea. I say, you can still do the squash and special washer deal but have a redundant key if for nothing else but to help assemble and time correctly. The better design would be a spline, you know like CV axles etc. strange that is a cost effecting deal for that area of an automotive part and not on the end of a crankshaft.
And all the above bad mouthing of keys, how long have they been the main stay in automotive engines made in the USA? If its garbage it would have never been used and discontinued yesterday by every auto engine manufacture in the country.
On the last post above, just hang the correct length of lever on that damper and pulley assembly and you will loosen that nut. How many impregnated washers are used? One on both sides of the sprocket?
Your incorrect about trusting a taper to hold. All machining center manufactures add a key on each side of the 40 or 50 taper spindles to keep the tool holder from slipping. I'm sorry I'm not understanding the logic.

 

[LionelHutz]

Where is the engineering disaster? I'm not sure why a properly designed setup that works as built at the factory would be considered a disaster. Isn't that considered a success?

If you're just spilling your griping into more forums hoping for more sympathy then I'm pretty sure you'll find that every engine manufacturer has managed to screw up a few engines designs or parts of a few engine designs in their history. Again, no real disaster for anyone but the manufacturer.

 

[TugboatEng]

Keyway failures were VERY common on most of the first gen v8's from all manufacturers.

https://www.google.com/search?q=key...droid-verizon&sourceid=chrome-mobile&ie=UTF-8

Now that manufacturers are having to offer warranties up to 100k miles they've had to make a few improvements to their designs. What you don't like is that these improvements cost more to fix in the instances that there is a problem. However, there are fewer instances so the overall cost to the manufacturer is lower when the warranty period is considered.

 

[LionelHutz]

No keyways were not a common issue on GM engines. GM then changed to a no keyway balancer and that's been very reliable too. You won't find any widespread proof of issues either because you're just pulling that claim out of your ass.

 

[TugboatEng]

Ok, I was being dramatic but when buying a used SBC crankshaft the keyway was an important inspection point as many of them did experience wear. Whether that was the fault of engineering or s backwoods mechanic...

Build an engine that can be maintained with a crescent wrench and someone will maintain it with a hammer.

 

[GregLocock]

If it's an OHC then use the camshaft for timing, because frankly you don't care what the FEAD/ harmonic damper are up to, only the relationship between the cam and the crank.

Cheers

Greg Locock


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[SwinnyGG]

Where is the engineering disaster?

Everything that looks like a problem but actually isn't a problem is an engineering disaster to OP.

I'd love to know how many engines this dude has seen come into his shop with the cams mistimed because a taper or press fit pulley on the crank nose slipped due to an actual design problem, and not due to incorrect installation by some shade tree mechanic. I bet it's zero. But we'll never know.

 

[CWB1]

JMO but having repaired far too many shafts as a tradesman due to failed keyways I prefer to do without unnecessary failure modes. Given the ever increasing reliability of modern engines and vehicles I'd call keyless cranks a win. I'm getting ready to trade off my latest daily, despite 230k the only non-standard maintenance I have done is rear brake shoes. Front brakes are factory original as-is everything on-engine.

The test engines I have always seen used for oil testing were single cylinder research engines with relatively few production parts.

 

[Reverse_Bias]

There are plenty of time engineers don't put enough thought into assembly and especially repair when they design a product. Just cause it's theoretically possible to take something apart and put it back together without breaking it doesn't make it good design practice.

 

[GregLocock]

OK, and how often in its life does the front pulley need to come off the crankshaft?

Never.

I would guess that the vast majority of light duty engines are scrapped with the the cylinder head bolts, and mains, untouched since they were assembled in the factory. If you can persuade sufficient numbers of /new/ car buyers that easy reinstallation of the crankshaft pulley is a priority that they will pay for, then it might happen.

Personally, I'm grinning at the thought.

Cheers

Greg Locock


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[BrianPetersen]

Crank pulley - but not the timing belt pulley - needs to come off every time the timing belt is changed, where so equipped. I seem to recall that on the vw engines, that front pulley bolted on with 4 bolts and you didn't have to touch the timing belt pulley or the big bolt that held it in place. But it's been a while. Current car isn't due for t-belt until 240k and I'm not going to bother, car won't be worth the cost of doing the job by that time, might as well just drive it.

 

[bimr]

OK, and how often in its life does the front pulley need to come off the crankshaft?

Never.

I just changed the front pulley (harmonic balancer) on a Mini Cooper with 60,000 miles because the rubber compound on the balancer failed.

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