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xti
User Rank
Iron
Re: Another Vibration Problem
xti   3/24/2013 7:31:32 PM
NO RATINGS
Yeah - I always used a scattershield on manual trans cars. One is supposed to use a scatter blanket on autos, but they only encircle the main body of the transmission anyway, so it wouldn't have helped in this situation.

They also restrict airflow around the trans, and make it a bear to work on. Who would have expected that a little 327 in a street car should need one anyway?

Maybe some monstrous big block (which went in the car later...) - but not a little mouse motor.

A friend nearly chopped his '56 Chevy in half when his clutch exploded. There's a pic on the net of the inside of a '55 that looks almost exactly like his car looked. Just type in 'clutch explosion', and you should find it.

Looks like someone took one of the old style 'rip the top off the can' style can openers to the dashboard.

Scary. Fortunately, he somehow made it out in one piece. The first thing he bought for his next car? You guessed it.

William K.
User Rank
Platinum
Re: Another Vibration Problem
William K.   3/24/2013 6:50:17 PM
NO RATINGS
At least at the dragways that I used to visit, modified cars were not allowed to compete unless they had an adequate scattershield. I don't know if that would have helped in your situation, but it did allow for drivers walking away from cars with blown up clutches on several occasions. Scattershield and roll cages are our friends.

corey872
User Rank
Iron
UOA?
corey872   9/7/2012 10:01:31 AM
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Surprised they didn't take an engine oil sample and send it out for used oil analysis.  That would have easily shown elevated levels of iron, copper and lead in the oil from the crankshaft and bearings which were being destroyed... or if any other engine component was damaged, it would have a contaminaiton signature in the oil as well.  Bad head gasket, you'd see glycol/coolant in the oil.  Bad valve, bad sparkplug, weak compression - would likely show up as fuel in the oil from that cylinder misfiring.  This is pretty much standard practice in industry...guess we can't expect the 'SAE Certified' monkeys to do the same.

MYRONB
User Rank
Gold
Re: Another Vibration Problem
MYRONB   8/24/2012 1:28:45 AM
NO RATINGS
Re:  Engine vibration thread that morphed into a Heathkit thread:

To:  xti and others who have tried to help on my repair of a Heathkit IP-2715 power supply.

(Please see the morphed thread from around 05/13/2012)  I was able to get this old supply going by redesigning the regulator and driver circuits.  I removed the dead and unobtainable Heathkit regulator chip and the low-signal NPN pre-driver and associated components from the Heath PC board.  I installed components I chose onto the modified board.

 I used a Texas Instruments LM317 voltage regulator chip to feed the base of the 2N3055 driver transistor which is Darlington-connected to four paralleled power transistors.  By the way, I did replace the (fractured) mica insulator under the 2N3055 transistor.  I used the equations in the application notes to calculate the values of fixed resistors and a voltage adjustment potentiometer.   The supply works just fine now.  I plan to make my circuit modification available on a Heathkit forum for all users of this Heathkit power supply.

 Many thanks to all who made suggestions.

 Best regards,

 Myron Boyajian

xti
User Rank
Iron
Re: Another Vibration Problem
xti   6/17/2012 5:13:10 AM
NO RATINGS
Don't feel too badly that you didn't get it right away. I think it took me the better part of a day to figure out what had happened.

Early GM alternators have a fan blade assembly that consists of a flat piece of ~18g steel with the outer diameter bent back into a bunch of little blades that act as airfoils that pull air through the alternator. Sort of like a shallow, one-sided squirrel cage fan.

The fan is sandwiched between the alternator pulley and a step on the alternator shaft. The back surface of the tips of the blades only clear the body of the alternator by about 1/8" - if that.

The blades are not connected to each other at the tips, and some of the blades are slightly larger than others - probably to stop any possible harmonics that might be generated at certain RPMs.

The stock alternator pulley has a diameter of slightly less than 3".

The stock crankshaft pulley has a diameter of approx. 7", giving a ratio of about 2.5:1. If the engine is doing 7500 RPM, the alternator is doing nearly 20,000 RPM.

One of the larger blades was bent outwards slightly by the extreme RPM, and contacted the end of the bracket holding the alternator onto the motor. The blade was immediately ripped off the fan, and exited the scene by punching its way through the hood.

The missing blade threw the fan out of balance, and shook the crap out of everything.

At low RPM, the out of balance condition was not noticeable, as the blade weighed virtually nothing.

It took a quite while to figure out what caused the hole, as there was no obvious source for it. 

Every time the engine stopped, Murphy's Law ensured that the spot on the fan with the missing blade would hide at the bottom of the pulley out of sight, of course.

Who would even think to look for something like a blade missing on the alternator fan? I certainly didn't.

If it hadn't punched through the hood, I would probably have been driven mad trying to figure out where the vibration was coming from, as there would have been no clue as to the source.

(I guess my guardian angel had a strange sense of humour that day. I'm certain that I have one, because I'm still here after doing many totally inane things...)

Racers often put larger diameter pulleys on the alternators, and smaller diameter pulleys on the crankshaft to lower the RPM of the alternator to save power. It turns out that it also stops fan blades from coming through the hood.

I guess I was lucky the entire armature didn't explode. That could have been very messy, as it is quite heavy.

The next weekend, my car was proudly sporting new pulleys. But I left the hole in the hood. It was too good a conversation piece. Besides, it was too expensive to fix anyway.

Just another one of the joys of having a car with too much horsepower. But they're great fun, even with all the inevitable carnage...

Dave James

My basic motto in life: If some is good and more is better, then too much is just right.

Critic
User Rank
Platinum
Re: Another Vibration Problem
Critic   6/16/2012 7:18:01 PM
NO RATINGS
xti:  well, the hole in the hood seems like it would be in line with a cylinder.  However, any scenario I can think of, all of which involve pieces of the engine penetrating the hood, would cause vibration at idle as well.  It seems like only parts of the rotating assembly would have sufficient momentum to penetrate the hood.  I give up on this one!  I am not very good at diagnosing vibrations anyway!  What happened?

xti
User Rank
Iron
Re: Another Vibration Problem
xti   6/9/2012 11:50:15 PM
NO RATINGS
Yes, he did. His was quite a bit more spectacular than mine, but my adventure was distressing enough for me...

Along with numerous other ones that were also a bit nerve wracking.

 

Here's a new vibration puzzler for you:

Car - 1964 Chevy II (somewhat relevant)

Engine 450 HP 327 (also somewhat relevant)

Colour - Blue (totally irrelevant)

Scenario:

Car is at dragstrip. Launch car @ 5500 RPM stall (new converter), reach 7500 RPM, shift into 2nd; reach 7500 RPM, just about to shift into 3rd, when there is a loud bang, (a bit hard to hear above the open headers, but audible); and small hole appears in the hood about 18" to the left of center, 30" in front of the windshield.

The ensuing vibration scared the crap out of me, and caused me to abort the run immediately. Which really sucked, as it was the best run of the day to that point.

At idle, there was no vibration at all. As the RPM was increased, the vibration got REAALLY bad.

What happened?

 

Critic
User Rank
Platinum
Re: Another Vibration Problem
Critic   6/9/2012 11:21:29 PM
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Shades of "Big Daddy" Don Garlits!  He DID lose part of his foot.

xti
User Rank
Iron
Re: Another Vibration Problem
xti   6/9/2012 8:52:31 PM
NO RATINGS
Hey Critic -

The balancer would be about the only thing that could cause a gradual increase in an unbalance condition. Any other scenario (other than a loose bolt in the bottom end) would cause a sudden, not a gradual change.

Some new engines don't even have a timing mark on the balancer, so it would be almost impossible to spot a rotated outer ring unless the ring had moved 'horizontally' as well (towards or away from the engine).

About the only way to tell if it was bad would be to put on a new one and try it.

Sounds like your Ford dealership needs some troubleshooting lessons. And they might have considered reading a manual before destroying your timing cover.

Turkeys.

Many years ago, I had a minor vibration issue with the 450 HP 327 in my '64 Chevy II. I had recently installed a 5500 RPM stall speed torque converter on my TH400, and had noticed a slight vibration at about 7500 RPM that wasn't there before.

It was pretty minor, though, so I didn't worry about it. Bad idea.

A couple of weeks later, as I took it past 7500 RPM (I know, young and foolish) there was a rather spectacular explosion. Metal shrapnel ripped through the floorboard and firewall, smashed the distributor, cut the transmission cooler lines, and littered the street with chunks of metal and transmission fluid for two blocks.

This converter was only 8" diameter, and had three 1/2"x1"x2.5" long steel tabs welded to it, which I had attached to the 11" flexplate with 1/2" L9 bolts.

The tabs broke off the converter, spun around on the bolts, blew the entire front of the transmission housing off, then the tabs and bolts ripped through the flexplate and came up through the floor of the car.

Great fun. One piece came through the floor directly under the gas pedal, blew it in half and hit the bottom of my boot. Fortunately, they had super thick soles on them. I'm lucky that I didn't lose a foot...

They later redesigned the mounting for these converters to use a continuous laser cut ring instead of separate tabs. A nice touch, but little overdue unfortunately.

I still have the car - with the hole in the floor - but it hasn't been on the road for nearly 30 years. Maybe someday...

Critic
User Rank
Platinum
Re: Another Vibration Problem
Critic   6/9/2012 5:22:52 PM
NO RATINGS
xti:  depending on how you set up the 'scope to check the ignition pulses, you may have found the problem.  It turned out that the outer ring of the harmonic balancer had spun relative to the inner part of the balancer.  This was not at all obvious from looking at the balancer.  When the machine shop checked the balance, they called me and asked me to bring them the engine front cover, so they could see where the timing pointer on the cover was relative to the TDC (0°) mark on the balancer.  When we saw that the TDC mark was about 40° from where it should have been, it was apparent that I needed to replace the balancer.

If I had checked the ignition timing, it would have been obvious that something was wrong with the position of the timing marks, but there was no reason to check the timing, as it is not adjustable and the engine was running fine (other then the vibration).


I now know that I should not believe a harmonic balancer is good just because it looks good- the angular position of the outer ring has to be checked as well.

When I re-assembled the engine, I did not bother to make it "like new;" cylinders and crankshaft journals were still within Ford acceptable dimensional limits.  I simply honed the cylinders and replaced rings, bearing inserts, and gaskets.  It cost me about $650 for parts, including the new balancer and a new front cover, which comes with a new (external) oil pump.  I had to replace the front cover because the Ford dealership broke it- they neglected to remove one of the lower bolts, which is hard to see, so when they pulled on it, it broke, leaving part of the cover attached to the block.  When they put the cover back on, they just gooped up the fracture with RTV and didn't bother to tell me they had broken my car.




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