View Comments: Newest First|Oldest First|Threaded View
<<  <  Page 9/11  >  >>
User Rank
Re:Heathkit Repair
xti   5/13/2012 7:43:57 PM
Also, keep in mind with a kit, you can never assume that it was built correctly in the first place - even if it worked at some point, as was demonstrated to me on several occasions.

User Rank
Re: Heathkit Repair
xti   5/13/2012 7:35:32 PM
Hi Myron

We never had any of these come in for service, so I don't have any direct knowledge of them. They seem to be very simple, and should be rock solid, though. Heathkit very rarely built turkeys, and I don't think that was one of them.

We did however, have a power supply with a similar problem that eluded us for quite some time. We were never ones to give up on a problem, though.

This supply would run unit it got hot, then it would blow the output fuse. Nothing we tried worked.

As ridiculous as it sounds, the Service Manger finally decided to tear the unit apart - all the way to its individual bits and rebuild it from scratch - using only the components that came out of the 'carcass'.

He shredded it, grabbed a manual, and rebuilt it from the ground up, testing every single part as he put it back in.

As he went to mount the output transistor on the heatsink, the manual said to install it using a mica insulator.  There was no insulator in the pile of parts.

It turned out that the original builder had neglected to install the insulator. Every time we tested the output transistor, it was fine, so we never took it off the heatsink.

The heatsink was black anodized, and therefore technically non-conductive, however there was a tiny burr on it that would evidently short the collector to ground - but only when the sink got hot enough to expand a little bit.

A huge amount of energy went into this repair, which could - and probably should, have taken no more than 5 minutes on the jiffy bench.

The moral of the story? - ALWAYS look for the most complicated possible causes first. It's more fun that way, and guarantees you will have a job for some time to come. Just don't tell anybody what the real problem was when it turns out to be the first thing you SHOULD have looked at.


User Rank
Engine Shakeup/Heathkit Repair
MYRONB   5/13/2012 12:44:32 PM
To xti:  May I digress here?  The readers have made good comments on the shaking engine to which I really can't add, so I'd like to ask xti a Heathkit question.  Do you recall working on an IP-2715 regulated power supply?  I am repairing one for a friend.  It has good unregulated DC output, but no regulated DC.  The output transistors are OK and by injecting a current into their bases I get an output voltage.  I replaced the blown driver transistors and replaced the blown regulator chip (no longer available) with a 741 op amp and modified circuit.  The supply worked fine for a while and then the chip and drivers blew again.  Perhaps they are overloaded trying to deliver the required base current to the output transistors.  Components and soldering job all check OK.  Heathkit forum contributors say the supply was a piece of junk from the get-go and to s-can it, but I say it's worth salvation--it seems well-built and the transformer is husky with plenty of copper and iron.  I don't want to re-invent the wheel, but unless you have any helpful hints, I'm ready to redesign it from a series-pass transistor system to a switch-mode design.

Regards, Myron Boyajian

User Rank
Re: Overlooking the obvious
kenish   5/12/2012 1:08:45 AM
< I wonder if the car company would take responsibility for this even outside of a warranty. Seems this type of error would extend responsibility to the car maker even outside the standard warranty>

Reminds me of an incident in a major motorcycle magazine in the 80's.  It was the bad old days of Harley-Davidson.  The magazine bought a bike anonymously for a long-term test of the product and dealer support.  They got to evaluate dealer service pretty quickly...the bike had a mysterious vibration that a string of dealers were unable to diagnose.  The magazine finally tore down the bike themselves and figured out the crank was assembled with two LH weights!  H-D refused to honor the warranty since the engine was serviced by an unauthorized party!

The major national mag did a scathing article, H-D pulled their ads for awhile, and I'm sure the two actions lost the Motor Company thousands of prospective customers! 

William K.
User Rank
Engine shake stumps service.
William K.   5/11/2012 11:36:49 PM
In about 1979 I designed a system at Sun Electric, for installation on engine test stands as part of the new engine hot test system, that examined amplitudes of engine vibration at the crank, canshaft, and firing frequencies. It was determined that the system would detect any missing bearing part in the V-8 engine 100% of the time. The customer declined to purchase this option, even though it did work very well and was both reliable and not very expensive. A missing bearing half is a fault that gets very expensive to repair as soon as the engine is installed, but the claim was that it was so rare that there was no economy in checking for it. Go Figure.

User Rank
Bearing down on the situation
xti   5/11/2012 10:13:32 PM
To clear up a few things - this was a new, unmolested car - but this was 1970 or thereabouts - well before computers took over service departments. The main bearing caps were all installed - just the lower bearing shell from the #3 main journal was missing.

The upper shells in 350s have a groove, the lower shells are solid. There would obviously be a leakage path at the ends of the groove, but as mentioned, the pumps in 350s can put out a lot of oil. It's also likely that the upper bearing shell turned slightly, which would at least partially cover the oil passage in the block - in which case there would be minimal, if any loss of pressure.

The only thing that stops bearing shells from spinning is the crush between the upper and lower shells. No lower shell, no crush. There are tangs on them, but they really don't do that much, other than as assembly aids.

I don't think that a missing bearing could be construed as a common occurrence, so a service tech could be forgiven for not considering it as a possible cause. A weak bypass spring in the pump, or even a piece of crud stuck in the bypass valve could cause the low oil pressure. I don't know exactly how low it was, but it was evidently high enough to dissuade them from pulling the motor.

The engine lasted about 6 months from new before the crank broke. If it was run at higher RPM, it would probably failed sooner, but this was a family car - it probably never saw more than 3000 RPM in its life.

And yes, it was fully warrantied, and probably would have been even if it had lasted past warranty.

If it had a forged crank, they would probably never have found it, as it never would have broken.

Charles Murray
User Rank
Re: Overlooking the obvious
Charles Murray   5/11/2012 7:36:42 PM
Kleetus, I agree with you. It would seem as if this car would be unlikely to survive very long this way. Yet the issue of warranty has not been mentioned, which makes me think it lasted quite awhile. I don't understand.

User Rank
Re: Overlooking the obvious
ChasChas   5/11/2012 1:33:16 PM

I've been there - afraid to look for trouble where you don't want it to be.

Like Schrodinger's cat, it's not dead till you look at it - so don't look.

Doug B
User Rank
Re: Overlooking the obvious
Doug B   5/11/2012 12:07:43 PM
Someone needs to find a new Service Crew! That's the trouble with having service personnel diagnosing engine issues. Since the advent of the "crate engine" no one gets inside the engine anymore. They replace the entire engine. There is very limited understanding of the engine design and it's operation.

In this case the low oil pressure is the overriding clue (as it so often is). There is only one thing in a Priority Main oiled engine that can cause the oil pressure to behave that way. In all modern engines the oil pump design is capable of producing far more oil volume and pressure than there is demand, by-passing the reserve.

With a full understanding of the design and operation of the engine the first thought that came to my mind was crankshaft.

BTW, 350 Chervolet engines use the 5th main bearing as the thrust bearing, not the 3rd.

User Rank
Re: Overlooking the obvious
kleetus   5/11/2012 10:09:23 AM
I find it hard to believe it didn't have this problem from day one, let alone some point in time 'down the road'. With the bottom cap missing, the lower half of the bearing shell would also be missing. This would lead to an immediate lost of oil pressure. I can't remember for certain, but I believe the center bearing has a radial groove for oil distribution, and is also the one responsible for end play float.

Article leaves out what year impala this is... if it was a late model, I guarantee it wasn't a 350... and it's also front wheel drive.

<<  <  Page 9/11  >  >>

Partner Zone
Latest Analysis
Imagine being able to illegally download a physical product the same way you can with music and video. The advent of desktop, home, and prosumer 3D printers is having huge repercussions in the intellectual property domain.
Our latest Design News Quick Poll reveals that readers are facing serious cyber security challenges.
Ford will be the first automaker to commercially use Alcoa's tough & fast Micromill aluminum alloy process and materials, debuting on several 2016 F-150 truck components. Alcoa will also license its Micromill process and materials technology to Danieli Group.
Even as an increasing number of instrument manufacturers migrate toward modern touch screens, many engineers say they still prefer the tactile feel of knobs and buttons, a new survey says.
Caterpillar Inc. demonstrated this week at Design and Manufacturing Philadelphia that heavy industry can reap big benefits from 3D printing.
Design News Webinar Series
10/1/2015 11:00 a.m. California / 2:00 p.m. New York
9/10/2015 11:00 a.m. California / 2:00 p.m. New York
10/20/2015 8:00 a.m. California / 11:00 a.m. New York
11/10/2015 11:00 a.m. California / 2:00 p.m. New York
Quick Poll
The Continuing Education Center offers engineers an entirely new way to get the education they need to formulate next-generation solutions.
Oct 5 - 9, Standards for the Internet of Things (IoT)
SEMESTERS: 1  |  2  |  3  |  4  |  5  |  6 |  7

Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.
Learn More   |   Login   |   Archived Classes
Twitter Feed
Design News Twitter Feed
Like Us on Facebook

Sponsored Content

Technology Marketplace

Copyright © 2015 UBM Canon, A UBM company, All rights reserved. Privacy Policy | Terms of Service