A $5 part *****kills***** a $4000 Generac generator

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On 7/22/2010 10:08 AM WW spake thus:

Nitrile is the word you're looking for here.
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Mebbe coat this rubber ditty in some kind of silicone caulk (they make a Silicone III?) or some flexible epoxy? There's even a kind dip for plier handles that gives a very sturdy flexible-ish coating. Proly some other stuff. Pliobond adhesive?
Does this bellows thing wear in one place, or does it fail anywhere? This could affect how you choose to coat/seal this thing.
Another possibility is make some kind of adapter, and just use a tougher flexible tubing.
--
EA

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Ok... Some questions here...
Your generator is a little baby one compared to the 8 cylinder cat diesel generator sets I used to help the electrician maintain at the place I used to work...
(1.) How many hours of run-time do you experience between failures of this particular part... Parts and service on generator sets are measured in hours of running time rather than months or years...
(2.) What is the recommended service interval for that particular part in hours? You stated that you had installed the generator after you experienced a storm resulting in two weeks without power...
You haven't described how often the generator performs a "self-test" and runs while switching the emergency loads to run from the generator...
(3.) If this part is causing failures for your gen set why not replace it on a periodic basis even though it is not yet consumed? It is a $5 part to ensure that back up power is available... I have seen thousands of dollars worth of parts replaced annually on two huge cat diesel gen sets to maintain their operational status even though the parts have not yet failed...
Banks of batteries to start the generator were replaced every year in the fall to ensure fresh good batteries would be available to crank the generator during the coldest of winter days even though the battery pan was heated... These generators where integrated into the building automation computer system so they were monitored by many various sensors during their 20 minute exercise run time each week down to the sine waveform the generator was putting out on each phase and if some aspect was out of parameters the gen set could be examined and serviced to make sure it was running in top condition long before it failed...
This sounds like an interesting thing to read up on in the service manual for your gen set to see how often your failing part should be replaced...
Are you sure that there is not something unique to your generator's installation that is causing this part to fail? Animals or insects? Something environmental which could be weakening the rubber?
~~ Evan
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Evan wrote:

Approximately 1 failure every 10 running hours.

Generac has very explicit service intervals for some items, such as spark plug, valve lash adjustment, etc. It makes no mention of this particular part regarding preventative maintenance / replacement.

Weekly for 13 minutes per week.

I could and I will, but since Generac never recommends it, and the Generac service technician who replaced the first one under warranty seemed very surprised that it had failed in less than a year, blaming it on "a faulty bellows rubber part which has been re-designed", I can only assume that this is NOT supposed to fail this way. It is also a PITA to replace and would be way better if it merely held up longer.

As a retired electrical engineer, I have read the owner's manual as well as the service manual cover to cover. This item is not covered.

A chemist friend of mine opined that a variety of synthetic rubber products are susceptible to airborne chemicals such as lawn pesticide spray, and can weaken as a result. A possible explanation, and one which prompts me to consider a silicone hump hose as a replacement. Also could justify the approach of applying a coating to the bellows by dipping it in some magic "goo" to coat the exposed surfaces. I consider this explanation to be a bit of a stretch, but not entirely sure.
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Duct tape?
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1) Frankly, at $5 per it's no exactly a bank breaking repair.
2) That said, from the picture is looks like it could handle a LOT of vibration and relative motion between the carb and the air filter. I don't think a simple hose would work or, worse, it would transfer too much force between the two parts and damage one or the other.
3) and THAT said, since it connects the carb with the air filter, it would operate with a slight negative pressure. You might try "repairing" an old bellows or rein-forcing a new bellows with "liquid latex on the OUTSIDE.
You also might want to see whether the engine mounts are all sound. But it looks like the vibration is sort of built into the design.
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John Gilmer wrote:

Thanks for your comments John. The $5 cost for the part is really irrelevant. The frequent failures and the resulting loss of confidence that this standby generator will truly work in the rare occasion when I really need it are the big issue. And finding a way to avoid having to replace this part every nine or ten months is the mission I have been on here.
What I have (finally) learned is that the Generac "Master" technician, sent out during the warranty period from a very old and established Generac dealer in this area, made 2 huge mistakes.
The first mistake was to assume that the $5 rubber bellows was at fault due to a defect in manufacture, telling me that a newer, improved part was being installed. The folks at Generac tell me this was not true whatsoever.
The second mistake, and the crucial one, was that this same technician made no effort whatsoever to see *****WHY**** it failed. I now see, having taken apart and photographed the parts, and getting excellent help here on this newsgroup, that the rubber bellows was being distorted quite severely at rest, making it pre-loaded and distorted.
It turns out that there are some slotted adjustments to move one end of the assembly around, thus allowing for correction of the misalignment.
This slotted alignment set-up is NOT mentioned in the owners manual or the service manual. The technician apparently did not know that there was an adjustment, and replaced the broken bellows with another one, which then failed once again in less than a year. Had the root cause been identified, I would have been spared all of the subsequent replacements, all of which I have performed, assuming that the rubber bellows was somehow weak or defective.
I briefly did install a "hump hose" made of silicone, before the misalignment and adjustment option was discovered, and it appears that this may have also "solved" the problem by providing a stronger connection. But as others have pointed out here, and I observed, the use of a hose, especially a stiffer and less compliant hose, transmits a lot more vibration into the remaining parts, and is not an optimal solution.
I think I have this problem solved, but the real test will be if I have no further issues for the next several years. Other owners seem to be getting very good reliability, and I hope to join the happy users now that this is resolved.
This newsgroup has been an invaluable resource to me, and I am sincerely very grateful for the really outstanding suggestions and guidance. Thank you !!!
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Lost meat from freezer: $475 Grandpa stroke, cost of ambulance ride $600 Grandpa's night in hospital $7542.36 Lost work at home office for two days $364.24 Motel room till Generac part comes $175
Yeah, it's only five bucks.
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On Sun, 25 Jul 2010 14:59:13 -0400, "Stormin Mormon"

I guess with all that on the line you should have paid for a more reliable unit, had it serviced more frequently, or had another spare.
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On Sun, 25 Jul 2010 14:59:13 -0400, "Stormin Mormon"

If winter, bury the meat in the snow.

Largely covered by insurance.

Go ice fishing.

Fish all night!

Glad the OP might have a fix with his experience and adjustments.
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wrote:

Have you observed this with the engine running. Perhaps the intake pulses induce an oscillation in the bellows causing a fatigue crack.
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