# HS720CC Spark Plug Cover Fail and Noise Issue



## CalgaryPT (Dec 7, 2016)

Years ago when the HS720s came out I decided to upgrade. This way I could give my well maintained HS520 to an elderly friend who struggled with his sidewalk. He had a big box two stage that was unreliable (that is to say I was tired of fixing in -35C). I didn't really need the extra HP of the 720 here in Calgary as the 520 was fine up to 1 foot. But my friend is such a nice man and I hated to see him struggle. He was also too far away for me to do his walk conveniently (which I would happily do, except I already do 13 properties for free and my back ain't getting any younger). So I upgraded to the 720, and gifted him the 520, which he loves. I got a new 720. Everyone wins.

The 720 is a bit heavier than the 520, and one thing I noticed years ago when I brought it home was the wheels lock more than on the 520. Likely this is due to the few extra pounds, as this is already a known Honda feature/glitch/oddity.

The 720 is also louder—significantly louder. I even measured it with a decibel meter years ago, although I forget the readings now. I just chalked it up to the larger engine and the fact that it was the commercial (HS720CC) model with the GX block). Anyways, the past week we've been hammered with October snow in Calgary and I noticed the spark plug door keeps popping out. Likely this is because I just changed the augers, which always causes more vibration initially until they break in. Also, I suspect the rubber fittings the hold the cover in place are wearing.

When the door kept popping out and I'd replace it...then I noticed that a BIG source of the extra noise was that darn door rattling around when it was put back in place. Once it pops out, the noise diminishes noticeably. Put the door back in and—at least until it pops out again—the noise is way louder. In fact, with the door out, the 720 is about as quiet as the 520 used to be; in fact it just purrs instead of rattles.

So now I have two reasons to fix the spark plug door. One is so that it stays in, but the second is to reduce the noise.

Wondering if anyone else has the same issue, and what fixes you applied to solve it?


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## tabora (Mar 1, 2017)

Perhaps some thin rubber edging on the flanges that the door sits on would both rattle-proof it and help it stay in place?








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## 2badknees (Jan 28, 2017)

tabora said:


> Perhaps some thin rubber edging on the flanges that the door sits on would both rattle-proof it and help it stay in place?
> http://[URL]https://www.ebay.com/it...upid=104612011820&rlsatarget=aud-622524040998la-934793863176&abcId=2146002&merchantid=6570404&gclid=EAIaIQobChMIg8ODiZDO7AIVD77ACh2KMQrGEAQYAiABEgJWZfD_BwE[/URL]


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## 2badknees (Jan 28, 2017)

ie; open cell weather stripping, found at the local hardware store. It's soft and effective. Closed cell is too robust.


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## Big Ed (Feb 10, 2013)

I more ideal for the Cloth Tape Guys use list. 

You wonder why they didn't think of that when they built it.
I know Saving $$$$$$. 

I see on one side under the plastic there is metal, unless it gets hot Velcro might help too.
I bought a roll of industrial grade and I find a lot of uses for it.
Sticks real good.


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## CalgaryPT (Dec 7, 2016)

tabora said:


> Perhaps some thin rubber edging on the flanges that the door sits on would both rattle-proof it and help it stay in place?
> 
> 
> 
> ...


Good idea, kinda where my mind is heading too. Thanks.


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## CTHuskyinMA (Jan 14, 2019)

Looking forward to seeing what you come up with for a solution. I have the same exact issue, a broken off tab and the cover comes off pretty quickly when in use. I was thinking about some painter's tape, but that won't look very _professional. _I was at Lowe's yesterday and they had a new machine on the floor. The door design hasn't changed. Out of curiosity, I opened it and it was so hard to do that I actually cut myself. Obviously, I could order a new door, but you have to believe that it will just break again at some point.


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## CalgaryPT (Dec 7, 2016)

CTHuskyinMA said:


> Looking forward to seeing what you come up with for a solution. I have the same exact issue, a broken off tab and the cover comes off pretty quickly when in use. I was thinking about some painter's tape, but that won't look very _professional. _I was at Lowe's yesterday and they had a new machine on the floor. The door design hasn't changed. Out of curiosity, I opened it and it was so hard to do that I actually cut myself. Obviously, I could order a new door, but you have to believe that it will just break again at some point.


My thoughts exactly. My tab isn't broken, so I think I'll have the same issue if I buy a new door. Given that Honda wanted $113 for six scrapper bar nuts and bolts this week, I can't imagine the cost of a new door.

I'll get to the problem in the next few weeks as I am fabricating a custom headache rack right now  So I've requested no snow until it is done.


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## Grunt (Nov 11, 2013)

CTHuskyinMA said:


> I have the same exact issue, a broken off tab and the cover comes off pretty quickly when in use.


Maybe a piece of Velcro under the lip??


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## CalgaryPT (Dec 7, 2016)

Grunt said:


> Maybe a piece of Velcro under the lip??


Yeah, that's on the short list for sure. Some of that industrial velcro is almost too strong, but I've read they all fail in cold temps (the adhesive at least). It's one of those solutions that needs some pondering for a bit before I try anything. For now I removed the cover altogether because the machine is so much quieter. 

I'll definitely post whatever I come up with. Since I retired I savour these little puzzles. Keeps me away from too many wobbly pops


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## JB-IA (Oct 25, 2021)

CalgaryPT said:


> Years ago when the HS720s came out I decided to upgrade. This way I could give my well maintained HS520 to an elderly friend who struggled with his sidewalk. He had a big box two stage that was unreliable (that is to say I was tired of fixing in -35C). I didn't really need the extra HP of the 720 here in Calgary as the 520 was fine up to 1 foot. But my friend is such a nice man and I hated to see him struggle. He was also too far away for me to do his walk conveniently (which I would happily do, except I already do 13 properties for free and my back ain't getting any younger). So I upgraded to the 720, and gifted him the 520, which he loves. I got a new 720. Everyone wins.
> 
> The 720 is a bit heavier than the 520, and one thing I noticed years ago when I brought it home was the wheels lock more than on the 520. Likely this is due to the few extra pounds, as this is already a known Honda feature/glitch/oddity.
> 
> ...


I have the same model and the same problem. Online information is sparse. The cover stayed on a couple of years then came off. I ordered a replacement because I thought it might have broken but it wasn't - the replacement came off, too. In the past year I taped it down with a small piece of duct tape and removed it during the off season to keep the tape residue off. I'm anxious to see a better idea. Thanks to all.


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