OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines Briggs 9 Series - Damaged Muffler Bolt Thread

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Hi Everyone,

So ive been rebuilding an old briggs 3.5hm (92908). I never noticed when i stripped the motor down the muffler had only one bolt holding it on, anyway i discovered today that a bold has snapped into the cylinder. so silly me went, "well i'll just drill that and use a bolt extractor set" to fix this issue, wrong. I drilled the hole wonky and have drilled the cylinder

does anyone have any suggestions what i should do now?! ive been on ebay and i cant even find this part i believe its "298922"

Did you drill right through so there is a hole or did you stop before going that far? if not go and buy a round screw in type muffler and job is done.

Hello Brendan_D

The are not really too many options.

The cheapest fix is to fit a standard 9 series screw-in muffler.
Otherwise, a repairer will need to re-coil with a thread insert if you would
like to fit a hush-tone muffler.

Hope this helps.
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JACK

hey, thanks for the speedy replies. im freaking out here haha. i only drilled a few mm before i realized i had moved the drill and wasnt drilling the center of the bolt. well i had already ordered a new muffler "132106-754" from the outdoorking, i was hoping to keep it original and how it was whats the difference between the muffler i have now and a screw in muffler you mentioned? i did wonder what the thread was for :P if i was to have it drilled out and had an insert put in to retain the muffler that was on there, where would i go to have this done like what kind of shop? a mower shop or some kind of engineering shop? im not confident anymore haha.

Hello Brendan and Joe

The screw-in muffler is round, smaller, and more noisy.
Some manufacturers chose the optional Hush-Tone for market placement reasons.
It is a quieter, larger, and more expensive muffler.

If you have ordered a new muffler, the cheapest option is to have it re-coiled.
I understand why you would like to keep it to the original 'spec'.

Hope this helps.
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JACK

dont let it shatter your confidence , it happens to everyone . i did it too but didnt drill it out , just saw the thread and fitted a "pot" muffler . just a little CRC and screw it in slowoly , cleans the treads as it goes in , same a tapping . slow and lube , out and more lube . they look ok too and most had an option of b oth so really no biggy .
as joe said , just throw a different muffler on , as long as you didnt drill too deep ...

,Dave
ps , next time , file it flat , centre pop it and drill straight that way the drill bit wont move of centre take it slow and easy always

Thanks for your replies jack, i appreciate your help.

Where would i go to have this kind of work done? im trying to google somewhere local but im not sure what sort of place would do something like that.

If i can have this done somewhere successfilly i will be much happier than the screw in option, but at least i have a back up option of the screw in.

haha my confidence is a little wrecked vccomm. Thanks guys for your help. So you think putting in the screw in type wont take away its originality?

Motorbike shops are a good place to get a snapped bolt out like that, they have the right tools for the job... but it may cost a little more now you have made it harder to get out hope it works out cheers..

Hello Brendan and Dave

Any automotive engineering shop can do this work.
More experienced lawnmower repairers can do it too.

The issue is securing the block for an accurate drill and then screwing in
an insert. Prices can vary. At least get some quotes.

In term of originality, it won't be the same will it?
However, a 'pot' muffler will not interfere with restoring the specification at
some future point. It's up to you and economics.



Hope this helps.
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JACK

it really depends on the machine . most had the option of hushtone or pot mufflers . or did i miss what the machine is ? hehehe that time of night .
if its a restore then sure get it cut out , if its for use ? then just change it either or really .
hushtone only really takes the POP out of the tone . but if its for use ? the spark arrester isn't top of the tree , might get sparks and hmmmmmmm close to summer soon

Always centre punch the bolt before starting to drill to stop it wandering off like that. I reckon with a punch mark at an angle into the hole you have created you could probably get a small centre drill to start then go to a larger drill and slowly bring it to the upright position enough to get an easy out in and remove the old bolt. If you have only gone down a short way you probably have enough thread left in the hole to make a bolt hold. Use a Loctite thread retaining compound to make sure it doesn't come loose. You will probably need to go to an engineering supplies company such as Blackwoods for a centre drill or order one of Ebay. If you are not familiar with them it is a short drill with a small diameter that then steps up to a larger diameter. They are used in lathes to put a centre hole in metal for locating a live or dead centre.

When drilling out if enough still is sticking file it flat, center punch it, and using split point premium HSS drill bit drill as previous mentioned. The use a smaller bit to create a centering hole also helps. As for the off center you can use a cone shape carbide rotary file and cut back to re-center. Above all it takes time and lots of being patience.

You might wonder why I mention using premium drill bit well here in the States anyone is selling supposedly HSS bits. The problem is a lot them are of low quality and dull very quickly when used on any steel especially muffler bolts. Also most HSS bits should not be spun above 1500 rpm to prevent overheating them which will cause them to fail quickly.

It was mention using a screw/bolt extractor. My experience on old engines this doesn't usually work here as the remains are usually galled (fused) in place especially with muffler bolts. I have snap off extractors and had to drill them out using a carbide drill bit then either install helix coil or resize them.

The problem with re-tapping to same size is that remaining threads of the previous screw will fall out most times and you just end up stripping the hole. It is best just to install a helix coil if your planning on using that particular hole and save the time of not having to redo the work.

Hello AVB and Contributors

AVB, I think you are a most knowledgeable contributor on Briggs to
these forums, and you have wide experience of the USA scene.

This post has proven most valuable for the service issue of sheared muffler bolts.

chris125 has pointed out that motorcycle shops have good knowledge on this.
Joe C and vcomm have defined the choices to be made.
aussietrev has added information on centre-punching and retaining compounds.
AVB has added the importance of quality drill bits, bit speeds, and the better approach
being helix inserts for a good job.

All in all, a very good resource on this issue.

Thanks to all contributors.
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JACK

ok im going to pipe in now, as this might be an easy solution, it looks like youve still got some meat on the sheared off bolt, so get yourself a cold chisel, center punch, screwdriver etc, and try to unscrew it by tapping it out, it might work on the un-drilled area, the hole you drilled might come in handy to get the cold chisel in to tap it out easier

Hi Guys,

Just a quick update. Thank you all for your suggestions and comments, this forum has turned out to be a great resource.

So the results of my issue were as follows:

I spoke to a gentlman i used to work with who is a refrigertation technician but is quite handy with metal work. He took a small piece of right angle steel and put some holes in it and then bolted the right angle into 3 of the head bolt threads. This allowed him to hold the cylinder in his vice straight.

He then used a milling maching to put a small hole exactly where the middle of the old bolt was a few mm deep. once this was done, that hole was used as a pilot hole to drill by hand out the remainder of the hole he then used a 1/4 unc tap to retap my hole to the exact size it was.

He has done a fantastic job and you cant even tell anymore my mistake even happend and even better it cost me nothing.

Over all very happy i am able to retain my original muffler. I am thankful for all youre suggestions.

I have attached a photo of the reuslt with my nice new bolt in the hole that was ruined.

Hello Brendan

Well that's a good resolution to the problem.
May I ask for the Members, what have you learnt from this experience?
[Apart from knowing a 'mate' ]

All very muffled.
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JACK

Hey Jack,

Anything can be fixed witht the right tools and knowledge


Im glad I found out that I had the option of the "screw in" kind of muffler. I would not of known this if i had not of posted on here.

Oh and yes knowing a "mate" helps hehe! I was prepared to pay to have this solved, but just so happened he had the tools available to him and the knowledge to help me for the price of my smile and a thank you.

Thank you all for your input its been excellent.