OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines Briggs 375 with a stuck blade plate bolt

Hi Guys,

I was just working on this mower. The engine after some repairs is going sweetly however I flipped it over to clean underneath and replace the blades and I encountered a problem. The photos are pretty self explanatory. It came to me with only one bolt holding the plate onto the boss. The 3 small bolts were not installed.

I have tried to get the centre bolt out but it is stuck solid. Unfortunately I have burred the sides a little.

I am hoping somebody could share a trick because this mower runs really nicely and I dont want to move it on before I fix the blade plate area. Hoping its a reasonably easy fix.

a nice tight 5/8 or whatever size it is IMPACT socket should do the trick if you have or have access to one ? hopefully the broken bolts wont be too hard to remove as they would have just sheared off just a few taps and they should come out .
check the main bolt isnt stretched though as then you will have the fun of getting that one out too

When a bolt or nut comes to me burred like that, I file the flats carefully until it is a tight fit on the next sized socket, which would be 15 mm in this case. Use a six point socket on an impact wrench. Don't waste your time with 12 point sockets for any bolt that is done up tight, you just spoil the hexagon. And don't waste your time with a breaker bar, either. You'll be surprised at the remarkable difference the right gear makes. Once you try it, you'll never spoil a hexagon like that again.

No go with the impact wrench. The bolt head is stuffed. Damn previous owner stuffed around with it so much
Any other suggestions?

I will try your filing suggestion. Thanks for your assistance.

wrench ? we meant rattle gun , tap the socket onto it but dont hit it too hard as damage is easy as you know . grumpys suggetion is a good one , a little hard but it does work well . never had a problem with a rattle gun though . they are on ebay for about $85/95 now for electric ones .
i bought one a while ago and it works well , sometimes im too slack to fire up the air here

Everything they said ^^^^^ Rattle gun

Hello fella's, I love hearing everyone's methods, I don't have a rattle gun.
To get that off, my approach is to cut the bolt head down, to the next size down socket with a 1mm blade in an angle grinder.
Then I will try to shock the bolt loose with a breaker bar and a big hammer. The way I hold the bar against the blade plate with my left hand is a technique.

If that doesn't work, I chock the blade plate with the right sized piece of wood to stop it moving, and use a pipe extension on the breaker bar. Leverage can be your friend.
Just sharing my methods.
Jaffa, enjoy all the possible fun you can have with that.

Hi Peter, Rattle gun with a single hex 14mm socket is the way to go.
Looks like it's also missing one of the engine mount bolts, the one just behind the rear of the fuel tank.

I have been using my rattle gun hooked up to the compressor and its a no go. I was using the 14mm socked as indicated.
The problem lies in the fact the bolt head is pushed into the metal plate. It does not have a washer and lock washer like it should have to enable you to grip the head of the bolt fully. With a washer and lock washer it enables you to grip and yes with my rattle gun it normally comes off with ease.
I am learning towards Marks suggestion and cutting the bolt down to the next size. I am not worred about marking the blade plate as its already damaged from not being connected propery. By marking the blade plate slightly I am hoping to get a bit more grip on the bolt head.
After doing some more reading I found a suggestion stating that cutting a slot into the middle of the bolt might work to fit a large screwdriver into the head. I was worried this might make the situation harder again.
Suggestions?

I suggest you avoid making a screwdriver slot. You can deliver little torque with a screwdriver bit compared with a six point socket, and the slot will weaken the bolt head to a fairly serious extent.

I had thought your bolt head was originally 5/8" A/F, but if you actually had a 9/16" bolt head (14.28 mm) and you were able to put a 14 mm socket on it, the bolt head must be substantially damaged.

The absence of the washer under the bolt head makes the situation worse, because the end of the socket is slightly radiused, further reducing the amount of engagement. If you are prepared to damage the blade plate, you can apply an angle grinder to grind back the blade plate around the bolt head by a full millimetre, then hand file or, if you have one, apply a diamond cutting disk in a small angle grinder, to make a perfect hexagon head out of the mangled mess you currently have. You will probably then need to undercut the blade plate from beneath the new hex head, because initially you'll have cut a hexagon into the blade plate when you cut one onto the bolt head.

Making perfect hex heads is a tricky process, and you need to succeed first time because every time you make it an extra size smaller, you reduce the torque you can apply to it. This is a process I've been through a fair number of times, though not on lawnmowers, and I've had both successes and failures. The failures were always because I didn't achieve a perfect hexagon of the perfect size to fit firmly into the six point impact socket.

And if you finally find you've had too many tries and there isn't enough head left to continue, you just grind the head off the bolt, then grab the bolt-shaft that was formerly inside the blade plate with vice-grips and unscrew it from the PTO. You are only out one bolt, which was pretty much trashed when you started, and one blade plate which is pretty much the price of a ticket out of this mess.

seeing as the bolt is already butchered , it you have a mig, or arc welder ,you can lay some hot weld on the bolt head , build up a lump of weld on the bolt head big enough to grip with some vice grips, this is what car engine rebuilders do to remove broken rusted in bolts studs ect , the concentrated heat often does the trick .

good luck damo

Does the bolt come open clockwise, or counterclockwise?

It is a normal right hand thread - the bolt is the one that screws end-on into the standard Briggs PTO (crankshaft extension, or output shaft).

Ok, here's another idea. Get youself down to Supercheap auto and buy a 9/16 single hex socket that is non impact(just a standard Cr vanadium type). Use that on the rattle gun but wear some eye protection and gloves incase the socket disintegates. The standard sockets dont have such a deep radius carved out on the underside and should hence sit deeper around the bolt. Also the thinner wall will also enable it to get down deeper.
I've been using a standard cr-van socket for a couple of years now and it hasn't failed me yet. The problem with the cheaper impact guns(like the set i own)that come with a set of sockets is that they're metric and are always a nuisance trying to get off 9/16 bolts with the slightly smaller 14mm soccket that's supplied.

That has also worked for me too bigted and havn't had one shatter either of that size so far , but protective eye wear is a Must. The rattle gun I have has 4 settings and I set that to the highest setting which is number 4 on my cheap set, but firstly set on 2 to try and bed the socket first to avoid slipping. Sometimes tapping the socket on first if the bolt has been tampered with beforehand helps.

Thanks for all the pointers. The rattle gun wasn�t an option as the bolt head was far too indented into the blade plate because the previous owner obviously forgot to put a washer and lock washer before tightening the bolt. Thanks for the tip of using the standard socket. I�ll keep that in the memory bank for next time, noting of course the potential safety concerns.

I ended up going with Mark and Grumpys suggestion. It took some careful grinding to keep a nice hexagon. After about 10 minutes of careful grinding and then re-testing with a 13mm socket the bolt came out relatively easily. The trick in this case was grumpy�s suggestion to cut into the blade plate (which was already damaged) and allow the compelte bolt head to be gripped with the 13 mm socket.

I had to grip the boss with a set of multigrips because it was spinning in the absences of the 3 snapped bolts.

I ended up putting on a round plate plate with four blades for that nicer cut. I also had to replace the boss because of the broken bolts. I have a couple of second hand bosses off wrecked mowers so it wasn�t a problem. I have included a couple of photos below.

Thanks again for all your help

Peter

Excellent job jaffa , I've never had to do this but it's great that you've showed how this can be done if need be.

Nicely executed, Peter. That blade plate was very deeply penetrated by a spinning spring washer at some point, and wasn't salvageable anyway, so you didn't lose anything by grinding it.

another fun fact on Briggs engines a perfect replacement for the center bolt is a flywheel bolt out of a Holden 186 straight 6