Broken headbolt

JAG43 · Sep 20, 2019

Replaced head gasket on my 21hp Briggs. Everything was going fine until the headbolt at the eight o’clock position snapped at the thread level. I’ve managed to drill an off center hole but the Easy Out isn’t doing its job. Any suggestions? Can I put an insert in the block?
Thanks
John

jp1961 · Sep 20, 2019

Hi John,

I haven't had much success with easy outs.

You could try heating the area with a propane torch to see if the easy out will extract the broken bolt.

Only other option, would be to take it to a machine shop to see if they could remove it and place a helli coil in the block or try drilling and tapping to the next larger size.

There are YouTUbe video's showing guys welding a nut to the broken bolt and extracting it that way, if you want to try.

Regards

Jeff

Scrubcadet10 · Sep 20, 2019

I'm with JP, take it to a local machine shop and have them do it.

bertsmobile1 · Sep 20, 2019

Do a search for "Stud removal" or "bolt removal".
There are special electro spark erosion machines designed specifically for this purpose.
There are water plasma machines designed to do this as well.
Oz is a tiny market and we have a dozen workshops who do nothing but this and for me a mobile workshop that comes to me & does the work in situ.
Not cheap @ $90 (AUD) but worth every penny.
I had one bloke who did a bolt at the back of one of the rollers in a position I could barely get a flat wrench into.
Usally all that is needed when they are done is to run a tap through the hole to clean the thread.
In the land of oppertunity & enterprise there must be people doing the same thing.

JAG43 · Sep 25, 2019

The broken head bolt is circled in yellow at about the 7 o’clock position. I’ve drilled a very off center hole in the bolt and easy outs aren’t working. On the top side at about 11o’clock position is a locating pin. The distance between the head bolts is 3 1/4 inches and it is about the same on the bottom side if you consider the broken head bolt as a locator pin. Is the broken head bolt critical to the integrity of the engine? I’m thinking this thing might runs quite well if I just put it back together. I’m sure smarter guys than have an answer. I’m just using the machine as a lawn tractor and have removed the mower deck.
Thanks,
John

Scrubcadet10 · Sep 25, 2019

I dont think it would interfere with structural integrity of the engine, but you *might* blow head gaskets in that are due to there being no torque, or not get a good seal.

bertsmobile1 · Sep 25, 2019

As it is there are not enough head bolts on these engines which regularly blow head gaskets as it is.
There is no way the clamping force will be consistent enough for the engine to work without leaking for more than a 1/2 dozen thermal cycles.
So if you want to et a lot of practice replacing head gaskets put it back together the way it is.

If you don't want to take it out then get a Dremel tool or equivalent and a pack of carbide cutters.
To et that deep you will probably need a flexiable shaft drive as well.
Put on some Nitrile work gloves to prevent you hands from very sharp metal splinters and cut the bolt out or at least cut the hole back to centre then drill it out.
When you have a pilot hole that is centred then drill the thread out in one hit .
people make the mistake of stepping up the hole one drill size at a time which will guarantee you run off centre and wreck the cutting edges of your drill bits to boot.

Worst case is you will either have to helicoil the hole or tap it next size bigger.

JAG43 · Feb 24, 2020

I finally got the broken stud out but there wasn’t enough material left in the case to chase up the old threads. I noticed that the headbolts actually terminates outside of the cylinder finns so I drilled the threads out and used a long grade 8 bolt and nut on it. So far, so good. A much better alternative than scrapping the engine. John

StarTech · Feb 24, 2020

bertsmobile1 said:
When you have a pilot hole that is centred then drill the thread out in one hit .
people make the mistake of stepping up the hole one drill size at a time which will guarantee you run off centre and wreck the cutting edges of your drill bits to boot.

I actually have right the opposite result on keeping the bit center and I don't worry about the bit getting dull as I have a bit sharper if needed. Now of course I free hand the drilling too. ONe thing about bits is that you got to have good quality bits; those big box store bits are lousy for me to use. Some can't drill the first hole without dulling.

Hammermechanicman · Feb 24, 2020

Well........ twist drills......drilling out broken head bolts. After a lot of weeping wailing and gnashing of teeth i do it this way. I made a steel jig about an inch tall with a holes that fit 1/8" drill, 1/4" drill and a center punch. I use other head bolts to clamp the jig down so to stay straight. I have some good drills but the Hazard Frought cobalt ones and a drill Dr do just fine. I can usually get the broken piece out and save the threads.

Broken headbolt

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