Snapped thermostat-housing bolts

[Vinnie]

Hi,

Today I wanted to replace my thermostat and install a new thermostat-housing. All went well untill both bolts broke off leaving most stuck inside. So much for wd40...

I'm going to have to drill them out which shouldn't be hard but I'd like to know, if anybody knows, how deep I should/could drill. The bolt looks close to M6 thread (the bolt is probably imperial but I can't guestimate imperial). Could I put M7 or M8 in it?

Here's a pic to visualise my pain ;-)

I left the gasket and thermostat inthere for now.

I don't wannt screw up my engine so any tips are much appreciated!

Thanks,

Vincent.

 

[will e]

Hey Vinnie!

If I remember correctly the bolts go into the water passage. If you remove the thermostat you should be able to 'feel' the ends of the bolt.

Drilling out is your best bet. You might put a magnet in there to pick up smalls pieces. Not a requirement but it wouldn't hurt if you have something that would work.

The threads are going to be imperial. I would use a tap/die and clean them up a bit. I would use studs and nuts instead of bolts. Do not try to make metric work. The only way you can do that is drill/tap to a larger size metric.

 

[secluff]

Vinnie, the factory bolts are 5/16"-18 x 3/4". I would drill out at least 1/2-3/4 of the way into the existing bolts and then use an "Easy out". When you reverse your drill they bite into bolt and hopefully back the bolt out. If you don't have access to one, then drill the bolt until you can safely break it into pieces. I would try to stay with the standard bolts or studs and nuts as will e suggested. Just keep in mind your drilling into your block and if something messes up while trying to drill metric, you've got bigger problems.

 

[Don C]

I agree with staying with standard size, if possible. If finding the correct size bolts is a problem, or if the threads are messed up, you can convert to M8 by using Heli-Coil thread repair.

 

[mach1000]

Happened to me before. What the guys said above. Magnet is a good idea. Shop vac too! Don't want metal pieces messing up your water pump bearing. I replaced my bolts with stainless bolts.

 

[Qcode351mach]

Easy out is as pointed out ..I would use a propane torch on low to heat the area before you attempt removal -You could weld a nut on or a bolt on whats left get on it right after welding as the heat will make it easier to remove. personally I would attempt welding a nut on since it looks like you have enough "meat" protruding from the block--you lay the nut on top then weld in the center of the nut to the broken piece immediately try to remove while still hot.

Then there's this tool also

 

[Carolina_Mountain_Mustangs]

I was a tool & die maker for several years and had to get lots of broken bolts out. If you can get a left hand drill they will sometimes grab and screw the broken bolt out. I stay away from easy outs. If you break it then you are in trouble high speed steel you cannot drill it. Just get the center of the bolt and drill small at first then out to the tap drill size if needed. The L.H. drill bit saved me dozens of times.

The absolute worst case is drill it small and use a pencil grinder and grind until you see the threads break through then tap the remainder of the bolt out.

When you go back together always, always use anit-seize on the bolts that are in the water neck and water pump. In fact use on any bolt that is not torque critical.

David

 

[nailpounder]

also might want to apply pb blaster or rust solvent to the stds a time befor you try to remove them

 

[mjlan]

If the holes go into the water jacket, is there enough room to push them out the bottom? you may able to increase the drill size drilling all the way through, sometimes when the bit grabs it will spin the broken portion out the bottom if the hole is open.

 

[Paul of MO]

The bolt holes do not penetrate into the water jacket. They bottom out in little ears cast into the block.

Left handed drill bits are your best bet as David suggest. Second would be welding the nut on. I agree that easy outs are neither easy or able to get much out.

Paul of Mo

 

[87fox72mach]

Make sure when u reinstall to use never seize on the threads. Will prevent that problem in the future.

 

[Vinnie]

Thanks for all your info guys! Much appreciated!

I don't have welding or heating equipment and if I did, I'd be scared since it's right next to the fuel line... Go on, you can call me chicken ;-P

Also I'm not the biggest fan of easy outs and I really wouldn't want one of those to snap inside.

So I'm going to happily spend a day drilling I think. I went over just now to see if I could get there with my drill and when I remove the distributor cap I can reach it quite alright.

I'm a little confused still about wether or not the screws penetrate into the water jacket. Some say they do and some say they don't? I guess I'll get the thermostat out and check with a mirror or something.

I looked up the way bolts are measured in imperial lingo and if I'm not mistaked the thread is 3/4" long, right? I should be able to feel when the drill is all the way through.

Don't think I have any more questions. I may not have time for this sooner than 2 weeks from now though :-/ But I'll let you all know how it went when I did it

Cheers!

Vincent.

 

[Don C]

I don't believe they go through, either, but it's been quite a while since I changed my thermostat. If it is a "blind hole", a regular tap won't work to clean up the threads, due to the long taper to make it easier to start, and will bottom out. You'll either need to get a blind hole tap or use a die grinder to remove some of the taper on a regular tap.

 

[turtle5353]

I never have luck drilling stuff out. Probably because I never have sharp bits!!! I usually weld a nut to the broken off end. Even if theres just a little bit sticking up of the old bolt, you can hit it with a mig welder. the heat from welding usually helps break it loose and you can put a socket on the nut and back the broken bolt right out. I have done tons of exhaust manifold bolts that way.

 

[Don C]

I agree with the other posts regarding easy outs. They are no good for bolts that were broken off because they are frozen (rusted) in place. Chances are they will just wedge the broken bolt in tighter, due to the way they work. They work OK on a bolt that is free and was broken off by overtightening or sheared off.

Drilling them out is not easy to do, it's difficult to be centered and drill straight, so the threads don't get messed up. I think that I have had to install Heli-Coils about half the time I have tried to drill them out.

Welding a nut on is the most consistent way of successfully removing them. You just have to keep the nut centered on the broken bolt. The same size nut works fine when the broken off bolt protrudes some. If it is flush or indented it becomes riskier and I would use a nut that is a size smaller.

 

[73pony]

While I have generally had good luck with the easy out method based on your picture I would suggest welding the nut on as well. There seems to be a decent amount of meat sticking out, plus as mentioned earlier the heat from the welding will help to break it free. Also try some PB Blaster on it. WD-40 does not work to free up seized bolts.

 

[Vinnie]

Right, so I should try welding before drilling is what most of you recommend. I can understand that but I can't weld (but I wouldn't mind learning ) and I'm not liking welding right next to a fuel line... How dangerous is this?

 

[73pony]

Put up something like a heavy set of leather gloves to shield the fuel lines and you will be fine. Your not going to be running a long bead, just welding a nut onto the stud.

 

[Jeff73Mach1]

I was a tool & die maker for several years and had to get lots of broken bolts out. If you can get a left hand drill they will sometimes grab and screw the broken bolt out. I stay away from easy outs. If you break it then you are in trouble high speed steel you cannot drill it. Just get the center of the bolt and drill small at first then out to the tap drill size if needed. The L.H. drill bit saved me dozens of times.

The absolute worst case is drill it small and use a pencil grinder and grind until you see the threads break through then tap the remainder of the bolt out.

When you go back together always, always use anit-seize on the bolts that are in the water neck and water pump. In fact use on any bolt that is not torque critical.

David

I was going to post, but this is most of what I was going to say and a bit more.

In follow up I will say that if you can file the broken of bolt flat and then use a center punch to dimple it before you start drilling it can be easier to get it started and keep it centered.

If you haven't drilled a lot of metal, I will add that you don't want to use high speed, moderate pressure and lower speeds work well with a bit of cutting oil to keep the drill cool and the chips drawing out.

Don't chuck drills in too deep-the chuck should not be above the shank of the drill or it will break. Start small and work up in single size increments and it will go much faster than trying to use too large of a drill.

You should only need a left handed drill when you get close to your maximum drill size.