Broken thermostat bolt

[Makade]

I have a 2000 Mercury 250 EFI and while changing thermostats one of the bolts broke off deep right before the powerhead.

It does seem there are still a few threads in the cylinder head

i am debating whether to tap the head and install a shorter bolt or drill it out.

Anybody have suggestions or experienced the same problem????

Thanks in advance!

[bradburd68]

Center punch and a left handed drill bit run slow. Left hand bit will bite it most times and unscrew the piece out.

[Robby321]

Running in salt? Might be well corroded in. Try L/H drill but if enough meat, drill and tap next size bolt up. Heli coil too maybe? Timesert?

[Chaz]

If you use a shorty to make a thermostat cover bolt, you lose the head bolt part of it. If it was my luck it would pull water in the cyl from loss off clamp load ..

To get it out, first thing is to make the top of whats left flat. If you have or can get a 5/16" end mill you can put it in the hole and touch the end up, then center punch it. If you have a transfer punch set, that will ensure you dink it in the middle. If not use a punch that is big enough to use the walls to your advantage to hold center.
Drill a small hole in the center, again use a piece of tubing to help center . Once you have established a center hole, "quickly heat the aluminium" as stated use a .125-.150 left hand drill bit .. if you play your cards right . the heat will expand the alum away from the bolt and the correct pressure on the bit will drive out the broken bolt .. don't break the bit ..
I have bought every type of extractor there is on the market. the ones that don't try to spread the material as you increase pressure seem to work the best.
if the above doesn't work, you can pull the head, this way it's right in front of you , and you already have a good piolet hole to work from ... good luck

[Jay Smith]

I’d use the left hand drill after you center punch , start with small drill and go larger u til it weakens the bolt then apply a penetrating fluid then use ease out after you let penetrate fluid do it magic After removal use anti seze ..

Good luck ,
Jay

[Makade]

Thanks for the tips guys. I ordered left hand bits and drilled progressively from 1/8" to 1/4" and it wouldn't budge. I didn't try the easy out as the bolt was probally too deep to use one anyway. I finished drilling with a 5/16 bit. I was hoping I could tap in place without removing the cylinder head but even with a extension tap I would have to oversize the hole in the head which looks like I have plenty on the exterior but the water jacket on the inside is probably too close for comfort. Soooooo now I'm thinking I have to remove the head and will go with a time sert in the power head for the thermostat bolt but this brings up a few more questions. How many more head bolts will I break and if there are any tips or tricks to do before I go at it. Also I have been reading up on these bolts and it seems there is some debate on whether they are TTY or torque to angle and reusable???

[flabum1017]

new bolts are always a good idea no matter what. Be sure to either grease them ot use perfect seal on them to help prevent them from corroding again.

[Capt.Insane-o]

Pull the head off and use heat and hope. The quality of fasteners used on the 3 liter motors is poor and that is being nice.

[flabum1017]

Pull the head off and use heat and hope. The quality of fasteners used on the 3 liter motors is poor and that is being nice.

And if you break any bolts pulling the head, put the head back in place to use it as a drill guide to drill the broken bolts straight and center

[Jay Smith]

All great advice heat only the female boss you want her to expand giving you better chance of removing bad actor , NEVER heat the male bolt it has the opposite effect on the situation...

Good luck ,
Jay

[RSWORDS]

Looks like the threads broke above the block. Remove the head, screw a nut on the bolt (or bolt it centered if broken off flush). Weld the center of the nut to the broken bolt (the heat will help break the corrosion) let it cool. Heat the aluminum around the bolt and spin it out. I do this weekly on salt water motors anytime I can weld a nut on the fastener. Been the best solution I have found.

[Euroski]

Had good luck with this kit from Snap-on over the years before retiring from VW/AUDI...

https://store.snapon.com/Combination...--P630634.aspx

[flabum1017]

Those square extractors are better than the wedge type; the wedge type will expand the bolt making it tighter in the bore....

[Makade]

Ok so reality set in and I pulled the cylinder head. Luckily all the bolts came out without any trouble, pretty good for a 19 year salt motor. Any way I ordered seals and bolts which I just got in tonight and Mercury changed the part number from 82446050 to 8M0045380 on the bolts.
while comparing new to old the original are non magnetic stainless steel and the new ones are either 304 stainless or coated steel can't say but they are definitely magnetic. Wondering if the design change is for the better or worse????

Also I ordered the 2 upper bolts that catch the thermostats housing and they are same as original and were around $11 each and the new style were just under $4 a piece.

[Makade]

I thought I made up my mind to fix the bad hole with a helicoil as they make a 24 mm long one and the drill size required leaves me plenty of room for the head seal but I just was reading a old post on here about how much better the time serts are. I was reluctant to go with the time sert as the longest insert I could find was 16 mm and the counterbore required will put the insert really close to the head seal. Anyway I was hoping some of you experts could offer some advise on the preferable insert route. Btw I already have the helicoils in hand and also ordered the time serts to be delivered tomorrow just don't want to have to do this twice!!!!