Broken Thermostat Housing Bolt

[Wilburx13]

Hi all - looking for some insight. While replacing the thermostats on my 2006 BF225, I broke two bolts on one thermostat housing. I know - tough lesson learned. One bolt had some threads showing and was relatively easy to remove. The other is about a half inch down, under the tensioner pulley mounting plate. We've tried a few different methods to get it out, including a screw extractor set, but haven't had success and are worried we're going to start doing more harm than good.

To make things easier, we're probably going to remove the tensioner pulley mounting plate, but to do so we'll have to remove the tensioner pulley and idler pulley. The belt is in good shape, so not looking to replace it, but when we put everything back together is there anything we should be cognizant of in terms of timing? From what I can tell reading-up, as long as we ensure the TDC marks on the crankshaft and camshaft pulleys are all aligned with their marks when we put everything back together, we should be good.

Any advice is appreciated. My father-in-law, who is helping me, was a diesel mechanic for 20+ years, so he's mechanically inclined, but just want to make sure we're aware of any pitfalls specific to a Honda engine.

The bolt I broke is in the hole with the red X in the attached picture.

 

[airshot]

Find a small short drill called a " center drill" the same OD as the hole with the broken thread. This will make a small hole directly centered on the broken screw. After the center drill made the small hole in the center of the broken bolt, get a " left hand " drill bit to drill out the screw. Being left handed it will be run backwards, as the drill grabs the broken bolt it will unscrew it out !! Spray some WD40 or other oil in there to make it easier.
If your unsure, visit a local machine shop and they will show you this simple process. They may even loan you the drills to use...

 

[MattFL]

Drill, tap and insert a helicoil or time-cert. There are kits online that include the drill bit and insertion tools. If it's broken below the surface, measure the size of the hole with a caliper and get a center-drill with an outer diameter the same size as the hole. Search Harbor Freight for "center drill". That will poke a small hole right in the center making it much easier to drill in the center of the bolt. If you can find a left turning bit, use one and with any luck it will start unscrewing. Take your time, use oil on the bit and go slow. Also use a new bolt as a guide for how deep to go, don't go too deep.

 

[MattFL]

Find a small short drill called a " center drill" the same OD as the hole with the broken thread. This will make a small hole directly centered on the broken screw. After the center drill made the small hole in the center of the broken bolt, get a " left hand " drill bit to drill out the screw. Being left handed it will be run backwards, as the drill grabs the broken bolt it will unscrew it out !! Spray some WD40 or other oil in there to make it easier.
If your unsure, visit a local machine shop and they will show you this simple process. They may even loan you the drills to use...

We were typing at the same time! Are you the one who suggested the center drill to me several months ago for my BF50 exhaust plate issue? It worked fantastic.

 

[Scott Danforth]

a trick I learned years ago, similar to center drill.

use a set of transfer punches to center punch the very center of the bolt. use a 1/16" drill bit to start drilling the bolt. once the hole is about 1/8" deep. switch to left handed drill bits, starting with 1/8" then going larger if needed. eventually it will grab and spin the bolt out

 

[airshot]

a trick I learned years ago, similar to center drill.

use a set of transfer punches to center punch the very center of the bolt. use a 1/16" drill bit to start drilling the bolt. once the hole is about 1/8" deep. switch to left handed drill bits, starting with 1/8" then going larger if needed. eventually it will grab and spin the bolt out

Transfer punches also work great, the only advantage if a center drill is a little nicer starting hole than just a punch mark. The whole idea here is to get a true on center starting hole for the left hand drill bit...