Strongest M6 tap
Discussion
I need to remove a broken glow plug. To do this I will need an M6 tap but I am paranoid about breaking it off in the remnants of the plug leaving me with no choice but to remove the head. What would people who are in the know recommend as being the strongest (least likely to snap) tap?
shovelheadrob said:
You don't use a tap to remove a broken glow plug, if that is the limit of your engineering knowledge I suggest you get someone else to do the job.
Sorry, I might not have made my self clear. You need to understand the process of removing a broken glow plug. On the engine I am working on the threaded bit is not generally the thing that causes the issue, it's usually the tube that the electrode sits in that becomes stuck in the head. The procedure is to drill the threaded part out using a guide bush so's not to damage the head then tap a thread into the glow plug tube and use a high tensile bolt and spacers to draw the tube out.
It's not my car and usually if a plug is stuck I would advise the customer to leave it alone. On this plug the electrode had come out of the plug leaving no alternative but to replace it.
There are new taps available with spiral flutes, any one used them and are they any good? I dont care if the tap is scrap once it's done it's job I really just don't want it to snap off in the remainder of the plug.
I did originally think of easy outs but if the hex sapped off the plug as it was too tight I don't really want to take a risk with a piece of HSS getting snapped in the head.
This one has lost the entire electrode, what remains is an open ended tube so I will have to plug it with some dumdum or the likes.
I only initially intended checking and changing the ones I could change and soaking the others in penetrating fluid over a couple of weeks but the electrode was sticking out 25mm, well on it's way to a high speed rendezvous with the underside of the bonnet. The owners were going to Belgium later that day! I had to reinsert the electrode and make up a steel strap that was bolted to the head at either end and pack it in to make sure it would stay put. Worked a treat but now we need to tackle the plugs properly.
This car ha been a bit of a problem from day one. His fire seals started leaking so he took it to the local garage who kept it for 10 weeks then gave him a bill for 2500€. A week later they were leaking again, back it went. The owner had enough of the garage and asked me to look at the plugs, I noticed two fire seals were leaking again, by the time they came home there was a 4th leaking really badly.
Honestly, our local garages are stunningly bad. I have another friend with a 1972 SL350, he took it to a different garage to have the timing chain replaced. A year later he gets it back and it's not running right. That's right a full year to install a new timing chain wrongly! I have that job in the new year.
I only initially intended checking and changing the ones I could change and soaking the others in penetrating fluid over a couple of weeks but the electrode was sticking out 25mm, well on it's way to a high speed rendezvous with the underside of the bonnet. The owners were going to Belgium later that day! I had to reinsert the electrode and make up a steel strap that was bolted to the head at either end and pack it in to make sure it would stay put. Worked a treat but now we need to tackle the plugs properly.
This car ha been a bit of a problem from day one. His fire seals started leaking so he took it to the local garage who kept it for 10 weeks then gave him a bill for 2500€. A week later they were leaking again, back it went. The owner had enough of the garage and asked me to look at the plugs, I noticed two fire seals were leaking again, by the time they came home there was a 4th leaking really badly.
Honestly, our local garages are stunningly bad. I have another friend with a 1972 SL350, he took it to a different garage to have the timing chain replaced. A year later he gets it back and it's not running right. That's right a full year to install a new timing chain wrongly! I have that job in the new year.
Quick update.
It took me ages to get the electrode back out, it kept on sticking and as I assume it is tungsten, I didn't want to break it off near where I was going to have to drill and tap. After plugging the tube with dumdum I very carefully drilled the threaded portion of the plug out. Then I was able to tap a thread into the remainder of the tube and screw a high tensile M6 bolt into it and using washers, try to draw it out. This didn't work, it was stuck fast.
In the end I decided to start the engine and let it warm up for 15 minutes, the temperature barely registered on the gauge so I decided to take it for a bit of a drive. I packed my overalls on top of the broken plug, now blocked with the bolt, shut the bonnet and set off. I managed to get about 300 meters up the hill from my house when the remainder popped out making a bang phut phut phut. Result! I had a bit of a panic as smoke started coming out the bonnet, I thought my overalls might be catching fire but it was just diesel fumes.
Drove the car back to the garage and replaced the glow plug and checked the other ones I couldn't get out before. Number 5 was stuck fast and showing a high resistance but as number 5 is almost impossible to get to with a drill with the engine in place it will have to stay there. The glow plug light has now been removed at the request of the customer.
Also, just to say the Gheuring helical tap was great, thanks for the recommendation.
It took me ages to get the electrode back out, it kept on sticking and as I assume it is tungsten, I didn't want to break it off near where I was going to have to drill and tap. After plugging the tube with dumdum I very carefully drilled the threaded portion of the plug out. Then I was able to tap a thread into the remainder of the tube and screw a high tensile M6 bolt into it and using washers, try to draw it out. This didn't work, it was stuck fast.
In the end I decided to start the engine and let it warm up for 15 minutes, the temperature barely registered on the gauge so I decided to take it for a bit of a drive. I packed my overalls on top of the broken plug, now blocked with the bolt, shut the bonnet and set off. I managed to get about 300 meters up the hill from my house when the remainder popped out making a bang phut phut phut. Result! I had a bit of a panic as smoke started coming out the bonnet, I thought my overalls might be catching fire but it was just diesel fumes.
Drove the car back to the garage and replaced the glow plug and checked the other ones I couldn't get out before. Number 5 was stuck fast and showing a high resistance but as number 5 is almost impossible to get to with a drill with the engine in place it will have to stay there. The glow plug light has now been removed at the request of the customer.
Also, just to say the Gheuring helical tap was great, thanks for the recommendation.
Gassing Station | Home Mechanics | Top of Page | What's New | My Stuff