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ngoma 10-01-2017 10:53 AM

Head Bolt Broke Off In Block
3 Attachment(s)
It was time to replace the head gasket on the 85 745. Too much oil was accumulating in the cooling system, and the oil leaking to the exterior was creating an enviromental problem. Otherwise the engine was running great, well worth a head gasket change. It is my mileage king, giving a consistent 35 MPG avg. city/highway mix.

One of the head bolts snapped off during removal. #9 in this diagram.

We tried penetrating oil, chisel, propane torch heat, drilling, ez-out. Now want to try the fill-it-with-weld and weld a nut to it method. Since I don't have welding equipment and no experience I will see if a mobile welder can do it.

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R.Mojica 10-17-2017 04:17 AM

there isn't anything to weld to. might be better off drilling it all the way out or sending it to a machine shop.

ngoma 10-17-2017 10:37 PM

Yes that appears to be the case. I decided I will need to drill it out and install a Time-Sert. Just have to figure out how to keep the drill centered and perpendicular.

RedArrow 10-18-2017 05:00 PM

How about some real "dentist's tools"?
Idk why but that came to my mind since space is very limited

anders 10-19-2017 01:41 PM


Originally Posted by ngoma (Post 12231)
Yes that appears to be the case. I decided I will need to drill it out and install a Time-Sert. Just have to figure out how to keep the drill centered and perpendicular.

I would use an old cylinder head as a drill guide. It will the keep the drill bit centered and true.

ngoma 10-20-2017 09:56 AM

Yeah I thought about that. Makes sense. Now just have to find an old head laying around!

My other thought was to grind out the bolt remains from the first few threads, then run a bottoming tap thru to try clean out the rest.

Hendo 10-20-2017 04:36 PM

As you know, I'm not much of a mechanic so I'm hesitant to offer advice.

BUT.... You can probably fab a drill guide out of aluminum bar stock... use one of the other head bolts to hold it in place.

Drill-press accuracy is probably good enough. But any machine shop (or DIYer) ought to be able to make one for you for not much cash. They could do a steel one easier than you can at home on a drill press.

Use an oversize hole at the clamping bolt so you have some wiggle-room.

Maybe try an undersize drill bit. Maybe even a left-handed bit if you can find one.

Good luck and let us know how it goes!

ngoma 11-02-2017 02:53 PM

2 Attachment(s)
I ordered the Time-Sert kit m12 x 1.75 x 30mm.
The hole is just under 30mm deep below the counterbore (on the one I measured, assuming they are all the same depth). The flange of the insert will probably stand at least 6mm proud of the counterbore base since the insert cannot be installed to the bottom of the hole. The included tap is not a true bottoming tap so cannot thread to the bottom of the hole.

Dremel should be able to cut off the protuding section of the insert.

Our drilling session attempt at extracting the remains of the broken-off bolt managed to get the drilled hole off-course by 1-2mm (toward the IP side)-- hoping there is enough slop in the gasket and head's bolt holes to allow for this when reinstalling.

One great tip from Time-Sert: Cover the block deck with packing tape (like that wide clear tape for taping up cardboard boxes) to make a kind of "dental dam" to protect the oil ports, cylinder bores, etc. from metal chips and other foreign matter during drilling and tapping operations.

That's where we are at now, after cleaning up the other bolt holes and the steam port holes that were packed solid around #5.

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ngoma 11-07-2017 10:48 AM

Got the Time-sert thread repair kit installed. That got me thinking about the 12mm deep counterbores for each hole. Does anybody know the reason? Why don't the threads start right at the block deck instead of 12mm below the surface?

v8volvo 11-08-2017 10:46 AM

Maybe something having to do with distortion of the block deck if the threads start too near the surface?

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