Snapped head bolts b7100

[Dennis]

I have a snapped head bolt ( one of three) that poses a bit of a problem. Previous owner (12 years ago) did a bodgy job trying to remove it and what is left is a hole about 7mm deep and 4mm wide in a 7mm bolt.

In the past I have used an "Easy Out" reverse thread extractor for this sort of job however this old drill hole is quiet deep already and I am concerned about doing more damage. There are also cuts from a cold chisel that have bitten into head surface around the bolt hole. This might result in difficulty screwing out the bolt as the burred suface seems to be pushed into the outside of the bolt

Any ideas about how to approach this. Would it be reasonacble to leave this butchered bolt alone, replace the other two snapped ones and run with a bolt short.

I have known about this snapped bolt for a while but recently removed the rocker cover to find 2 more snapped bolts. The tractor has been running with these 3 snapped bolts for 12 years.

Should I re torque all bolts when I install the new ones and in what way?
ie do I loosen all the others right up and retighten or can I just tighten the new bolts to correct specs.

Finally can I simply take the whole rocker assembly off (to access bolts) and back on at the brackets without any adjustments. I know I'll have to adjust valve clearances after tightening head.

 

[Bellinghamster]

So just the bolt heads snapped off, flush with top of the engine head, not flush with the top of the block? (I assume since you're talking about the rocker assy being in the way, it's near the top of the head)

If it were me, I'd remove the "good" bolts and pull the head off which would expose the bolt shanks and allow you to get a good grip on them to turn them out. I'd also replace ALL the head bolts. Something has obviously gone wrong with the 3 (overtorqued?), raising the suspicion that the others may follow suit. Replacement B7100 heads are very scarce, and you don't want to risk warping it. ~$50 for a head gasket and probably about the same for new bolts and you'll never have to worry about it.

The rocker assy is easy to remove and reinstall, just be sure to get all the pushrods in their sockets of the rocker arms before you start tightening things down. If you don't move pushrods around (and you shouldn't) you probably won't even need to adjust valves, although it'd be a good excuse to check their clearances.

edit: now that I re-read your post it looks like you successfully remove 2 of the 3 with the head on. If the drilled hole in one remaining is reasonably centered get a reverse flute drill bit (as large as you can go without getting into the head casting) and give it a go. You can always drill down a ways, stop, then switch to a smaller drill and try the easy-out a little deeper down. As for retorquing - I'd just torque the new bolts to spec. incrementally. Loosening the others will risk causing the gasket to seperate.

 

[Dennis]

Thanks for the help guys. Appreciated.

I managed to get two of the bolts out without even drilling by wedging two thin screwdrivers into small space between bolt and head and applying presure to grab and centre the bolts and then wiglling them out progressively; bit by bit.

That's where my luck ended.

The 3rd, previously butchered, bolt would not shift after attempts with 3 different sizes of extractors. I got one extractor to grab but after a bit of torque it chewed out of the bolt.

I think the bolt is being wedged in by the cuts from the cold chisel that have pushed the head block surface metal into he bolt.


The other theory is that an extractor tip has broken off during the previous attempts and is putting sideways pressure on the bolt.

I started drilling down deeper (to about 12-15 mm) but the drill has hit something that is catching it up.

I thought this might be the old extractor tip.

Drill hole still looks like it is going straight but I am getting a bit wary of how deep I go and what I could possibly drill into.

Any advice welcome