Topic: Broken bolt stuck in head

[Chad]

BIKE IS A '77 CB750 F2

So I had a small oil leak from what looked like the rubber nickels. Since I head the head exposed to replace the rubber nickels, I though I would check the torque of the head while I was in there. I read in another post on the forum to put thread sealer on the bolts beneath the rubber nickels because they are exposed to the atmosphere. I went to take out the 1st one (#19 in the tightening sequence pictured below) and the bolt snapped leaving the broken off threads of the bolt stuck down in the head.

So.... the obvious question, what the heck do I do now? 

[calj737]

I'm not completely familiar with that head, but I suspect if you remove the rest of the bolts securing the head to the cylinders, you should be able to reach the remaining portion of the bolt where sheared, and turn it out.

This of course requires the removal of the head, but I don't see another safe option.

[iron_worker]

Well I've never worked on a F2 but on my K4:

#1-16 are the head studs which are 8mm and require the 18ft*lb

#17-22 are 6mm (I think? ... but definitely a smaller thread than the studs) and probably only require ~6-8ft*lb

Hopefully someone else can confirm that. Maybe it's a difference on the F head.

IW

[Chad]

I'm not completely familiar with that head, but I suspect if you remove the rest of the bolts securing the head to the cylinders, you should be able to reach the remaining portion of the bolt where sheared, and turn it out.

This of course requires the removal of the head, but I don't see another safe option.

Ya that's what I'm hoping for. If I remove the head and am able to get the bolt out, I'll be a happy camper at this point. Hoping I don't have to take this to a machine shop to get it removed.

Does anyone have a picture of the bottom of an F2 head? Specifically where this bolt comes through? I was planning on getting this thing put back together today and getting back on the road. There go my plans 

Well I've never worked on a F2 but on my K4:

#1-16 are the head studs which are 8mm and require the 18ft*lb

#17-22 are 6mm (I think? ... but definitely a smaller thread than the studs) and probably only require ~6-8ft*lb

Hopefully someone else can confirm that. Maybe it's a difference on the F head.

IW

Yes. That is true. I have HD studs with 12mm nuts and 17-22 are 10mm bolts. I'm not sure what the torque is supposed to by on them. Anyone know?

[70CB750]

Picture of the bottom of an F head?  There is not much to be seen, but here you go.



The smaller hole on the very right is the one.

More pictures:

http://forums.sohc4.net/index.php?topic=115305.125

[Chad]

Picture of the bottom of an F head?  There is not much to be seen, but here you go.



The smaller hole on the very right is the one.

More pictures:

http://forums.sohc4.net/index.php?topic=115305.125

Thanks for the pic. I'm off to remove the head. Sucks in a way, but now I'm motivated to throw some paint on my motor since I'm going to have it apart. Trying to look at the bright side 

[Davez134]

Those bolts are not open to the atmosphere, they insert into top surface of cylinder jugs. Unless I'm missing something, you should have easy access to it after removing head.

[MCRider]

Your premise is flawed. The 4 bolts under the pucks do not leak. They are positiioning bolts to draw the head down prior to torquing it down. They must be removed and replaced routinely on teardowns.

The 4 STUDS that can leak because their holes are tappped straight thru to the atmosphere are not in any of your diagrams. (I'm a bit of an expert on these as I've had many leak).  Having read the posts about these studs, you should have come across a comment that if the studs have never been removed and you have no need to remove them, then leave them alone!  The 4 bolts you are messing with now have to be removed on teardown, and so do not qualify as leave alones. So it would have broken ossibly anyway.

They would be visible on the top of the head, on the exhaust side. in a soldier's row. Threaded into holes that empty into the plug cavity. Across each from the bearing caps bolts, which go in the ntake side. It looks like the studs may be just visible in your shop pcture, but the top view makes it hard to see.

I disagree with the sequence. Maybe because yours is a later model. I was raised to NEVER loosen the main head nutts before taking those positioning blts out.  If you do, the relaxing of the head puts pressure on the bolt heads and...they break.

[Chad]

Those bolts are not open to the atmosphere, they insert into top surface of cylinder jugs. Unless I'm missing something, you should have easy access to it after removing head.

Your premise is flawed. The 4 bolts under the pucks do not leak. They are positiioning bolts to draw the head down prior to torquing it down. They must be removed and replaced routinely on teardowns.

The 4 STUDS that can leak because their holes are tappped straight thru to the atmosphere are not in any of your diagrams. (I'm a bit of an expert on these as I've had many leak).  Having read the posts about these studs, you should have come across a comment that if the studs have never been removed and you have no need to remove them, then leave them alone!  The 4 bolts you are messing with now have to be removed on teardown, and so do not qualify as leave alones. So it would have broken ossibly anyway.

They would be visible on the top of the head, on the exhaust side. in a soldier's row. Threaded into holes that empty into the plug cavity. Across each from the bearing caps bolts, which go in the ntake side. It looks like the studs may be just visible in your shop pcture, but the top view makes it hard to see.

I disagree with the sequence. Maybe because yours is a later model. I was raised to NEVER loosen the main head nutts before taking those positioning blts out.  If you do, the relaxing of the head puts pressure on the bolt heads and...they break.

You guys are both right. I'm an idiot. 

But good news, I got the bolt out. Came out pretty easy.

MCRider, are you talking about the four studs that hold the cam holders in place? (Pic below). In BrandEn's Leak-Free Top End thread I believed he talked about these being a source for a leak.

[Jerry Rxman Griffin aka MuthaF'er]

You disagree with a sequence in a manual? How's that?

I would speculate only that he started removing bolts in the reverse order thus attempting to release the 6mm first and #19 snapped the head??

The HEAD of the bolt is exposed as previously said it threads in the block.

Thanks for posting that picture. First I've seen of it showing the order that includes the 6mm. Too bad it also does not have the 6mm torque value.

[MCRider]

Yes, that's a great pic, "soldiers row". IF you follow those studs path down into the sparkplug cavity you'll see the tapered bottom of the holes that were drilled and tapped by the factory. The threads are hanging out there for all the world to see. Those studs are sealed from the factory. I've never seen or heard of leaks there unless they had been removed for head cleaning and/or port work.

Then when you thread them back in, innocently without sealer, they wick oil down their shaft and it literally drips out the bottom of those holes, at about the 3rd fin of the head. Same place as the pucks, so it can be confusing. They require a very dry instalation, with a good sealer, low torque, and set up time, Mike told me to use a high temp Teflon sealer, good for high temp oils.

[MCRider]

You disagree with a sequence in a manual? How's that?

I would speculate only that he started removing bolts in the reverse order thus attempting to release the 6mm first and #19 snapped the head??

The HEAD of the bolt is exposed as previously said it threads in the block.

Thanks for posting that picture. First I've seen of it showing the order that includes the 6mm. Too bad it also does not have the 6mm torque value.

Well as you say, I'd never seen a sequence which included the 4 6mm bolts. IS that a Honda Manual?  In my upbringing that is because they are not material to the holding down of the head, as the nuts are. They are simply to postion the head and draw it down against the dowels and the gasket. Protocol would dictate to do the inner ones first then the outers, to a nominal 6m bolt torqe of 8ft lbs or so. Then you go to work on the head nuts.

OCICBW

In removal, one would remove all 4 first. That way when you losen the head nuts. the relaxing of the head doesn't increase the torque on the bolts to the point where they break, as here and on many threads in the past.

[calj737]

6mm bolts only take 6-8 ft. lbs of torque. They are "decorative" not structural.