Topic: broken bolt on head how important

[winkster2005]

hello everyone.

I have a quick question. I was putting the head back on my 74 cb 750 and after torquing the head nuts I started to tighten the 4 head screws that are under the rubber discs on top of the head. When I got to the last one that shares a space with an outer spark plug it snapped.  How important is this bolt to the engine. I know that might sound silly because obviously they wouldnt have put it there if they didnt need to but what are your thoughts on leaving it alone or removing the head and trying to remove the snapped off part of this screw?

[70CB750]

Where it snapped?

If all it needs is to take the head off and use a pair of vice grips to get the broken bolt out, I would definitelly do that.

Or does it have to be drilled?

[winkster2005]

the screw is flush so it would need to be drilled. Also, do you think I can reuse the head gasket? I copper coated it.

[flybox1]

Do it properly while the engine is out.
I would be prepared to order a new gasket. 

[Old Scrambler]

Being prepared to order the gasket, Yes....but since it was not heat-cycled, I would chance re-using it IF no damage when removing the head. Be sure to re-torque after a 24-hour or longer period from initial installation.

If the removal of the broken cap-screw is clean........GREAT.  If not...........a Time-Cert is much stronger than a helicoil.

[70CB750]

If you can find EDM service in your area, they would "spark" it out for you.    That's the best way.

Forget easy out I never saw easy out that worked.

If you try to do it yourself, use left hand drill bit(s).  It will either spin it out or drill it.

[MCRider]

Here's my 2c. IF the engine is done, leave it alone. Those 4 bolts are used to align the head on the cylinder and draw it down a tad before getting it on with the head nuts. Once the head nuts are tight. you can take thsoe 4 bolts out and throw them away, they do nothing except keep dirt out of the holes.

I'd move on and fix it at the next overhaul cycle. IMO

[markb]

I might have to disagree.  If you tighten the four 6mm screws first they will be loose when you tighten down the head nuts.  I believe you should tighten the head nuts first and then the 6mm screws.  Reverse when removing otherwise the 6mm will be real tight.  Also I would fix it as long as it's apart and not in the frame.  If you put every screw in and tighten them properly you still might have an oil leak but leaving one loose on purpose will reduce the odds even more.  My 2 cents.

[MCRider]

I might have to disagree.  If you tighten the four 6mm screws first they will be loose when you tighten down the head nuts.  I believe you should tighten the head nuts first and then the 6mm screws.  Reverse when removing otherwise the 6mm will be real tight.  Also I would fix it as long as it's apart and not in the frame.  If you put every screw in and tighten them properly you still might have an oil leak but leaving one loose on purpose will reduce the odds even more.  My 2 cents.

I agree. I have suggetsed the same protocol as you, here several times. Except this first step: You use the 6mm to draw down, the head aligns itself, it doesn't bind on the dowels, and gives the gasket its initial squeeze.

but not very tight. Then the head nuts, then the 6mm one more time. But at that point they don't do anything. But if you don't tighten them to a nominal 6lbs or so they will back out.

If you draw the head down with the head nuts first, no harm. But by then the 6mm ers are really worthless.

The reverse is true as you stated. Many has been the head where the owner has removed the head nuts first. The relaxing of the head tightens the 6mm ers to the point where they break off when trying to remove. Or round the head, or such.

Our only real disagreement may be what the op should do about it.. I wouldn't waste the breath or head gasket on fixing it on an engine that is otherwise done.

My experience here is from the dragrace shop where I worked. The owner threw those screws away as they just slow you down, when thrashing on an overnight rebuild.  I don't think there is any threat from an oil leak on these 4, but... its not my bike.

[DaveBarbier]

Just my 2 cents, but did the screw head shear off fairly clean? If I were you I'd first try to center punch the screw and try to drill a hole and use an EZ Out. Those thing have never worked for me but in this scenario the threads are probably not seized in the head and might easily be able to be backed out. You may have over torqued it or something. I'm thinking an EZ Out could work for you. Then if the threads in the head aren't stripped you can put in a new screw and not even mess with removing the head again. It beats the alternatives of leaving it alone and assuming it won't leak oil or removing the head, buy a new head gasket and reassembling. Worst case the EZ Out will snap and you'll be in the same situation as you are right now.


---
1978 Honda CB550K

[70CB750]

Actually, snaped easy out is much worse situation.  The bolt can be drilled, but easy out is harder steel and than you are stuck and no option to drill.

I can imagine working easy out for large diameter screw; naybe, but easy out for M6 will be what? 4mm at max, it will snap if you look at it sideways.

[DaveBarbier]

Actually, snaped easy out is much worse situation.  The bolt can be drilled, but easy out is harder steel and than you are stuck and no option to drill.

I can imagine working easy out for large diameter screw; naybe, but easy out for M6 will be what? 4mm at max, it will snap if you look at it sideways.

Oh I misunderstood, I thought the screw was flush with the cam cover. I read your post on removing the cover and using vice grips. In that scenario it wouldn't matter if an EZ Out was in it or not. But he said it's flush with the head. Yeah, a broken EZ Out would suck in that situation.

Don't mind me! Carry on!


---
1978 Honda CB550K

[markb]

I agree. I have suggested the same protocol as you, here several times. Except this first step: You use the 6mm to draw down, the head aligns itself, it doesn't bind on the dowels, and gives the gasket its initial squeeze.

I like that idea.  Makes sense and can't hurt a thing. 

[MCRider]

I agree. I have suggested the same protocol as you, here several times. Except this first step: You use the 6mm to draw down, the head aligns itself, it doesn't bind on the dowels, and gives the gasket its initial squeeze.

I like that idea.  Makes sense and can't hurt a thing. 

Thx. As a baby mechanic, I was given an engine to disassemble. I learned about the order of loosening those screws and head nuts. Removed the head nuts first, then went at the 4 screws with an air impact and broke one. Luckily it was coming apart, not going together, so fixing the break was easy.

[calj737]

Thx. As a baby mechanic, I was given an engine to disassemble. I learned about the order of loosening those screws and head nuts. Removed the head nuts first, then went at the 4 screws with an air impact and broke one. Luckily it was coming apart, not going together, so fixing the break was easy.

There's a lesson here: using the proper technique and sequence whether you are disassembling or assembling an engine matters. Improper sequence leads to damage. Improper technique leads to damage. Both of these lead to more time and money spent. Whether you intend to replace or not, it's always a best practice to do it properly and carefully. Unless you're in pit lane thrashing against the clock, do it right. Do it once. Never do it over again.

Build to last is the only way to do it in my book. Then it's the last time you'll ever have to build it.

[winkster2005]

UPDATE:

After reading posts on here I decided that if I don't fix it the motor MIGHT be fine but if I fix it I know I don't have to worry about that missing screw becoming a problem.  I took the head of yesterday and the fiber head gasket was trashed but luckily the screw broke on an angle and I was able to file a screwdriver slot in it without hitting the jugs.  It came out without any problems.  So I have a new gasket coming and 4 new screws coming from the local honda shop. I'll probably run a tap down the hole before I start assembling to make sure there's nothing in there stopping the screw.  Thanks everyone for the input.  I'm new here and I'm glad to have a big community of enthusiasts to help me with my build.

[70CB750]

Well said, sir

[Don R]

It probably would have been OK but now you will sleep better.

[evanphi]

It probably would have been OK but now you will sleep better.

FWIW, I just opened up my top end last night... and PO hadn't installed ANY of those 4 M6x35mm flange bolts. Bike has run just fine, but leaked. As MCRider explained, these bolts are largely for alignment, so I think that is why I leaked.

[MCRider]

It could have leaked for a completely unrelated reason as well. Those 4 bolts are not near any oil source of consequence, unlike the pucks, cam bearing studs, or oil return passages.

[MCRider]

It probably would have been OK but now you will sleep better.

Yes, and sleep, literally and metaphorically, is important.

[winkster2005]

When I was trying to figure out if the broken bolt would be an issue The main thing I thought might hapen is a leak since theres nothing on the outside of the head to keep the head gasket from blowing out the side.