sheared cam cap bolt
 

I posted the following on the main help forum, but wanted to see if any others had any of the same issues specifically with the 250 or have any comments.

"OK, I was reinstalling the cam shaft bearing cap & one of the bolts did not torque properly. I backed it out and the kawa bolt was stretched. I went to NAPA & got a new bolt and it kinda felt the same so I backed it out and it was OK.... so back in it went and it never seated properly either....

the bolt is sheared off even with the top of the head platform for the cam bearing cap.

How do I get it out & what should I do?

Try another bolt and use lower torque?
Drill it and tap it larger?

All the other bolts snugged down just fine. I was tightening to 8 ft-lbs.

Help. "

Personally I would take another 8mm bolt and grind the threaded end to a point and tig or mig weld it to the broken stud. That way your not drilling the broken stud exposing the open head/valves to debris/metal chips. The heat will expand the aluminum and the new bolts hex head can be wrenched out easily. Easy outs are another option but with the engine in the frame sometimes getting to the problem area is another factor.

The above repair is very easy with a tig welder, mig tends to be more messy but will do the trick.

After removing the broken bolt, use a bottoming tap in that hole to be sure the threads are okay.

Good Luck.

^^^^What he said. Weld, remove, tap.

Too bad.

You've got good tips as to getting the broken piece out.

Now as far as what happened, likely one of two things: either you were overtorquing the bolt (intentionally or not) or the bolt was too long for the hole (bottoming out). My guess is the latter.


To prevent it from happening again:

Verify that your torque wrench is calibrated correctly and that you are using the correct torque value out of the service manual. Do not use a lower torque value - the one in the manual will be correct. If you use a lower torque value, the bolt will not be preloaded sufficiently and will very likely come loose or break in service. Also, do not drill and tap it larger, absolutely no need for it, and likely to do more harm than good.

Verify that you have a bolt of the correct grade and length. Make sure you didn't swap bolts from different positions - sometimes the OEM will use different length fasteners in different holes - if you did a swap, the bolts you broke may have been too long, and you may also have a too short bolt in another hole, which is potential cause for another failure. More than anything verify that the bolt is not bottoming in the hole.

Verify that you didn't leave out any washers that may belong on the bolt, as this will have the same effect as making the bolt longer - maybe too long.

Verify that there are no debris in the bottom of the hole in the head that the bolt may bottom out on.

Verify that the threads in the head are tapped to sufficient depth.

Lutz is dead nutz on with the bolt being too long. I did the cam mod and found the bolts were two different lengths. The torque on these is only a hundred something inch pounds.

I have learned so much on this forum. The above two lessons go into the safe for future use. Thanks Lutz and RaceGass!

I place a nut over the broken bolt and weld that. Its easier. You can't weld the nut to the head because its aluminum.

Your cam shaft cap has 2 bolts that are longer, they go in the holes with the dowel pins. Proper torque by the book is 106 Inch pounds.

If the bolt was too long, then you have a short one in the wrong place too.

What is the # on the head of the bolt? 8.8 is similar to our grade 5 and 10.2 would be grade 8. If its just a 7 then its a butter bolt.

durielk, where ya located? I'll get it out for you.

David

Well more to the story, first off I am an idiot. I did not check the replacement bolt, going on the assumtion that the auto parts gave me the right threads... wrong. The replacement bolt must be seized in there, I am going to try to get it out this morning.

At this point, I figure there is a 50-50 chance the threads are trashed. Should I bore to the next size & tap or go helix coil? That bolt is the one with the rear right locating pin, which may be a problem.

If I need to go much bigger, I am thinking on taking the head back off & to a machine shop as the locating pin may need to be enlarged, alternatives to that:
Leave it out.
Enlarge the pin & bolt cutouts for it, have the machine shop make a new larger pin.
Have the machine shop install a small pin somewhere else not on the bolt, but since the cam does not have any "bearing or enclosing race", if the pin is off the bearing is out of alignment.

thanks

You need the dowel pin. The cam bearings were bored with those pins in place.

Take your time, remove the dowel to give more room to get the bolt out. IF the theads are wrong, the bolt twisted off because of it, Its going to be a little tough to get out. I would weld a nut to it first.

Next run a bottom tap in the hole to see if there are enough threads left.

IF it does come out and the threads are lunched, a helicoil Kit is the way to go in aluminum. (available at NAPA for about $50.00) It will keep center. No need to drill, just run the tap for the helicoil in the head slowly with some thread cutting oil for ALUMINUM. Brakleen will work great if you can't find anything else for cutting oil.

Unfortunately removing broken bolts is a part of my day job. I have helicoils in 20 or so sizes American and metric.

I had a honda SOHC 750 that pulled all the bolts out of the cam cap for one side of the engine while riding (2 cylinders). I put in helicoils on the road. Never had any more trouble.

David