Cylinder head

Just wondering. Do you have a couple of torque wrenches? The manual should have the specs for most bolts, but even then it's a good idea to reference the general bolt tightening chart in the manual for comparison. Also, some bolts should be tightened to INCH-lbs. It's also a good idea to stop & think before tightening anything.

martin_csr wrote: Just wondering. Do you have a couple of torque wrenches? The manual should have the specs for most bolts, but even then it's a good idea to reference the general bolt tightening chart in the manual for comparison. Also, some bolts should be tightened to INCH-lbs. It's also a good idea to stop & think before tightening anything.

Agree! I'll never understand someone tightening up a bolt until something breaks when if one follows the torque specs that will not happen. :blink: Ed

650ed wrote:
Agree! I'll never understand someone tightening up a bolt until something breaks when if one follows the torque specs that will not happen. :blink: Ed

Thoes stupid stretch bolts down inside the cam chain area will snap before reaching factory recommended torque. Be careful with thoes.

I do have a torque wrench/owners manual and was just about to torque when snap.
Only one so it was prolly on its way out is my guess.

Never had a bolt break when torqued to specs. These old heads suffer from weakened metal and you typically pull the threads out getting close to torque specs. The CORRECT bolts torqued to the CORRECT specs don't break -- unless the bolt was previously overstretched. They are engineered to withstand more than that. May get a cross thread or corroded hole jamming the bolt going in, but a good bolt still will not break until over torqued.

VTEC wrote: Never had a bolt break when torqued to specs. These old heads suffer from weakened metal and you typically pull the threads out getting close to torque specs. The CORRECT bolts torqued to the CORRECT specs don't break -- unless the bolt was previously overstretched. They are engineered to withstand more than that. May get a cross thread or corroded hole jamming the bolt going in, but a good bolt still will not break until over torqued.

Incorrect.

These are stretch bolts that are supposed to be torqued to 22 ft-lbs, but if you try they will snap.

Nessism wrote:

VTEC wrote: Never had a bolt break when torqued to specs. These old heads suffer from weakened metal and you typically pull the threads out getting close to torque specs. The CORRECT bolts torqued to the CORRECT specs don't break -- unless the bolt was previously overstretched. They are engineered to withstand more than that. May get a cross thread or corroded hole jamming the bolt going in, but a good bolt still will not break until over torqued.

Incorrect.

These are stretch bolts that are supposed to be torqued to 22 ft-lbs, but if you try they will snap.

I've never installed one of those stretch bolts, but I was told that they only snap when you re-use them. They're designed to stretch and keep tension so that they don't need to be re-torqued when the rest of the accessible bolts are.

Whatever the case, they really don't need to be torqued much. My kz750 had a leak at the front of the block when I got it, so I replaced the head gasket and found that the previous owner had obviously broken that bolt, removed it, and used a different, slightly shorter bolt and stripped the threads in the block. I thought the bolt just wasn't tightened so didn't realize until reassembly, so I just measured the depth of the hole and got a bolt as long as I could without bottoming out so it would reach the remaining thread. I tightened it until it was 'snug' - perhaps 8-10ft-lbs. No leaks.

Regarding this entire thread - which bolt snapped? The valve cover bolts can corrode into place and snap easy. Replace as best as you can, go easy on the torque, and use some anti-seize on the threads if you can. You could probably get away with a missing bolt here, but use some sealant.

The camshaft cap bolts snap easy enough too, sometime when taking them out. They just need to be replaced, if you get some grade 8 bolts and torque them to spec they won't break again. If the hole is too damaged here, I'd be included to use a helicoil.

If it's a head stud, that's mounted to the block, so it's a head-off job to helicoil the block.

Nessism wrote:

VTEC wrote: Never had a bolt break when torqued to specs. These old heads suffer from weakened metal and you typically pull the threads out getting close to torque specs. The CORRECT bolts torqued to the CORRECT specs don't break -- unless the bolt was previously overstretched. They are engineered to withstand more than that. May get a cross thread or corroded hole jamming the bolt going in, but a good bolt still will not break until over torqued.

Incorrect.

These are stretch bolts that are supposed to be torqued to 22 ft-lbs, but if you try they will snap.

I'm referring to an excessively stretched bolt. Every bolt normally stretches when torqued, That's how it keeps the component held down tight. An overly stretched bolt is typically over- torqued or was subject to extreme heat. Many service manuals give specifications (mostly for head bolts) to measure the distance between threads to determine if the bolt was over-stretched and should be discarded. If you're saying the correct undamaged bolt broke when applying the correct torque, it's either an uncommon factory defect, or you're missing something.

VTEC wrote:

Nessism wrote:

VTEC wrote: Never had a bolt break when torqued to specs. These old heads suffer from weakened metal and you typically pull the threads out getting close to torque specs. The CORRECT bolts torqued to the CORRECT specs don't break -- unless the bolt was previously overstretched. They are engineered to withstand more than that. May get a cross thread or corroded hole jamming the bolt going in, but a good bolt still will not break until over torqued.

Incorrect.

These are stretch bolts that are supposed to be torqued to 22 ft-lbs, but if you try they will snap.

I'm referring to an excessively stretched bolt. Every bolt normally stretches when torqued, That's how it keeps the component held down tight. An overly stretched bolt is typically over- torqued or was subject to extreme heat. Many service manuals give specifications (mostly for head bolts) to measure the distance between threads to determine if the bolt was over-stretched and should be discarded. If you're saying the correct undamaged bolt broke when applying the correct torque, it's either an uncommon factory defect, or you're missing something.

These particular bolts that appear at the front and back of the cam on these engines are torque-to-yeild bolts . The manuals won't give measurements to determine if they have been over-stretched, because if they have been used once, then they need to be replaced. They're designed to deform permanently under the specified torque.

I've personally not broken one of these bolts, but I wouldn't be surprised if they do fail in 'normal' circumstances. If you put a little oil on the thread of any TTY bolt and torque it up, it will almost always break. With clean undamaged threads and surfaces, and a new bolt they should be OK. But when working on a 40yo bike in your garage, that's not usually the case, there doesn't need to be much deviation to break one. And since they just don't actually need to be very tight, it's probably best to go easy on them.

I suspect the 22 ft-lbs spec is a mistake. Not the first time KHI made that error.

If you look at the general spec page for 8 mm bolts they specify 12 to 16 ft-lbs for coarse thread and a bit lower for fine thread. By the looks of the bolt, if you over torque it I think it would fail where the thread meets the neck down portion. That's where the greatest stress exists.

My torque wrench(s) are made by Precision Instruments with Snap-On branding. High quality stuff.

The bolts in question started to yield at something like 18 ft-lbs (can't remember exact number.) I was turning the wrench but the dial wouldn't go any higher so I stopped. Just another example where you have to use judgement, not just trust the torque wrench.

Nessism wrote: My torque wrench(s) are made by Precision Instruments with Snap-On branding. High quality stuff.

The bolts in question started to yield at something like 18 ft-lbs (can't remember exact number.) I was turning the wrench but the dial wouldn't go any higher so I stopped. Just another example where you have to use judgement, not just trust the torque wrench.

Thank you. Now I understand what torque to yeild mean. You need a dial type torque wrench. All I have ever owned were click type. Beyond the old school swing arm pointer type sold at sears 100 years ago that I only trusted to torque lawnmower heads. Never understood how you torque to yeild with the click type wrench. I get it now. With a good dial wrench you watch the dial and when the value stops climbing that is the Torgue to yield value...

Another learning opportunity. I love the KZR school!!!