I am looking for some bolts and having no luck finding them. They are 5/16-18 x 3/4 Grade 5 and the head is flat with no markings. They are from the Jetfire but not GM bolts. They are from the AiResearch turbo and would have been supplied from them. Any ideas where to find them? I looked through the AMK fastener site and found two that were to small and to long. Nothing the size I need.

Any ideas? I really do not want to reuse the old ones because they are in the exhaust side and usually brake off when taking the turbo apart. I was just lucky to get these out.

 

I don't think you'll find them available without markings. The markings ensure that proper strength fasteners are used. You could.......
1. wrap the threads with cloth backed sandpaper,
2. chuck snuggly in a drill press, drill chuck,
3. hold a cloth backed sheet of sandpaper (grit side up) on drill press table
4. gently press the head of the bolt down to remove the markings.

 

I would be suspect that without a headstamp, the bolts are grade 5. There is a federal law that states all bolts have to have the manufacturers headstamp and that includes the grade rating. What makes you think they are grade 5 bolts?

 

I can't say for sure but as much force, heat and oil I was using to get them out I am sure grade 2 would have broke. They go into the turbine side of the turbo and gets as hot as the exhaust manifolds.

 

I did think about removing the markings of other bolts. I am about ready to send my bolts off to be re-coated so if I do that I need to get it done so I can include them to be re-coated. That or just live with the markings of another bolt.

 

stainless has no markings...sandblast and plate.they need anti seize or they break coming back off..

 

They may be something other than a normal Grade 5 bolt. The thought crosses my mind that they could be something special like an AISI H-13 or H-19 steel.

 

I wondered about that myself. Not really sure what they used but I know I was really bearing down on them. Once I got them to move the slightest amount I just went back and forth for a very long time as it worked the oil into the threads. The second day after soaking they came out. They look good but it worried me to reuse them.

I hate to do it but I have another really low hour original turbo that I am sure the bolts will come right out of. I may swap these bolts out for those and then worry about it when I rebuild that turbo.

 

On another note, They do not have a very high torque spec. I never knew it till I come across an AiResearch blueprint of the turbo but they are only torqued to between 100 - 150 inch lbs with locking tabs to keep them from backing off.

 

I'd do this.

I understand your attention to detail, and I appreciate it. Me personally, I view the correct spec bolt as more important than the markings or lack thereof, but I think you are going after OCA perfect here, so the stainless idea could work.

 

Stainless Steel bolts are in fact marked. I believe there is 5.4, 7.9, and 10.8 grades.

 

Are you sure these are not metric designation for torque specs? Every metric bolt I have is marked with these designations. I have stainless bolts that have grade markings and plain heads, as well as alloy bolts with grade markings.

 

I guess I am partially incorrect. Those are not Stainless Steel grades.
They ARE metric grades (strength). From reading on a Fastenal site, there is a standard and markings for Stainless steel.

 

From looking at the Fastenal site, a 5/16" torque spec is within the upper range of grade 2 range, as I read it. 100-150 in/lbs is actually 8.3 ft/lbs-12.5 ft/lbs.
I am wondering if ARP would be a good source of information and bolts for the on the subject.? Joe P. could certainly shed some light on the subject.
Lock tabs are mechanical "locks" to prevent backing off and have no relationship to the amount of torque on the bolt. It does cross my mind what/if grade markings were used in 1961 through 1963.when they built the turbo.

 

Most 5/16 bolts I see have a torque spec of closer to 20 Ft Lbs. All the other bolts on the turbo have some kind of markings. These 8 that go into the turbine housing (hot side) do not. I have used just plain grade 5 bolts before and will work fine, just like to have the flat unmarked heads. The more I have thought about it, I think I will just use the bolts from my low hour turbo and file down others for that turbo later.

 

More like "OCD" than OCA... For sure not worried about OCA, their standard is much lower than mine on the Jetfire model. There is a Jetfire that is converted from automatic to 4 speed, has a non 1962 color that is completely different than the color marked on the cowl tag, and many other things not "correct" on it and is a senior preservation car. There is a total of two people (maybe three) that would know these bolts were not correct if I used something else. It is my own OCD that is getting me here.

 

From a number of standpoints, bolts for high temperature joints must be carefully selected. Among the problems that can occur are

• gradual relaxation of stress (preload, or torque value)
• gradual elongation of the bolt, called creep
• different rates of expansion between the bolt and the flange can increase or decrease clamping force as the temperature changes, leading to leakage or breakage
• accelerated corrosion

In fastener terms, the bolts for the turbo scroll certainly reach high temperature and the engineers had to select carefully.

As my fellow Texan, edzolz, said, the lack of head markings on the bolt indicate Grade 2 or lower strength. The stated torque values are also very low, perhaps as a way of lessening relaxation and elongation.

A possible source of information would be to call the turbo manufacturer (if they are still in business) or any prominent turbo manufacturer. Ask to speak to technical service and ask about bolt selection. Tell them your interesting back story so they get drawn in and more willing to help. The tech service department will have access to the development engineers and, at a minimum, will be able to call you back with an answer.

Good luck. Keep us informed.

 

Excellent suggestion VC455 !!!!!!!!!! Also excellent information.

 

I have talked to some different turbo companies and so far everything I have ever talked to them about they say is really outdated and not willing to help. (can't imagine why a 1962 turbo would be outdated, lol) I even sent a shaft and impellers to a place to have the balance checked. When they got it they told me it was far to outdated for them to even check. The compressor wheel presses onto the shaft and they said that they have never seen anything like that in a turbo and had no way to take it back apart without affecting balance. They only spin 90,000 RPM so we just rebuild them without checking balance. If the bearings were good then the balance was likely ok.

The one place that seams to be willing to help has little time. I believe I am going to send him some parts and see if he can modify them to accept a new style carbon seal that would be more available.

 

I now believe you are correct about these being a grade 2 bolt. I just can't believe I did not brake them. I was looking as several from the hardware store and they do still make grade 2 with no head markings. As low as the torque is on them the only thing to worry about is long term rust. This car will never be driven enough or be in the weather enough to really have to worry about that. I think I am just going to get grade 2 bolts from the store and not worry about replating originals.

 

Bare steel bolts will rust quickly and they will need to be drilled out next time, even if you use high temperature anti-sieze.

Discuss with some platers and tell them you want to have a plating that will withstand 1700°.

If you can't get an answer, I would have the grade 2 bolts copper plated and then electroless nickel over copper. The copper eliminates pinholes and the nickel is great at high temperature. It isn't very expensive and will prevent rust.

I am amazed you can't find a turbo manufacturer to answer a simple question.

 

They are zinc coated from the store and I believe that is the same coating as the originals

 

Instead of new grade 2, if the old bolts are in good shape I would reuse them. The torque is very low, so not worried about stretch. They will probably last another lifetime.

 

Zinc melts at 780°. That is not the coating on the originals.

If you are not ready to try your own plating, use the originals as Eric suggested.

That will give you time to research the correct coating.

 

You guys are on it! I forgot that I got some factory photos when I was at the Heritage center. These are clearly black or at least a darker color than the zinc.

 

It's because the engineers that he has spoken to must not have any interest in old cars, or are so busy that they are overwhelmed with work. When I worked for GM SPO 20 years ago, we used to love getting calls that kept us away from the phones for a bit, trying to run down hard-to-find info for employees' old rides.

Keep trying, Eric. Eventually, they are going to pass your number over to someone whose interest will be piqued.