Sheared rocker arm assembly bolts - what grade replacement?

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hurley
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Sheared rocker arm assembly bolts - what grade replacement?

Post by hurley » Mon Apr 08, 2019 1:50 pm

Hello all,

Short version: what grade bolts should I use to replace the three off-center rocker arm assembly bolts?

I am toward the tail end of a Petros-style head gasket replacement. I decided to replace the exhaust valves and corresponding valve stem seals, which went fine, but when I went to reinstall the rocker arm assembly, I followed the torque sequence for the main five bolts, and accidentally torqued to 18 ft-lbs instead of 13 (because I misread the manual, mixing up ft-lbs and N-m). Then I went to torque the three remaining off-center bolts, but it didn't feel right; I could tell they weren't tightening properly. I switched to a ratchet instead of the torque wrench, and cautiously proceeded, and then eventually to a tiny 1/4 drive ratchet, not wanting to strip or break something.

Of course, my gut feeling was correct, and a bolt snapped. Fortunately, it didn't come completely apart, so I was able to back it out. I removed the other two, and noticed they were all "necked" from stretching, and the one that snapped had several cracks in the middle. I'm hopeful I didn't damage the aluminum threads since the bolts were evidently stretching to absorb the force.

So I did some digging in the manual and on the forum, but I can't find a torque value for those specific bolts, just the five main ones. I am also wondering what grade to use for replacements?

I'm thinking of keeping it under 9 ft-lbs when I install the replacement bolts, since that's the torque for the cam cap bolts, about which I found several people warning of their propensity to shear. Thoughts?

Thanks,
Matthew

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Petros
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Re: Sheared rocker arm assembly bolts - what grade replacement?

Post by Petros » Mon Apr 08, 2019 6:06 pm

bummer, I thought I read at one time they were 6 ft-lb bolts (those are the small bolts with the 10mm head, correct?). I usually hand tighten with my 1/4" drive socket set, too easy to over do it with 3/8 or larger socket set. an inch pound torque wrench would be more accurate, and easier to handle, but I do not have one.

I would think at least grade 3. I stripped one once, and put a coil insert into the head. that solved the problem with soft threads in the aluminum head, the thread insert is more durable and stronger, spreads the bolt load better, and will not wear out as easily from removal and replacement too often (I have removed it a lot of times in my car). I considered putting inserts into the rests of these bolt holes as a preemptive measure, but figured I could wait until I damage another one to that.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
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hurley
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Re: Sheared rocker arm assembly bolts - what grade replacement?

Post by hurley » Mon Apr 08, 2019 6:30 pm

Thanks, Petros! They are indeed the small bolts with 10mm head. I actually have an in-lb torque wrench, so I'll be sure to use that, and I'll try 6 ft-lbs.

Edit: I looked up Grade 3 bolts, and found an image showing two radial tick marks on the head of the bolt, which is exactly what I saw on the damaged bolts I pulled. Funny, I hadn't been able to find any pictures showing just two tick marks yesterday when I was searching online, and I suspect I will only find Grade 2 or Grade 5 at the local hardware stores. I'll just go with Grade 5, or Grade 3 if they have it.

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Re: Sheared rocker arm assembly bolts - what grade replacement?

Post by teranfirbt » Sun Apr 14, 2019 1:27 pm

If you aren't getting OEM bolts, you'll want grade 10.9. These are the metric equivalent of SAE grade 8 and should be torqued to 13 N-M (113 in-lb in 'merican).
If you're having trouble finding these locally, belmetric.com will have what you need.

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