The Stovebolt Site Forums The Shop Area Engine Shop Cyl Hd bolt identification.

Yesterday, I spent some time in chasing out the threads in my engine block and went on to cleaning up the head bolt threads. I have a 55 235 and feel pretty confident that they should all be grade 8. While handling one of the shorter bolts, I noticed it was grade 5. So, I went back over all the rest and found that I could not identify most Can some one help. What I found follows:

All of the long bolts were marked similarly - the heads were marked with 2 concentric circles. I suspect that these are original, and there fore grade 8.

5 short had 2 concentric circles and the letter F.

1 short had just the concentric circles

2 short are grade 5 (Biz bag!)

1 short was grade 8 with the letter F

1 short I guess was grade 7 - 5 radial lines, but they were not spaced equally around the bolt.

V
Bob

Grade 8 is probably right. 1/2-13 grade 8 torque value is listed as 80 and 90 for 1/2-20. The shop manual specifies 90-95 ft. Pounds for the factory head bolts so I would think grade 8 would be in the ballpark..

That being said, and Just my opinion here, I would not mess around with standard grade 8 bolts. First, if you look closely at the factory headbolts, they are a shouldered bolt. A standard grade 8 will not and the engineers specified a shouldered bolt so I actually think used headbolts would be a better call. I have built about 30 235/261 motors over the years, always reused the headbolts. No failures. Who knows where the grade 8 you are buying was manufactured, or whether it will in fact hold up to the correct torque, or will properly locate the head (remember, no dowel pins).

I will take a look at a set a spare head bolts (55-57] and see what the head markings look like.

So I looked, Couple of different head markings, circle with a raised B, circle with a plain f.