Head Bolt Lengths

WEll said Jim.


Gary Parsons

The original bolt lengths listed in the parts list are for the original heads, with original gaskets and original washers. These days very few people are using original heads and original washers. No one is using an original head gasket. Since there have been several different "new" heads made over the years, the best way to determine the length of bolts you need are to measure. First measure the washers you are using - Check them all. Measure the thickness of the head at the bolt holes. There are three different thickness at the bolt holes. Measure the thickness of the head gasket you are using.

Last is the thread engagement - as a general rule the minimum thread engagement should be 7/16". Check all the holes where the bolt may bottom out to see how much you have from the surface of the block to the bottom of the hole. Make sure you leave a gap and also allow for gasket crush.

The bolt length (blot length is measured from the bottom of the head) you need will be the sum of the washer, head thickness, gasket thickness and thread engagement.

Lastly make sure the threads in the block are good. If there are any questions put threaded inserts in the block.

I wrote "I have never seen" not never. I can't. I am talking about bolts in general, and don't now about 810/12 Cords in particular.
CORDiallyMike

If the head is NEVER included, how do you explain that the in the pricelist document the lengths are longer?

I have never seen bolt lengths include the heads.
CORDiallyMike

Thanks for the wakeup Tom. I sadly missed your comments in posting. I usually am not missing anything in a members post.


Gary Parsons

I appreciate people pointing out that the wrong head bolt lengths can damage the block. I already knew that; that's why I'm asking the question. I was mystified by the question of where I got the lengths in my original question when I started by stating just that. But just to further clarify that, I've attached the cover of the manual and the conflicting source pages. I've also included a drawing showing my measurements of the depth of the holes in my heads. What I would really appreciate is someone measuring one of the longest stock head bolt they have on hand and reporting the result here. Thank you in advance.

To Tom in San Diego.
It's been too many years to recall the correct lengths of the Cord head bolts, but let me add a major caution. Cord blocks have been ruined by using bolts extending too far and crushing the inner casting of the block on the far side of the water cavity. Different lengths are used depending on the thickness of the head. E.g. original, Bohnalite, or newly cast. This is in addition to the different lengths depending on what row they are in on the head. Some of the current Cord club members will know. So before putting a bolt in, check the depth of clearance for whatever bolt you use. Tom Hartz

There is a danger sometimes speculating on a answer. It is VERY EASY to crack the block if the head bolts are too long, especially on the top row of bolts and the extreme right and left bolts on that row. Also original heads or newer thicker replacement heads have different length of bolts needed.

Questions.... Where are you finding these new bolt lengths? I believe Stan in Wellington Kansas has the bolts needed for new head bolts. But they have the new strenght marks on the heads and they are NOT as thick on the heax as the original head bolts are. ALL these head bolts enter the water jacket. So I'm thinking length is not important. But please wait around for others better in the know than me.


Gary Parsons

In the Cord Service Manual, document RD172-11-35 gives the three head bolt lengths as (smallest to biggest) 1+5/16, 1+21/32 and 2+1/32 while the parts price list gives the three lengths as 1+9/16, 1+13/16 and 2+5/32. Confusingly, they differ by 1/4, 5/32 and 1/4 respectively. Since the price list lengths are all bigger, it would seem those lengths include the bolt head. Sound Correct? If someone has a stock head bolt over 2", measuring it would give the definitive answer. Thanks, Tom in San Diego.

On any bolt, the thickness of the head is never included in the measured length. Hope this helps you find what you are looking for. I'm located about 80 miles north of you. If you need me to look at something I can drive down most any time.
Gary Parsons

As we know the stock head bolts have unusually thick heads. They are expensive but can be replaced with easily available bolts if they are of sufficient strength. The original look can be approximated if the strength pattern on the heads are carefully machined off and they are trimmed to the correct lengths listed in the manual. My question is: Do the lengths listed in the manual include the head or are these lengths just for the shaft/threaded part? And if the lengths include the heads, how thick are the stock heads?
Thanks,
Tom in San Diego