FYI: Head bolt depth misconceptions.

[Anonymous]

Greetings guys,

When asking questions about my head rebuild & a few associated problems I had in the initial stages, several people advised on using washers with the head bolts if the head had been resurfaced to prevent the bolts from bottoming out. Wondering if this is a possible point of concern & feeling that Ford would not likely use a bolt the same length as the hole depth, I did some measuring.

The experiment:
Performed on a 170. With the head gasket & head on, I measured the hole depth. Then, I measured the bolt length. (Whew! this scientific stuff is time consuming;-)

The findings:
The head bolts were an average of 1/2" shorter than the holes. The obvious exceptions being the 2 that have no bottom because they hit the water channels.

Conclusion:
Unless you remove more than 1/2" from your head, you probably don't need washers. I would imagine a 144 & a 200 would have the same results.

Disclaimer:
Always measure before skipping washers. The previous owner may have replaced the bolts with something slightly longer at some point.

Hope this saves somebody a trip to the hardware store looking for 7/16" washers. Most places don't have them. Napa does.

Happy trails,
David K
63 Comet
seattle

 

[Junk-Falcon]

pppp

 

[addo]

A grade 8 hardened washer is only a few cents when you can find them. I advocate them for a few reasons: As you say yourself, the bolts may have been changed, also, the runout of the thread can not be accurately predicted in the hole bottom. Then, there's the issue of the hard, smooth surface to evenly load up, meaning more accurate torquing.

On an aggregate basis, I think you'd log more cases of bolts breaking than bottoming out, though.

Adam.

 

[CZLN6]

Howdy David & All:

We have found similiar results as yours in many 200 blocks, but not all. We have also found variances in supposedly stock bolt lengths as well.

I am an advocate of using washer for many reasons, already listed, plus, consider a few more variables;
*junk/crud/rust/assembly oil accumulated in the hole bottom.
*less than precise, quality machining from the factory.
*Don't assume that machined dimensions are the same on 144/170/200/250.

I decked a '72 250 block .070" and milled a '78 head .030" and assembled with a FelPro composite gasket @ .050" compressed thickness. That's a total of .100" less, but add back about .025" for the additional gasket thickness for .075" less- Bolts bottomed out.

In all cases, measure to be certain, clean all bolt holes and threads before assembly, use only a small amount of thread lube, and we still recommend using head bolt washers even if you don't need them for depth clearance.

Thanks for sharing your research David. It is always best to check for yourself and to know what you have. Using washers, or not, is your choice.

Adios, David

 

[Anonymous]

Hi Guys,
Yes, I believe, as stated, that everyone should measure what the holes & bolts are & decide if you need washers. I definitely agree that they may be helpful in spreading the load more evenly around the hole. Looks cleaner too.

Thanks for the extra input.

David K
63 Comet
Seattle

 

[twentyover]

Dave- did you measure the depth of the hole or the depth of the full thread? usually, they'll use a plug or starting tap, and look tohave a clearnce between the end of the tap and bottom of the hole- if no, you break a tap when it bottoms.

To measure the depth of full thread, measure the bolt length then run it down the hole until it starts to tighten up. Measure the distance from the casket surface to the bottom of the bolt head and subtract that value from the bolt length. Thid value is the legth of the tapped hole.

You can always run a bottoming tap down a hole to add additional thread length.

 

[Anonymous]

To measure the depth of full thread, measure the bolt length then run it down the hole until it starts to tighten up. Measure the distance from the casket surface to the bottom of the bolt head and subtract that value from the bolt length. Thid value is the legth of the tapped hole.

Here's an old trick my pop showed me and I've used it on every rebuild I've done. After cleaning the threads and running a tap, simply run each bolt down snug in it's respective hole before putting the head back on. Mark the bolt with a marker where it intersects the deck. now remove the bolt, put it in it's appropriate head location and see if the mark shows through the bottom of the head. If it does you have a clearance issue requiring washers, But as david says "we still recommend using head bolt washers even if you don't need them for depth clearance."