Board index Flathead Power-Technical Questions, Answers, and Suggestions 45 Flatties WLA head bolt torque

WLA head bolt torque

Moderators: Curt!, Pa

Post Fri Mar 05, 2010 7:27 pm

Posts: 186
Hello all; I'm just about to do the first 500 mile service on my 45 flathead. Just wondering, is there a need to re-torque down the heads. There is no leakage any where, and if its not broke, I like to leave it alone. Page 241 of Bruce Palmers book states 60-65 ft/lbs. Nothing mentioned in the military manual. Seams a lot to me. What are your thoughts on this.
I have standard #5 low compression WLA alloy heads.
Regards Keith Atkinson

Post Fri Mar 05, 2010 10:24 pm

Posts: 745
Location: Pa. , USA
Hi Kieth, did you record the torque setting at assembly ? that way you can see the difference if any and re-torque to that setting. If you are using head gaskets they should be re-torqued, 60-65 lbs is correct but only if you have good threads and not alot of slop, if threads are worn 50-55 lbs is adequate IMO , Tim
Vintage roadracing, Class C, AHRMA # 335

Post Fri Mar 05, 2010 11:43 pm

Posts: 186
Thanks for the reply. No! I didn't record the tension when I assembled the engine. My engines are dead stock WLA, so I am using solid copper gaskets. I might go with the 50-55 figure. My head bolts are originals, not repro. Iv'e made up 6 inch long extension to fit my torque wrench, so that I can get at the bolts without removing the tanks. I have to study the math for the extension calculations. Most web sites quote lbs/inch, not foot/lbs. 60/65 Foot/lbs, seams a lot, considering M20's engines are only 28/30 ft/lbs.
Keith Atkinson

Post Sat Mar 06, 2010 1:16 am

Posts: 1604
I would take the tanks off, and get the torque spanner in the proper position. Head bolt torque is important and cracked cylinder heads are expensive and time-consuming.
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Sat Mar 06, 2010 6:53 am
Pa Site Admin

Posts: 5543
Location: Ohio USA

The official Harley Davidson 1959-73 service manual states torque at 65 ft. lbs.. Pa

Post Sat Mar 06, 2010 2:01 pm

Posts: 186
As always. Thanks Pa

Post Sat Mar 06, 2010 2:02 pm

Posts: 2677
Location: Los Angeles, CA
Pa wrote:
The official Harley Davidson 1959-73 service manual states torque at 65 ft. lbs.. Pa

Is that the same for aluminum heads PA?

Post Sat Mar 06, 2010 9:11 pm
Pa Site Admin

Posts: 5543
Location: Ohio USA

Don't know why they would not note a different torque for the iron heads Chris. My factory service manuals, 1959-73 and 1959-68, both use the same torque spec. The manuals do not suggest a different spec for a different head material. These shop manuals would have been used by dealer repair personel. I've been using the 65 spec and I have not cracked any heads yet...knock on wood. Pa

Post Sat Mar 06, 2010 10:00 pm

Posts: 54
Location: Ontario, Canada
the only flathead 45's produced between 59-73 were servicars
and they all came with cast iron heads.

I torque my 45's aluminum heads to 55 lbs.

Post Sat Mar 06, 2010 11:39 pm

Posts: 975
Location: Markt Einersheim, Germany

Check this:


I posted this out of one of our manuals at work.


Post Sun Mar 07, 2010 7:15 am
Pa Site Admin

Posts: 5543
Location: Ohio USA

Yeah.... I'm very lucky I have not cracked any heads. Wonder how many heads dealership mechanics have cracked ? I ask this because the service manuals show aluminum heads in their illustrations, right next to the 65 ft. lb. torque spec. Chris got me thinking about the iron over the aluminum so I went through all of my 45 literature. Oddly, The only other reference I could find came from the 1943 Motorcycle mechanics Handbook / The Armored School / Motorcycle Department, Fort Knox, KY.. On Page 20 of this book, it calls for "approximately" 40 ft. lb.. This number sounds a bit to loose to me but less does sound more logical. Aluminum expands under heat much more than iron. This expanion should create a tighter seal at the head to cylinder surface, were as with iron, expansion would be barely noticable. The military service manuals leave the torque settings mainly up to feel. So would probably be more wiser to go loose than tight. It is easier and cheaper to re-torque or replace gaskets, than it is to replace heads or broken head bolts.

Post Sun Mar 07, 2010 12:26 pm

Posts: 575
Location: devon,england
hi guys, way i look at is ... standard h-d head bolt spanner. tighten until ur hand hurts ...obviously going oppersite bolts and working up from loose to snug ,quite tight ,tight ,very tight,hand hurts tight.
bloody hell aint like there is wet linners or water or oil or actually anything , 5:1 compression isnt going to blow out a gasket unless its not tight and tight is ft.
regards jib
Dude, check out that jibhead, he's crazy. Hasn't been sober for 40 years

Post Sun Mar 07, 2010 3:05 pm

Posts: 54
Location: Ontario, Canada
When I was a lad my father tought me that tight is tight
and to tight is broken.
I will often tighten a part as the service manual describes it
as evenly tight
and then take a torque wrench and see were it sits
and then adopt that # ft lbs as my spec.
If no issues occure thats the torque spec for next time.

Post Sun Mar 07, 2010 6:35 pm

Posts: 49
If the head is attached by 7/16" diameter head bolts, I still recommend 60-65 ft-lbs torque, regardless if the head is iron or aluminum, . While the Ft. Knox book suggests a 40 ft-lb setting for aluminum heads, the entire sentence reads "The head bolts are 3/8 inch in diameter and opposite bolts should be drawn up with a torque wrench to approximately 40 foot pounds." The 40 ft-lbs quoted is for 3/8" diameter bolts or, to be more precise, for the 3/8" diameter studs that were used on 1950 and earlier iron head 45 motors and which were used by the US Army prior to 1940.

As to cracking a head, personally I have never cracked a head, iron or aluminum, using the 65 ft-lb setting and a criss-cross torque pattern. As to pulling the threads from a bad hole, I'd rather the threads pull when I am rebuilding a motor than later when it is on the road. A heck of a lot easier to repair, although a pain, when you're in your shop with all of your tools. As it stands, if I am rebuilding a motor and the threads are visibly bad or questionable, I am going to repair the threads before the barrel is installed.

The real concern in torqueing heads is that all the bolts are drawn up evenly using a criss-cross pattern. The criss-cross pattern will prevent warpage of the head and improper stretching of the gasket. The proper torque will prevent a loose bolt or two from a causing a blow head gasket and/or a warped head. Aluminum heads warp more easily than do iron heads.

Post Sun Mar 07, 2010 9:28 pm
Pa Site Admin

Posts: 5543
Location: Ohio USA

Thank you Bruce. That definately sets my mind at ease. :D Pa

Post Mon Mar 08, 2010 6:36 am

Posts: 186
I spoke with several fellows at work. Qualified diesel and automotive mechanics for example.
Advised to follow the criss cross patten when torqueing up.

Use lubrication on the threads. Never seize, copper coat. Grease.
Not too much though.
No problems with giving false tension.

Don't puss around while tightening the bolt. Slow but direct, until the torque wrench clicks.
Thread stretch takes over if done too carefully.

Go up in increments.

Interesting to hear for sure, but will follow the Harley Davidson advise first.

If the bolt feels mushy, its obviously pulling the thread.

My heads don't leak, so might just go with 50/55 ft/lbs for the first 500 mile service, and see how that goes.


Post Wed Apr 10, 2013 4:55 pm

Posts: 1
I like to tighten head bolts 1/2 turn before they break

Post Wed Apr 10, 2013 7:38 pm

Posts: 1604
I would have thought that 50-55 ft/lb was plenty for a copper gasket and alloy head. Bruce Palmers comments re even tightening in a regular pattern are very much to the point. I've often felt that the well-known problems with Triumph heads were related in art, to neglect f this by back-yard mechanics in a time when torque spanner s were rare.
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Thu Apr 11, 2013 11:32 am

Posts: 111
and make sure that none of your bolts aren't bottoming out.

Post Thu Apr 11, 2013 11:34 am

Posts: 111
make sure your bolts ( ARE NOT ) bottoming out.


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