Head bolt torque specs for '31 Chrysler Straight 8

[Gunsmoke]

Simple question today, what is recommended torque for fitting head on a '31 CD8 Chrysler engine (8cyl). I have a new head gasket and have cleaned the threads on all 27 head studs and secured them tightly in the block. I also note there were no washers on the head when I removed the nuts 3 weeks ago. Anyone know if they used plain washers or did nuts just go direct on block? I have the pattern for bolt tightening. Any other suggestions?

[Spinneyhill]

Torque wrenches didn't come into use until the mid to late '30s. In the absence of any information, use generic values for grade 2 bolts of that thread and diameter.

 

1947 MoToR's Manual says 52.5 to 57.5 pounds feet on cylinder head nuts on all Chryslers for 1935-51, including 8s.

Edited August 17, 2018 by Spinneyhill (see edit history)

[keiser31]

This may help....

[Gunsmoke]

Thanks K31, I have the sequence diagram. This chart appears to say Chrysler Corp all 1933-54 headbolts 65-70 ft/lbs. It says Chrysler 6 1924-32 60-65 ft lbs. So no mention is specifically made of '31 8 cyl cars. As car is likely to be largely a Sunday driver, I'm inclined to go at 60-62 ft/lbs, and after a few drives re-check to see everything is still tight. I have 3 different engines here, this engine came with regular 3/4 hexagon head nuts, no washers. A second head from a '31 Deluxe CD8 car had 5/8" acorn nuts with thin stainless steel washers, and I plan to use these. BTW, 2 of the head bolts also secured the "Town&Country" horn bracket (3/16" thick steel with recessed holes for head nuts), based on it's thick base (about 3/32" bearing surface), I will likely use a 3/4 regular hexagonal nut there and no washers.

[c49er]

Studs and nuts are generally torqued less than head bolts.

This because the bolts are course threads into the block.

The studs are fine thread at the top end with the matching fine thread nuts.

[Spinneyhill]

Just ensure the cap or acorn nuts don't bottom out before they reach torque. You will break the stud if it does. That is why washers were used under them.

[Carsnz123]

I always laugh at the factory torque specs for Bentley 4 1/4 engines. "An experienced technician with a 6" wrench." They're a whole lot of 5/16 studs so you don't need to crank them up much. 

 

/not very helpful in this case 

[Gunsmoke]

In my above August 17 post I mentioned that I was going to re-use the acorn nuts and stainless steel washers that came on one of the heads. Getting ready to proceed this week, an engine re-fitter friend cautioned me to never use stainless steel washers on a head, they are too soft, will distort under torque and gradually original torque setting will be lost. So I bought some grade 8 hard 3/8" washers and re-drilled the center holes (were 13/32) to 7/16" so they are a snug fit over the 7/16" studs, but not too large overall compared to the 5/8" hex nuts. So many lessons to learn, this one being for head torque situations always use "hard washers"!

[Spinneyhill]

3 hours ago, Gunsmoke said:

So many lessons to learn

 

Also, with the washer on, make sure the length of thread visible on the stud is sufficiently less than the depth of the acorn nut that the nut doesn't bottom on the end of the stud. You will break the stud before you reach torque. I know this because of experience on a motorcycle when I was .... a while ago.

[Spinneyhill]

On 8/19/2018 at 4:17 AM, c49er said:

Studs and nuts are generally torqued less than head bolts.

This because the bolts are course threads into the block.

The studs are fine thread at the top end with the matching fine thread nuts.

Um, the charts show a higher torque for fine threads compared to course threads. e.g. 7/16-14 are 32 ft.lb while 7/16-20 are 36 ft.lb.

[Gunsmoke]

Yes Spinneyhill, I checked acorn depth to confirm lots of room for stud. These are 7/16" fine thread and about 60 ft lbs should do. Today I made a new set of plug wires using the old ones as a pattern, they fit in a nice wiring loom, makes for a neat arrangement.

[ply33]

Don't know but I suspect the acorn nuts were somebody's attempt to dress up the engine. Generally on Chrysler built vehicles of that era I only seen nuts with no washers. But I have absolutely no documentation from that era to back up my suspicions.

[Spinneyhill]

3 hours ago, Gunsmoke said:

These are 7/16" fine thread and about 60 ft lbs should do

My chart shows 55 ft.lbs for 7/16-20 Grade 5 dry bolts. I think you might be a bit optimistic assuming they and especially the block are that good.

Edited September 16, 2018 by Spinneyhill (see edit history)

[c49er]

7 hours ago, Spinneyhill said:

Um, the charts show a higher torque for fine threads compared to course threads. e.g. 7/16-14 are 32 ft.lb while 7/16-20 are 36 ft.lb.

I  use the values specified in the factory Chrysler,Dodge,DeSoto and Plymouth shop manuals when working on these MoPar cars...

Head studs with nuts are a lower torque value as shown on the six engines and also the same on the eights if studs are used.

On the eights

[Spinneyhill]

4 minutes ago, c49er said:

I  use the values specified in the factory Chrysler,Dodge,DeSoto and Plymouth shop manuals

A very good resource.

 

But was the metallurgy the same in 1941 as it was in 1931? I suppose that is the owner's or mechanics choice.

 

These numbers indicate studs equivalent to Grade 5 bolts and the block being strong enough to sustain that load.

Edited September 16, 2018 by Spinneyhill (see edit history)

[c49er]

I will say this...

I know a person who has a C2 Airflow. .

It had the 323 Straight 8... he torqued the head nuts to 70 lbs.( 7/16" X 20 studs and nuts)... head replacement...

On the middle to rear drivers side of the block slightly below the studs  a 3" long crack appeared a couple weeks later.

The over tightened studs pulled up the top deck of the block.

The block since has been "Lock-N-Stitched and now is fine.

I'd be careful especially on the old engines so as not to over stress the castings... JMO.?

 

[Spinneyhill]

Yes. The other thing is that there is probably not as much iron as there was - corrosion of the water jacket will see to that.

[Gunsmoke]

Thanks for the further advice, will go for 50-55 ft lbs and see how things go. Don't plan to button it up for another few days.

[c49er]

I'd re-torque again... hot.

[Spinneyhill]

10 hours ago, Gunsmoke said:

Thanks for the further advice, will go for 50-55 ft lbs and see how things go.

Be careful! I wouldn't go far past the grade 2 bolt spec. unless I was sure the bolts and block are better than that.

 

Poor @RichBad may be showing the results of over-tightening on his Dodge Brothers engine.

 

[c49er]

I'd say go maybe less after reading about@RichBad and his woe's too!

[RichBad]

I only went to 35lbs (that assumes my wrench is correct which I’m going to get checked).  Also, I’d never do it hot (many a wise man has told me that and I tend to believe them).  If your wall thickness and thread depth is good you may be fine - in hindsight mine weren’t great (the Dodge engine isn’t that great for this to start with).

[c49er]

How about a cold re-torque? I've done that too.

The head on a flat head engine IMO should be carefully re-torqued after the initial run in..

All the MoPars I work on are all mid 30's up through the early 60's. I don't want leaks or cracks?

[Gunsmoke]

I've posted a note in the aforementioned post, such a dreadful outcome. RB did not indicate if block had been magna-fluxed for any cracks before refinishing, I was ready to go with a block this past spring until a magna-flux revealed minor cracks in water jacket above valve train (likely from freezing), an almost impossible spot to see and even harder to fix. Little wonder some people opt for modern engines eh! So I guess 35-40 ft/lbs is target for now, once engine is started up and run a couple of times, we will know if that is OK. A new head gasket, $50, a new block, priceless.

[RichBad]

I had my head crack tested and pressure tested.  That said, I think they may have done that before they removed the old head studs which could have stresses it?

 

i was told the process for the Dodge engines was to gradually tighten to 45, then let sit for a while to settle, re torque then start and run engine and allow to cool and then do a final torque to 45.  

[Spinneyhill]

4 hours ago, RichBad said:

i was told the process for the Dodge engines was to gradually tighten to 45, then let sit for a while to settle, re torque then start and run engine and allow to cool and then do a final torque to 45.  

 

Hmm. Half way between Grade 2 and Grade 5 recommendation. I wonder where that number originated, because it wasn't published by Dodge Brothers before 1934.

[RichBad]

28 minutes ago, Spinneyhill said:

 

Hmm. Half way between Grade 2 and Grade 5 recommendation. I wonder where that number originated, because it wasn't published by Dodge Brothers before 1934.

Someone with far more experience of Dodges than me and who has done many 100,000s of miles in them

[Gunsmoke]

I torqued the head on the CD8 yesterday, started in the correct sequence at 25 ft/lbs, then went to 40 and finished at 50 ft/lbs. Everything went well. I don't plan to start engine for a couple more weeks, at which time I may re-torque to 55. I have rebuilt fuel pump, water pump, gen, starter, cleaned oil pump, refitted distributor, made new set of plug wires, new plugs, as well as having refaced and lapped in the valves. Since engine internals looked excellent, have cleaned and replaced oil pan and oil sump screen, cleaned out the oil filter, and plan is to start engine as it is and see how it runs. I did clean out the water jacket (and flushed out the head) thru the frost plugs etc, putting new plugs back in tomorrow. Next steps are fitting manifolds and carb and connecting cooling hoses to rad.  

[Spinneyhill]

Do you really want to start it? You will fill it up with moisture and dirty oil then leave it for ? years while you do the rest of the car?

[Gunsmoke]

Before I proceed with a major rebuild of car, I want to judge whether the engine/transmission and rear end are relatively good as is (i.e. will be fine for a Sunday driver that gets 1000-1500 miles a year). So I will plan to back car out under it's own power, maybe run it up the street just using Ebrake as braking, going no faster than 10MPH,  and if everything seems fine, proceed accordingly. If something in drivetrain is faulty, again proceed accordingly. 

 

If a running engine is buttoned up tight, and gas drained from fuel system, I understand sitting for a couple of years is not an issue. I recently rebuilt a '31 straight 6 Chev, the engine had not been run for 42 years. I removed valve cover and cleaned up the OH valves, changed the fluids, cleaned up starter/generator and fuel pump, and the car started up like it had been running the day before. It still runs well 10 years later. The CD8 engine above I understand was last run about 50 years ago,  the internals were in perfect order, not a speck of corrosion on any cylinders, rods and crank well oiled, valve train well oiled, etc. I think the key to not getting moisture etc into a sitting engine is to ensure all air passages are properly sealed off, and keep in dry storage (a dehumidifier might work). If engine etc runs well, plan is to pull drive train (engine/trans/driveshaft) out, remove all miscellaneous parts (shocks, gas/brake lines, steering assermbly, etc) and send rolling chassis for sand blasting. Cheers

[Spinneyhill]

When before you shut it down, squirt a bit of oil down the carburetor to prevent stuck valves later. This works on my Dodge 8.