Torque specs crank?

[fsnooks]

What are the torque specs for the crank nuts?

[keiser31]

For a 1926 DB?

[fsnooks]

yes.

[Spinneyhill]

There probably weren't any.

[R.White]

BY coincidence I have just finished this job on my '26 touring.    I would be inclined to tighten "just enough and no more" on these bolts. There is a temptation to make the castle nuts line up with the hole in the bolts when fitting the split pins.  I don't think this is a good idea. Try using another nut; that sometimes works.  As a last resort you could  shave a little bit off the nut or use a very slightly smaller split pin - but don't say I said so.

 

The larger main bearing nuts are easier to align because there are two holes in the studs so you get two chances to line up the holes. 

 

A previous owner had obviously over tightened the big end bolts as the threads had begun to strip.     As I was having my engine overhauled I asked the machinist to make me some new  bolts but unfortunately he suffered a motorbike accident and was unable to get them done.  I then had an idea.  By re using the original bolts but putting a reasonably meaty flat washer under the nut I was able to take up the big ends on an undamaged part of the thread.  Again, I have not done up the nuts with too much force.  

 

 

[Spinneyhill]

Based on Ray's experience, then, if I were to use a torque wrench, I would use less than the generic figures for Grade 2 bolts of size and thread you have.

 

These days, there seems to be a move towards using thread lock cyanoacrylate on these nuts and dispense with the split pin....shudder!  They must be totally clean and dry for this to have any chance of working. Just make sure the thread lock has gap filling properties coz those old threads are probably not too flash any more.

[R.White]

I personally would never rely on thread lock alone. Some people say it is O.K. to use Nylock nuts in an engine. They have a max. operating temperature of 250F. 

 

 

   

Edited May 6, 2017 by R.White (see edit history)

[cahartley]

When using a torque wrench with slotted nuts the rule is if the slot doesn't line up with a hole to back it off to the nearest slot......NEVER tighten more.

[Guest]

I have always removed the nut and filed it so that when proper torque was reached the slot lined up.  A Packard mechanic told me this was the correct way.  I don't know if it is correct or not but it has never failed me.

[R.White]

6 hours ago, Tinindian said:

I have always removed the nut and filed it so that when proper torque was reached the slot lined up.  A Packard mechanic told me this was the correct way.  I don't know if it is correct or not but it has never failed me.

 

Yes, that is what an engineer told me quite recently.

 

 

[cahartley]

^ I have three friends who are engineers.

Without exception they over think everything....... 

When these engines were being assembled on the line I highly doubt anyone was filing nuts to coincide with torque specs.

There is always a range, not only in the specs, but also in the accuracy of the torque wrenches.

If one eight of a turn had a deleterious effect I think there wouldn't be an engine on the road that would have survived to this day....... 

[Spinneyhill]

I have read in shop manuals to go to the next hole for the pin = slightly tighter, except for things like bearing preloads. I agree with cahartley. The thought of thinning a nut frightens me. What if the previous three owners did it? It could become too thin to be done up to the torque you are attempting to use and pull through. And what a pain in the tripe farting about trying to get it just right. Nah, bad idea, IMO.

[R.White]

After I had tightened the big end bearing nuts to what I felt was tight enough, I checked with my torque wrench to ensure they were all the same and the wrench clicked at 45 Ft Lb. The mains are a larger size and seemed happy at 50Ft lbs.  

 

I have heard that you need to allow for a "crush" factor (where the shells sit very marginally proud of the rod and cap) to prevent them from rotating in use.  I would have thought the shims would have achieved this.

 

What experiences have you guys had of this practice? 

 

Ray.

[Spinneyhill]

The shells I have seen have a little tab pushed back on them to lock into a little slot in the cap, to prevent them turning. Surely, if the insert ends are proud the insert will sort of wrinkle when you crush it into the cap and you will have a locally (over) tight fit? You would see this on your plastigauge with variable clearance?

[R.White]

1 hour ago, Spinneyhill said:

The shells I have seen have a little tab pushed back on them to lock into a little slot in the cap, to prevent them turning. Surely, if the insert ends are proud the insert will sort of wrinkle when you crush it into the cap and you will have a locally (over) tight fit? You would see this on your plastigauge with variable clearance?

 

You may well be right.  I have not needed to mess about with mine as they are a snug fit and as they have shims between them I can't see how they can move anyway.  I just remember reading about it some time back.

 

 

[cahartley]

I just thought of another thing to consider.

Torque specs as relating to bearings aren't only for developing fastener strength but also function to retain the "roundness" of holes involved.

Excessive tightening is worse than not enough as it will cause the hole to become slightly out of round and/or stretch the fastener which can lead to failure.

Not a good thing when you are dealing with bearings....... 

[R.White]

One of the factors that determines the torque in reality is not so much the figures given but the condition of the threads.  Another, probably more importantly, is that there is a huge difference depending on whether the threads are lubricated or dry.  

[Douglas S]

Just starting to reassemble the engine, 1917 Dodge.

Breakaway torque specs were 75 ft lb on Connecting Rods. Front main was 110 ft lb while # 2 & 3 were 75 ft lb. I used 75 ft lb on all 3 mains and plasti gauged clearance readings were 0.003 - 0.004. Am I in the right ball park? 

[Mark Gregush]

On 5/6/2017 at 6:09 PM, cahartley said:

When using a torque wrench with slotted nuts the rule is if the slot doesn't line up with a hole to back it off to the nearest slot......NEVER tighten more.

Don't know where you got that rule, but you should never back off to line up with the hole on a torqued fitting. Or did you mean back way off and start over just bring the nut to where it lines up with the hole and slot? The best is to remove the nut and try another or as suggested above or take a little off the bottom and try again. 

Edited April 21 by Mark Gregush (see edit history)

[Mark Gregush]

17 hours ago, Douglas S said:

Just starting to reassemble the engine, 1917 Dodge.

Breakaway torque specs were 75 ft lb on Connecting Rods. Front main was 110 ft lb while # 2 & 3 were 75 ft lb. I used 75 ft lb on all 3 mains and plasti gauged clearance readings were 0.003 - 0.004. Am I in the right ball park? 

I would suggest 40 to 45 on the rods, 75-80 mains sounds about right for all three mains and .0015-.002 on the clearance for rods and mains.  

Edited April 21 by Mark Gregush (see edit history)

[nat]

The original torque specifications, (for the cylinder head), are "very tight".  

I usually use specs from 1940's and 1950s manuals for the same diameter, thread pitch and, (preferably), application.

There are lots of charts.  I'd be inclined to use the specs for grade 5 uncoated fasteners.

I'm not a big fan of Fastenal but here's their chart.

 

https://forum.esk8.news/t/fasteners-what-they-are-whats-in-your-kit/4664/42?page=3