TR2/3/3A Connecting Rod Locking Tab Deformation

I'm disassembling a TR3a engine for overhaul and discovered the locking tab washers appear to be deformed. Being new to Triumph engines, I wanted to make sure of what I am looking at. Also, would someone please direct me to a good engine disassembly, reassembly thread? The red book leaves a little to be desired for detail sometimes.
Thanks,
Steve Baker

Steve, here's a link to a good series of videos on TR3/4 engine rebuild, including degreeing the cam.

Regarding the locking tabs. My bet would be for the previous person to have caused that deformation when the bolts were tightened down.

From the direction they are deformed it's as if the rod bolts were actually loosening. All of the rods exhibit this.

mastaphixa said:

From the direction they are deformed it's as if the rod bolts were actually loosening. All of the rods exhibit this.

Click to expand...

Maybe the tabs were re-used? Ends bent down to remove the bolts, then tapped back up after bolts were torqued, but bolt heads ended up in slightly different rotation.

You should always build with new locking tabs, and they are cheap. It appears your PO re-used the tabs.

Here's a few documents that might help
https://drive.google.com/open?id=0B2H2NJt34OffN2FkZjI2NjktNWJiMy00YWExLWIyNjctOTYzNmI3OTg2ODM0

https://drive.google.com/open?id=0B2H2NJt34OffYTA1NTNmMGUtMTVjMy00NDEzLWJjN2YtNTc1OWRkNjE4MjY4

https://drive.google.com/open?id=0B2H2NJt34OffMWQ4N2EzZGQtNjc0Ny00YmE2LWFiN2UtZWYzMjNjNGFiYzY4

Personally, I've quit using locktabs altogether. Double check that the bolts aren't too long (I've never found any that are, but doesn't hurt to check), then lock them with oil resistant Loctite.

If you want to know why, pick up a copy of the book Carroll Smith wanted to call "Screw to Win". (Unfortunately, better known as "Nuts, Bolts, Fasteners, and Plumbing Handbook")

In accordance with Carroll, if you ditch the lock tabs, you should tighten to a bolt stretch value rather than a torque number.

CJD said:

In accordance with Carroll, if you ditch the lock tabs, you should tighten to a bolt stretch value rather than a torque number.

Click to expand...

Kind of hard to know what is. You might check this discussion:
https://www.britishcarforum.com/bcf/showthread.php?108883-ARP-Bolt-Torque-Specs
Tom

I've recently been trying to educate myself about bolts, how they loosen, and how to keep them tight. One result is that lock tabs really are not a good way to keep bolts tight, and you may be seeing an example of that. You can replace those bolts with the more modern TR4 stretch bolts, which I'd recommend. The following article is a little whimsical, but I think basically correct:

https://www.mogsouth.com/2018/05/10/keep-it-tight-grass-roots-motorsports-5-10-2018/

Thank you all for your input. I think I will order a set of TR4 rod bolts. Am I reading the Moss catalog correctly that part number 320-450 is $16.99. Is that a piece?

Yup. Check the "Where Used" tab, it says you need 8 of them.

Loctite is a bunch cheaper. And as I read it, all Carroll said is that measuring the stretch is a more accurate way of checking bolt tightness than using a torque wrench. There's nothing about it being "required" if you use Loctite instead of locktabs.

PS, a slight inaccuracy in the GRM article. Deformed thread locknuts are reasonably readily available, and not very expensive. I get mine at McMaster-Carr where a box of 50 3/8-24 in Grade 8 (equivalent) is $7.32. https://www.mcmaster.com/92501a430
A box of 100 is $9.22 at FastenerMart. https://www.fastenermart.com/NT163-2622.html

I use them a lot (they work worlds better than Nylocks); but obviously not on rod bolts.

I think the stretch bolts are about $9 at Rimmer; even with shipping, it should be cheaper. They ship really fast, too.

There are a number of effective locking washers in existence. One is called Nordlock; if you search around, you can find lots of types and the results of Junker tests, which show how effective they are.

As for me, I went with the stretch bolts. They are proven, and I don't want to risk my engine by experimenting with other things. I bought some 3/8" and 5/16" Nordlock washers, though, and I plan to use them to replace tab washers in some less-critical places.

Carroll Smith also says lock washers are useless, because they do not do anything until the bolt is already loose!

Ah, the lockwasher controversy. I've heard the same from other knowledgeable people. And, the opposite from others.

Look at https://www.boltscience.com/, and you will see a vibration (Junker) test showing that the lockwashers are less effective than a properly torqued bolt. But then see https://www.youtube.com/watch?v=IKwWu2w1gGk ; around the 2:35 point there is a plot showing that the lockwasher is quite effective. So apparently they are OK for some things but maybe not others. It would be nice to find some analysis showing exactly what is going on, and under what conditions they are useful or not useful.

I know, I'm a geek, but I still find this kind of thing loads of fun.

Read Carroll's book and you will get the straight story about fasteners. I have a degree in mechanical engineering, and his is the only book that truly covers ALL the fastening topics thoroughly and correctly. This stuff was studied in depth over a hundred years ago, and the tech has not changed. You and I do not have the time or budget to re-learn the wheel...just go to the book!


I only use lock washers because they are what the factory used and I restore to "original" as much as possible. On my performance stuff I only use hardened, ground flat washers or nothing at all. To me, locktite is for the odd cases, where the factory ignored the rules. For example, Harley uses a million of those tiny steel bolts into aluminum casings. If you try to torque those to proper stretch, they will strip the aluminum case. Thus...lokctite! If designed properly, they would have used studs. And, speaking of studs...another use for locktite if you have a stud that is used a lot and you want to prevent the stud from spinning out of the block when removing the nut, such as our valve cover studs.

Well, I better not get going too much!!