Big End Advise Please

[Zetomagneto]

Interesting video, the test shows the bolt in shear, our small end bolts are in tension providing a clamping force to the small end with no relative movement of the bolt within it's hole.I do not feel this test is applicable to small end bolts, and therefore to the use of spring washers in this location.
I always use rectangular section spring washers and agree with Ruairidh's modus operandi.

[Alan]

In general, three conditions are required for a fastener to stay fastened. One, there must be sufficient clamping load to prevent relative movement between the joint faces. Two, the clamping load must be greater than the cyclical loading imposed on the fastener by loading or vibration, or whatever. Three, the sum of the underhead and thread friction must be greater than the unscrewing torque generated by the clamping load and helical thread. Satisfy these and the joint will not come undone, and it doesn't matter what sort of washer is used, but spring washers do assist with underhead friction. The boltscience page shows a bolt with inadequate clamping load reacting to a shear force across the joint. It was going to loosen whether or not the washer was there.

[Dave Wortley]

R,
That's the video. I was thinking more of the theory that if you have an imperfect bore in the little end, you would not achieve much clamping force. Therefore the rapidly alternating loading generated by the piston boss /gudgeon pin friction torque at the joint between gudgeon pin and little end would "rock" the clamp screw in the clearance hole for the screw,the screw pivoting in the little end tapping. This would cause loosening of the clamping of the screw even further. Anyway I think I will carry on using loctite and spring washer here. Also of course I will never be using conrods with oval bores in the little ends. The clamping method is poor anyway even if they are perfectly round. Much better to have bushed conrods with circlips in the pistons to prevent gudgeon pin ends scoring the cylinder bores.

[Hedd_Jones]

I best not tell you that I run with gaps on my little ends. Gaps between the brasses that is.

This is on my traction engine. Adjusted by 'feel' with a threaded taper wedge.

It takes about a minute to adjust one if its clomping.

No spring washers, just a locking nut done up 'FT'

[Ruairidh Dunford]

I am going to stick to that method as well Dave.

[Colin Reed]

Hi all,
Castellated nuts on big ends or main caps we allways used Lock wire and a lot small end bolts had a hole in the head which was wired around the rod.
No Tabs or spring washers and the only washers used hardened flat ones
nylocks  at the time mainly used on Aircraft but not on the Engine.
and Locktite  not available at the time
Lockwire is still readily available

Cheers Colin
NZ

[Ruairidh Dunford]

I recall seeing Aerotight ® lock nuts used on big ends years ago.

[Dave Wortley]

I know this is irrelevant but been to see the Laxey Wheel today on the Isle of Man where we are on holiday.The mechanism is virtually silent, the only noise coming from the water as it falls out of the troughs on the wheel. What a contrast to the screaming motor bikes whizzing round the Mountain Road. Apologies for this bit of irrelevance!

[Colin Reed]

I recall seeing Aerotight ® lock nuts used on big ends years ago.

Hi Ruairidh,  Late 50s When doing 10,000 hour Automotive Machinist Apprenticeship ( Engine Reconditioning )
                  In NZ
Cheers Colin

[Robert Leigh]

I have had no troubles with new little end bolts for over 20 years Hedd - have you?

I had the head come off one little end bolt I had put in new, and only discovered this when I decided to strip down for a new rear main. This was on the slightly tuned Ulsteroid engine, and the con rod had cracked downwards from the clamping split. Main difficulty was removing the rest of the bolt without damaging the piston. I mig welded a lump onto the broken face of the bolt shaft, without fixing it to the con rod, and wound the bolt out with some mini mole grips. It can work, but I think there was an element of luck involved!