No woodruff key on lower belt redrive pulley

[adamjedgar]

Hi guys,

I pulled apart a belt redrive assembly and noticed the aluminium crankshaft pulley is a tapered fit with no woodruff key.

Also, the pulley retaining nut whilst flanged has no washer, so its biting directly onto the alloy damaging the surface finish when being tightened up.

Do these two things sound right to you guys?

Anyone got pictures of how their belt drive engine pulleys are mounted onto crankshaft I could look at?

[AndyB]

Tapers usually don't have keys. If the nut is tight, they will not slip.

[adamjedgar]

thanks Andy...it has never slipped on me yet but i did wonder as my engine rebuilding experience is with model aircraft engines, lawn mowers, motorcycles, cars, and diesel truck engines. Never had anything to do with redrives such as this.

Also, for those who may be wondering...the black dust is mostly a result of my incessant spraying wd-40 on electric starter thus collecting dust from anywhere and everywhere.

Edited October 29, 2020 by adamjedgar

[paul simkin]

Hi Adam, 

it has been common practice on car engines for many years now not to use keyed on pulleys for cranks and cams, often not even tapered. The crush of the special ‘torque to yield’ bolts holds them perfectly. With your pulley nut I’d tighten it to the correct torque, with a dot of medium strength thread lock and then tippex a couple of dots on the nut and the pulley as a quick check to see they haven’t moved in the future, and as a reference if you ever had to remove it away from the workshop for some reason and didn’t have a torque wrench handy, but then you’ll get all sorts of opinions about how applying thread lock will alter the torque applied to reach the same clamping force, like the “ greasing or not greasing a bolt “ debate. 
Regards. Paul. 

[adamjedgar]

Hi Paul, I've reinstalled the drive pulley and tensioned it up to correct setting. It's not very high torque though...40n.m

 

I guess I will know soon enough if that isn't good enough...the pulley will slip on the shaft.

Edited November 1, 2020 by adamjedgar

[AndyB]

40Nm is about 4 kg hanging on a 1 meter wrench, which is quite plenty for a taper with under 30 hp on it.

As for the grease or not......with grease the deviation in actual achieved torque is much smaller than the deviation in achieved torque without grease ie 40 Nm with grease could achieve say 35 to 38 actual but without grease it will be a bigger variation such as 30 to 38 actual. What is wanted is to be as close to desired as you can.