MGB & GT Forum

I have been reading old posts to get advice about tightening the knockoffs on my Gt. A number of people reccommended using 4lb hammers. This considerably heavier than the hammer which I have and wish to replace. The only 4lb hammers which my local hardware store has are steel mallets which areobviously unsuitable.They have Thor two headed hammers with plastic on one side and I think zinc or aluminium on the other, but the are pnly about half of the 4lb some have suggested. I'm worried that if I use too light a hammer I may not tighten the knockoffs enough! Any advice would be appreciated.

The "heft" is more a concern in knocking off rather than on. FWIW
Copper or lead alloy are good choices and the larger Thor units were mostly supplied to larger eared KOs....Jag, AC, Aston, but strangely AH in some cases. While a loose KO is NOT a good thing, keep in mind that reasonably tight unit turns in such a way that going forward it would only get tighter.

I think you are overly concerned...

If you wish I can supply either the proper small or large (copper and rawhide on the two faces) marked and made by Thor.

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Regards,
Robert Kirk

kirkbrit@yahoo.com
E-mail PLEASE for quote/questions/orders

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Beat or match most retail/delivered quote

While the copper or lead hammers are era appropriate, I prefer the more common dead blow hammer that you can get at any hardware store. It could be plastic cased weight, or rubber cased weight. In any case, who cares, they don't mar the ears and still get the knock-offs on and off.

I much prefer the long handled steel wrenches as supplied by Moss and others.

Mike

I would like to know the theory about these tightening up by driving.

Why would they?

Especially on the rear.

Assume a slight amount of radial play on splines.

A knock off is grabbed on the wheel outer taper and is tapped medium tight.

Under acceleration and braking the wheel will move within the spline play each time.

Are they suggesting that as you drive forward, the knock off is tightened , then when you brake, it grabs the thread and it slips on wheel taper to get a new purchase?

I think the taper hold would be far stronger than the greased thread hold, so the knock off would stay where it is.

It sounds a bit far fetched to me.

I must be wrong somewhere, as the book says, the wheels can fall off if towed backwards.

4 lbs will knock on easier because of the mass, but it is also harder to accurately wield. You are more likely to hit the fender unless you make allowances and roll the car so that the wings are in a safe position.
Lee's suggestion of a deadblow hammer is a great solution unless you have to be period correct.

Any of these plastic-coated hammers will do the job...

http://www.google.com/search?q=dead+blow+hammer&sourceid=ie7&rls=com.microsoft:en-US&ie=utf8&oe=utf8

Don't get one from Snap on... they are NBG.

This is what I have........ Even beter than a copper hammer...

http://www.thorhammer.com/Hammers/Dead_Blow/Hammer_id_20-2020

Thor is a 5 min drive from me, but they don't sell to the public!

I carry both...a dead blow plastic encased hammer and a long knock off wrench. My whole life I used to murder the knock offs. Now I've learned to lighten up and not kill them when tightening.



Edited 1 time(s). Last edit at 2009-06-09 06:45 AM by comart45.

Many thanks to all who took the time to reply. The heavy dead blow hammer definitely seems the way to go. May have to go mail order as availability locally is very limited.

Whats NBG?

It is all to do with kinetics - and the good old Force = Mass x Acceleration. Newton taught us that a stationary body will remain stationary until operated on by an external force, similarly, a moving body will continue to move in a straight line, until affected by an external force.

So, when the car accelerates, the knock-off nut resists the acceleration (it doesn't want to turn) - this effectively tightens up the nut. The process continues even at uniform speed because of small forces (inertia and windage) trying to slow the nut down - so the wheel is always trying to make the nut spin at the same speed - and the nut is trying to slow down!

If you put the hubs on the wrong side - you will have the opposite effect - the nuts will loosen! You can also loosen them by driving backwards - but it takes a while!

The effect is still there with regular lug-nuts, but they don't have as much mass, so the friction is typically enough to hold them in place. However, some cars (Rolls Royce for example) and most heavy trucks do have left-hand threaded lugs on the right side hubs!

So there you go - it actually has nothing to do with relative movement between the hub and the wheel!

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Eric Marshall

kellybell Wrote:
No Bloody Good

Limey Wrote:

I think you are making half of that up.

You say that the KO tightens because it resists acceleration.

Braking has much more force, so why don't they spin off when braking ?

pooch2 Wrote:
Nope - all true, clearly you were not paying attention in physics classes. I SAID the KO tightens because it resists acceleration AND still continues to tighten at constant speed due to the inertia of the KO. Braking WILL loosen them, but the amount of time you spend driving is MUCH greater than the time you spend braking - so the nuts become much tighter than can be loosened by braking. Oh, and braking does not necessarily have "much more force" - as I said, Force = Mass x Acceleration, so the force during acceleration, or deceleration depends on the RATE at which you change speed.

Try re-installing your wheels (correctly), then immediately accelerate slowly to about 30mph and slam on the brakes - if you are lucky, you will loose all 4-wheels - honest!

If what you say is true, explain why the right side of the car has left-hand threads! They wouldn't be needed unless what I say is true - and it would save a heck of a lot of money in tooling - you would only need one front, one rear hub, and one KO - in fact you need two of each!

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Eric Marshall