Crankshaft permissible end float

nortonspeed · Mar 19, 2018

Why did Norton increase their permissible end float for the 850 MK3 from .005"-.015" to a (IMHO) excessive .010"-.024" ??

Fast Eddie · Mar 19, 2018

Well, firstly I’d challenge the notion that .010-.024” is too much. What failure mode does .024” cause? Nothing that I can think of at least.

Too little end float however would stress the crank, crank cases, and the main bearings. Leading to numerous potential failure modes.

So, perhaps the reason was the factory saw failures from to little clearance, so upped the figure?

nortonspeed · Mar 19, 2018

Well I agree too little end float isn’t desirable either however I am talking about too much end float and I can think of possible problems that could occur with .024” end float like messing up the little timing degree scale or premature wear of the oil pump worn gears and primary chain/belt (out of line).

comnoz · Mar 19, 2018

nortonspeed said:
Why did Norton increase their permissible end float for the 850 MK3 from .005"-.015" to a (IMHO) excessive .010"-.024" ??

Because when the end float is less than about .010 on a stock motor or .015 on a high revving race motor you will start to see damage on the ends of the superblend rollers and the thrust surface of the races.
The crank actually gets longer as the revs increase.

kommando · Mar 19, 2018

I thought given the skipping rope of an centrally unsupported crank analogy it would get shorter as the centre expanded, glad I read this as otherwise I could have used too little end float.

Nater_Potater · Mar 19, 2018

kommando said:
I thought given the skipping rope of an centrally unsupported crank analogy it would get shorter as the centre expanded, glad I read this as otherwise I could have used too little end float.

Think of where the crank's mass is located; it'll try to sling away from the throws, effectively straightening out the crank. 'Scary thought...

Nathan

worntorn · Mar 19, 2018

A friend has an 850 he purchased new in 1973. It was his only vehicle for 12 years so it saw lots of use.
It has 128,000 miles and has never been apart further than head off once for a new gasket.

The end float now is about 55 thou. It still runs fine but is down in power due to blowby etc.

Glen

ashman · Mar 19, 2018

I think people over think about end float and worry to much about it, in 43 years of owning mine and a few rebuilds I never messured the end float I just put it back together, for 38 years it was a everyday ride except for tear downs and injuries was the only time it wasn't ridden and every rebuild new main bearings but the old mains were still good, the crank has only been split once in that time to do the sluge trap but it had very little sluge in it, in fact it had bugger all.

Ashley

baz · Mar 19, 2018

From memory I think my old mk2a had 24thou float the motor had not been apart on that bike it was fine running like that

Crankshaft permissible end float

nortonspeed

Guest

Fast Eddie

nortonspeed

Guest

comnoz

kommando

Nater_Potater

worntorn

ashman

baz

Similar threads