Bent crank or worn race- Andy / Dennis ??

[Gumnuts]

Just hoping to hear more about HOW TO check whether a crank is bent.

re : Andy ' put in a V block an measure the run off.'

Have a spare 084 case that was told had worn journals/ race.Would be good to know whether the crank is :censored: or salvageable ?? Can't see any movement in the bearing sleeve.But i guess it would'nt have to move much under load.Yet you could be hard pressed to notice movement doing a stationary check of the sleeve.
On reading another thread i get the gist of what is said about measuring the run off , but not the application.
Pic or two would be appreciated.

HOW FAR DOES A SAW NEED TO BE STRIPPED DONE TO MEASURE RUN OFF

- Graeme. :greenchainsaw:

 

[Tzed250]

This is not a chainsaw, but same theory. If the crank is straight, then the needle on the dial indicator will not move. I the crank is bent the needle will move back and forth when the crank is rotated.

 

[Gumnuts]

This is not a chainsaw, but same theory. If the crank is straight, then the needle on the dial indicator will not move. I the crank is bent the needle will move back and forth when the crank is rotated.

Wow.'A pictures worth a thousand words' .Understood.

Have a mechanic friend whose selling up workshop,retiring.Will see if he's got something like that gauge, i can use.

rep given.

- Graeme :greenchainsaw:

 

[Mad Professor]

Some of the dial indicators will have a large magnetic base. Set up the V-blocks on a steel table and the base will stay put.

Also play close attention to where the bearings seat and the seals contact the the crank, smooth, concentric, no pitting.

 

[Gumnuts]

Some of the dial indicators will have a large magnetic base. Set up the V-blocks on a steel table and the base will stay put.

Also play close attention to where the bearings seat and the seals contact the the crank, smooth, concentric, no pitting.

Will do .Thanks for the tips MP.

 

[RiverRat2]

If your crank is still in the saw you must anchor the saw some how,,,ratchet Binder, large C clamp, etc, etc, if its out and you use v blocks with that small a crank the v blocks must be secured as well to get accurate Run out readings,,, on the dial indicators,,, FWIW,,,

 

[Lakeside53]

...and use a "last word" type of indicator... like 30 thou full scale - you are measuring 10ths... a typical dial indicator showing 1 thousandth (inch) per division will be hard to resolve a small run-out; it will however show a really bad crank..


Carefull with the picture above - the extension can be a problem if not perfectly seated axially and radially, and in any case will tend to magnify errors. I'd measure on the bearing journals and on the clutch side, also the clutch drum bearing surface.


If the crank is in the saw, maybe you can mount your dial indicator to a plate secured onto the bar studs. You'll be limited to measuring against the clutch bearing journal, but...


I tried to get an answer from Stihl as to what run-out was acceptable.. the message I got back was "the factory said 1-2 10ths"... but relative to what I wasn't sure!

 

[Fish]

Dennis "WHO"???????

Greffard?

 

[wireedm]

...and use a "last word" type of indicator... like 30 thou full scale - you are measuring 10ths... a typical dial indicator showing 1 thousandth (inch) per division will be hard to resolve a small run-out; it will however show a really bad crank..


Carefull with the picture above - the extension can be a problem if not perfectly seated axially and radially, and in any case will tend to magnify errors. I'd measure on the bearing journals and on the clutch side, also the clutch drum bearing surface.


If the crank is in the saw, maybe you can mount your dial indicator to a plate secured onto the bar studs. You'll be limited to measuring against the clutch bearing journal, but...


I tried to get an answer from Stihl as to what run-out was acceptable.. the message I got back was "the factory said 1-2 10ths"... but relative to what I wasn't sure!

Yes, use an indicator graduated in ten thousandths (.0001") "Last Word" is a brand name given by Starrett.

Any time someone says the spec is so many tenths, they mean ten thousands of an inch, otherwise they would mean tens (.1") which would not even be in the ballpark. It's definitely in inches, .3mm would be .0118", which is way too much, and .0003mm is 0.0000078", which is WAY too little but very concentric. lol

Be SURE to measure as close to the center of the crank as possible to get the most runout measured on the indicator. The closer you are to the support bearings, the less actual runout will be shown.

 

[Tzed250]

In the original post i was trying to keep things simple.

Tha only real way to acurately measure a crank is between a set of precision centers.

>crank<

The part is placed between centers and the clamping side loaded enough to prevent any play, but not so much as to induce stress.

Two dial test indicators are placed with the contacts on each main bearing journal.

This will show both radial and axial runout.

Pressed together cranks may be trued by removing the from the fixture, and lightly tapping the into square.

An example of a crank truing stand:

 

[Gumnuts]

If your crank is still in the saw you must anchor the saw some how,,,ratchet Binder, large C clamp, etc, etc, if its out and you use v blocks with that small a crank the v blocks must be secured as well to get accurate Run out readings,,, on the dial indicators,,, FWIW,,,

Apologies it took so long to get back to you .Case is down to bones .

 

[Gumnuts]

Dennis "WHO"???????

Greffard?

Master Dennis Cahoon !!!



He does love JB - hehe

 

[Gumnuts]

...and use a "last word" type of indicator... like 30 thou full scale - you are measuring 10ths... a typical dial indicator showing 1 thousandth (inch) per division will be hard to resolve a small run-out; it will however show a really bad crank..

I tried to get an answer from Stihl as to what run-out was acceptable.. the message I got back was "the factory said 1-2 10ths"... but relative to what I wasn't sure!

Hoping to see my retiring friend today.In the meantime have been checking the BAY for dial indicators.Trying to get clarity from them as to how fine a measure they are.Heres a couple.

http://cgi.ebay.com.au/Eclipse-Dial...ryZ55825QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

http://cgi.ebay.com.au/MAGNETIC-BAS...ryZ12581QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

http://cgi.ebay.com.au/Dial-Test-In...ryZ12581QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

WOULD YOU THINK ANY OF THESE ok

 

[Gumnuts]

lol

YOUR A SICK PUPPY - .... RED NOVAS .Sort of like saying the Lords prayer backwards.An i won't do that......hehe



- Graeme

 

[Dennis Cahoon]

Most of the chainsaw cranks I've checked new and used were between 1 and 3 thou. run out, but never have seen a bent one.

 

[Lakeside53]

I think guys confuse "bent" with a crank lobe moving slightly on one end of the big end pin. Uncommon on saws.

 

[RiverRat2]

Apologies it took so long to get back to you .Case is down to bones .

you can secure the entire crankcase,,, and if you do it on a metal table then magnetic bases for mounting the indicators will work fine,,, but be forewarned if you are not sure of the condition of the bearings then worn bearings could be causing the run out,, or slogged out cases,,,,,if you are seeing visible run out then I would think one of the two aforementioned scenarios is more likely than a bent crank,,,,,, JMHO to really check the crank it should probably be removed and set in a truing stand or a set of V blocks as others have already indicated,,,

 

[PES+]

I keep throwing out all the Stihl cranks cause I can't find one true to .001 MM

*resumes pushing pull cord*

 

[RiverRat2]

I keep throwing out all the Stihl cranks cause I can't find one true to .001 MM

*resumes pushing pull cord*

Freak!!!!!!

 

[Tzed250]

I keep throwing out all the Stihl cranks cause I can't find one true to .001 MM

*resumes pushing pull cord*

1 micron...pfft...thats nothing.