Fix a bent rod?

[BigDee]

I have a small Husqvarna saw torn down and it appears to have a bent rod. If I move the rod all the way to one side and rotate, it almost touches the crank; if I push it to the other side it has about 1.5mm clearance.

Once many years ago I straightened a B&S conn rod with a hammer, but it was a 3000 rpm clunker, not a 13,500 two-stroke.

I'm thinking I would need to support the rod at two points and apply pressure at the center of the bend.

Any experience you have with this would be interesting to hear. Thanks. Don

 

[palbin]

Most people do this "red neck" style (just testing this new
expression I have seen on media - perhaps not appropriate
here ...) - anyway, that means just finding whatever you
have to bend bar back right - BUT there exists special tools
for it - just look at the catalogue/web-page of a major chain-
saw equipment supplier - cost like a couple of 100 bucks or
so - perhaps really only worthwhile if you have a little bit big-
ger chainsaw business ... .

 

[w8ye]

Get another crank assembly

 

[BWS-LLC]

I personally wouldn't do it....

The thought of correcting it and stressing a certain part of the rod, then the thing going at a high RPM....

 

[palbin]

I tought "rod" was "bar" - sorry if I misunderstood that .
(What IS rod if not bar?)

 

[sunfish]

It should run fine as is, I wouldn't mess with it...

 

[palbin]

"Rod" - is it the "thing" that comes from the crankcase that
you fit the piston onto ?

 

[BigDee]

Get another crank assembly

Thanks. I know a new assembly is the right thing but the saw is old. This is mostly a curiosity exercise. And some might say I'm cheap.

 

[BigDee]

It should run fine as is, I wouldn't mess with it...

I like this idea. The rod does float in there after all. And it's only bent a little....

 

[BigDee]

"Rod" - is it the "thing" that comes from the crankcase that
you fit the piston onto ?

Yup, that's it. The connecting rod attaches the piston to the crankshaft.

 

[Marshy]

I personally dont have any confidence in the method you used to come to the conclusion that you have a bent rod... Other than what you described, is there any other reason you suspect a bent rod or was it just the observation you stated?

 

[cattoon]

Shop press and some decent luck? let us know how it turns out.

 

[Marshy]

If its not bent already it will be when done!

 

[sunfish]

I personally dont have any confidence in the method you used to come to the conclusion that you have a bent rod... Other than what you described, is there any other reason you suspect a bent rod or was it just the observation you stated?

That was my first thought. The parts of the crank he's measuring against is likely different side to side?

 

[zogger]

I tought "rod" was "bar" - sorry if I misunderstood that .
(What IS rod if not bar?)

connecting rod, between piston and crankshaft

 

[turtle561]

your con rod bearing is worn. that's just side to side play. unless someone beat on it trying to get a wrist pin out.
you should worry about up and down play, is it knocking ?d

 

[BigDee]

I personally dont have any confidence in the method you used to come to the conclusion that you have a bent rod... Other than what you described, is there any other reason you suspect a bent rod or was it just the observation you stated?

Well I have never used it as a "method" before, I have just noticed the side-to-side clearance. But I have never been looking for a bent rod before.

I have no other reason to think it is bent. (Except the broken piston skirt.) I cannot feel any unusual looseness in the lower rod bearing. My poor astigmatic eyesight made me suspect something so I started looking at it more carefully. Can you suggest a good method for assessing its straightness?

 

[BigDee]

your con rod bearing is worn. that's just side to side play. unless someone beat on it trying to get a wrist pin out.
you should worry about up and down play, is it knocking ?d

I received the saw in pieces. The side-to-side play is as usual. There is no up and down play that I can feel. It was pretty gummy when I got it. I washed it with old mix, oiled it with new two-stroke oil, and it all feels tight and smooth now -- just the way I like it.

 

[Marshy]

Can you suggest a good method for assessing its straightness?

No I cannot. It's not a common thing to check AFAIK. Maybe ask one of the saw builders?

 

[Big_Wood]

i very much doubt the rod is bent at all. it is probably just the difference at where the rod is sitting on the bearing from side to side. those rods will bend or twist quite a bit before it becomes permanent. if we were talking about rod stretch i would agree. the 3120 i last sold had something like .043 squish when i got it and i swear to god it was around .027 when i sold it. couldn't believe it but maybe milling did it to that saw. it was an actual test i did on rod stretch. it is why i don't really agree with any squish tighter then .020 on any saw. actually prefer between .025-.030 actually.