Conrod play

[flyin'chips]

Hi,

The problem: My Husqvarna 371xp has minimal radial play in the conrod bearing and noticed it after cleaning it completely with brake cleaner after tearing the saw down to change the crank bearings. The needle cage and what I can see of the needles don't show any pieces missing but I can feel a very small "click" when moving the rod up/down. It's quite difficult to notice as it doesn't feel if there's any twist or sideways pull. Can't really say how much - I would say very little but I'm certain it's not absolutely tight.

So what to do? Oem crank costs (in Europe anyway) allmost as much as a lightly used 371/372. I haven't read any really favourable comments or long time experiences on AM cranks. When do you gyus retire the crank latest? What are the most likely consequences for using a crank with a worn bearing?

Edit. Posted twice, could this be removed?

 

[Lee H]

Your crank may be fine. Cleaning with brake clean will clean all the oil out and make it
completely dry making it much easier to feel or hear play in the bearing. Hard to say
with out it in being in my hands. All bearings need some clearance or they would seize.

 

[BuckthornBonnie]

If a crank has excessive play at the needle bearing or signs of a spun main bearing, I don’t use it on a build. In theory and in practice, the needle bearing could fail and cause damage.

+1 on degreasing effects and carefully look it over...Feel where the problems are and try to see what’s hanging up. Put the connecting rod all the way down and see if it can hit the crank lobes. Then, see how it looks when fully extended...

 

[Michael Rupley]

Get a strong light and good magnifiers. Push the rod to one side and look down there at the bearings and cage. Do both sides. If you see a broken, flat, rusty or other than smooth bearing or split in the cage, that spells trouble.

 

[Stump Shot]

Bearings with the oil completely removed do have a little bit of clearance for said oil. If would say squirt some oil in and retry.
Myself, I like to confirm this by slightly rotating the crankshaft back and forth while watching the piston in the bore. If you can see the piston not move directly with the crank movement, it's done for sure.

 

[flyin'chips]

Thanks for all the comments and detailed advice!

 

[kneedeepinsaws]

Problem the way i see it is that the saw may run fine, but once you have a tiny amount of play it could accelerate exponentially.
That little click you feel is happening approx 90 times a second at idle. Combine that wIth heat and it will eventually start hammering a larger clearance than what you initially felt.
IMO given these conditions it may not take long before it fails. When that happens im not sure what else would or could be directly affected.

Others will chime in, it may be an issue that you can actually hear getting worse before a kaboom in which you can stop using the saw and plan for a new crank.

If these cranks are hard to find, it would be interesting to go to a machine shop and have them press out the pin for the connecting rod to crank to see if there is damage only to the bearings or the surfaces or both.

 

[flyin'chips]

I checked the needles and cage again with a magnifying glas and I can't find any visible damage except that the outer surface of the cage looks polished. What little can be seen of the pin there's no damage.
Tried then some 2c oil in the bearing. The rod spins/turns very smoothly and quietly but still if I gently push and pull the rod in just correct orientation there can be felt a very small play allthough it's even harder to feel now than when dry.

I didn't succeed in measuring the clearance but it's less than 0,05 mm/0.002" (the thinnest feeler gauge I have).
At the moment the whole saw is in pieces thus I cannot yet test the crank with the piston in the cylinder the way "Stump Shot" suggested.

Is there/does anyone remember/know if there is a measure in either degrees or in millimeters how much the rod is allowed to tilt sideways before judging it as junk? If the rod is in the middle of the pin, it cannot tilt enough to touch the lobes.

What i fear is exactly what ”kneedeepinsaws” wrote above. The small play might soon manifest itself in pieces of the needle cage or needles flying and destroying another piston.
Well maybe I just try the old crank and run it until it explodes. The saw has seen very rough life in professional use before coming to me and it's for my personal use only.

 

[kneedeepinsaws]

would be an interesting experiment to see how long she lasts.
My personal guess is that it will probably last a long time. I only say that cause you said the rollers are polished so it tells me that its already been running a while like that.

 

[Wilhelm]

Hi,

The problem: My Husqvarna 371xp has minimal radial play in the conrod bearing and noticed it after cleaning it completely with brake cleaner after tearing the saw down to change the crank bearings. The needle cage and what I can see of the needles don't show any pieces missing but I can feel a very small "click" when moving the rod up/down. It's quite difficult to notice as it doesn't feel if there's any twist or sideways pull. Can't really say how much - I would say very little but I'm certain it's not absolutely tight.

So what to do? Oem crank costs (in Europe anyway) allmost as much as a lightly used 371/372. I haven't read any really favourable comments or long time experiences on AM cranks. When do you gyus retire the crank latest? What are the most likely consequences for using a crank with a worn bearing?

Edit. Posted twice, could this be removed?

Problem the way i see it is that the saw may run fine, but once you have a tiny amount of play it could accelerate exponentially.
That little click you feel is happening approx 90 times a second at idle. Combine that wIth heat and it will eventually start hammering a larger clearance than what you initially felt.
IMO given these conditions it may not take long before it fails. When that happens im not sure what else would or could be directly affected.

Others will chime in, it may be an issue that you can actually hear getting worse before a kaboom in which you can stop using the saw and plan for a new crank.

If these cranks are hard to find, it would be interesting to go to a machine shop and have them press out the pin for the connecting rod to crank to see if there is damage only to the bearings or the surfaces or both.

Steel expands exposed to heat!
Obviously You are checking Your saw over cold, that little bit of play You are noticing may be normal factory tolerance play combined with some normal (healthy) wear - engine break in is engine wear.

My apologies if my logic is wrong, I had a long day I might just be brainfarting.

 

[kneedeepinsaws]

Steel expands exposed to heat!
Obviously You are checking Your saw over cold, that little bit of play You are noticing may be normal factory tolerance play combined with some normal (healthy) wear - engine break in is engine wear.

My apologies if my logic is wrong, I had a long day I might just be brainfarting.

Good point