stiffness in piston/crankshaft bearing (Stihl MS391)

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MartDalb

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Hey everyone

Installing a new piston on a Stihl MS391 here, and wondering why I keep having a "stiff" and not "loose" moving piston on the crankshaft top (connecting rod) bearing/needle cage. Bearing/needle cage itself seems fine, but when pressing in the piston pin, it is hard to move around.

Any tips? :)
 

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Or is it just...the way these go, untill used and it settles in? :reading:

(edit)
It is a meteor piston + pin.
The old original "pin" fits slightly better, with a litle more loose movement to it.
 
How does pin fit in bearing/crank out of piston? Move free?

If piston is not machined with pin holes aligned could be an issue, but never seen that.
fits fine into it, smooth moving around, but once needle cage and pin goes in the piston+rod it is stiff and not very easy to move around.
 
Mesuring inside. The original piston has 0.5mm more clearence at the spot of my tool on picture.
Could that pinch it? The needle cage does fit into the New and moves around, without being put on the rod.
Original has 15,5mm clearence, the new has 15mm.
 

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Mesuring inside. The original piston has 0.5mm more clearence at the spot of my tool on picture.
Could that pinch it? The needle cage does fit into the New and moves around, without being put on the rod.
Original has 15,5mm clearence, the new has 15mm.

This might be the issue, as posted above. The connecting rod is 15mm wide as well, and the rod only just fits into the new piston, being also 15mm and not as the old original 15,5mm.



Thought meteor made stuff that fits...what's this about?
 

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Is it possible to some how file the buttom, it should be very little clearence I need to make.

Any ideas?
 
Is it possible to some how file the buttom, it should be very little clearence I need to make.

Any ideas?
well...took my file, finest I could find. Filed down about .15 mm on each side, and now the piston moves freely and fits easily, by hand, into the connecting rod.

Guess that was fixed then...time will tell! :cheers:
 
Send it back.

Meteor quality seems to have issues. Have they moved production to CHI-COMS? Tecomec did, and now makes turds
Was just wondering that myself, certain things about P&C's like more casing deposits in ports, exhaust holes not being tapped deep enough and a few other things that make me wonder - something you would expect from China but not Meteor- even the box color has changed, - doing a 390xp yesterday and had to take a little off the bottom of the piston skirt because it was just touching the crank on BDC???? - be interesting to find out more'.
 
Was just wondering that myself, certain things about P&C's like more casing deposits in ports, exhaust holes not being tapped deep enough and a few other things that make me wonder - something you would expect from China but not Meteor- even the box color has changed, - doing a 390xp yesterday and had to take a little off the bottom of the piston skirt because it was just touching the crank on BDC???? - be interesting to find out more'.
Yeah...I contacted my seller.
He, as they do...?, quickly jumped to his defensive position and said, he was just a "seller" not responsible for the making of it.....:crazy:, anyhow..I explained my solution and that he should get a hold of Meteor, they might have the wrong measurements for this one (as all his stock ones were the same as mine).
It took me 5minutes to carefully file it down, so it is not a biggie, but pretty damn well annoying to run into this sort of stuff...got me frustraited late last nite :angry:.

Thanks to everyone in the thread!
The 391 is now resting a few days, waiting for the gasket to set etc.
 
Yeah...I contacted my seller.
He, as they do...?, quickly jumped to his defensive position and said, he was just a "seller" not responsible for the making of it.....:crazy:, anyhow..I explained my solution and that he should get a hold of Meteor, they might have the wrong measurements for this one (as all his stock ones were the same as mine).
It took me 5minutes to carefully file it down, so it is not a biggie, but pretty damn well annoying to run into this sort of stuff...got me frustraited late last nite :angry:.

Thanks to everyone in the thread!
The 391 is now resting a few days, waiting for the gasket to set etc.
I've tried to lay in a stash of NOS German Stihl wear parts for my saws, and a few parts carcasses.

A while back you could get Stihl chains off ebay ~$15 loop delivered. Glad I got box fulls of 0.325 and 3/8.
 
be ready for this kinda stuff across the board as manufacturers scramble to fill orders resulting in skipped quality...im finding most companies are fighting against covering their own warranties as they spit out crap instead of quality.
 
be ready for this kinda stuff across the board as manufacturers scramble to fill orders resulting in skipped quality...im finding most companies are fighting against covering their own warranties as they spit out crap instead of quality.
That was what I felt the second I said anything about "faulty product".
As if a seller is not responsible to cover buyers warranty :nofunny:, but atleast this seller is trustworthy, and the one and only supplier of Meteor etc in Europe. (More or less)
 
@MartDalb How did your modified piston work out? Did you replace cylinder as well? I may be doing a piston and cylinder on a MS391 so just curious to know how it went and how it’s holding up.
 
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