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[PTmowerMech]

That is the number I came up with for both models on my distributor website parts lookup system, and the official dealer Husqvarna parts lookup system.

I double checked this number. Triple checked it, actually. Both of the rings I got were the wrong ones.

 

[ILENGINE]

Being wrong, do they not fit inside the cylinder or don't fit the groove on the piston. I am wondering if there has been a change in production and the piston and ring have been changed but use the same part numbers.

 

[PTmowerMech]

Being wrong, do they not fit inside the cylinder or don't fit the groove on the piston. I am wondering if there has been a change in production and the piston and ring have been changed but use the same part numbers.

The ring slides over the piston without touching either side. (just barely).

 

[bertsmobile1]

slip them in the bore.
If they fit without overlapping then the rings are correct.
Now try the piston in the bore, upside down.
There should be .002' to ,oo5" clearance between the piston & the bore
Two stroke rings have to work in both directions and tend to be a lot springier than 4 stroke rings as they have to make a reasonable seal or the engine will not be able to be started in order to bed in the ring.
This is why a lot of manuals tell youto put fuel / oil down the plug hole before initial use.

 

[PTmowerMech]

Even when you close the ring gap, it still slides over the piston.
OD on new ring is 1.57. OD on the other ring, which is also new is 1.39.

 

[ILENGINE]

OK I went and pulled apart a junk SST25C which shows 530055120 which supercedes to the new 545154001 ring. The same ring and cylinder as your two items you are working on and measured the ring. The ring in the one I disassembled measured 1.39 OD.

 

[PTmowerMech]

OK I went and pulled apart a junk SST25C which shows 530055120 which supercedes to the new 545154001 ring. The same ring and cylinder as your two items you are working on and measured the ring. The ring in the one I disassembled measured 1.39 OD.

Thank you. Thanks the one I think. I wonder how that original number got tagged to that engine. I guess where it says "supersedes" it doesn't mean replaces. Because the 4001 ring definitely doesn't replace the 5120 ring.

 

[ILENGINE]

Thank you. Thanks the one I think. I wonder how that original number got tagged to that engine. I guess where it says "supersedes" it doesn't mean replaces. Because the 4001 ring definitely doesn't replace the 5120 ring.

No it means replaces. From further research there appears to be other people that have had the same issue with the ring/piston being too big for the existing cylinder. the cylinder part number also supercedes which makes me wonder if the bore didn't change and both have to be replaced to make it work.

 

[PTmowerMech]

No it means replaces. From further research there appears to be other people that have had the same issue with the ring/piston being too big for the existing cylinder. the cylinder part number also supercedes which makes me wonder if the bore didn't change and both have to be replaced to make it work.

That's a very good point. I haven't seen anything about that. But then again, I haven't looked at the matching numbers for the cylinder heads yet. I did find a ring on EBAY that may match. The pic shows the ring next to a scale. And from what I can see, is smaller than the one I just recieved. I'm gonna email and ask if his has a set of calipers to measure it. His part number is the one you gave me.

Seems that if they'd increase the bore, piston and rings, the part numbers would be different.

 

[bertsmobile1]

Soda can.... That's a good idea.


BTW, something you told me the other day, in a different thread about cleaning out where the piston ring fits, Nylon string (I just discovered) works very good.

while it s not part of your current dilema.
FWIW, unless the new rings bind in the piston, then cleaning the ring groove is usually a no no.
The side gaps are measured in 0.00001 " and damage to th grooves you need a microscope to see will render the piston useless.
I found that one out the hard way .
Even the pistons & rings made for machines that needed to be pulled down every year for decokes ( yes I am that old ) should not have their grooves mechanically cleaned.
As for your current problem.
Weed Eaters are a throw away brand & not meant to be repaired.
This is why the piston comes without the arrow stamped into the top as that adds to the cost of the piston,

Getting back to your problem.
Generally I get rings from Italy ( Grandinni ) and always order them by bore, width & depth , then coatings and not by equipment brand.
Amreicans have a problem doing this because the EU use mm and not inches.
They also sell through ebay Italy but you will find them listed by bore then in the details see most of the different brands & models that they fit.
Just about any brand ring will fit.
There is no profit in selling a single ring through the dealer network so just about zero care is taken or when it is ( like Stihl ) the prices are disproportianely high to the cost of the equipment .
Down here there are no Weedeater parts available at all as they have no network being a chain store brand.

OTOH, you usually have to buy a full sleeve from them and I have found that listing the remaining rings turns a nice profit.
I sell them through ebay, packed in a plastic coin container which costs very little to post.

I did look up your model and noted that they do not publish any of the important mechanical specifications in the owners manual so there is no way for the mug end user to know what the bore & stroke is .
According to Jacks, there are 2 different engines for a FB 25 but according to the part numbers all the parts are the same si it looks like the ARI database got udated with the new number and they applied it to both engines.