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Makotosun

Help with Top End Rattle?

  • MarkT
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Replied by MarkT on topic Help with Top End Rattle?

Navigating the quagmire of Yamaha pistons and rings can be a nightmare.  I'm impressed you were able to find a piston and corresponding rings! 

Many parts changes were made.  There's probably at least half a dozen Yamaha OE pistons that would work perfectly.  Several look the same to the naked eye.  Piston ring grooves were changed...  on the 175 they used various combinations of conventional and keystone rings...  both conventional, combo of keystone and conventional, and both keystone.  You could even buy optional cast iron rings from Yamaha to replace the chrome rings...  which was a good practice if you were just replacing rings as new chrome rings may never seat into a used bore properly. 

Ring style should match groove style.  That's why I mentioned the "reverse insert" to verify both grooves in your new piston are keystone to match the rings.  A conventional ring in a keystone groove won't fit unless the groove is too wide for the ring...  but keystone rings will often fit conventional grooves and the mismatch is invisible after assembly.  But it's a bad idea to use a keystone in a conventional groove. 

Manuals and parts diagrams are riddled with mistakes as well.  Some MAJOR mistakes.  So unfortunately you can't trust that either.  (For example, many clutches in your model are assembled wrong because the "exploded parts diagram" was used as a guide.)
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
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Last edit: 04 Jan 2025 10:50 by MarkT.
04 Jan 2025 10:47 #41

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  • dogman
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Replied by dogman on topic Help with Top End Rattle?

I got my cylinder and new piston back from Bill Bune's shop.

I think I have an issue with the rings

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Once again, the part numbers I ordered (and are listed on the boxes):
Piston 1st oversize .25mm over - 251-11635-00
Rings 1st oversize .25mm over - 251-11601-10

My ring gap is .019" on one ring, and .021" on the other. The service manual says .006-.014". Please tell me I'm measuring it incorrectly. I'm measuring with the the ring about 10mm from the top of the bore and leveled using the piston. The strange thing is those numbers match my old measurements with the old rings prior to the machine work. Could just be coincidence, but seems a bit suspect. I suspect the new rings are wrong.

I also measured the old and new pistons. Old is 65.77mm. New is 66.01mm.

Bore to piston gap is .0015".
11 Jan 2025 16:05 #42

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Replied by MarkT on topic Help with Top End Rattle?

Sounds pretty normal for Yamaha rings to me.
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
11 Jan 2025 21:18 #43

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Replied by automan on topic Help with Top End Rattle?

Rings are always on the large side as for end gap. as said
Measure at expected bore diameter.
10mm from top may be bigger that at 10mm from bottom(where the ring does not ride)

Ring gaps on 2S engines are not as critical since ring pin fills the majority of the gap.
We are trying to form a labyrinth seal in reality.

cliff
12 Jan 2025 08:09 #44

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Replied by dogman on topic Help with Top End Rattle?

Well, I'm thankful for the help I'm getting here. If I just had the manual to go from I would go crazy. I can continue reassembly :D
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12 Jan 2025 08:18 #45

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Replied by dogman on topic Help with Top End Rattle?

She's back together and I've been riding a bit over the last few days. The rattle is gone. I'll post an "after" video when I get a chance.

Thanks to all for your guidance. I learned and lot and enjoyed the process.
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15 Jan 2025 07:15 #46

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