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Makotosun
Help with Top End Rattle?
- dogman
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Replied by dogman on topic Help with Top End Rattle?
I pulled the cylinder.
Piston:
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Ring gap measurement location:
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Piston:
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Ring gap measurement location:
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- No ring expanders
- The rings were completely free in the grooves
- The wrist pin is tight in the piston bore
- No play in the wrist pin/bearing/rod small end
- Ring gap is out of range for both rings (measured at the top of the cylinder bore, see pic)
- .019" for the top ring
- .021" for the bottom ring
- The service manual says .006-.014" is the acceptable range
- Axial play on the small rod is .032" which is in spec (max .078")
- Axial play on the large rod end is .018" which is in spec (max .019")
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- RT325
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Replied by RT325 on topic Help with Top End Rattle?
How many thou blade can you get between the skirt & bore.
06 Dec 2024 13:08
#22
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- dogman
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Replied by dogman on topic Help with Top End Rattle?
I will check. Should that be measured with the piston skirt flush with the cylinder skirt?
EDIT: with the cylinder upside-down and the piston in the bore (basically TDC), I can get a tight .005 blade in there. I just went in about .25".
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- RT325
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Replied by RT325 on topic Help with Top End Rattle?
Should I be the bearer of bad news. OK I will be. It has about 3 times the std clearance of 1.8 thou. Ya probably doing it a bit different to me but clearance is clearance. If you have a good set of vernier you could get a good enough skirt measurement to end up with a good idea of size. I'm happy to be put right on my methods but piston has 97 on top so I think the clearance is on the piston so will be close to 66mm. 65.97 (help someone if I'm heading off course. I got given some digital vernier so I'll go measure a standard CT1 piston & edit this shortly. OK edit, found a piston identical to yours which has 97 on top but measures 65.94 so in theory gives .06mm clearance to 66mm bore. That's a new piston. .06mm in my head equals 2.4 thou which is about half of what you have. Then bore wear comes into it too, often in the port area & just above the exhaust port but can be at the top of the bore also with sometimes a visible mark. Put the piston in upside down with cylinder the right way up & slide the blade in past the skirt. Have the skirt about 10mm above the exhaust port then feeler blade measure. Sorry, ill pull my head in now, I've caused enough problems.
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- RT325
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Replied by RT325 on topic Help with Top End Rattle?
Also, sorry to be a pain but original rings do have expanders behind them so look closely as they get Carboned into the base of the groove & become invisible. If the motor has never been apart then they should be there but only about 5 thou thick. Hacksaw blade scratch around there would find them & grooves need cleaning out anyway. I just ebayed ct1 rings & shows expanders but we're 1st oversize. Yours has the letter K on top as does my piston. K means keystone which is a tapered top surface on the rings to help avoid sticking in the grooves. OK rant over lol.
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- RT325
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Replied by RT325 on topic Help with Top End Rattle?
Ok, just to be a double pain--but looking at your pics on the TV screen & saving then expanding--in piston pic #2 expanded i can see the high points of the expander in the lower groove. Can see the shiny spots at regular spacings. Sorry to keep emphasising that point but feel its important. Also happy to be wrong--i think, lol.
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06 Dec 2024 22:49
#26
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- dogman
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Replied by dogman on topic Help with Top End Rattle?
If you have a good set of vernier you could get a good enough skirt measurement to end up with a good idea of size.
I don't. Mine broke a while back and I put some on my Christmas list
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Maybe my neighbor has some I can borrow.
Put the piston in upside down with cylinder the right way up & slide the blade in past the skirt. Have the skirt about 10mm above the exhaust port then feeler blade measure.
I'll do this today and post my findings.
original rings do have expanders behind them so look closely as they get Carboned into the base of the groove & become invisible. If the motor has never been apart then they should be there but only about 5 thou thick. Hacksaw blade scratch around there would find them & grooves need cleaning out anyway.
I'll dig a bit and look again. I just looked up pics and now I know what I'm looking for.
EDIT: Not sure why quotes aren't working
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I don't. Mine broke a while back and I put some on my Christmas list
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Put the piston in upside down with cylinder the right way up & slide the blade in past the skirt. Have the skirt about 10mm above the exhaust port then feeler blade measure.
I'll do this today and post my findings.
original rings do have expanders behind them so look closely as they get Carboned into the base of the groove & become invisible. If the motor has never been apart then they should be there but only about 5 thou thick. Hacksaw blade scratch around there would find them & grooves need cleaning out anyway.
I'll dig a bit and look again. I just looked up pics and now I know what I'm looking for.
EDIT: Not sure why quotes aren't working
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- dogman
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Replied by dogman on topic Help with Top End Rattle?
Put the piston in upside down with cylinder the right way up & slide the blade in past the skirt. Have the skirt about 10mm above the exhaust port then feeler blade measure.
I was able to fit a .004" blade using this method.
original rings do have expanders behind them so look closely as they get Carboned into the base of the groove & become invisible. If the motor has never been apart then they should be there but only about 5 thou thick. Hacksaw blade scratch around there would find them & grooves need cleaning out anyway.
I do not see any expanders. I soaked the piston in acetone for about 2 hours and ran a hacksaw blade around the grooves. Also scratched at it with a pick to see if I could grab anything. I think they havedisappeared disintegrated. Here is a link to the full size image: i.ibb.co/VJQshDn/20241207-144208.jpg
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I was able to fit a .004" blade using this method.
original rings do have expanders behind them so look closely as they get Carboned into the base of the groove & become invisible. If the motor has never been apart then they should be there but only about 5 thou thick. Hacksaw blade scratch around there would find them & grooves need cleaning out anyway.
I do not see any expanders. I soaked the piston in acetone for about 2 hours and ran a hacksaw blade around the grooves. Also scratched at it with a pick to see if I could grab anything. I think they have
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- Reed valve Richards
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Replied by Reed valve Richards on topic Help with Top End Rattle?
This thread is very informative, thanks for posting (excellent pix) and thanks so much for all the technical analysis

Yo Joe, Go Joe
07 Dec 2024 16:51
#29
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- RT325
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Replied by RT325 on topic Help with Top End Rattle?
Umm, ok apologies in order, sorry about the chief. I'll get my eyes tested & stop relying on $2 shop glasses.
Piston clearance is at rattle clearance but if you only want to replace the rings i'm sure she'll carry on for a while yet.
Piston clearance is at rattle clearance but if you only want to replace the rings i'm sure she'll carry on for a while yet.
07 Dec 2024 23:32
#30
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