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Post by bamaguy on Jul 1, 2011 17:22:38 GMT -5
These are new piston rings for Roketa 250 . Which one of these rings goes in the top groove and which is second groove? I'm thinking the darker one goes in the top (compression ring) Hate to have to ask but I never done one of these engines before. alfonzo.pixa.us/images/19359507/%20Rings-2
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Post by Rebel on Jul 2, 2011 1:10:53 GMT -5
It has more to do with the profile of the ring, those photos do not show enough about them. Some[place Kliff posted some information about rings, if you search through some of his posts you might find some better info. When I have replaced rings I just matched up what came off with the new ones, but that has been on cars and Honda 90 motors. Here is a page from the linhai yamaha manual Attachments:
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Post by bamaguy on Jul 2, 2011 3:01:53 GMT -5
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Post by Rocketdog on Jul 2, 2011 5:51:45 GMT -5
That's usually how they go in and the markings go up. Shinny ones the top ring and the dark ones the second. I'd bet that was right.
RD
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Post by bamaguy on Jul 2, 2011 11:22:50 GMT -5
Anybody looked at these crank pictures? Looks like it got hot. Not sure if the Chinese done that making the crank or afterwards. Looks like they ground the crank with a loaded up grinding wheel. The rod is a funny color to. I have never see the inside of one of these motors so I don't know what is the norm. The piston and wrist pin looked ok. I wonder if anybody has had a cracked cylinder on one of these. I may need to get it checked before I put it back together. Guess everyone is tired of my motor questions but this is my only source for info. Maybe it will helped someone else out sometime.
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Post by Rocketdog on Jul 3, 2011 8:17:58 GMT -5
I don't have a 250 Bama. But that's what the 150s and 50s look like. Check and see if the clearances are ok. If so your fine.
RD
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noday
Non-Com
"Sparky" Electronics Research and Development Officer
Posts: 90
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Post by noday on Jul 3, 2011 8:32:03 GMT -5
looked at your pics. the crank discoloration sure looks like from the factory. The discoloration is local, only on 1 side where it was ground.down.
the rod color is "normal"
the heat needed to cause that much color change would have caused readily visible damage to the aluminum case and piston, which is not present.
for a crank to get that hot, in the engine, you need bearing failure to generate the heat ...that would mean a big clunk when you rotate the crank. pretty obvious.
the piston is not melted, the rings are intact, so there was no preignition/detonation heat from the combustion chamber to burn the crank.
looks like a garden variety coolant failure so that you had a head gasket failure.
the rest of the engine pretty much Ok other than for some accelerated wear of the cylinder bore surface.
the cylinder sleeve needs to be honed, at the least.... that interior bore surface should be very smooth... like the bottom part.
you need a cylinder hone that fits the bore size.
if the rough ares do not hone out, it will need to be overbored by a machine shop. depending on how much metal has to be remove to clean up the bore, you will need an oversize piston & rings to match the bore size.
I have seen just honing and leaving the small pits/scratches, etc. that means you leave extra oil in the defects that is burned during combustion. so you use oil and the exhaust smokes.
the principals of a top end rebuild are the same for all 4 stroke engines. you need tolerances at final assembly that are close to the designed specs for that engine.
a loose final assembly will still run for quite a while.
most of this comes down to cost and intended use.
if the intended use is occasional & minimal cost is desired, loose is OK.
if intended use is regular with high miles then you go for designed specs.
tolerances for bore size, etc are in your engine shop manual.
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Post by bamaguy on Jul 3, 2011 14:04:40 GMT -5
Thanks for the help. I rented a cylinder hone from Auto Zone. I was looking for a hone and the guy told me I could borrow one of theirs. You just pay a 27.00 deposit you get back when you return it. Think I have honed about .001 out of that cylinder and still got just a little of that bad place left. Tues wen the holiday is over I'm going to get that cylinder checked for cracks. Last night I used a big woodworking clamp and clamed a piece of gasket over the water outlet. I filled the coolant chamber with gas and let it sit over night. I was told gas will leak throgh when water won't. Didn't show any sign of leaking but i'm still going to have it pressure tested. Appreciate the help.
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noday
Non-Com
"Sparky" Electronics Research and Development Officer
Posts: 90
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Post by noday on Jul 4, 2011 7:44:57 GMT -5
you have to be careful using a cylinder hone to remove metal or small localized defects.
that leads to a jug shaped and/or an out of round bore. the intended use of a hone is to refinish a bore surface that has been smoothed by ring wear or after reaming.
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Post by Rebel on Jul 6, 2011 0:01:27 GMT -5
often times a brake cylinder hone will work on small motors. should you want your own check those out.
when you hone you should move it in and out the entire length of the cylinder and it is a good idea to hone the cylinder when you put new rings in. Sounds like you arson the right track.
Clean the heck out of everything before it goes back together.
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