Question about getting a new piston

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avg_joe
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Re: Question about getting a new piston

#31

Post by avg_joe »

Well, I tore it down again. Aluminum shavings on the piston, and the rings were pretty stuck in the grooves.
Head looks good. Top of the piston looks good. Valves all look good. Cam and lifters all look good at first glance.
Wondering why it got hot enough to fry in just a couple of minutes.

It still makes me feel sick just to look at it.
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Re: Question about getting a new piston

#32

Post by wingrider »

I don't recall if you mentioned it, but what did you set the ring end gap at?
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Re: Question about getting a new piston

#33

Post by avg_joe »

There was a sheet with the rings, that gave a formula to figure end gap, based on application. I don't remember what the numbers were, but I went by the 'heavily modified' column. And I thought I was being generous with the fit, making sure it wasn't tight.
I was poking around on my workbench, looking for that sheet, but haven't found it. I guess it is possible that I screwed that up.
Suppose that there is any chance that the piston is still good, and I could just put rings in?
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Re: Question about getting a new piston

#34

Post by avg_joe »

I found that sheet for the rings. The first thing that comes to mind is.....The formula is bore x .00something inches.
Maybe I didn't convert my metric bore to inches before I plugged it into the formula.

The sheet lists automotive applications. I wonder if because this is air cooled, it would get hotter, and need bigger gaps?
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Re: Question about getting a new piston

#35

Post by robin1731 »

General rule of thumb, .004" for each inch of bore for the top ring (.0045-.005 for modified engine). .005" for each inch of bore for the second ring (.0055 for modified engine). And recommended gap for oil rings regardless of size is .015".
The numbers for the top and second rings are for N/A engines. Air cooled or water doesn't matter.

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Re: Question about getting a new piston

#36

Post by avg_joe »

That's what my sheet says as well. It specifies a .010" end gap for the oil ring scraper rails. Unless I screwed up the metric to inch conversion, that's what I did. I will stuff the rings back in the hole, and take another look. But I distorted them a bit getting them off the piston, so may not come together right anymore.

I just got home from work, so my garage is pretty cold until the fire gets going. I'll dig around and see what else I did once it warms up a little. I like it to be at least 50, and 60 is even better.
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Re: Question about getting a new piston

#37

Post by avg_joe »

O.K. I re-checked my math, and with a 101mm piston, it's a 3.976 bore after conversion.
Plugging that into the formula gives me .018", and .020" for the rings.
I checked the rings, and that's what I get.
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Re: Question about getting a new piston

#38

Post by avg_joe »

Well, I think I figured out what happened...
The gear that turns the oil pump is held in place by the side cover. There was apparently a washer that was held in place when I took the cover off. At some point, this washer fell out of it's place, and I didn't realize. I had found this washer, but didn't know where it came from, so I didn't know where to put it back to, and wasn't sure it even came from inside the engine...
When I took the side cover off, the gear on the oil pump shaft had slid out far enough so that it wasn't engaging, therefore not pumping oil.

So now the question is....Did I ruin everything, or could I put some new rings, and a new head gasket in and call it 'fixed'?

On one hand, I am relieved to figure out what went wrong.....On the other hand, I am quite frustrated that I destroyed all that effort with a simple blunder.
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Re: Question about getting a new piston

#39

Post by gltriker »

quote from post#31: "Aluminum shavings on the piston, and the rings were pretty stuck in the grooves."

So......The Aluminum shavings were actually accumulated on the piston skirt and cylinder wall, not on the top of the piston?

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Re: Question about getting a new piston

#40

Post by avg_joe »

More like scattered and sticking to the top of piston, and around on the cylinder walls like ashes would. At first glance, I thought it was ash.
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Re: Question about getting a new piston

#41

Post by avg_joe »

Since I am becoming the poster child for what not to do during an engine rebuild.....Here are some pics.
First pic is what I wiped off the cylinder wall. There was a little bit more than that initially, but not much.
Image

Then a view of the piston...
Image

Image

Looking down the bore...
Image

The scratches on the piston are visible, but can't really feel them. And the cylinder wall shows no scratches.

What do you all think? Is it worth putting new rings on that piston, and putting it back together?
In the garage:
1977 GL1000
1982 GL1100 with California Side Car hack
1982 FT500 Ascot(Wife's bike)
1983 FT500 Ascot
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Re: Question about getting a new piston

#42

Post by avg_joe »

While we're looking at my blunders.....Here is what I think happened.
When I took the side cover off of the engine, the washer was probably stuck in place by surface tension of the oil, and I didn't notice that it was even there. Then at some point, that washer fell off the cover, and became another misc. part on the bench. I didn't take the washer off, so I didn't know where to put it back.....so it didn't get put anywhere. At that point I wasn't sure it even came out of this project.
Image
Once I took the side cover off again, and saw the oil pump gear not engaged, I figured out what happened.(I think)
I have looked at the parts diagrams, and it doesn't show that washer anywhere, but as you can see, it fits perfectly....
Image
Image

That last picture has the washer in place, and you really can't see it. I guess I can understand how I missed it the first time, but it really bugs me that the diagrams didn't show it. I have spent a bunch of time looking at diagrams, and exploded views, trying to figure out how to put this thing back together correctly. If it was printed anywhere, I would have seen it, and maybe not blown up my engine in minutes flat.
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1977 GL1000
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1983 FT500 Ascot
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Re: Question about getting a new piston

#43

Post by robin1731 »

Any place in the engine that lives on oil was damaged. Crank, rod, cam, transmission maybe.

No way would I do anything without a complete disassembly to look all moving parts over.

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Re: Question about getting a new piston

#44

Post by avg_joe »

The crankcase was full of oil, and after the first run I pulled the tappet adjuster covers off, and poured some oil directly into the valve cover to fill the pockets. The cam and rocker assemblies look good, no bluing or galling at all.

I realize that a complete disassembly would be wise....but question whether it would be wise for ME to do it.
We are on page three of this endeavor already, and look at the carnage.....Not sure further disassembly will get me any closer to assembly.
The crank is discontinued, so I don't know what I could do anyway. Other than dump another hundred bucks or so into bearings.
I have already decided that I would keep my eye open for a better donor engine for any future projects, because this one probably wasn't the best candidate in the first place. I sure hate to throw it all away, at this point, if I could get it together and running for a couple seasons.
In the garage:
1977 GL1000
1982 GL1100 with California Side Car hack
1982 FT500 Ascot(Wife's bike)
1983 FT500 Ascot
1983 XL600R(with some 85 parts)
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Re: Question about getting a new piston

#45

Post by robin1731 »

Well, ok then.

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1976 Goldwing Super Sport
1985 Honda Elite
1976 KZ900 Dragbike
1992 ZX7 Dragbike (KZ900 style motor w/NOS)
and a rotation of various purchases
Randakk approved Carb Rebuilder
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