Author Topic: 1980 CB125S seized piston (Read 8708 times)

Pielz · « **Reply #25 on:** May 12, 2020, 12:41:25 pm »

Quote from: grcamna2 on May 12, 2020, 09:52:12 am

That's the small pin that fit's into the camshaft to 'key' the points advance mech at the correct position.

Awesome! You guys are dang experts man.

Couldn't find it in the manual or anything so thanks so much.

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Pielz · « **Reply #26 on:** May 12, 2020, 04:08:34 pm »

So this is probably gonna need replaced, huh? Wonder if JB Weld would be okay for this? Anyone have any guidance?

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Pielz · « **Reply #27 on:** May 12, 2020, 04:42:56 pm »

Got the piston unsiezed btw and the kick starter works perfectly

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grcamna2 · « **Reply #28 on:** May 12, 2020, 05:13:44 pm »

Pielz,
I have a few of those parts;what's the condition of the inside of your cylinder,a few pics and well-lit close-ups will help.

Pielz · « **Reply #29 on:** May 12, 2020, 06:54:59 pm »

Some of that is rust, some is hard build up carbon. I just sprayed some carb cleaner in there a min ago

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grcamna2 · « **Reply #30 on:** May 12, 2020, 07:48:44 pm »

I may still have a one size over oem Honda piston or 2 in my stash:if I could possibly see how deep those pit/rust marks/holes are then I could see if one size over(.25mm) or bigger will work in that.I do have an oem Honda cam chain tensioner part,I'm sure.I wonder if you would use some emery cloth on the bore of that cylinder,it will make it much easier to see the condition of it. Bill

Pielz · « **Reply #31 on:** May 12, 2020, 08:17:59 pm »

What about some 0000 steel wool? I was going to soak it in some pinesol to soften up that carbon and the old gasket material tomorrow

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grcamna2 · « **Reply #32 on:** May 12, 2020, 08:39:10 pm »

Quote from: Pielz on May 12, 2020, 08:17:59 pm

What about some 0000 steel wool? I was going to soak it in some pinesol to soften up that carbon and the old gasket material tomorrow

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if you don't have emery cloth,a small sheet of med/fine sandpaper will clean it up;#0000 steel wool is Way to fine.
Looks like some of that rust is caked inside there,you may need to scratch it off of there with something sharp.

Pielz · « **Reply #33 on:** May 12, 2020, 08:50:30 pm »

I thought about getting a honing tool from harbor freight that'll work. I'll have to see if they have them in stock tomorrow.

I might be able to carefully use a razor blade for that, yeah?

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grcamna2 · « **Reply #34 on:** May 12, 2020, 09:52:15 pm »

Quote from: Pielz on May 12, 2020, 08:50:30 pm

I thought about getting a honing tool from harbor freight that'll work. I'll have to see if they have them in stock tomorrow.

I might be able to carefully use a razor blade for that, yeah?

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Sharp safety razor blade will work also,be careful

754 · « **Reply #35 on:** May 12, 2020, 11:03:02 pm »

I don't know if 2nd over will clean it up , those pits are deep.
I don't think 1st over will do anything, the pits would have to be about 4thou deep max.. a hair is about 3 thou.

grcamna2 · « **Reply #36 on:** May 12, 2020, 11:11:45 pm »

Quote from: 754 on May 12, 2020, 11:03:02 pm

I don't know if 2nd over will clean it up , those pits are deep.
I don't think 1st over will do anything, the pits would have to be about 4thou deep max.. a hair is about 3 thou.

I was looking at those rust areas at the top of the cyl..
May need to get another cyl, Ebay.

The next model/yr., 1981' CB125S uses the exact same crankcases as the XL185S.The spigot where the sleeve fit's is(70mm i.d. across) much larger.You would be able to build that engine into an XL185 very easily as you'll probably need to replace that cylinder and you could use the same head.There is a cheap China cyl./piston kit(some of them come through having slightly tight final clearance:a quick pass with a Quality Sunnen is all it needs to get it to.001" spec) on Ebay:61mm piston and cylinder kit,145cc and usually goes for about $60-70.
That 1980' model has the small spigot.Would you measure across that crankcase spigot/mouth just to see exactly what it's dimension are ?

grcamna2 · « **Reply #37 on:** May 13, 2020, 12:02:05 am »

Quote from: Pielz on May 12, 2020, 08:50:30 pm

I thought about getting a honing tool from harbor freight that'll work. I'll have to see if they have them in stock tomorrow.

I might be able to carefully use a razor blade for that, yeah?

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I have tried using a cheap 'glaze breaker' hone numerous times;the new rings I installed didn't seat correctly and it used oil.The correct hone to do a Fine job is very expensive,but needed.
I need to hit the lottery and purchase my own machine shop;it would be simpler and easier than waiting for some of these independent powersports machinists to care about my small jobs..

Pielz · « **Reply #38 on:** May 13, 2020, 07:57:13 am »

What would you trust more, a cheap honing tool or a cheap cylinder kit off eBay? lmao. If this cylinder is totally borked anyway, it might be a cool experiment.

Having a machine shop would be beautiful.

Oh but sure, I'll measure across that for you! Unfortunately my calipers just broke so hopefully I can manage to get a decent measurement via some other tool. So you want me to measure the tube where the cylinder comes out of the jug? Just for clarity.

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grcamna2 · « **Reply #39 on:** May 13, 2020, 08:39:15 am »

Quote from: Pielz on May 13, 2020, 07:57:13 am

What would you trust more, a cheap honing tool or a cheap cylinder kit off eBay? lmao. If this cylinder is totally borked anyway, it might be a cool experiment.

Having a machine shop would be beautiful.

Oh but sure, I'll measure across that for you! Unfortunately my calipers just broke so hopefully I can manage to get a decent measurement via some other tool. So you want me to measure the tube where the cylinder comes out of the jug? Just for clarity.

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Pielz,Some of those cylinder kits come through very close,I would just check them before installation.
I want you to measure the large hole in the engine cases where the cylinder goes into:the spigot size.I would like to know that to see if one of those big bore cylinders will fit.I'm sorry to hear your calipers broke.. You may try to use another accurate method,I want to know in millimeters.

Pielz · « **Reply #40 on:** May 13, 2020, 10:19:52 am »

Gotcha, I'll report back with measurements! Currently taking some fine sandpaper to the cylinder walls to see what were dealing with. I'll post pics when I'm done for evaluation

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Pielz · « **Reply #41 on:** May 13, 2020, 10:49:49 am »

After a bit of cleanup. Probably unusable, huh. Gotta go out and get another set of calipers to measure spigot

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grcamna2 · « **Reply #42 on:** May 13, 2020, 12:19:21 pm »

Yeah.. I'm not sure just how deep those rust pit holes actually are

Pielz · « **Reply #43 on:** May 13, 2020, 12:39:04 pm »

They're probably about 2-3 thou deep. Im headed home with calipers I'll have that measurement for you

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Pielz · « **Reply #44 on:** May 13, 2020, 01:19:04 pm »

63.5 mm +-.1 is the measurement I got across the spigot hole there in the top of the crank case

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grcamna2 · « **Reply #45 on:** May 13, 2020, 01:40:28 pm »

Quote from: Pielz on May 13, 2020, 01:19:04 pm

63.5 mm +-.1 is the measurement I got across the spigot hole there in the top of the crank case

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Ok,
I will now try to somehow figure out by that Ebay listing what the measurement of that cylinder liner O.D. is and see if it will fit your spigot,if that is an option you want ?

Pielz · « **Reply #46 on:** May 13, 2020, 01:43:35 pm »

Heck, if it'll work with my head and valve cover I'll take a few extra CCs of displacement, especially if it's money I'd be spending regardless.

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grcamna2 · « **Reply #47 on:** May 13, 2020, 01:52:06 pm »

Quote from: Pielz on May 13, 2020, 01:43:35 pm

Heck, if it'll work with my head and valve cover I'll take a few extra CCs of displacement, especially if it's money I'd be spending regardless.

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One of us could send an Ebay message to that seller and ask them what the O.D. dimension of the bottom of that cylinder liner is.I think,from what I remember that it is wider than 63.5mm because the 61mm piston needs a thicker liner in case you bore it out a few times:it would be more than your spigot i.d. opening.. from memory,about 67mm o.d.

I think other cylinder/piston kits are there on Ebay for the CB125 size barrel o.d. if you want that cheap China kit style.. it's cheaper than quality oem with the machinist boring it out.

grcamna2 · « **Reply #48 on:** May 13, 2020, 02:20:27 pm »

I found that other China kit that will fit your bike on Ebay.
Were you going to do a long term restore of this bike to original? or just a fun play bike
I would get that cylinder checked by a quality machinist to let you know if a 1mm(max over-bore CB125S oem piston)OEM Honda piston and rings will be able to be used,if the rust isn't too deep.I like oem quality because I think oem is the best. Imo

Pielz · « **Reply #49 on:** May 13, 2020, 02:59:50 pm »

It's going to definitely be a fun bike to mess around with and not a full restoration. eBay parts special for all the lights and whatnot. I appreciate you going through all the effort to research that stuff for me.

I'll probably use a Chinese cylinder kit and hope for the best. Although a bigger bore would be awesome if I could eek a bit more power out of it.

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Author Topic: 1980 CB125S seized piston (Read 8708 times)