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Discussion Starter #1
I'm a new member and have started a few cb projects. Currently, I have (2) cb350, and (1) cb100 engine torn down. One of the 350's is a K0, the other is a K4. I'm at the point of all of these where I need to make a decision what needs to take place with the pistons, rings, and cylinder walls. Both of the 350 motor's pistons were replaced by the previous owner(s), and the 100 was frozen until yesterday when I knocked it free with a hammer. I have a new piston and rings for the 100 so I'm planning to measure that, to figure out what size it is and have the cylinder serviced accordingly. What I'm really looking to figure out is what I should do with the 350s. I've soaked the K0's pistons in seafoam for about 4 weeks, scrubbing them occassionally with a soft copper wire brush. I was surprised to see how well they cleaned up. All the carbon deposits are gone from the top of the piston (see picture), and I'm sold on the seafoam product. I'm currently soaking the K4's and following the same process.



Here are the options I've laid out, and would appreciate some opinions on what to do here.

1. Bore/hone the cylinders, new pistons, new rings.
2. Hone the cylinders, new rings
3. Hone the cylinders, re-use the piston and rings
4. Slap the thing back together, and see how it does.

Pictures attached... thanks in advance for the help.
Left Piston - 1969 K0.JPG Right Piston - 1969 K0.JPG 1969 K0 Pistons Clean.JPG 1969 Piston Head.JPG 1969 K0 Piston Scoring.JPG 1969 K0 Piston Scoring 2.JPG 1969 K0 Cylinder Wall Left.JPG 1969 K0 Cylinder Wall Right.JPG 1974 K4 Cylinder Wall Left.JPG 1974 K4 Cylinder Wall Right.JPG
 

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I believe its not a good idea to re use rings. You always have to seat them which requires a hone. To do it on the cheep just get rings, and lap the valves. Then break it in with a high zinc content oil.
 

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It is possible to put it back together just the way it was, all the parts in their same places including the ring gaps. It should run pretty much as it did before. If you're going to hone the cylinders, replace the rings.

Determining whether you can just hone and re-ring, hone and replace pistons and rings, or bore to a larger size requires an assessment by a qualified machine shop which I would suggest doing in any case.

This is one of those things that qualifies for the "as long as I'm in there anyway" factor.
 

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Always hone you can't not do it. Once you took the rings off those pistons you have to re seat the rings which requires a hone. If you can't determine which way the rings where exactly you'll have to at least replace those and hone the walls.
 

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I have reused rings several times. Mostly when replacing leaking base gaskets. You must definitely hone the cylinders when doing this though. But I always run the pistons, and cylinders to my machinist along with a spec sheet, and have him measure them for clearances. The best places to go are automotive machine shops (I go to a local Carquest shop) that have the equipment small enough to do motorcycle parts. A few phone calls should find one. They will be a lot less expensive, and do better work then the mechanic at the motorcycle shop who only occasionally does machine work.
Your cylinders in the picture look a little pitted. I would say from what I see there, you are going to need a bore, and pistons.
TOOLS
 

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I agree with Tools, some of the pictures make the cylinders look pitted. They might clean up with a hone job. A machinist could tell you. Also, you need to use a parallel hone tool to make the cylinders straight and round. A lot of people will use a three prong glaze breaker and call it a hone job. You don't want to do all of this work and have a smoker.

Another critical item is the ring grove in the piston. The gap between the piston and ring is critical. Look it up in the Honda shop manual. On my 450 it is about .002. My pistons were up to .028. If this is out of spec you will wind up with ring flutter. This will reduce compression at high RPM. The ring must seal to the cylinder and piston.
 

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Discussion Starter #7
Thanks everyone for taking a few minutes to review and respond. I have taken everyone's suggestion, and based on the work I've already put in, I'll be taking your advice, spending the money, and doing it right. I planned on using bore-tech from the beginning because I have a hard time going to a local machine shop in Atlanta and not knowing the quality of work I'll wind up with. That being said, all 3 jugs are carefully wrapped, packaged, and ready for shipment next week. Thanks for all the help and advice. I'll post pictures of the progress when everything returns.

Happy Labor Day.
 

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Discussion Starter #9 (Edited)
TexasMark,

Couldn't agree more. Everything was very well packaged, clearly marked (I sent multiple items to these guys), and the work was excellent. I have since done more work to the engine in regard to reassembly, and am just realizing that with any luck, my cam and rocker arms should arrive today.

IMG_2609.JPG IMG_2610.JPG

IMG_2614.JPG IMG_2617.JPG

IMG_2618.JPG IMG_2619.JPG

After investigating my old fat cam, I noticed that the threads were stripped badly and there was some very bad overheating that occurred on the tach side. I was told by the P.O. that there had been some oiling issues, which I discovered were due to some gasket material finding its way into an oil passage (which means the parts engine becomes a second project). I sourced another cam on eBay and got a pretty good deal on one in very good condition. My only problem is that the two were not exactly alike. I remember reading on the forum (outtobie) that the fat cams are interchangeable throughout the early years/models which call for them, however, before I go any further I'd like to ask those on this forum that very question. Particularly, the numbers were different between the two. My original read: 1,3,4 whereas this new cam reads 1,0,2. Not sure what these numbers mean. My first guess is that they're ratios of some sort or a production run indicator or something. Guess it would have been better to ask everyone here prior sending the cam off to deltacam for service.

Overheated Tach-side cam journal & Cam thread strip issues:

IMG_2625.JPG IMG_2749.JPG

IMG_2750.JPG IMG_2751.JPG

Any suggestions on the cam thread issue? I am hoping that I can have it serviced by someone and re-use it, if possible. Also, I plan to continue this thread until the bike is complete, so if anyone can advise how i move this to the proper section, I would appreciate that too.
 
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