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Discussion Starter #1
I am tearing down the top end as part of an effort to get the thing running - we found a couple of things that did not make sense and so at the behest of my HondaTwins mentor Steve, tore down the top end to get a look at the camshaft. Well it is now being sent out to vacation on the west coast with Delta Cams as it had some pitting.
At this point, I have not removed the jugs. I am going to be replacing the eight studs (one was poorly repaired) and yes I can do that without removing the jugs. My question is when I pull the jugs are there any gotcha's removing or re-installing? A coworker with a lot of experience on these bikes indicated there was not much to it and said I would not need a ring compressor or the like to get the pistons back into to the cylinders.
It has been a long time since I have done this and then it was on a Harley shovelhead and I think the cylinders are at opposite strokes, whereas I think the Honda twin stroke is the same (both at the top or bottom at the same time). I am probably way wrong. Also I had two separate jugs to work with, meaning I could work on one piston at a time.
The last motorcycle engine I worked on is pictured in case anyone has an interest.
engine.lookingdown.jpg
 

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Yes, a 180 degree (TYPE 1) engine. The cylinders are pretty easy to slide over the pistons without a ring compressor, though. If you've ever done a twin with a 360 crank, the 180 degree ones are easy compared to that.
 

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One "gotcha" to watch out for...there are two small rubber retainers on top of the shaft for the lower camchain roller. It's very easy to drop those into the crankcase if you're not careful disassembling things. When you're pulling the jugs upward, make sure the base gasket between them and the engine case doesn't peel up, exposing the retainers. Number 11 in the illustration.
honda-cl350-scrambler-1968-k0-usa-cam-chain-tensioner_bighu0018e6006_a9be.jpg
 

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Discussion Starter #5
Well, displayed my lack of knowledge of general engine function. As to the gotcha, definitely will make sure the gasket stays low. Hope it was not sealed somehow. I noticed one of the gaskets I removed was attached to the upper, not lower assembly. Seemed odd at the time.
head.jpg
 

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Discussion Starter #6
Pulled the jugs today. Think I avoided the i gotchas. One of the cylinders doesn't look as clean as the other. Kind of expected markings on the pistons indicating 10 over or something. Could these be the factory pistons?
Buying a set of studs from a forum member. May go ahead and swap out all. I did drop a couple drops of penetrating oil around each stud.


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Discussion Starter #9 (Edited)
If they are not marked they are STD. Looks like you need an overbore and new pistons.
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Kind of expected that when I saw the right cylinder. Hopefully, the only machine shop I know (Clay's Machine Shop in San Antonio) can handle this. Guessing they will do these small cylinders.
Would I expect that the first oversize (.25 over) would suffice.
So the next ka-ching will be two pistons, two sets of rings and wrist pins and the machine shop work. I did notice that Common has the kits at about $155 each.
Piston - 13102-312-010;
Ring set - 13021-391-004.
Are there good aftermarket options?
 

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I'd research the available piston overbore sizes and let the machine shop tell me what overbore it needs before ordering new pistons and rings.
 

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Discussion Starter #12 (Edited)
The bigger challenge in my neck of the woods is a machine shop willing to do this. I talked to the proprietor of the shop that rebuilt the top end on my old harley. His minimum size is 2.5 inches in diameter, which might cover me. The manual indicates the bore starts at 2.501 inches. He really only works on Harley's but was OK just doing the cylinders at $55 per. I would just need to provide the pistons, rings and the clearance called for between cylinder and piston. Any feedback would be appreciated.
also when the parts manual refers to .25/.50/.75/1.00 what units are they referring to "over" standard - ie .25mm/.50mm/.75/1mm?
 

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$55.00 is not bad for boring a cylinder. I charge $45.00 to bore up to 1mm over. After that, it is $55.00. The 0.25, 0.50, 0.75... does refer to the oversize.
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Discussion Starter #14
Can one make an educated guess as to how far over I should go with my next set of pistons based on the images provided. A coworker, who messes around with all sorts of the older bikes suggested I would be pretty safe going .50mm over based on the same images I provided. He was of the opinion going with new reproductions was a better option than NOS suggesting the improvements in metallurgy would be a benefit from OEM NOS made some 40-50 years ago.
 

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Can one make an educated guess as to how far over I should go with my next set of pistons based on the images provided. A coworker, who messes around with all sorts of the older bikes suggested I would be pretty safe going .50mm over based on the same images I provided. He was of the opinion going with new reproductions was a better option than NOS suggesting the improvements in metallurgy would be a benefit from OEM NOS made some 40-50 years ago.
I thought I did that all ready.:confused: But I doubt 0.50 mm is going to clean that up. If those pits are more then 0.010" deep it won't. You might get by with 0.75mm over. But I would just go 1.00 mm over rather than buy pistons and then have to buy another set because the cylinders did not clean up.
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How far do you want to go? The stock sleeve should be good for 4.00 mm over. I can bore the block for a larger sleeve if you want to go larger.
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The bad news is you may have to open up the bottom end of the engine to find and extract those "missing" bits of piston skirt......They went SOMEWHERE....
 

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Discussion Starter #20
The bad news is you may have to open up the bottom end of the engine to find and extract those "missing" bits of piston skirt......They went SOMEWHERE....
Did I miss something - very likely - but I don't recall seeing broken piston skirts.
 
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