Boring the CA95 Cylinder

[Smithers]

Here is the reason for boring the Honda cylinder and replacing the pistons and rings. They don't run so well when the pistons are slapping around from some worn out pistons or a bad boring job. People in the old days used to just throw anything they had together just to get the bikes going sometimes. This "mechanic" decided that he could just bore the cylinder a little and knurl the piston skirts to compensate for the increased diameter hole. Either that or the guy charged the poor owner for new pistons, roughed them up like you see with the knurling (crosshatch design stamped into the sides of the pistons) and send the guy on his way. I wasn't happy to discover this when I removed the cylinder head and it made sense considering how horrible the motorcycle sounded when it last ran. Plus all sorts of oil was flying out the exhaust pipe from every pipe joint.

You can also see how the nickle/chromium plating has worn off. The plating, of course, is done to decrease the friction on those high revving pistons. These bikes can really rev higher than you might realize. It amazes me still.


This process of boring the cylinder is quite an important task so I decided to start a thread for it. I scored some .25 over pistons and rings on Ebay that will be going into this particular Honda 150 since one of the cylinders is spurting out a little oil from the exhaust. I assume the rings are bad, thus scuffing up the cylinder walls. I could have just honed it out I guess but going a big larger with some new pistons is the ultimate fix.

I have a vertical milling machine so I was set on using it to run a boring head down each cylinder and have some fun in the meantime. I talked to a couple people in the engine modding/tuning industry and they pointed me in a couple directions for tooling and techniques. I learned a lot from their experience and even got a hot lead on a CAD engineer that has a waterjet machine! This will come in handy for my Lexus V8 swap into my Tacoma =) but that's another project.

Today I spent a lot of time talking to my friends who are machinists by trade and for fun. I found and borrowed a nice boring head for my mill but it's a tad too big. Then I realized the person I needed to talk to lived right down the street from me and he has the largest and most expensive collection of machining equipment in the county (that isn't strictly government owned). I visited him with the intention of just borrowing a correctly sized boring head and a couple cutters if he had them but we got to talkin. He offered to let me into his factory to take care of it "the right way" as he put it. So basically we're going to find some time next week to give my cylinder head the most accurate boring/honing job ever done on Honda CA95. What a dream this will be.

I will be carefully taking apart the engine this weekend and going through the whole motor checking it out from top to bottom. Since I have a few days till the cylinder work I will take the time to paint the cases and heads grey and then the Honda 150 cylinder black. Once again I'm going a little more overboard on another project than I had originally intended!

[Smithers]

Well I took the cylinder off and discovered that the reason is was showing all sorts of carbon and oil coming from one cylinder (out the exhaust) is that some backyard mechanic improperly bored it. It already had .25 over pistons so the brand new ones I just bought aren't going to work. The cylinders had been bored too much and they even tried to put some cross hatch grooves in the bottom skirts of the pistons. Back in the day they used to do this to try and seal the piston better but in this case it was done to compensate for the over-boring. It didn't work.

SO I bought some .75 over pistons and rings and had it bored out by Hal's Machine of Paso Robles. He did an absolutely perfect job of it and even explained that the pistons weren't perfectly matched. When I went to pick the parts up he explained that he had properly bored one hole larger than the other to make up for the difference. Perfect! I couldn't have asked for more.

[dracor85]

Smithers, where did you find the .75 over pistons and rings? Also how much displacement does it add to the motor do you know?

[Smithers]

Hey there, I bought them on Ebay. There are genuine Honda parts from Thailand. They seem to have the most parts over there still. You could do the math for the difference in displacement but it won't add one bit of power. The increase is purely for increasing the size of the piston to compensate for the very slight increase in bore size due to surfacing or honing the cylinder wall to smooth them. Back in the day the variance in machined parts was much greater than what is produced in modern times. Therefore you would have some cylinder and piston sets that were matched better than others from the factory. Plus the alloys didn't last as long as most quality engines of today. So every now and then it was normal to tear down an engine and replace the worn piston rings (which might have scratched the cylinder wall requiring some honing of the cylinder).

So basically the oversized piston and rings sold by Honda were for prolonging the life of the engine whereas these days new engines last a long long time. You have to imagine that back then spark plugs didn't last even 10,000 miles and the points still require regular cleaning and replacing on these engines.

I have met a couple guys who used to build these engines with larger pistons for racing. They also built custom crankshafts and rods. That kinda stuff can be done but it just requires experience. Engines are so disposable now that people never do this kind of work anymore. You can just buy a larger Chinese knock off engine for less than putting together your own custom performance kit.

[62benly]

I took my engine into a shop yesterday. We measured the bore and they were already .2 over. So we decided to go .5 over. The trouble is I can't find any .5 over pistons on eBay, there are rings but no pistons.

Im wondering why smithers went all the way up to .75. Is it because .75 are easier to find?

Thanks.

[Smithers]

Hey good morning, More Power! Nah just kidding. Yeah the .75 was the only thing I could find at the time and I wanted to get it done. With todays oils being 100 times better I'm not even worried about wearing them out to the point that it will start smoking or piston slapping again. The bike won't be ridden another couple thousand miles in it's lifetime - or my lifetime at least .

There are some .50 pistons and rings out there somewhere so you could start throwing out some emails requesting some. Try and contact the sellers of the Honda parts on Ebay and ask them if they have a set of .50 for you. If they don't have them in stock they might be willing to find a set for you to make the sale. Of course you can always call Ohio Cycle or whoever and ask them too. Get the part number and throw it in the magic Google machine.

Here we are... my .25 over pistons which are for sale Neat picture though.


And here is the closest picture I can find of the new Honda pistons .75 over. They are in there somewhere:

[62benly]

Smithers!!!

I called ohio and he said he had .5 over but only of a certain kind and needed my engine #. So I hope my engine # matches up. I'll call him back tmrw cause im at school.

By the way, what kind of oil do you use? I want to use the stuff that smithers uses.

[Smithers]

A certain kind? Maybe he meant a certain model of Honda. Weird. I would get the part number that he gives you and double check it b4 paying of course. Or give it to me and I'll check it out 4u.

I'm just throwing out this info for everyones benefit - 62benly knows most of this.

I wouldn't run synthetic - especially if you haven't put all new seals in it! And any oil that is made today is WAYYY better than what was sold when Mr. Honda designed his engines. Just grab anything you have laying around as long as it's not too thick - no 40wt haha. A regular 30 or a 10-20 or something will be plenty of protection. Just don't use Penzoil whatever you do. In just about every single case of engine failure that I have ever witnessed in my life the problem wasn't the oil, it was the lack of oil!

Thinner weight oil is always better to use than thicker unless the mfg calls for such a thick oil. All of the oils today protect so well and they don't break down for the longest time compared to oil in the days of old, haha. You don't want to overwork your oiling system with a thick oil. Think hot engine trying to suck pancake syrup through small straw. Then the circulation suffers. Back in the day oil would break down and thin out regularly. That's why thick oil exists for in the first place... and for heavy equipment.

I grabbed some Valveoline oil from my neighbors garage to fire up the CA95 after the rebuild. I was out of 30. I ran the thing for a few miles and drained the oil and replaced it with some Supertech Wal-Mart brand or something. It's perfectly good oil as it is just a rebranded oil so they can capitalize on the discount oil market. I'm not going to say which oil it is cause I don't want to make this an oil thread.

Just stay away from Penzoil. I've opened up many engines in my short life and I can tell right away the ones that have been fed that crap.

[62benly]

So I called Ohio again this morning. He said my bike needed the "early" pistons which he only had in aftermarket. Part number 13103-206-000. He did'nt sound too enthusiastic about aftermarket pistons.
Im not sure whats different about the "early" pistons, but he seemed to think my bike needed them. So, as of now im not quite sure what to do. Maybe i'll call my shop and have em hold off on the bore in case I need to go bigger.

[Smithers]

Well who makes the aftermarket pistons? Probably ART. I would have no problem running aftermarket. He might be referring to the part number as they converted all the older part numbers to the newer system of numbers as the Honda catalog of parts grew into the billions or whatever the number is. He was probably not sounding enthusiastic because you were making him cross reference the older part numbers! You were just making him work a little and who wants to actually WORK at their job? Gimme a break. If you are an engine builder with hands-on building experience that has encountered multiple engine failures do to low quality aftermarket pistons I'll listen to you maybe. But people saying that an aftermarket piston isn't as good as the factory labeled one... yeah whatever. Nowadays manufactures have most of their components built by other companies and shipped to them for assembly. Clutches, master cylinders, transmissions etc are almost produced by a specializing mfg in every case. Honda was definitely on top of his game and made his stuff in house because there was no one else that COULD make quality pistons in the designs he needed. But soon after there were specialty companies that stepped up and just adapted their production line to copy his specs.

I would just order the piston kit and get the thing running. If they aren't so enthusiastic I would ask for a discount on the items because apparently you are doing them a favor for taking those crummy parts off their shelves for them. Seriously.

And if you put that part number in the magic Ebay right now you get a result of a .50 piston that has ART cast on the side of the piston. That relates to Sudco Mfg. in Japan. I found this as well: Contact Sudco and inquire about the piston rings. Sudco is a mjor suplier of MC parts including ART Pistion Kits. Their emaill address is: [email protected] or visit their website: www.sudco.com/art.html.

I would just email them for fun to ask them about some old Honda pistons... you never know. But they have been making pistons forever so if anyone, they would know maybe. Yeah NEVER let anyone bore cylinders without the desired pistons in hand! The factory Honda pistons I bought were slightly different sizes and the holes were bored accordingly and labeled. Today we have MUCH better production methods than they did back then when they were manufactured! They didn't have near the consistency in both materials or production.

Order up a CA95 piston kit and get rolling. =]
Don't forget new circlips for the piston pins.

[Smithers]

I also found this company's website. They are Seminole Powersports out of Florida. They list all the parts and numbers so who knows if they have access to them. Kinda spendy so I would call them and act like I didn't see the website. Then if they give you the high prices I would act shocked and they will probably give you a normal price to make the deal go through. It's worth a try.

Of course for general info to make life easier: Before you call for parts from anywhere find the part number yourself and confirm it. I never let people look up parts for me. It's just another area that your order can get screwed up. And make them read the part # back to you as well. Then when you give them the part number they can confirm it with their results as well to give you the definite conclusion. The Seminole site gives the result of a 1959 CA95 and they don't show it for other years... probably because they all use the same part numbers.

[Jetblackchemist]

The piston knurling was used to help keep oil up in the cylinder, the old timer justification for the practice is if the piston is slick below the rings oil won't stay up and lubricate the cylinder that well, so knurling is one of those old sneaky tricks of the trade. I am thinking about knurling my pistons when I start balancing the crank.

Some people still glass bead below the rings for the same reason, this isn't suggested unless you have forged pistons, as glass beading fragments into the aluminum creating small glass shards to wreak havoc later. I am sure the sleeves were very well oiled even after things went haywire.

[Smithers]

I'm going to ask around about this. I have met a lot of gents in the last couple of years that will give me an earful if I ask such a question. Can't wait for the lectures I'm going to get on the subject.

[Jetblackchemist]

Lol trying to kick the hornets nest? Whats weird about old guys is it like they are in a race to disseminate all their information, cause they are too old to race and just want to pass the torch and not be buried without passing along their hard earned information.

[Sam Green]

http://www.youtube.com/user/draghondama ... Hkb4BN_d_s

Remind this old man not to pass on any more information on these old bikes, I'm too busy racing.

Sam.