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The Honda CA95 / Benly 150 Restoration The little brother to the CA160 in our family of Hondas

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  #1  
Unread 05-23-2015, 05:53 AM
grubsie grubsie is offline
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Default Anybody have an idea what caused this?

Got out of work early yesterday so I registered my 1963 and took it out for a spin and went about 5 miles to get it inspected. On the way back, about a 1/2 mile from home, the engine seemed to be losing power almost like it was running out of gas so I pulled over and it sat there idling away but it sounded like a super loose lifter on the shifter side or severe piston slap. No smoke though but there was some smoke coming out of the breather tube from the head.

I hobbled it home, checked the oil level which was fine. I let it cool then checked valve clearances which were fine. So I pulled the engine and tore the top end down last night. Plenty of oil everywhere on the parts. Everything looked fine except for the shifter side piston. It was scuffed pretty bad and the cylinder also. The rings were free also. Took the rings off and the piston was really sloppy in the cylinder. The other piston looked as good as new except for carbon on the dome along with the cylinder. I have never seen only one piston like this.

Just finished tearing the rest of the engine down to clean out any crap (aluminimum) from the piston scuffing getting in the engine and ordered new oversize OEM pistons and rings.
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File Type: jpg ca95 intake.jpg (132.9 KB, 17 views)
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  #2  
Unread 05-23-2015, 04:27 PM
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Roberd42 Roberd42 is offline
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Wow that looks like 2 stroke lean seizure. I wonder if it wasn't getting oil on that side somehow. Plenty of oil on the crank on that side? got me stumped.
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Unread 05-23-2015, 05:59 PM
grubsie grubsie is offline
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Yeah it does look like a 2 stroke seizure. There's probably around 300 miles on this rebuild/bore. There was plenty of oil everywhere and no stuck rings.

The only thing I can think of is the pistons themselves although the clutch side piston looks like new. When I sourced the parts off ebay, the ad stated that the pistons were OEM but when they arrived, they were in boxes labeled SK. SK's are aftermarket. The OEM rings were sourced from a different seller and came in OEM boxes. I noticed that the wrist pins were a little more snug than the ones in the original pistons so I am wondering if that may be another contributor although the wrist pins seemed fine.

Water under the bridge now. Cleaned out the lower cases, tranny, clutch and other misc parts. Will button up everything tomorrow and wait for the new top end parts.

I really needed to take the engine out of the bike anyway to repair the small nick in the paint on the top engine case in the back where the starter cable comes up into the airbox area. That little nick was really bothering me.
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Unread 05-23-2015, 07:24 PM
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Roberd42 Roberd42 is offline
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Hmm. Ring gaps were ok when you assembled? Wrist pin and both clips good on that side at disassembly? What are the ring gaps now I wonder? I'm wondering how it affected only one side and the other is ok. That steers me away from timing or fuel problems as they run on a joint plenum. Stuff happens but it's almost like forensic science to figure out why to avoid a repeat.
Possibly you got lucky on the other side running oem rings/wrist pins on aftermarket Pistons. Some Pistons run a different style ring than oem. Not sure about what's out there for the benly.
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Unread 05-24-2015, 04:04 AM
Spokes Spokes is offline
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The picture of the bad piston looks like some of the pistons I found in really old engines.

I imagine that the rings may of been the wrong size. Perhaps they were oversize. The oversize rings installed on an aftermarket piston, stuffed into the cylinder caused extreme wear. Once the wear opened up the bore you lost compression in that side.

Another consideration is assembling the pistons and wrist pins without assembly lube. Assembly lube is key to providing a barrier between metal surfaces until the circulating oil reaches the moving part. That side of the cylinder began to bore itself out being dry the first thousand rpms setting the stage for extreme wear.

The SK pistons are not that bad. I have been "burnt" on aftermarket rings though.

Be careful with snug piston wrist pins. I again suggest using assembly lube when reinstalling wrist pins and new rings.

At this point I would bore the cylinders to match the oversize pistons.
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Unread 05-25-2015, 04:54 AM
Michaelclark50 Michaelclark50 is offline
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Spokes:
I happen to be at the point of putting my top end back together. I will be sure to go back and put the lube on the wrist pins as I did not do that when I assembled them. Any other suggestions or assembly notes for the barrel/head assembly?
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Unread 05-25-2015, 12:12 PM
Spokes Spokes is offline
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I use a liberal amount of assembly lube in the cylinders to provide a temporary barrier between the rings and the cylinder walls. Yes, coat the wrist pins before inserting them into the piston and rod.

I also coat the cam shaft lobes and soak the tappet assembly and cam chain.

The point of using assembly lube is to provide a temporary barrier between metal surfaces until the engine oil gets to the assembly.

When the engine starts, do not rev the engine! Allow the engine to remain at idle for at least 5-10 minutes. You can throttle up to 1/4 throttle and back after that.

After 30 minutes, change the oil and check the magnet in the drain plug. You may see some slivers or "metallic hair". Clean the magnet and install new oil.

The next oil change can be at 25 miles. Try to avoid free revving the engine until you are sure the engine runs fine. Good Luck!
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Unread 05-25-2015, 03:05 PM
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Yep all what he said, I usually don't lube the Pistons, rings, or cylinders (beyond a very thin layer of oil for rust prevention) to prevent any glazing. With these engines I guess it doesn't matter much being older and lower performance. Here's an excerpt from klemm vintage (two stroke guys but same concept):

About “Dry Top End Assembly” - One step that helps reduce break-in times is to assemble the top end with no oil at all on the piston skirt or cylinder walls. This step has a history worth telling.

In the middle 1960s and early 1970s American muscle-cars were a very popular item on automotive showroom floors. At that time, it was standard procedure for Detroit manufactures to assemble all automotive engines with a generous helping of oil on the cylinder bores and pistons. When these muscle-cars were first fired up, the assembly oil on the bores would burn onto the bores as a glaze that took a very long time for the rings to wear through before sealing.

Unfortunately, this assembly process caused problems for salesmen in the showroom. When prospective buyers took a muscle-car out for a test drive, it was a given that there would be at least one full throttle blast involved. During that full throttle blast, the poorly sealing rings allowed considerable oil to pass, and the brand new muscle-car would leave a big plume of unattractive blue oil smoke that could be seen in the rear view mirror…. Buyers were understandably put off by anything that appeared to be “already burning oil”.

This was a very real problem that Detroit had to address. In time, they learned that if they assembled the top ends dry, with no oil on the bores or pistons, they could avoid this initial burned on cylinder glaze. The result was much shorter ring sealing times (because the rings didn’t have to wear through that glaze), and the absence of blue smoke from those important test drive blasts.

This same rule applies to two-strokes … vintage or not. Some owners shy away from this assembly process because they fear scoring the piston … but it is an unfounded fear. On such assemblies, we do apply assembly oil to all the lower end bearings. In the first moments of initial combustion, that lower end assembly-oil disperses on the bore in even quantities that are easily enough to avert any kind of scoring. In addition, it bears noting that the lubrication needs of an unloaded engine spinning at very low rpms are very minimal. We have been assembling high performance two-strokes in this way since the early 1970’s. It works … and it results in greatly reduced ring sealing / break-in times.
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  #9  
Unread 05-26-2015, 08:03 AM
grubsie grubsie is offline
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Quote:
Originally Posted by Roberd42 View Post
Yep all what he said, I usually don't lube the Pistons, rings, or cylinders (beyond a very thin layer of oil for rust prevention) to prevent any glazing. With these engines I guess it doesn't matter much being older and lower performance. Here's an excerpt from klemm vintage (two stroke guys but same concept):

About “Dry Top End Assembly” - One step that helps reduce break-in times is to assemble the top end with no oil at all on the piston skirt or cylinder walls. This step has a history worth telling.

In the middle 1960s and early 1970s American muscle-cars were a very popular item on automotive showroom floors. At that time, it was standard procedure for Detroit manufactures to assemble all automotive engines with a generous helping of oil on the cylinder bores and pistons. When these muscle-cars were first fired up, the assembly oil on the bores would burn onto the bores as a glaze that took a very long time for the rings to wear through before sealing.

Unfortunately, this assembly process caused problems for salesmen in the showroom. When prospective buyers took a muscle-car out for a test drive, it was a given that there would be at least one full throttle blast involved. During that full throttle blast, the poorly sealing rings allowed considerable oil to pass, and the brand new muscle-car would leave a big plume of unattractive blue oil smoke that could be seen in the rear view mirror…. Buyers were understandably put off by anything that appeared to be “already burning oil”.

This was a very real problem that Detroit had to address. In time, they learned that if they assembled the top ends dry, with no oil on the bores or pistons, they could avoid this initial burned on cylinder glaze. The result was much shorter ring sealing times (because the rings didn’t have to wear through that glaze), and the absence of blue smoke from those important test drive blasts.

This same rule applies to two-strokes … vintage or not. Some owners shy away from this assembly process because they fear scoring the piston … but it is an unfounded fear. On such assemblies, we do apply assembly oil to all the lower end bearings. In the first moments of initial combustion, that lower end assembly-oil disperses on the bore in even quantities that are easily enough to avert any kind of scoring. In addition, it bears noting that the lubrication needs of an unloaded engine spinning at very low rpms are very minimal. We have been assembling high performance two-strokes in this way since the early 1970’s. It works … and it results in greatly reduced ring sealing / break-in times.
I am in this corner having raced 2 strokes for many years. I did however use just a hint of 2 stroke oil in the top ends but definitely used a sufficient amount on the bearings.

I have always practiced the same thing with 4 strokes and have never had a problem until this particular problem. Whatever caused this, happened all of a sudden and I doubt it had anything to do with assembly lube not being used.

I talked to the mechanic that I am going to bring my cylinders for re-bore and he thought along the lines I did that it was a two fold issue. After market pistons combined with a tighter than usual wrist pin fitting. This side was tighter than the other or the old pistons. He told me that he bets that the cylinder got a little ovaled on the inlet and exhaust side because the wrist pin wasn't allowing the piston to move as it should.

Kind of makes sense I guess.
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  #10  
Unread 06-01-2015, 07:16 PM
grubsie grubsie is offline
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Think I discovered the cause tonight as I was finally able to get back to reassembling the lower end of the motor. I didn't notice it until I was assembling the clutch. One of the tabs on a friction was missing. Don't know how I didn't notice it when cleaning the parts. It looks like it just fell? broke off? I am wondering if it or many pieces of it found their way into the gear case and somehow got into that particular cylinder first before anywhere else because the other cylinder looks fine and that piston only has a few very fine scratches in it upon inspection when cleaning.

I sure hope this was the cause. I am definitely ordering new friction discs.

Last edited by grubsie; 06-01-2015 at 07:19 PM.
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