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...because every day is MotoGP day when you own a CBR 125r...
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PostPosted: Wed Apr 23, 2014 2:25 pm 
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Racing ECU (!!)
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Location: Parksville, BC, Canada
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Hi Folks;

Ever since I got the bike two years back (with 700 kilometers on it) I've noticed that 5 => 4 downshifts intermittently go into what's commonly called a 'false neutral'. It only happens once in a while and I originally thought that once the engine & transmission had some decent mileage on it (let's say, 5,000) that it would go away. This has not proven to be the case :laugh: Though not as common an issue it still does it and I've only heard from one other user that has ever experienced the same thing so this is a bit of an oddity.

Earlier this year we installed two aftermarket camshafts for beta testing. I was thinking of creating a nice camshaft package for these bikes and offering them up for sale. Unfortunately, both camshafts failed miserably and almost rounded off the exhaust lobes. This meant that a LOT of metal went through the engine oil and was circulated around even though I changed out the oil in each case.

What's surprising is how well this engine handles steel in the oil. This is due to the engine using single-groove roller bearings throughout. They are darn near indestructible. Nevertheless, the bike vibrates more then it used to, steel shavings flowing through the oil is not a good thing, no matter how well the engine is designed and there's still the issue of the 5 => 4 downshift 'false neutral'.

So, the plan is, to split the case, go into the transmission and look for whatever might be causing the 5 => 4 downshift issue. At the same time I'll replace every roller bearing and pull the bearings off the crankshaft and replace them as well. For me, this will be very interesting as I'm curious to see what bearing wear the engine will exhibit. I heard from some folks in Asia who seemed to indicate that the bearings are often shot on this engine. Time to see if there's truth to that :top: I'm also very curious to see what the crankshaft specs out at given all the high RPM riding this bike has seen. It's spent, literally, days at 11,000 RPM+ and routinely bounces off the rev limiter in 6th.

I also honed out a spare cylinder so it's getting new rings (again). I've found that the factory cylinder finish on these engines is actually quite rough necessitating a significant break-in period. I've 'plateau' honed out my spare cylinder and put a considerably fine finish on it just to avoid such a break-in and aid in much faster ring seating.

Anyway, this thread will contain all the pics and such from this adventure and, as importantly, what wear we find in there. It should be an interesting trip - if you're into this kind of stuff :cool:


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PostPosted: Wed Apr 23, 2014 3:01 pm 
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Racing ECU (!!)
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We'll start with clutch cover removal and then remove the 4 bolts holding the custom clutch springs, plate and bearing in place...


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PostPosted: Wed Apr 23, 2014 3:05 pm 
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Then we'll move outside and remove the clutch center lock nut (specialty socket) as well as the primary drive gear lock nut.

This is made much easier with air tools and an impact gun along with the transmission in gear...

And then we'll leave the engine on it's side to allow more oil to drain from it (meaning less on my desk!) :laugh:


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PostPosted: Wed Apr 23, 2014 3:09 pm 
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Here's something interesting....it's a shot of our magnetic drain plug. What makes it interesting?

It's size and location. It's almost pushing up on the oil filter (close but not quite). This puts the magnet directly into the oil suction path. So all oil being drawn into the engine has to go right past it. It's my opinion that this is much better then the 'generic' magnet on a plug that sits in the bottom of the sump....


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PostPosted: Wed Apr 23, 2014 7:55 pm 
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Yeah I even went one step further and epoxied a Rare Earth magnet (the same size as the magnet on the drain plug).

I did this for 2 reasons. One, I felt that the magnet on the drain plug was a bit weak, and 2, I wanted to extend a bit further inside the case...

Cheers!!


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PostPosted: Fri Apr 25, 2014 12:31 am 
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I'll use your tip about the heat gun to try and remove the two remaining bearings in the case that I haven't got out yet. They're blind holes so you can't get them from the backside with a bearing punch. I could heat the back of the case though and then maybe they'll fall out.

I found out that the bearings are a mix when it comes to quality. All of what Honda may consider 'non-essential' ones appear to be of the cheap variety. The ones I have ordered are top quality Jap bearings so it's getting all new ones. I haven't pulled the one off the crank yet. We'll see how that one goes :huh:

I learned some really interesting stuff in there. For one, the factory covered up some of the oil passages with sealant. The service manual specifically states to not cover those passages and they were....

I also found some shavings in really interesting places. Connecting rod side clearance was way, way below tolerance spec though so that's really good. It's an expensive item and I'm quite certain that the bearings were the source of my vibrations. Almost all of them show signs of turning in the case - not good at all and I was pretty surprised about that....

On the transmission front, I've started looking closely at it to try and ascertain where that intermittent 5 => 4 downshift 'false neutral' is coming from. Thing is, it's a rare occurrence. I am seeing some slightly abnormal wear on two of the gears though so they may well get replaced. The nature of it is intermittent so some thought as to how the transmission works will be required to gain a better understanding of where/what to look for.

I am very surprised how well other things look. Virtually zero wear on the shift drum, zero wear on the shift fork shaft, almost zero wear on the transmission (with the exception of those two gears). The typical near zero wear on the cylinder (although I have one on standby that I plateau honed). The stock camshaft, with the overly high rate HD valve springs has held up really well. The connecting rod and crank look good.

But, all the bearings are shot. Not one of them was in decent shape. When they were installed they seemed OK but once removed and cleaned it was clear they were finished. In fact, I think I got to them just in the nick of time. Any more riding time and I probably would have had to buy new case halves due to wear from them spinning in their bosses...

When the new ones go in they will get a liberal coat of lock-tite. All in all though, I'm pretty happy and I'm very positive about what the outcome will be. It's been vibrating more then normal for some time. I can recall how smooth it was when new and those days are far back there so this should restore, literally, as new performance on both the smoothness and power front. Hopefully, the new higher quality bearings will perform better.

Thing is though, this bike has seen nothing but severe service it's entire life so for others reading this - I wouldn't read too much into it. It also has 25,000k on it now - the majority of which has been racing at top RPM for almost continuous periods.

I'm still waiting to hear about the prototype camshaft. It's been delayed but they assured me they were getting at it this week.....My hope has been to nail it all down in one shot in preparation for the ride with my nephew up North. I know he's going to want revenge for my cleaning his clock the last time we went out so the bike's going to have to be perfect - and then some (he's got a 2010 R6)

I asked the bearing engineers about getting the highest quality bearings for the crank and they said they could actually get some that are $400 each (!!). I passed on those and settled for some Japanese NTN's :top:

One thing's for sure, the bike will be as new again. The problem is that it just makes it that much easier to bounce off the rev limiter in 6th. Something has to be done about that thing.....

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Marvin Miller
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...because every day is MotoGP day when you own a CBR 125r...


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PostPosted: Fri Apr 25, 2014 8:28 am 
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I might be able to copy/PDF sections of my Haynes Manual (i.e. the engine over haul section for instance) and send them to you if that would help or give you a different perspective...

Cheers!!


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PostPosted: Fri Apr 25, 2014 11:50 am 
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grenadiers wrote:
I might be able to copy/PDF sections of my Haynes Manual (i.e. the engine over haul section for instance) and send them to you if that would help or give you a different perspective...


Appreciated, but I'm not sure it's going to help. I have the FSM (factory service manual) and, with respect to the transmission, it's an odd intermittent issue so I knew from the outset that trying to nail it down was going to be difficult. For all I know, it may even be a design issue.

The new bearings will show up early next week (they are coming in from Edmonchuck) and at that point I can test fit the assembly and watch how it works in an effort to gage what might be causing the issue. I didn't have a lot of time on tear down to look into it - I needed to get the bearings and some other parts coming asap to minimize the downtime.

With respect to the transmission, it may be one of those things that never gets cased but, we'll try!

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PostPosted: Sat Apr 26, 2014 3:05 am 
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Much appreciated write up Marvin. Always great reading your overhauls and inspections on the wee thing. Cheers.

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PostPosted: Sat Apr 26, 2014 2:36 pm 
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Thanks DG! Of course, this job means my place is full of bike bits until Tuesday when the bearings/Honda orders are slated to come in. It will be nice to get things going back together...mind you, I still have to pull the bearing off the crank and install the new one :blink:

Even typing out this reply is a bit of fun as the keyboard is sitting on top of one of the crankcase halves.. :laugh:


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...because every day is MotoGP day when you own a CBR 125r...
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