Cb400 Super four hyper vtec NC39 Gearbox problem

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Tarlowb
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Bike owned: CB400SF NC39, '88 NC23 tri-arm
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Cb400 Super four hyper vtec NC39 Gearbox problem

Post by Tarlowb » Sun Jul 08, 2018 10:39 pm

Hello Greybikers

In April 2017 i was riding my bike, and hit a false neutral between 5th and 6th. i quickly pulled the clutch lever but it wouldn't find either 5th or 6th. At this point the road revs were much higher than the idle speed the engine was now running at and in the confusion, there was a series of clacks and crunches and it found 5th gear.

I pulled over to investigate and the engine would rev fine, so i tried riding it, no problem through 1st - 5th but 6th was skipping, my heart sank. :cry: :shock: :down:

It has been back on the road for two weeks, and i have documented as much of the process as i could.

This is my write up detailing how i fixed it for anyone who has got this issue,had this issue or may have this issue in the future. it will include how i removed the entire engine, sourced parts and managed to get her working again. i appreciate there are people who know what they are doing on this forum, but I've learnt a lot from this experience as well as using the pages for information to so if nothing else i'm happy to give some knowledge/experience back.


Quick History: Im not a mechanic, just learning as i go, I've been riding since 2012 on a 125, passed my full test in 2016, had a 650 bandit, sold it after a year and got the NC39 and love it :grin:

Tarlowb
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Re: Cb400 Super four hyper vtec NC39 Gearbox problem

Post by Tarlowb » Sun Jul 08, 2018 11:43 pm

To start with, here is a photo of my bike :grin:

Image

Tarlowb
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Re: Cb400 Super four hyper vtec NC39 Gearbox problem

Post by Tarlowb » Sat Jul 14, 2018 4:11 pm

The bike was stuttering in 6th gear, not smooth like clutch slip, more like the symptom of worn dogs on the gears. I didn't think this was the case as it only happened in the v-tec threshold. but after a little more riding, it realized it WAS also present under the VTEC threshold too, anything more than 40% throttle and its skipping.

I had a chat with a few biker friends who had different opinions ranging from adjusting the clutch, changing fuel, checking for speed limiters etc (its a Japanese market bike, but because it doesn't have the traditional front wheel speedo drive like the NC31,that was unlikely to be a factor. the speedo is electronic and there is a sensor above the engine, but below the airbox, which must have been converted to mph. the dials still go up to 200 but there is a sticker that says MPH where it used to say KPH)

All were incorrect. I have a powertech end can on it and replaced with the stock can, but still the same, I even checked the spark plugs, HT leads and ignition but all were fine. I then contacted Grame France of GFracing in his workshop, he said it was definitely a gearbox failure, but he could fix it if I took the engine out and delivered it to his workshop near Scarborough.

This may be no big deal to a mechanic or a motorcycle restorers etc, but I was seriously hesitant and apprehensive about the task ahead of me. right, some more photos next (having difficulty uploading them doesn't matter what size for some reason? any tips other than the ones on the main board?)

Tarlowb
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Re: Cb400 Super four hyper vtec NC39 Gearbox problem

Post by Tarlowb » Sat Jul 14, 2018 4:33 pm

Image

alright, photobucket seems to be ok for hosting and resizing. :peace:

I waited a few months to start as I was about to move into my first house (garage to work in 8-) ) and did the things I already knew how to do which was remove the seat and tank. to remove the tank remove the two side panels and after that, undo the big bolt at the back of the tank. there are a five connections to the bike. fuel and vacuum lines on the left side of the bike, fuel sender electrical connector on the right hand side and two breathers/overflow? rubber tubes towards the rear of the bike. after this, the whole thing should slide backward a few inches and then be free to lift up.

At this stage I had brimmed the tank with petrol to prevent condensation and added some fuel stabilizer, drained the oil, and the coolant. the coolant hose can be seen looped back on itself into the reservoir, but was connected just under the brass coloured coolant top up tap, top right.

Tarlowb
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Re: Cb400 Super four hyper vtec NC39 Gearbox problem

Post by Tarlowb » Sun Apr 21, 2019 12:20 pm

Hello again GB

I have been riding my bike since my last post and the gearbox is all good. classic case of starting a thread and forgetting about it! apologies.

Once the engine was out, and transported to GFracing, I had a general clean of all the bits you cant access with the engine in the frame and twiddled my thumbs. After a few months I collected the engine as a there were a few issues with the procurement of engine component and the time frame wasn't looking good.

I had found a Japanese NC39 parts manual which I used to identify the parts in the gearbox, and managed to find sellers for them all. I have a copy of this if anyone wants it, just send me a PM, or I can send it to the admins to add to the document library?

As I had my engine back, I took it too my local mechanic in the midlands, who was hesitant to undertake the work as he hasn't worked on a VTEC before, and understandingly, didn't want to mess it up. but after a bit more information, I convinced him to try.

He had the sump off and inspected the gearbox for damage, and identified that two parts would need replacing, a gear and one of the three selector forks. I expected a much larger bill in all honesty! I said I would order the parts and could he hold onto the engine for a couple of weeks.

I managed to order these parts from hondamotorcyclepartsonline, an Australian company also called north coast power sports? tiny little shop in NSW. total bill for the parts delivered was £120, great value for genuine Honda parts!

Once these were delivered (2 weeks, not bad from Oz to the UK) I delivered them to the mechanic who popped them in, new gaskets to the alternator cover and the clutch cover, which were readily available.

Re-assembly was the same as the disassembly but i have photos of both, I'm not going to clog up the forum as there are over a hundred, the bike I now running well with new oil, coolant and filters.

If anybody has any questions or needs advice, fire away!

Indosuperfour
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Re: Cb400 Super four hyper vtec NC39 Gearbox problem

Post by Indosuperfour » Sat May 04, 2019 4:55 am

Tarlowb wrote:
Sun Apr 21, 2019 12:20 pm
Hello again GB

I have been riding my bike since my last post and the gearbox is all good. classic case of starting a thread and forgetting about it! apologies.

Once the engine was out, and transported to GFracing, I had a general clean of all the bits you cant access with the engine in the frame and twiddled my thumbs. After a few months I collected the engine as a there were a few issues with the procurement of engine component and the time frame wasn't looking good.

I had found a Japanese NC39 parts manual which I used to identify the parts in the gearbox, and managed to find sellers for them all. I have a copy of this if anyone wants it, just send me a PM, or I can send it to the admins to add to the document library?

As I had my engine back, I took it too my local mechanic in the midlands, who was hesitant to undertake the work as he hasn't worked on a VTEC before, and understandingly, didn't want to mess it up. but after a bit more information, I convinced him to try.

He had the sump off and inspected the gearbox for damage, and identified that two parts would need replacing, a gear and one of the three selector forks. I expected a much larger bill in all honesty! I said I would order the parts and could he hold onto the engine for a couple of weeks.

I managed to order these parts from hondamotorcyclepartsonline, an Australian company also called north coast power sports? tiny little shop in NSW. total bill for the parts delivered was £120, great value for genuine Honda parts!

Once these were delivered (2 weeks, not bad from Oz to the UK) I delivered them to the mechanic who popped them in, new gaskets to the alternator cover and the clutch cover, which were readily available.

Re-assembly was the same as the disassembly but i have photos of both, I'm not going to clog up the forum as there are over a hundred, the bike I now running well with new oil, coolant and filters.

If anybody has any questions or needs advice, fire away!
Sounds like you've a big things to do in back time.. 8-)
Nice share.. so at the end, how many part items that you replace to restore the bike?

Tarlowb
Settled in member
Reactions:
Posts: 39
Joined: Tue Oct 11, 2016 9:37 am
Bike owned: CB400SF NC39, '88 NC23 tri-arm
Location: West Midlands
Re: Cb400 Super four hyper vtec NC39 Gearbox problem

Post by Tarlowb » Sat May 04, 2019 6:43 am

Indosuperfour wrote:
Tarlowb wrote:
Sun Apr 21, 2019 12:20 pm
Hello again GB

I have been riding my bike since my last post and the gearbox is all good. classic case of starting a thread and forgetting about it! apologies.

Once the engine was out, and transported to GFracing, I had a general clean of all the bits you cant access with the engine in the frame and twiddled my thumbs. After a few months I collected the engine as a there were a few issues with the procurement of engine component and the time frame wasn't looking good.

I had found a Japanese NC39 parts manual which I used to identify the parts in the gearbox, and managed to find sellers for them all. I have a copy of this if anyone wants it, just send me a PM, or I can send it to the admins to add to the document library?

As I had my engine back, I took it too my local mechanic in the midlands, who was hesitant to undertake the work as he hasn't worked on a VTEC before, and understandingly, didn't want to mess it up. but after a bit more information, I convinced him to try.

He had the sump off and inspected the gearbox for damage, and identified that two parts would need replacing, a gear and one of the three selector forks. I expected a much larger bill in all honesty! I said I would order the parts and could he hold onto the engine for a couple of weeks.

I managed to order these parts from hondamotorcyclepartsonline, an Australian company also called north coast power sports? tiny little shop in NSW. total bill for the parts delivered was £120, great value for genuine Honda parts!

Once these were delivered (2 weeks, not bad from Oz to the UK) I delivered them to the mechanic who popped them in, new gaskets to the alternator cover and the clutch cover, which were readily available.

Re-assembly was the same as the disassembly but i have photos of both, I'm not going to clog up the forum as there are over a hundred, the bike I now running well with new oil, coolant and filters.

If anybody has any questions or needs advice, fire away!
Sounds like you've a big things to do in back time.. 8-)
Nice share.. so at the end, how many part items that you replace to restore the bike?
Hey Indosuperfour

All of the work on the gearbox is complete, and the part numbers that I needed are the following;

FORK C GEAR SHIFT 24212MBE000
Gear m3-m4 23451MY9750

Also the gasket sets but those were easy to find :)

Do you happen to run the Instagram page by the same name? Image

Sent from my EML-L09 using Tapatalk


Indosuperfour
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Re: Cb400 Super four hyper vtec NC39 Gearbox problem

Post by Indosuperfour » Sat May 04, 2019 6:47 am

Tarlowb wrote:
Sat May 04, 2019 6:43 am
Indosuperfour wrote:
Tarlowb wrote:
Sun Apr 21, 2019 12:20 pm
Hello again GB

I have been riding my bike since my last post and the gearbox is all good. classic case of starting a thread and forgetting about it! apologies.

Once the engine was out, and transported to GFracing, I had a general clean of all the bits you cant access with the engine in the frame and twiddled my thumbs. After a few months I collected the engine as a there were a few issues with the procurement of engine component and the time frame wasn't looking good.

I had found a Japanese NC39 parts manual which I used to identify the parts in the gearbox, and managed to find sellers for them all. I have a copy of this if anyone wants it, just send me a PM, or I can send it to the admins to add to the document library?

As I had my engine back, I took it too my local mechanic in the midlands, who was hesitant to undertake the work as he hasn't worked on a VTEC before, and understandingly, didn't want to mess it up. but after a bit more information, I convinced him to try.

He had the sump off and inspected the gearbox for damage, and identified that two parts would need replacing, a gear and one of the three selector forks. I expected a much larger bill in all honesty! I said I would order the parts and could he hold onto the engine for a couple of weeks.

I managed to order these parts from hondamotorcyclepartsonline, an Australian company also called north coast power sports? tiny little shop in NSW. total bill for the parts delivered was £120, great value for genuine Honda parts!

Once these were delivered (2 weeks, not bad from Oz to the UK) I delivered them to the mechanic who popped them in, new gaskets to the alternator cover and the clutch cover, which were readily available.

Re-assembly was the same as the disassembly but i have photos of both, I'm not going to clog up the forum as there are over a hundred, the bike I now running well with new oil, coolant and filters.

If anybody has any questions or needs advice, fire away!
Sounds like you've a big things to do in back time.. 8-)
Nice share.. so at the end, how many part items that you replace to restore the bike?
Hey Indosuperfour

All of the work on the gearbox is complete, and the part numbers that I needed are the following;
FORK C GEAR SHIFT 24212MBE000
Gear m3-m4 23451MY9750
Also the gasket sets but those were easy to find :)
Do you happen to run the Instagram page by the same name? Image
Sent from my EML-L09 using Tapatalk
Actly not that much parts that you change right? but quite take some time to collect them from another cntry espclly. :grin:
Yeah, I run the IG account as same as my account here.. feel free you can DM me as well.
;)


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