CB 400 Project Big One - questions from South Africa :)
Posted: Thu Jan 21, 2010 3:08 pm
Hi, all :)
For my first post here, I need to ask a few questions...
A lady friend of mine has had a CB400 Big One for about a year (dead standard). Another mate of mine has just bought a lightly-modified one (braided hoses front and rear, JMCA-legal exhaust). I don't know what year-models these bikes are, but I presume both are 'Spec 1' (neither of them have VTEC.)
Since I helped them both buy these bikes, I've been roped in as the designated mechanic.
What I need to know is:
1 - What spark plugs do the non-VTEC engines use as standard, and at what electrode gap?
When I gave the standard bike a check-over before I let my friend ride it, the dealer that sold it fitted it with mismatched plugs - there were two NGK CR9Es and two CR9EH-9s. I replaced the CR9EH-9s with CR9Es and gapped them all to 0.65mm. The plugs are near replacement now, and seem to be carbon-fouled. I have a mind to replace them with CR8Es.
2 - How can one determine the year-model of these bikes by VIN code?
3 - What method of top-speed restriction is used on these bikes, and what is the easiest way to bypass/disable it?
4 - What are the standard intake/exhaust valve clearances for these engines? Is measurement done hot or cold?
5 - The standard bike's chassis number starts with 'NC31' (CB 400), but the engine number starts with 'NC23E'.
Could this bike have been the subject of an engine transplant from a CBR 400 at some stage...? (And if so, what would the correct spark plugs be THEN?)
Thanks muchly to anyone who can answer these questions! :)
In return, I'd like to share some tips that my lady friend and I have picked up after running her bike for a year:
We struggled to find replacement tyres in 110/70-17 and 140/70-17. I know from running track-day bikes that the wider you go on the rear, the more reluctant the bike will be to change direction, so we wanted to keep the tyre size standard.
We eventually found that Kenda K671s are brilliant, available in all popular sizes for small greys and are very reasonably priced (about 35% less than equivalent Bridgestones or Michelins).
In the beginning, we were confounded by a starting problem: the bike would crank and crank, but wouldn't start. I eventually found that if the kill switch is in the 'Off' position with the ignition switch 'On', the bike will still crank over without starting, but won't produce a spark. Problem solved by flipping the kill switch to 'On'.
The standard bike, for some reason, had huge instability problems over 160 Km/h or so - it would start to weave so badly that if you didn't back off the throttle, you were in deep trouble.
I cured the problem by dropping the front triple clamps down the fork stanchions by 20mm, steepening the head angle a bit.
In conjuction with lowering the rear shock preload adjustment collars to minimum preload, this also means my friend can now put both her feet flat on the ground (she's 5"3).
The ignition switch/steering lock could sometimes jam to the point where it was impossible to turn the ignition key in the lock (it felt like there was a physical obstruction jamming the mechanism.) A squirt of Castrol DWF down the key slot sorted it - WD40 would probably work just as well.
The speedometer drive on the wheel failed after six months or so (the nylon driven gear had been chewed up by the aluminium drive gear).
I picked up a second-hand replacement that the breaker was sure had NOT come from a CB 400, though it looked identical, and the number of teeth on the driven and drive gears were the same. When pressed, he guessed that it had come from an NC21, NC24 or NC29.
For my first post here, I need to ask a few questions...
A lady friend of mine has had a CB400 Big One for about a year (dead standard). Another mate of mine has just bought a lightly-modified one (braided hoses front and rear, JMCA-legal exhaust). I don't know what year-models these bikes are, but I presume both are 'Spec 1' (neither of them have VTEC.)
Since I helped them both buy these bikes, I've been roped in as the designated mechanic.
What I need to know is:
1 - What spark plugs do the non-VTEC engines use as standard, and at what electrode gap?
When I gave the standard bike a check-over before I let my friend ride it, the dealer that sold it fitted it with mismatched plugs - there were two NGK CR9Es and two CR9EH-9s. I replaced the CR9EH-9s with CR9Es and gapped them all to 0.65mm. The plugs are near replacement now, and seem to be carbon-fouled. I have a mind to replace them with CR8Es.
2 - How can one determine the year-model of these bikes by VIN code?
3 - What method of top-speed restriction is used on these bikes, and what is the easiest way to bypass/disable it?
4 - What are the standard intake/exhaust valve clearances for these engines? Is measurement done hot or cold?
5 - The standard bike's chassis number starts with 'NC31' (CB 400), but the engine number starts with 'NC23E'.
Could this bike have been the subject of an engine transplant from a CBR 400 at some stage...? (And if so, what would the correct spark plugs be THEN?)
Thanks muchly to anyone who can answer these questions! :)
In return, I'd like to share some tips that my lady friend and I have picked up after running her bike for a year:
We struggled to find replacement tyres in 110/70-17 and 140/70-17. I know from running track-day bikes that the wider you go on the rear, the more reluctant the bike will be to change direction, so we wanted to keep the tyre size standard.
We eventually found that Kenda K671s are brilliant, available in all popular sizes for small greys and are very reasonably priced (about 35% less than equivalent Bridgestones or Michelins).
In the beginning, we were confounded by a starting problem: the bike would crank and crank, but wouldn't start. I eventually found that if the kill switch is in the 'Off' position with the ignition switch 'On', the bike will still crank over without starting, but won't produce a spark. Problem solved by flipping the kill switch to 'On'.
The standard bike, for some reason, had huge instability problems over 160 Km/h or so - it would start to weave so badly that if you didn't back off the throttle, you were in deep trouble.
I cured the problem by dropping the front triple clamps down the fork stanchions by 20mm, steepening the head angle a bit.
In conjuction with lowering the rear shock preload adjustment collars to minimum preload, this also means my friend can now put both her feet flat on the ground (she's 5"3).
The ignition switch/steering lock could sometimes jam to the point where it was impossible to turn the ignition key in the lock (it felt like there was a physical obstruction jamming the mechanism.) A squirt of Castrol DWF down the key slot sorted it - WD40 would probably work just as well.
The speedometer drive on the wheel failed after six months or so (the nylon driven gear had been chewed up by the aluminium drive gear).
I picked up a second-hand replacement that the breaker was sure had NOT come from a CB 400, though it looked identical, and the number of teeth on the driven and drive gears were the same. When pressed, he guessed that it had come from an NC21, NC24 or NC29.
