1967 CB450K0 Black Bomber Rebuild - By Royhall

[AshimotoK0]

My main question on all of this is ...will the later 5-speed complete rotor/starter clutch fit a Bomber? ... These are at least available at reasonable cost used, from time to time, (as I just found when I got a really nice one with the chhain and motor sprocket too for £120 from DK). Seems that Honda went though may design changes on the DOHC twin bikes starter system  but the fact that you find the later assemblies in nice condition but every Bomber assembly seems to be, at least, semi-fooked, indicates that if you can fit the later assembly it's the best option in terms of reliability.

According to Nigel Harris (a member here) .... In a post  HondaTwins in 2009, he stated there that he has a K5 system fitted to his Bomber. I will try to contact him via email to confirm.

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[royhall]

To be honest I think any 450 unit will fit but you need to have the whole kit like you got from DK. Trying to replace one part is full of danger. I think even DK have realised that so they now sell them as a complete unit.

[AshimotoK0]

My original 1967 Bomber rotor is at work Roy. But this is a close up of it ... It had thin tabs (look how bad it is though)   

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[royhall]

That looks stepped back from the outer diameter. If so that would be correct. I think they changed it to the thicker lugs to stop them snapping.

[AshimotoK0]

That looks stepped back from the outer diameter. If so that would be correct. I think they changed it to the thicker lugs to stop them snapping.

But all of the later rotors I have seen have thin lugs including the 500T? I have emailed Nigel Harris and Ray Hull to ask if the later parts deffo fit a K0. I thhought i had read somewhere that the really late rotors dont fit ...something to do with the key-way.

 I think I am going to fit an old crank, barrells and pistons and strarter system to some old crankcases and load the other end of the crank up on a test rig at work .. just to check it out and also to test an early K0 used assemby that's from bits that Jason (Woodside) want for his press bike, from the parts he kindly sent to me.

[royhall]

Just had a parcel from CMS with the latest rotor attempt. Will have a go this weekend and report back.

[royhall]

The new parcel from CMS contains an alternator rotor for the K2 that had the odd part number. As everybody in the know was saying that 68-74 were all the same I risked it. The £200 wrong item has gone back to Silvers for a refund so at 75 Euros plus P&P this one is a big saving.

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Don't know why it was priced differently as it turns out to be the same as the K1 to K4 items, some of which are over 700 Euros at CMS. The best part is it fits my starter clutch perfectly and the timing marks are correct. So that's all a bit of a result really.

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Not sure why but the rotor is stamped CP450 instead of CB450, the CP being the police bike version. First thoughts were that the police bike may have a higher output alternator to deal with radios and lights etc but it measures the same and the magnetism (although not scientific) feels the same whilst pulling a piece of mild steel off it.

So happy days, built up the rotor and starter clutch and refitted to the bike. The hope was that now the starter is correctly held on the shaft centre it would engage okay. I couldn't have been more wrong, it was actually worse. The starter would engage for a short time every fourth or fifth try, so that's a fail then. On stripping down again I found the sprocket drum to be worn about 4 thou, would that be enough to stop it working?

Anyway, after a 4 hour internet marathon I have turned up no parts whatsoever either new or old. Other than sit and wait for a possible DK unit, I am now at a loss for what to do. DK told me about a week ago that they didn't have any in stock nor have they got any CB450's in to strip at the moment. Plus there's probably hundreds of other owners worldwide looking for the same parts. I am surprised that nobody has come up with a way of adapting more modern parts to do the job as this problem has been around for a long time.

Any ideas would be most helpful thanks.

[AshimotoK0]

I wonder why that part is dished on the front Roy,compared with all of the other 450/500 rotors I have seen or is it just the illusion on the photo?  Image off CMS is below. I guess it was cheaper because of the surface rust (which is only cosmetic).

The CP Police model has a 360° crank AFAIK.
 
Do you have the figure for the correct diameter of the sprocket part hub that you need?


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[royhall]

No it's definitely not dished Ash just an illusion. I miked all dimensions and it's the same, although miking a strong magnet was interesting. Is the dimension you need on the sprocket the part that engages the rollers, I will measure it this afternoon. It has a step worn into it at the rollers edge so I will measure the diameter there. I'm in old school English money though. Thou's will never be beaten.

[royhall]

Forgot to mention that I checked all the sprocket part numbers and they are all the same from K1 to K7.

[royhall]

Ash. The hub diameter is 1.651" and 1.647" on the worn surface. The bush diameter is around 0.837" although it's hard to measure with a telescopic gauge due to the oil scroll.

[Bryanj]

4 thou is way more than enough to cause the missed starting problem, if you could get some made you could get the grear slightly ground till true and use oversize diameter rollers.

From memory, on 750,  there is only just over a thou in difference between the deep end of the slot and the shallow end of the slot the roller sits in which would suggest anything over a thou wear is too much

[AshimotoK0]

I just measured two that Jason (Woodside) sent me last week to fix a unit for him and they are both on the upper size you gave Roy or more. I really need too take to work to measure though, as my larger micrometer was last calibrated in 2002  ... Interesting that on one of them, you can deffo feel undulation, where the rollers have indented the surface. I will also take the DK sourced one to work to measure and report back.

How about the  outer clutch part Roy ..is that OK? Item 7

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[royhall]

There are indents in the outer but until I assemble it with a good sprocket it's hard to tell. My hub looks very smooth it's just very even wear that you can actually see by eye, defo shot.

[Bryanj]

Way back when i used to have to repair the odd 750 and several 500 twin you could see the gear looked like a threepenny piece(only more facets) whilst new were like a crankpin grind