CB450K0 etc Top cam idler modification

[AshimotoK0]

I started this discussion on the CB450 Bomber Facebook group and also HondaTwins .net but hope it's of some use to CB/CL450 owners on here.

Wondering what everyone does when rebuilding a bomber engine in terms of replacing the front idler assembly?(14610-283-000). These are virtually unobtainable NOS and I reckon all used ones will have hardenened rubber idlers after being inside an engine for around 50 years. I know Cappellini does a replacement sprocket for this part but how about the rubber rollers? My buddy Graham Curtis does a fix on a CB72/77 camchain tensioner roller by re-machining the outside of the rubber surface to reveal a non-hardenened rubber surface underneath. I thought about doing this on the 450 but would like to maintain the geometery of the chain path and keep the same roller diameters. I removed one of the rollers from a scrap CB450K0 assembly and one from a scrap CB750 camchain tensioner (the roller part is also the same on a CB250/350K twin as the 750). My theory is that you could take a 750/250/350 idler wheel and machine it to the same size as the Bomber ones. Only difference is that the Bomber one has a plain bearing and the 750 etc ones have a needle roller bearing but the centre pins are exactly the same diameter on both types. Plus some shims would be necessary to prevent the side wall of the idler contacting the metal holder. I tried to annotate this on the attatched photo.

Also I found that the Kawasaki KZ650 has sprocket type idlers with the same number of teeth as the Bomber and wondered if this could also be adapted to fit the Bomber....however at least there are parts available from Franco Cappellini to deal with a badly worn sprocket. David Silver also sells the single sprocket idler for this engine, which again may be able to be modified. The Kawasaki design is very neat as it has  built in rubber cushioning and there are quite a few decent used ones out there (there are two in the Z650.... I got mine from DK). My old spoked wheel Z650B1 was a beautifully designed engine and I am surprised those bikes don't sell for decent money ...perhaps if they had fitteda 4 into 4 exhaust like the Z1 it would be more desirable.

Franco Cappellini also does a repair for the camshaft sprockets (if cam has the pressed on type sprocket)

http://www.cappellinimoto.it/catalog/motorbike/CB450K/product/37


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Cappellini's sprocket fix link :  http://www.cappellinimoto.it/.../motorbike/CB450K/product/13

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[AshimotoK0]

Update .......I pressed out the needle roller bearing from the CB750 / CB250/350K rubber idler and the plain bush from the CB450K0 one. I was expecting some kind of rubber-to-metal bonding on the 450 one but it pushed out quite easily and no sign of any bond, just a centre groove. Good news is that the O.D. of the needle roller bearing is slightly smaller diameter than the plain bush so my plan is to make the plain bush from the 450 a press in fit into the CB750 one and also take the overall thickness of the 750 rubber roller down to exactly the same as the 450 one (about 0.5 mm difference). This means that the pressed in bush will be slighly proud of the centre steel existing bush, so that the roller, when spinning, will not contact the sides of the holder assembly. This will then replicate the original roller with it's plain bush. I sent a message to Cappellini's agent in the USA asking if I can buy the axle pins they sell for their sprocket conversion as a separate item, to use on my modified rubber rollers.

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[UK Pete]

Love your enthusiasm ash, hope it all works out

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[AshimotoK0]

Franco Cappellini also sell a refurbished assembly but I suspect they have used rubber rollers. Not quite clear though . This is the USA eBay description from their agents.                             
   "Description
Honda CB450 Cappellini Moto rebuilt original good used FRONT chain tensioner has new chain guide sprocket, #205. Franco's sprockets are sold separately, but rubber OEM Honda rollers are available only from Honda."
 https://www.ebay.com/itm/Honda-CB450-Cappellini-Moto-rebuilt-FRONT-chain-tensioner-w-guide-sprocket-205/172265886841?hash=item281bd8d479:g:FWEAAOSwOVpXfaQg

[UK Pete]

Hefty price tag

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[royhall]

Very thorough research Ash, nice one. Strangely all my rollers were in really good condition even the rubber parts were still pliable. I had been concerned about them. As you say the new ones are all gone. Definitely don't change the roller diameter though as in places the chain runs very close to the castings.

[AshimotoK0]

The plan so that I can maintain the correct diameter of replacement rubber rollers ..  One thing for sure my friend Graham Curtis is dead right .. take a hardened Honda rubber roller and skim a few mm off it and you are down to soft pliable rubber again.

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[SeanFD]

I just came across this post today.

When talking about hard and soft rubber, what do you mean by "soft"? Squishy soft? With just a little give?

I'v always found it difficult to make a decision without a new item to compare with.

[AshimotoK0]

I just came across this post today.

When talking about hard and soft rubber, what do you mean by "soft"? Squishy soft? With just a little give?

I'v always found it difficult to make a decision without a new item to compare with.

Just a little give without a hard 'skin' on the top