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Need Honda and clone cam advice

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lingeringstin...
Trackday Trickster



Joined: 01 May 2014
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PostPosted: 20:01 - 24 Jan 2023    Post subject: Need Honda and clone cam advice Reply with quote

For years I've been making engines out of mismatched Honda/Chinese parts. In general it works well because apart from some aesthetics in rocker covers and that sort of stuff the Chinese clones of the Honda Benly style engines are bolt for bolt and all the important parts interchange. China even makes better clutches and electronic ignition and things that Honda never bothered with.

A lot of the 125 and 250 engine bits are actually interchangeable and all you really need to be aware of is whether you're using a 180 or a 360 crank and cam. You can make a cracking little 200-ish engine that goes like stink using a 125 crank and head with shortened 250 barrels and pistons, but that incurs a bit of machining expense so I usually just build bog standard 250 engines with 360 cranks to keep everything simple.

However, during a recent engine build I've discovered two different cams in my piles of bits that BOTH appear to be for a 360 crank and I don't know which one to use. They are slightly different and I don't understand why.

I've identified them as a CA cam and a CM cam, but I'm having problems figuring out what the practical differences are between a CA and a CM engine.

Holding the two cams up to compare they appear to have the lobes in the same arrangements but the bolt pattern for the cam sprocket is different. I don't know if this is significant or if it makes no difference at all so long as you can get the timing marks lined up correctly.
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Nobby the Bastard
Harley Gaydar



Joined: 16 Aug 2013
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PostPosted: 20:07 - 24 Jan 2023    Post subject: Reply with quote

If the timing marks are on the cam and not on the sprocket then there is no obvious difference and are interchangable. Arguably there may be a slight difference between the tooth alignment but thats easy to check, compare the cam and sprocket and aligmment with tooth for both cams./
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WD Forte
World Chat Champion



Joined: 17 Jun 2010
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PostPosted: 21:42 - 24 Jan 2023    Post subject: Reply with quote

I just looked up a 1992 cm125C and 1995 CA125 Rebel
on Fowlers site and they both have the same Honda part number

https://www.fowlersparts.co.uk/parts/view/14110402730
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stinkwheel
Bovine Proctologist



Joined: 12 Jul 2004
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PostPosted: 00:11 - 25 Jan 2023    Post subject: Reply with quote

So do you have the sprocket that comes with each cam?

I suppose it would be a case of suck it and see. Might want to set the cam timing up using a degree wheel if you aren't sure you can trust the marks.

Are the cams the same profile/lift? Same base-circle diameter?
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lingeringstin...
Trackday Trickster



Joined: 01 May 2014
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PostPosted: 18:39 - 25 Jan 2023    Post subject: figured it out I think Reply with quote

As far as I could tell the lobes were exactly the same on both cams and I wouldn't be too bothered about a cam sprocket being half a tooth wrong in either direction because that's too little difference to matter really on an engine like this, but it turns out one of the cams has a slightly different sized central shouldered bit where the sprocket goes on, so only one of these cams would match up with the cam sprocket I had available.

I suspect that's down to a difference between a Honda cam and a 253FMM cam. I suspect one of these cams is a Honda one and I don't have a sprocket for that one.

I do know that if I use a Honda crank I have to use a Honda cam sprocket because Hondas used a duplex cam chain and the Chinky Benly clones use a simplex chain.

So anyway I've used the cam that I had a sprocket to fit and it all works fine now. I think I'll have to keep the other cam around for in case I ever have a Honda crank at some point and need to get a duplex cam chain sprocket, but to be honest the Chinky cranks and cams are perfectly fine and dead cheap to get brand new.

These Benly clones like the early Rebel 250's and these quadbike engines were never fire breathing monsters anyway. I use 125 heads on 250 quadbike barrels (bigger fins) with a single carb and an upgraded clutch and tweak my engines for a bit more compression by having the barrels milled off by a mil or two which effectively shortens the cam chain distance slightly so the cam sprocket is actually out by a wee tiny bit but it doesn't make any noticeable difference and I cobble a long bolt into the barrel as a manual cam chain adjuster and use needle roller bearings instead of those self destructing Honda style cam bearing shells.

I use YBR125 pistons because the bog standard pistons are a bit concave. It all just makes for a bit more poop to the pop.

Looks a bit weird but it works. Honda nerds will spot the differences.

https://i.postimg.cc/QMcX52FN/TURD.jpg

[url=https://postimages.org/][img]https://i.postimg.cc/QMcX52FN/TURD.jpg[/img][/url]
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