Broken camshaft. Repair possible?

Green199

Green199

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Hi guys,

Ive ran into a massive problem with my CB250. While trying to reassemble my topend, the lobe on my camshaft which the cam sprocket bolts to broke. A little corner piece snapped off, exposing half of the threads for the hole.

Similar this:
http://www.examiner.com/slideshow/honda-cb350-camshaft-woes#slide=1

Its not that extreme, but it is very similar.

I have looked around ebay for another camshaft but I cant find one. I dont have the funds yet to buy a brand new one, so was wondering if it is possible for it to be welded back on, and then the hole retapped?

I know it was heat treated steel. but was wondering if this was a possibility.

Ill get some pictures up tomorrow to show how bad it is.

- Charlie.
 
You don't want to have your cam explode at speed.
Get another one, if it broke during assembly something's wrong with it.

I'm sure someone here has one
 
SONIC. said:
You don't want to have your cam explode at speed.
Get another one, if it broke during assembly something's wrong with it.

I'm sure someone here has one
Click to expand...

Thanks for your input SONIC.

I can't locate another one in the UK, that's the problem i'm having.
 
it's not heat treated steel actually, it's chill hardened cast iron, if it were heat treated steel it could be welded fairly reliably, but cast iron isn't going to respond well to that kind of uneven heating. so yes, get a new cam, it's probably not going to fail catastrophically, but what will probably happen is the weld will break, letting the screw loose to go wedge itself somewhere important... then you'll have a catastrophy
 
http://www.ebay.co.uk/itm/Honda-CB350K4-complete-engine-less-carbs-spares-or-repair-CB350-not-CB250-K4-/281204631401?pt=UK_Motorcycle_Parts_13&hash=item41791a2769
 
Roc City Cafe said:
it's not heat treated steel actually, it's chill hardened cast iron, if it were heat treated steel it could be welded fairly reliably, but cast iron isn't going to respond well to that kind of uneven heating. so yes, get a new cam, it's probably not going to fail catastrophically, but what will probably happen is the weld will break, letting the screw loose to go wedge itself somewhere important... then you'll have a catastrophy
Click to expand...

Yeah that makes sense, Ill look around. Thanks Roc.

Umm yeah im watching that one mlinder. Ive emailed the seller asking if he could take the rocker cover off to look at the cam, but n reply yet.
What concerned me is that the breather has been open the entire time its been sat, so im guessing inside isnt going t be the best quality.
 
post a request on hondatwins.net

they have a lot of members into these things
 
There are two versions of the CB350 camshaft. Big lobe and small lobe. Location of the rocker arm pivot was different. I don't know which one the cb250 falls under.
A same year cb350 cam should work just fine though.
 
Im looking for the 'skinny' cam, atleast thats what I am/was running.

I recall someone mentioned a while ago about swapping a sl350 cam into their cb350. I was wondering if anybody had any information on this

- Charlie.
 
Skinny cam is the later version. I think the only time an SL had a different cam than it's CL and CB counterparts was the very first year, and pretty sure that was a fat cam.

Won't work.

A first year SL head, cam basket and cam would work, but you'd need different carbs, too, the SL's ran slide carbs, not CV carbs, if I remember correctly.
 
mlinder said:
Skinny cam is the later version. I think the only time an SL had a different cam than it's CL and CB counterparts was the very first year, and pretty sure that was a fat cam.

Won't work.

A first year SL head, cam basket and cam would work, but you'd need different carbs, too, the SL's ran slide carbs, not CV carbs, if I remember correctly.
Click to expand...

I thought you could use a fatcam as long as you also changed the rockers?

Yeah, I heard it was a later year sl cam, so a skinny one. Would any skinny sl cam fit?

Surely the cam wouldn't really effect what carbs you HAVE to run. I want to change to slide carbs anyway soonish, but surely the sl can run on CV carbs too?

Sorry for all the questions ::) :)
 
I don't think any SL had a fat cam. They were only made to 71, and I think 72 and 73 was skinny cam. I might be wrong though, been a while.

And it's not just the rockers that are different, the location of the rocker pivots are different in the cam basket.

As far as carbs go, I do believe the whole mounting of them is different. Again, I may also be wrong on this, but I don't think so.
 
You can run a fat cam, you need the rockers.

Are we talking about putting a 350 cam in the 250? Are they interchangeable?
 
Yeah, I just looked at the parts numbers, SL had it's own head goin on, at least by part number, where CL and CB shared part numbers.
 
SONIC. said:
You can run a fat cam, you need the rockers.

Are we talking about putting a 350 cam in the 250? Are they interchangeable?
Click to expand...

They are.

Are you sure about simply swapping rockers? I'm almost positive I measured a difference in rocker pin location between a fat cam and skinny cam cam-box.
 
Hmm Interesting. Shouldn't be hard to find one then.

I know of quite a few people who have done it.
Should be a straight swap for cam rockers and cam sprocket.
 
Hmm Ill try and find part numbers for the sl rocker box and for the cb rocker box and compare them.

I guess if they are the same, then an sl cam, rockers, and cam sprocket will be on there way.

Would the rocker pins need to from the sl as well? (Ill try and check part numbers).

If I can find one, I may try to go down the route of machining out the bearing end caps to fit a needle bearing conversion in....depends if I can get a cam for a decent price.
 
Green199 said:
Hmm Ill try and find part numbers for the sl rocker box and for the cb rocker box and compare them.

I guess if they are the same, then an sl cam, rockers, and cam sprocket will be on there way.

Would the rocker pins need to from the sl as well? (Ill try and check part numbers).

If I can find one, I may try to go down the route of machining out the bearing end caps to fit a needle bearing conversion in....depends if I can get a cam for a decent price.
Click to expand...

I don't think the rocker pins are different.

Why don't you just buy that seized 350 motor I linked to you? Substantially more power.
 
mlinder said:
I don't think the rocker pins are different.

Why don't you just buy that seized 350 motor I linked to you? Substantially more power.
Click to expand...

Because the auction has ended. And I have fully rebuilt my bottom end so far, so may just look at picking up 350 jugs etc

Just didnt want to drop £200 into something which probably has worse internals throughout than mine.
 
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