Snapped camshaft ??

[Yoke]

I have never come across this so I can't figure out why my camshaft snapped. I got a working donor engine, very soon after fitting it into the frame I could see there was issues there. I rebuild the rear head, replaced rings etc. Took the bike out for a spin, about an hour later, I lost compression on the front cylinder, got the bike back to the workshop, check compression and got 0. So I just took the cover off the head and turned it by hand, the camshaft is rotating but valves are not moving, looks like its snapped and there us some metal around oil and I need to install a new head now. I am happy to rebuild the front like I did the rear but has anyone see this before? I've seen this on car engines where a distributor bearing fails and snaps the cog at the end of the shaft but never on a bike?

[squirrelman]

something went wrong in the engine that caused that, like a dropped valve maybe or timing error. something stopped its rotation before it broke.

how many miles on it ?

[bones]

Wow, don't know that I have heard of a Hawk engine snapping a camshaft.
At least not in an engine that wasn't in a race bike.
Keep us posted on what made the camshaft break.

[Yoke]

I rotated it by hand all the way around 5 or 6 times, all marking where spot on and the bike drove for an hour before this happened. The valves are now in a shut position now that the camshaft is snapped. I stopped looking at that point as I got really pissed off with it. I got this engine to speed up the build process and it’s need nothing but disaster.

I am gonna pull the head off and look at the top of the piston when I’ve calmed down a bit and see if there is marks on the piston. I have built many engines, never a bros, but I have never seen this so I am quite confused. Unless it’s an oil pump issue, and the front ran dry. But seems like there is plenty of oil there.

[rpcraft]

Where did the camshaft snap? I'm not sure how it could be spinning and not moving the valves unless the cam lobes have been flattened. Are you sure the camshaft is moving and not the gear itself separate from the shaft? Is there a chance the cam gear bolts came loose and the gear is just spinning without the cam shaft? I've never really heard of one breaking straight up but I am sure racers are more experienced with that.

I've yet to have cams out of the heads so not 100 % certain of the cams are keyed to the gears with something like a woodruff key or if they use the bolts to lock them to the cams.

[Yoke]

No it’s definitely spinning the shaft, lobes are stationary from the bracket that’s holding the shaft down there is no movement. I will take it out later and see, I have just never seen this before and I have seen many engines.

[Fastmongrel]

Why did you have to rebuild the rear head if it was a working engine. On a V or flat engine if one cylinder is bad then the other is probably on the way to the same condition. Sounds like you were sold a scrapyard engine

[Yoke]

Yeah I rebuilt the rear because I had low compression on the intake cylinder, the valve was bent. I later discovered that the tensioner was damaged too. Someone also installed a long bolt on the tensioner so it bent the spring receiver. Front had good compression but she only ran for a short while, initially I thought it was a carb issue but then discovered all that. So I have rebuild the rear head, new rings and gaskets. Now she runs lovely on one cylinder if I take the plug out as the valves are not opening on the front.

I got the engine from the internet, the guy sent me a video of it running in the bike. There was lots of funny stuff, the water pump pipe shattered when I removed the hose, the engine had mixed coolant, the list goes on.

I know I bought a crap engine, what I don’t know how a camshaft can snap. The only thing I can think of is she ran dry of oil. If timing was off the. You would have bent valves. I just put it out there in case someone has seen this, I have 2 engines on a bench so I have part to fix it, I obviously don’t this to happen again.

I will take it apart when I have a sec and let you know.

[6]

Ummmmm m.

EHeehem Hordpower ehem.


That's a strange one dude...

[Zanderk]

Yeah I rebuilt the rear because I had low compression on the intake cylinder, the valve was bent. I later discovered that the tensioner was damaged too. Someone also installed a long bolt on the tensioner so it bent the spring receiver. Front had good compression but she only ran for a short while, initially I thought it was a carb issue but then discovered all that. So I have rebuild the rear head, new rings and gaskets. Now she runs lovely on one cylinder if I take the plug out as the valves are not opening on the front.

I got the engine from the internet, the guy sent me a video of it running in the bike. There was lots of funny stuff, the water pump pipe shattered when I removed the hose, the engine had mixed coolant, the list goes on.

I know I bought a crap engine, what I don’t know how a camshaft can snap. The only thing I can think of is she ran dry of oil. If timing was off the. You would have bent valves. I just put it out there in case someone has seen this, I have 2 engines on a bench so I have part to fix it, I obviously don’t this to happen again.

I will take it apart when I have a sec and let you know.

I broke a camshaft on a Yamaha XS400YICS once. I had just jumped a bridge at speed and then wheelied over an old railway line and it just clicked and stopped. Yamaha gave me a new engine despite it being out of warranty as they’d never seen it before. The cam just broke in half, so it does happen.

[Yoke]

I broke a camshaft on a Yamaha XS400YICS once. I had just jumped a bridge at speed and then wheelied over an old railway line and it just clicked and stopped. Yamaha gave me a new engine despite it being out of warranty as they’d never seen it before. The cam just broke in half, so it does happen.

Well its official, the camshaft snapped in half, its one solid bit of metal but it broke. Can't explain it but here is a video if your interested: https://youtu.be/Cv30YhYVKAA

[Bros Steve]

Thanks for the video. Bad luck dude. Keep us posted.

[Yoke]

I will take the head off this weekend and see. But the camshaft guide is in bits. So I am thinking it was an oil delivery issue now. I need to look at the pump too. It’s definitely a odd one.

[rcthirty]

I just saw your first video about the rear cylinder takedown

After seeing whatever junk was in the coolant passages around the 24 minute mark in your video it's no surprise it broke. That engine has been over-cooked. I wouldn't trust it any farther then I can throw it. Unfortunately for you this guy sold you nothing more then an expensive boat anchor. Really sorry about that. You might be able to salvage some components but be aware that steel that undergoes excessive heat decarbonizes, becomes brittle, and warps etc.

[rpcraft]

Yeah I didn't connect it to your earlier engine issues initially but that does seem like when you were taking it out there was a lot of resistance in the cam shaft and an extraordinary amount of effort to get the parts apart. Sadly I am not caught up on all your video's so like rcthiry is saying if there was other signs of heat damage sounds like you definitely may have some other internal issues to worry about. I'm about there on your build series so maybe can get it watched over the weekend and see what else is going on.