bent cam shaft

While trying to dx my cold starting issue, which turned out to be corrosion on the points plate, it seems that my cam shaft is bent. the timing is set best as possible and the bike runs great. I was going to do the push rod seals this winter.
think i should do the cam shaft as well or just leave it all alone as the bike is now running well.?

what do you mean the camshaft is bent, the whole cam or just the advance plate.
Hard to imagine the cam itself being bent.

As it was explained to me, it was difficult to set the timing because 'the cam shaft is bent...it doesn't spin in a circle...which is probably why someone put dyna ignition in it'

That's it exactly...how does that happen??

eric11 said:

That's it exactly...how does that happen??

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The cam shaft itself is a pretty beefy part and is seldom if ever bent. But the front "nose" of the camshaft is machined down to a fairly small diameter and has an even smaller threaded section to take a 6mm (thread size) 10mm (wrench size) nut to hold the ignition centrifugal advance mechanism with points cam onto the front of the camshaft where it sticks through the timing chain cover.

Now since point gap is a fairly precise specification - even a 1/1000" bit of runout or radial wobble will show up as quite a bit in timing variation.

As to how they get bent? Probably the same way that the little threaded sections get twisted off the front of the cam. "This here thingy looks like an important part Knute. Sure don't want it to fall off. Bring me that big Crescent wrench, willya?

eric11 said:

That's it exactly...how does that happen??

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How that happens is, perhaps, some previuos owner was ham-fisted and jammed on the nut that holds the advance unit. Do NOT over tighten anything.

You'll know, if the threads on the end of the cam don't look perfect, that the cam nose might be bent. It doesn't take much deflection to throw off the timing mark. Having owned early Airheads for 30 years, I've owned many a motor that was un-molested that exhibited that problem.

That being said, you are not in terrible danger.

It is more likely that your timing chain is near the end of it's service life. A timing chain that is slack will manifest as a slippery timing mark when using a timing light(strobe) to check the timing mark when running. The way that our airhead motors work is that; being 180 degree motors where the cylinders fire against each other, in the smallest sense, the motor stops the instant before either cylinder fires. The effect is more pronounced at low RPM. That's why we hear a rattly noise from the transmission at idle.

Most of the riders I know, and myself included, compensate by adjusting the the timing to AVERAGE OUT the "ghosting" of the timing mark in the apperture. If the the "S" mark ghosts, adjust your timing until the "F" mark is stable. The "F" mark is Full Advance, and that is what you want to be right when you're jamming down the road.

Don't over- think it.

Our AIRHEADS are really more like lawn-mowers than other types of machines. Don't over analyze these things.

Pretty interesting that Paul Glaves was composing an answer at the same time as me. I think we are both right on this one.

Thanks for the great explanations! Definitely makes sense now.

Sounds like you think I should let it go for now...same deal as the push rod seals?

A bent tip on the camshaft can create a situation called differential timing as mentioned above. This can be overcome by using an electronic ignition system. One type is the Dyna III that uses two pickup coils which can be independently timing to minimize the out-of-plane movement of the camshaft tip. I believe the Boyer ignition does this as well. The other way to go is to use a crankmounted ignition system. There can be no differential timing in this situation.

eric11 said:

Thanks for the great explanations! Definitely makes sense now.

Sounds like you think I should let it go for now...same deal as the push rod seals?

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Push rod seals, grommets, whatever you want to call them, can go critical in a hurry. If a grommet were to split or rupture, you'd be loosing an extraordinary amount of oil. If your bike is bleeding motor oil you should get on it right away. If your bike is oozing oil and you don't mind a dribble after every ride, you have to use your dip-stick frequently and not allow the oil level to get below the low mark.

Of course, a re-sealed motor is best.

Just don't let the motor get low on oil. I am living with this on one of my 750's. I find that I need to add about a shot glass worth of motor oil every 500 miles or so and the bike likes to mark its parking spot. That bike has been running for years like that. It's necessary to monitor the oil level to make sure it doesn't run out of oil. The next time I do a spline lube, I'm gonna do the rear main seal and oil pump "O" ring and then I'll replace my grommets since the bike will be out of service for a day or 2.

Anyway Eric, that's the way I approach this topic. Monitor your oil level, and you can get away with a dribble for a very long time.

Thanks for the really good advice...really happy that I joined MOA.

Just one more thing. I was not perfectly clear in my "set the timing" rant. While you might be able to get the F mark in the window at idle, (and yes, I have encountered more than one bike that was static timed to fire at the F mark) you want the the F mark in the opening when the advance curve plays out at around 2500RPM.
The cool thing about using a timing light pointed at the aperture, is that you can see the advance mechanism doing its thing as you increase motor speed.

With a timing light, one see's the "S" mark at idle with it rolling downwards and away while the "F" mark roatates into view as the advance mechanism does it's thing and finishes up at around 3k RPM.................The "S" mark is where one does a so called static timing with continuity checker type light or perhaps like myself and Ohm meter........Good luck.......Dennis

IIRC, the crankshaft rotates CW when viewed from the front. That would mean that when rotating by hand, the timing marks would travel from top to bottom in the timing window. The first mark to be seen would be the full advance mark, followed by the static mark and finally the OT mark.

With engine running and using a timing light, at idle the static mark would be visible somewhere near the center of the window. If you increase the speed slightly, the engine fires the spark a little earlier, thus the static mark would be a little higher in the window, almost appearing to rotate backwards. Continue adding throttle and eventually the static mark will completely disappear out of the top of the window. With enough RPM, say around 2.5K, the full advance mark will begin to appear, first in the bottom of the window, and eventually move upward to the center of the window around 3K RPM.

Resurrecting this old thread.

Hi all.

Well, I managed to bent the tip of the camshaft. Don't know how. I was replacing the new but no good points with me Noris points. I noticed that the point gap setting tool was not going in as smooth.

I put it all back together and was having a very hard time to set the static timing. I checked and set the points gap with a dwell meter. I previously had serviced the advance unit, cleaned and new springs. Also crankshaft sprocket, timing chain and tensioner are new.

Now the S mark is jumpy and I can't get the F mark to stay steady at any rpm. With the cover of and bike running I can tell the nut securing the advance unit oscillates.

Went for a ride and it rides much worse then it did. Tried to balance the carbs but with timing way off is a mute point.

So far all the threads I have come across suggest that crankshaft electronic ignition is the way to go. Also Dyna III seems to be an option but it uses the same advance unit and would have to set each cylinder separately. I understand the concerns a lot of owners have with regards to electronic ignition failing and being stranded far from home. So I thought with a crank shaft ignition I can leave all old ignition pieces in place and just discontent the points lead from the coils and connect if case of failing electronic ignition without much fuss.

Question is..

Is there any way to straighten the tip of the cam shaft while on the bike?

Thanks.

Wow...that's hard to think about. The tip of the camshaft is frickin' hard! Seems it would take a lot to bend it. I think you're on the right path. First thing I thought of was the Dyna...I have it installed on my /7. Yes, there are separate pickups for each cylinder to allow some fine tuning but if you're too far out, it might not work. I think you're best bet is to look at the crank-mounted ignitions. If ever the engine comes apart, you could deal with the camshaft at that point.

r60celo5 said:

Resurrecting this old thread.

I understand the concerns a lot of owners have with regards to electronic ignition failing and being stranded far from home.

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Oh for God's sake. Most cars have had electronic ignition since the 1980s or even 1970s. BMW Airhead motorcycles have had electronic ignition since 1981; K Bikes since 1983, and everything else all the time since. It is true that some aftermarket junk was sold in the early days of modifications in the 1970s and '80s but by now these "concerns" don't even rate as urban legends or old wife's tales.

Just as an example I will venture that if the Dyna system isn't any good they wouldn't still be in business 50 years later. And then you have Boyer and Endurospark and others.

So, with my rant over, I will add it is probably possible to straighten the nose of the camshaft but it will be a delicate task. The metallurgy is not intended to allow it to bend and bending it back can cause it to break off. I saw this happen once about 40 years ago. It most likely will take more than one attempt to get it perfectly centered again. Somebody might be able to describe a good technique: I can't.

I always was careful tightening the nut. No hammer used or anything fell on it.

No clue how it happened, looks like at least 3/8inch diameter. It would take quite an effort to bend it. Now that I think of it, is there a chance the bearing has gone bad making the tip wobble?

However, If it was the bearing, the tool used to set the point gap should be able to slide over the shaft tip easy, unless the tool is messed up too (possible since it's just an aluminum tube and can be dropped or impacted in any way). What are the chances both happening at the same time?

I have no beef with electronic ignition. Installed Dyna on my 76 Honda CB550 and am happy with how easy it starts and timing is always spot on.

However, If just by bad luck ...... the tip was bent.... or the bearing is shot plus the tool being being out of round ..... Its not unlikely that I get the one bad unit from the pile of electronic ignitions. Kidding.

Just ordered EDL-BOIGNS from bob's. But still would like to know if there is a way to bring it as close to straight as possible.

I image it will not be an easy task to get it back to straight. Thought someone might have tried before.

Any pictures of this?
OM