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[adamscarborough]

I'm trying to fit a set of high performance cams to my '93 500cc Bullet. I've carefully ground away at the engine casings to get the necessary clearance for the larger lobes, hopefully anyway, as I don't fancy taking any more metal off and it was a heck of a job.
Now, each cam spins freely on is shaft, but when both are fitted they bind togeather terribly, almost impossible to rotate by hand at some points. If I put the timing pinion back on and rotate the engine by the kick start everything rotates but must be under quite a lot of strain. Am I right to be concerned?

[adamscarborough]

Original Video - More videos at

[ric]

Sounds like you may have found a pair of cams from the bad batch with over meshing problems that were floating around not that long ago.
The teeth should mesh evenly throughout their complete rotation.
There have been slight differences with cam spindle diameters over the years. A pair of prototype cams with new undersized bushes which I reamed to fit my own bike for testing wouldnt even slide onto the spindles of the next bike they were going into. With greater clearances between bush and spindle you may not have realised there was a problem. Some owners I know would be happy to ream out the bush to solve the problem, but the correct solution would be to return them if possible and swap them for another pair without issues. .

[Adrian]

Sorry, my PC won't play your video, but just a thought, which cam spindles have you got in your engine, fixed or adjustable? If someone has fitted adjustable spindles in the past to compensate for a part-worn set of pinions on the old cams, they would need readjusting for a new unworn set.



If your bike has plain/fixed cam spindles it's possible the teeth on the new cam pinions have not been machined to the correct tolerances. If you have bought them from our hosts please get in touch with them, or whoever you bought them from.



I wouldn't normally recommend adjustable cam spindles in place of plain, but they would allow for a little extra clearance between the cam pinion teeth, ideally without opening up too much slack between the inlet cam pinion and the first idler gear for the ignition.



A.

[Adrian]

Sorry, my reply crossed with ric's.

[stinkwheel]

Just one thing I notice from the video is that the exhaust cam doesn't appear to be fully seated on the spindle as you're rotating it. This may not be relevant.



The cam itself is definately not binding/rubbing on something else? The followers aren't fouling something? Maybe apply some engineers blue (or scribble on it with a marker pen) to check it's not rubbing?



Incidentally, those look like standard, non-adjustable cam spindles.

[adamscarborough]

Thank you for your great replies.
Yes they are the standard fixed spindles (not adjustable), and individually each one rotates perfectly freely on the spindles. Yes you are right the exhaust one wasn't fully seated in the video, I hoped no one would notice, but it doesn't make a difference. They are so tight they are difficult to get on so they are on the same plane.

[Bullet Whisperer]

It might be worth considering that quite a few Bullet engines which are noisy with cam gear backlash start off quieter when cold, but as the engine warms up they get louder - this is because as it warms up, the engine 'grows' very slightly and the cam spindles end up being a tiny bit further apart. This might mean you could make sure everything is well oiled for assembly and when it is ready to go, take the tappet cover off and squirt lots of oil into the timing chest below, refit the cover, start and allow to idle until hot. Next, stop the hot engine, remove the timing cover and re check while hot. If all is well, refit the timing cover, repeat the oil procedure and you will be good to go. if the binding is still evident when hot, you may have a problem. you might be able to heat the relevant area of the crankcase enough with a heat gun [timing cover removed], if you don't want to run the engine like this and see if the cams free off by doing so.

[adamscarborough]

I've been in touch with H's and my cams aren't the problem batch. I have a few things to check, such as whether the bushes are concentric with the teeth and whether there is any damaged teeth, which is a posibility as these have been awaiting fitment for 8 years :/ I'm not quite at the stage of giving up.

[adamscarborough]

That was one heck of a job. I'll just come out with it... grinding paste :/
Well, I had nothing to loose, H said they wern't the problem batch and they were 8 years old.
I could have put them on Ebay but got nothing for them.
So, Assuming they couldn't be far out, I carefully applied grinding paste to the problem teeth, after an hour last night of slowly turning the gears buy hand and ending up with massive painfull blisters on my fingers! (and with little progress), this morning I made a tool to turn them by electric drill, after a very short time everything now rotates freely. I've spent another hour scrupulously cleaning everything. I don't think I've damaged the pivots so I think I'm happy.