1983 cam lob question for you engine experts!!

[ctbale]

1983 200X PROJECT: Got another cam I was thinking of using, the lobes are bigger. 1.13mm(.044") and 1.23mm (.048") IN/EX respectively. Mine is right in between new and service limit. This looks like a 200x cam? (1983) Is this too much rise, its about 1mm (.040") over new, it looks huge on the caliper, and that how much more my valves would open, how much does a "hot cam" add, maybe this IS a hot cam, I just want a reliable motor, so if this is going to be a pain to tune, might just keep my stocker, thanks! The top one is the new cam, bottom one is stock, there is a groove at the end of the top cam, is that for lube for the advancer? Thanks!!!!

[ctbale]

I just didnt want my rockers to float if the springs cant handle this rise, thanks

[WilliamJ]

What you need to do is put the cam in and see if the spring gets compressed too much. With the cam at full lift you must have another 1.5mm minimum total spring compression available to avoid coil binding. The reason you need so much clearance is that at high revs the spring coils do weird things, like oscillate at odd frequencies and effectively bind the coils, even if they don't actually bind when turned by hand. If the coils bind it ruins the followers and the cam lobes but it is easy to check before you run it.

As for whether it will bounce the valves - that's almost entirely dependent on how many extra revs you try to run to. Since hardly anyone has rev counters on their trikes it's a hard one to answer. The valves will only float if the cam shape as it reaches full lift decelerates too fast - I don't think that will be a problem but fitting new valve springs which are slightly stronger is easy and cheap.

To know whether the cam will make the motor a lot less tractable you would need to find out the duration of the cam - that is, how many degrees the valves are open for - and also how many degrees of overlap with the exhaust and inlet open at the same time. Measuring that is a fiddly job. Also important is that you check there is good clearance between the piston and the valves. Easy way to do this is to put some putty in the piston cut-outs and very slowly turn the engine with the cam timed in properly.

When you have a hotter cam you generally can, and should, run a little more compression to get the best from it. With more valve overlap the intake charge tends to get sucked out of the exhaust at low revs and more compression helps to rectify this and make the motor less cammy. Delivers more power at high revs too. There is no reason it should not be reliable if it is set up right in the first place - cam timing, ignition timing and mixture / jetting.
Bill