Need some help on this. . .

The way I think I understand the process is the cams are supposed to be at a certain point (lobes at a specific angle) and this would be per the manufacturer's recommendations??? Sometimes due to cylinder machining, gasket thickness, decking, etc. the dimension (overall height of the cylinder head) resulting in the cams timing being off by a small margin. So, the cam sprockets need to be pulled and re-pinned to adjust the timing back to the proper specs.

Is this correct or am I missing something? I don't know if I've ever seen the lobe position published on various cams??? This make me think I'm missing something.

Seems a ton of time could be spend trying different advances and retards on the same cams to see different power curves?

 

I am sure our cams could be off a bit, but the question is how much? So lets say you do go through all that work, get the cam sprocket re-pinned, would there be any noticeable difference?

 

Now your asking the right questions!

"...per the manufacturers recommendations... "

that would be for the 1972 2 valve engine they were designed for and according to the person that actually did the testing (which usually isn't the cam manufacturer) on the specific compression, carb, porting, etc... he had done to that engine. I am aware of no "shelf" grinds available for the DS650 that were "designed" for the ds650- they are all direct out of the catalog specs as they were originally designed.

"...Sometimes due to cylinder machining, gasket thickness, decking, etc. the dimension (overall height of the cylinder head) resulting in the cams timing being off by a small margin...."

Correct, but, who's to say that's bad on your particular engine. Setting them back to the catalog lobe centers might move the power the wrong way on your engine combo and hurt power.

"....Seems a ton of time could be spend trying different advances and retards on the same cams to see different power curves?..."

Oh, you're not mistaken there! Now, you see why "custom" cams cost so much!

Keep thinking!

222

 

This is the voodoo that has haunted me in my dreams!!!

I've heard of people that have degreed their cams and seen great results.

Seems the only way I will know for my case it to take the cams from one bike and put them in the other and run them both up the hill. . . Seems simple except the hill is 4.5 hours away and I don't like working on my bike when I'm at the hill (unless I have to [img]i/expressions/face-icon-small-disgusted.gif[/img] )

So, short of that I'm looking on spending a good chunk of money on something that may not be any help. [img]i/expressions/face-icon-small-mad.gif[/img]

Would be nice to know why one is so much faster than the other. I'm sure part of it is set-up (ti axel and ultrabuffs vs. stock axel and extreme haulers) but, I just can't think there is that much difference given there really isn't that much difference in set-up.

 

If your "scary fast" your fast enough......

 

I want both to be Scary Fast. . . [img]i/expressions/face-icon-small-wink.gif[/img]

 

Going to the hill and making the cam swap would be a great test. Remember twin carbs and single carbs are cammed totally different. I dont know if your running twins on both or not. Also if those engines have a different % of cross-section in the port you will need different cams in each engine.

If you get all the tools laid out a cam swap can be done in about 20minutes easy.

We used to machine the cylinder on the old 200x and 350x to retard cam timming for better high rpm hp.

 

[img]i/expressions/face-icon-small-happy.gif[/img] A little of the voodoo info getting out!!!!! I aint sayn nothing[img]i/expressions/face-icon-small-wink.gif[/img] other than now ya getting an idea why my motor hangs around there shop sooooo much LOL

 

well, just got done last night degreeing my cams in. they were 3 deg off.

it not as bad as people would think it would be. should be a good diff in the power.

ill keep ya posted.

 

Shmee, it's something I've thought about for a while but never pursued. I remember a post where MRHP was talking about testing cams on the DS and said we'd be surprised at what he found was working. Stock cams with slightly different timing? Less lift or duration? Those two would be surprises. What about advancing or retarding one cam like they do with YFZs? I'm interested in how you achieved the degreeing?