75 v 82 cams

Tonight, I had nothing better to do than to compare the height of these 2 different year camshaft lobes, following both of them passing the thumbnail test for wear on the top of the lobe.

I used a Frankford Arsenal caliper that zero's perfectly, and as I'm just taking a "difference" between the 2 components. Calibration, or the quality of the instrument shouldn't be issue, yeah?

OK, here's what I found! They where all very close so averages where:-

75 camshaft...
Inlet 1.465"
Exhaust 1.447"

As opposed to.

82 camshaft...
Inlet 1.452"
Exhaust 1.446"

There is no way that I could measure duration. And I have no opinion on that whatsoever.

But this is real time measurements of >32 year old equipment, but my deal is....

How does just 0.013" on the inlet cam make such a difference?

To measure duration use a degree wheel with the cam installed and measure the amount of degrees that the valve is activated.

I would imagine duration and valve timing - degrees before or after top and bottom dead center that the valves open and close - make the most difference in engine performance.

Steve you of all people, ought to know, valve timing is not optional on these machines, one tooth out, and the engine is toast!

So I'm thinking the difference is in duration, but what do I know? I'm just a guy with a caliper!

Well, on these cams, one tooth is equal to 9 degrees of rotation. Both opening and closing timing are affected.

According to the manuals, the difference in valve timing is as follows:

'75 - '77, '78 - '79, '80 - '83
5 BTDC, 5 BTDC, 5 BTDC - Intake opens (Before Top Dead Center)

50 ABDC, 35 ABDC, 43 ABDC - Intake closes (After Bottom Dead Center)

50 BBDC, 40 BBDC, 45 BBDC - Exhaust opens (Before Bottom Dead Center)

5 ATDC, 5 ATDC, 5 ATDC Exhaust closes (After Top Dead Center)

So the duration would be:

'75 - '77, '78 - '79, '80 - '83
235 deg, 220 deg, 228 deg - Intake

235 deg, 225 deg, 230 deg - Exhaust

So, 5 degrees before or after top dead center is the closest any valve comes to hitting a piston. One tooth off changes that by 9 degrees. That's trouble!

The difference in the cams is the closing of the intakes, and opening of exhausts, which happen near bottom dead center, so valve clearance isn't an issue - even with radical timing changes. Good stuff!

well ok its obvious that it dont take much to make huge difference ... this is the one thing honda got right ...the first time they built a better cam as they changed them only worse ones ...i have tried all the cams in all the oldwing motors there simply is no comparison ...oldwings like the 75-77 cams are better big time

Nice research there Steve and great explanation.

I think there's enough additional clearance between the head and piston of the 1000 that one tooth off will not result in a collision. Anyone who wants to check that, don't quote me as I am not positive. The valve starts lifting at 5 degrees, but the ramp controls how fast. I have done some recent "messing" with cam timing on my bikes. My butt Dyno conclusion is that 4 degrees advance is too much. Boosts bottom end, but hits a rev limiter at about 7300 rpm and seemed to start losing pull at 6500. I have it set about 2 degrees advanced right now. It's too cold to ride much here already. ( snowing yesterday) I did it to my hybrid, 1200 with 77 heads and to my stock 77. My initial feeling is that it brings a little more oomph to the bottom of the rev range at the expense of the upper end, as expected.

duration is the key to its aggressiveness 75-77 1000s the longest ..1100 next...1200 next and the 78-79 1000 bringing in the rear with the shortest duration time

[url=https://classicgoldwings.com/forum/viewtopic.php?p=132874#p132874:13d9h1ic said:

ekvh » Sat Oct 04, 2014 4:48 am[/url]":13d9h1ic]
I think there's enough additional clearance between the head and piston of the 1000 that one tooth off will not result in a collision. Anyone who wants to check that, don't quote me as I am not positive. The valve starts lifting at 5 degrees, but the ramp controls how fast. I have done some recent "messing" with cam timing on my bikes. My butt Dyno conclusion is that 4 degrees advance is too much. Boosts bottom end, but hits a rev limiter at about 7300 rpm and seemed to start losing pull at 6500. I have it set about 2 degrees advanced right now. It's too cold to ride much here already. ( snowing yesterday) I did it to my hybrid, 1200 with 77 heads and to my stock 77. My initial feeling is that it brings a little more oomph to the bottom of the rev range at the expense of the upper end, as expected.

Click to expand...

Just curious, how do you change the timing? Do you use offset keys or broach new key ways in the sprockets?

well eric been talking some way of doing this without letting in out yet how ...im curious too what hes doing to do this ?

I've been curious too.

Regardless how it's done the ignition will need advanced also to get any real benefit from advancing the cams.

Interesting comment, Slab. Why didn't you post that earlier? And read my mind while you're at it. LOL. I have been messing with advancing my cams on my schizoid hybrid. Advancing the cams naturally advances the timing on the 1000 heads. I set mine back to stock, 5 degrees. This past weekend, after noting the 1100 &1200 are advanced quite a bit, I set mine up to about 11 degrees. It was cold, so riding wasn't much fun, but I now have the 77 cams advanced 2-3 degrees and timed as said, 11 degrees. Performance felt really good. I also ground a little out of the stops on the advance mechanism to let it open more.

My hearing isn't the best and wearing a full face helmet, I couldn't hear any pinging. I run 91 octane.

I've been thinking of doing just that for about a year. Due to the very thin keyway and my schedule I have not attempted it yet myself. I really doubt there is any noticeable difference between 89 and 91 octane. Seems to me you are about as far as you can get with modified stock parts. Maybe you can further refine the cv carbs for a little better performance. Saving your change yet for a single carb or C5?

i am advace in the advancer on c5 ...i think 6 degrees...its early cant think .... but cam is not at all ...i experience no pinging what so ever ....seems the c5 is the only way to get good valve timing ...like spot on ... and then move advance with programming ...this really dose seperate the two deals ....and i think actually have benefits or deficits .....as i see it ...seems moving cam just moves everything and could cause negligible results

Moving the cams on mine bumped compression up 10-15 lbs. It is generally felt a compression boost is a power boost on the low end. On the 1000's since the ignition is off the cam, moving the cams either way, moves the timing, but can be adjusted either way. I believe the key is that the intake is closing sooner allowing it to squeeze more on the compression stroke. It also opens sooner and that might even cause problems on the bottom end at low idle speeds, but I haven't noticed it. I was afraid of advancing the ignition a lot, but I think it's better. It seemed to be much faster last weekend after the change, but that's just the butt dyno talking.

thats interesting ... you got 10-15 more compression ....hmmmm i have hard time here as hooch suffers nothing down low ...in fact im glad to have the gearing up so its not so dangerous ... but your statement on compression change also brings to light ....vacuum signal change on stock carbs ....hmmmm eric ....seems carburation is changed also ...might be something to that could be fine tune for stock carbs ...but this is why i am glad to be away from stock carbs there to dependent ...and cant stand on there own

Dropping Joe's single and intake on Eric's motor would be quite the ride indeed.

I have the VW manifold and a Weber 32/36 to try some day when I get time. It's quite the ride right now. I have the stock 764a carbs modified a little.