The Great Early Cams in a 1200 Debate

[ericheath]

Not looking to start any fights, just sharing information as best as I see it.

So I was just sitting there in 2017 sun tanning under the coconut trees in the Philippines, enjoying $2 a bottle rum and perusing how great life was with a 1200 and 77 heads/cams/carbs. Okay, I was a little bored too and was looking at eBay for return gifts for Schizoid. I’d left him/her/them for the winter and I didn’t need him/her/they getting mad at me when I returned. So I was just bumbling along and I came across a pic of a 1200 rocker arm. I had a set of heads at home but never took them apart. Those hydraulic valve adjusters seem so daunting after learning to adjust the 75-83 models. They were like black magic arts. I didn’t dare.

Part of my interest in this was that I’d never ridden another stock 1200, so although I love my multi-personality bike, I wondered whether it was indeed all it was “cracked” up to be. So I asked the good people here, there and everywhere about the ratio of the rockerarms. Most figured it was nearly the same. (I was in the Philippines and there weren’t any Goldwings there)

I’ve beat on my bike enough this summer and I was really wanting to go to Sturgis to meet the gang and bring the Zoid. But last Wednesday I had a wild hair up my butt saying, “Put the 1200 heads on and see how it is.” Hence the name of the bike. That’s enough, get back on topic. Sorry. No worries. So I tore it down and began perusing what I had. After reading the manual 124 times I took the heads of the 1200 apart.

Lemme tell you, dem rocker arms ain’t da same. That makes a 1000 words I’ve typed so far, so here’s a pic:

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Please see my signature because, I have been wrong before. But those are the two rocker arms on a 77 spindle. Intimidating, isn’t it?

I realize my numbers are just estimates and there’s some possible telegeometric wizardry that might change it ———- a LITTLE. But it ain’t changing much.

Say what you want about the HUUUUGE 2mm bigger valve of the 1000. (It’s pretty small 5% max) or say what you want about the smaller ports of the 1200 speeding up the intake charge to make a 10-12 hp jump using SMALLER valves. Honda hid a wee bit of info on this.

We were using the info published which was: cam lift. Cam lift is part of it, but with different rocker ratios, it is meaningless. It was there in plain site, under the voodoo valve adjusters where we couldn’t see it!!

Before I totally trash the idea, the one thing that the early cams does is bring a higher rpm band and with higher rpm usually comes more horsepower. But it also gives away some at the bottom end. And the bottom end gets you 60 feet faster.

Okay, I’m done! Flame away in a respectful, kind, sort of way so this post doesn’t get locked and folks who are can make an informed decision.

My advice at this point. It’s probably not worth it.

[Track T 2411]

While this perspective is interesting, the only way to truly compare the differences in actual valve opening height and duration would be to 'degree' out the respective heads, and measure actual valve openings. I've never seen a 1200 head/ cam, so I can't say with any certainty, but if there's any differences in the geometry, i.e. how the rocker arm rides on the lobe/ lifter, etc. that must be taken into account, as well. (I think...)

[desertrefugee]

I think the best way to settle it once and for all would be to flog both configurations (on the same bike) at the drag strip on days or nights where the weather is very similar. Science and specs only result in theories. The dragstrip settles it.

I never much worried about 60 foot times. Unless you're riding a real dog or are asleep on the line, a coupla tenths don't necessarily spell doom.

But, at the end of the day, the performance characteristics on the street will be a matter of personal taste. I kinda do appreciate being hard off the line. Stratospheric high-RPM blasts are less interesting.

[ericheath]

I measured valve seat to valve face lift, but with the 1200 adjusters I got varied readings, perhaps due to no oil or the shim height not being set. Or I maybe because I didn’t have everything torqued to spec. It was hot out. The two intake valves 1000 vs 1200 have nearly the same lift, but the 1200 exhaust lift is greater. A 75 cam in a 1200 head has huge lift but spring binding on the exhaust. Even with extra room for the lift in the piston head, the exhaust valve didn’t want to turn over. I didn’t push it because the springs appeared to be touching each other. (My pistons were already notched for the 1000 cams. It probably wouldn’t take much to get them to work, but as I understand it, cutting the spring seats would result in lower spring pressure. Sinking the valves would help, but you’d need different springs, I think. Putting early cams in without a change of springs would not let you utilize the higher rpm that the early cams could bring. You’d get a bigger opening, but that might hurt the bottom end and the chance of valve float with reduced spring pressure would limit the big rush at the high end? Maybe even lower the redline.

The durations are posted in the manuals. They vary a little. The last years of the 1200’s had ten degrees more overlap. (11/17/18 Correction: the 84-85 cams had twenty degrees overlap, the 86-87 had ten degrees overlap) The early cams had five degrees more duration. Openings and closings varied a little year by year. I never thought it was enough to make much difference.

I’m putting the 1200 heads on so I can at least judge for myself. I may try a different carb setup too.

[desertrefugee]

The durations are posted in the manuals. They vary a little. The last years of the 1200’s had ten degrees more overlap. The early cams had five degrees more duration. Openings and closings varied a little year by year. I never thought it was enough to make much difference.

Bingo! My '78 actually outruns my buddy's '76. He's a good bit heavier than me, but for sure there's no startling difference in performance. I actually have an early pair of cams, but am in no particular hurry to swap them in.

[robin1731]

snip...………..
I never much worried about 60 foot times. Unless you're riding a real dog or are asleep on the line, a coupla tenths don't necessarily spell doom.
.

Two tenths at the track is a life time. Five hundredths of a second (.050) in 60 foot times is about 1/10 in the quater. 60 foot time at the track is what we strive for. You have to get moving as quickly as possible if you want a low/quick elapsed time.

One oddity in drag racing. Example. I have a bike I use to run an index class of 9.90 seconds. That bike is capable of runing 9.30 seconds so it has to be slowed down to run that 9.90. The way I do it is leave the starting line under full throttle, then a time activates a throttle stop at .75 seconds in to the run. The after being on for 2.5 seconds (depending on various factors) the throttle opens fully again. Now, when it runs 9.90 seconds it runs an average of 143-145 MPH. When I run it without the throttle stop it runs 9.30 seconds at only 136-138 MPH.

What happens is when you slow it down the bike has more time to build speed. The same thing happens when you spin the tire more than usual.

And to answer the question in your mind. Yes, the throttle actually closes about 1/4 when the throttle stop is on. All bhappens at the carbs. The throttle grip does not move. It is very strange at first but after awhile you get used to it. Sort of throws you forward some the first few times you use it.

Back to the topic. To measure the actual valve lift with the different rocker arms you would have to remove the hydraulic adjusters. There can be no movement at all. When degreeing cams in a car that uses hydraulic lifters you have to do it using solid lifters, then put it back together with the hydraulic lifters you are using.

I am surprised the exhaust would get to coil bind with the 1000 cam in the 1200 head. What is the difference in lift between the cams?

.

[ericheath]

1200 by the book is 5.8mm lift, 1000 is 7.08mm lift.

How would I remove the hydraulic adjusters and operate the action? I removed the shim (mine had one shim.) I’m not real sure of how the hydraulic adjuster works, but without oil pressure, and no shims, wouldn’t it read greater than with a cushion of oil?

The leverage looks pretty conclusive.

[desertrefugee]

snip...………..
I never much worried about 60 foot times. Unless you're riding a real dog or are asleep on the line, a coupla tenths don't necessarily spell doom.
.

Two tenths at the track is a life time. Five hundredths of a second (.050) in 60 foot times is about 1/10 in the quater. 60 foot time at the track is what we strive for. You have to get moving as quickly as possible if you want a low/quick elapsed time.
.

Sorry to hijack slightly - but I think this almost fits - if we're talking about empirically assessing these changes.

Thanks for the expert commentary, Robin. I think I was also taking reaction time into consideration - and thinking more in street terms from a traffic light. Few will be running a GL at the track.

But, assuming the 60 foot time is due to poor RT, do you think a "capable" machine would be more able to recover from the holeshot disadvantage due to sleeping at the light than an actual poor 60 foot time? In other words, which is worse - poor 60 foot due to slow RT or poor 60 foot due to performance?

[robin1731]

Reaction time has zero, zip, zilch, nada, nothing to do with elapsed time.

.

[dontwantapickle]

Another hijack -
I would love to see a pic of your 9.30 second dragbike.

[ericheath]

The difference is huge.

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This is of the two rocker arms side-by-side on the exhaust valve. Too bad the 1200 rocker arm didn’t have a valve adjuster on it. It might be too much lift anyways.

[CYBORG]

Can someone explain to me why they would want to do all this stuff to a perfectly well engineered machine? What gains do you expect?

[ericheath]

That’s why I’m posting this. I always wondered if it’s as much a gain as said to be. I think this all started back in around 2010 when it was reported that a mechanic did it. It was all opinion reporting. I think we try and see numerical proof that a mod will work. The only differences in data available that I have seen was the cam profiles, cam lifts, valve sizes and carburation. I think it was always assumed the rocker arm ratio was the same. I’m posting this to show that the 1200 had more intake and exhaust lift despite having a smaller cam profile. The smaller intake valve might give away a little at high rpm, don’t know.

Being someone who did the mod, I’m posting this to perhaps show additional data before others do the mod. As suggested above until someone either Dyno’s it or races it a few runs, we won’t know.

As to why anyone would want to mod a perfectly good machine: human nature. Why add nitrous?

Perhaps, after seeing this info, someone who doesn’t like adjusting valves will put a set of 1200 heads and cams on an 1100 or 1000 and see a performance they like. It makes me curious.

[robin1731]

Another hijack -
I would love to see a pic of your 9.30 second dragbike.

I don't have pics of either dragbike on this computer. If you go to Randakks site and look where he has the list of his approved rebuilders you can see a pic of my fast bike.

.

[CYBORG]

That’s why I’m posting this. I always wondered if it’s as much a gain as said to be. I think this all started back in around 2010 when it was reported that a mechanic did it. It was all opinion reporting. I think we try and see numerical proof that a mod will work. The only differences in data available that I have seen was the cam profiles, cam lifts, valve sizes and carburation. I think it was always assumed the rocker arm ratio was the same. I’m posting this to show that the 1200 had more intake and exhaust lift despite having a smaller cam profile. The smaller intake valve might give away a little at hig. h rpm, don’t know.

Being someone who did the mod, I’m posting this to perhaps show additional data before others do the mod. As suggested above until someone either Dyno’s it or races it a few runs, we won’t know.

As to why anyone would want to mod a perfectly good machine: human nature. Why add nitrous?

Perhaps, after seeing this info, someone who doesn’t like adjusting valves will put a set of 1200 heads and cams on an 1100 or 1000 and see a performance they like. It makes me curious.

good answer.