Different year cams......

[oldnortonrider]

Somebody tell me...........(?)>before I do a long and involved search
on here; the info is on here somewhere> how are the cams and
valves different from the 1979s and the 1981s. I used to know;
I can't remember if the 1981s had larger valves. And if it was both intake and exhaust that had changed. Longer duration (?)>higher lobe (?) which year model cams?

[DiverRay]

The '78 had the most lift, IIRC, the '79 and '80 are the same, and the "large valve" '81 up are longer duration but less lift.
Again, this is all IIRC, as I'm at work, and almost brain dead from it.

[Dennyz]

According to the motors I have looked at:

'78 & '79 - cams have longer duration than '81 cams. '78-79 heads have smaller valves than '81s.

'80s can be either like a '79 or an '81. More often than not, the '80 is like the '81.

'78-'81 have the same lift.

[mro]

From the good book ???

Cam height E, F and SF
intake, 36.805mm ( +,- 0.05 mm)
exhaust, 36.305mm

lift
intake, 8.805mm
exhaust, 8.305mm

note: cam dia 78/79 is .04mm larger than 80/81 (excludes lobe)

G and SG
intake and exhaust 36.80mm ( +,- 0.05 mm)

lift 8.80mm

So....????? not quite what's been talked about before and some of what Dan has said makes a little more cents


mro
btw, at least for the 80/81 head you can use a cam height of 38.0mm (just happen to have some w/sloted sprokets

[oldnortonrider]

OKAY! everyone of you guys who were already at the front
of the class; you get to stay at the front of the class for at least
the next six months.

(?) Next question (?) > Has anybody put the "longer duration" (earlier model-cam) with the "larger diameter" later
model-valves)..
.........what did it do?

(Should have more torque at about any RPM under 6500....(?)

[xschop]

what he said

I talked with Maximan and he said Dan hodges recommended 79 cams with 80 head and 1200cc kit....I will be lightly porting head myself....

[Dennyz]

what XSCHOP said! (except I did not talk with Maximan)

[trbig]

I have the '78 cams on my '82 head with the larger valves. XJ's are supposed to be the slowest, but John said I accelerate faster than his and his has been bored. It seems to keep up with any of the stock XS's except for a naked one at the very top end.. (I have a full fairing and TWO of him on my bike... Hobbyman!) lol.

I still have the original cams and have been tempted to swap them and see if there is any difference I can feel..... just haven't done that yet.

Tod

[HobbyMan]

song pops into head -"can't touch this, do do do do."

[trbig]

Hmmmm Hobbyman....

I think of that same song when I my big overloaded butt and bike accelerates past your skinny butt and naked bike! (The bike looks better than you do by the way) lol... But then Hippie Dave flies by and the song goes away... then I pass by him on the top end.... the song comes back... then you creep by... Sigh...

I'm still thinking about trying one size bigger on the main jets and see what happens... but what I probably need to do is just ride easy and calmly in the back of the group like Dave does.. *Cough. lol..


Tod

[HobbyMan]

I do admit you have the aceleration. I need togo 1 up to probably

[trbig]

So... nothing scientific were you can put numbers down to, and I realize that every single XS is going to make a little bit different numbers, but compared to a few XS's I have rode hard with (Very limited number), it's done as well or better than them if they were stock, when it shouldn't be. Hobbyman's bike runs well, and as stated, mine will accelerate faster even with the full fairing, fairly loaded saddle bags, and with someone riding that weighs right at twice what he does. I have also rode a firends' '80G and know mine is quicker than his.

Dan Hodges warned me before puting the combination of stuff I have together (Jugs, head, and cams) and told me that the minimum clearance I needed to watch for between the valves to piston is a clearance of .060 inches. I found mine to be .132 inches... more than double needed.

I think my next motor, I want to try what the master Dan has suggested here. I have the head from the '78 motor with several bent valves. I might slap it on and check the valve to piston clearance and the piston to head clearance and see if it works. If it's too close and bends another valve... so what?? lol. At least I'll know. Here's a quote from him.

"I was wondering when someone would see the inherent possibilities of using the late pistons in the early head and it was the resident geologist who saw it.You can do the math and look at the pistons side by side in the photograph of the early and late pistons that were posted and see that this combination would result in a substantial increase of static compression.There would be no problem with VP clearence with this combo as the valve reliefs in the late pistons are larger than the early ones however the domes on the late pistons are larger than the domes on the early pistons and the chambers in the early heads are slightly smaller than the late ones and so you would need to measure the piston to head clearence with this combination and make sure you have at least .060 clearence.The clay method is a good method for measureing piston to head clearence.Cut it (clay) in thin strips and coat it with oil so it doesnt stick to the head and lay the strips on the piston top away from the valves,bolt on the head with a junk gasket,torque it down to 15-20 ft. pounds of torque,it doesn't have to be much for this and simply rotate the motor over very slowly by hand a couple of times and then remove the head and measure the strips of clay you placed on the piston tops and if you have .060 or more you are good to go.You can get by with .040 piston to head clearence but it's close.You always want to be on the safe side and leave some room for a margin of error.Using stock parts,a torquer motor would consist of late pistons with early heads used in conjunction with the late cams. A killer motor designed for a Special to beat up on V-Twin metric bikes would consist of the late heads cut .015-.020 for added compression and the early cams and a bag full of money.All of this might be a moot point as new ring sets for these stock pistons are getting hard to come by as they are no longer available from Yamaha.71.5 mm rings can be had,you just have to think and go outside the box."