GL1000 heads on GL1200

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mr.hotrod
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GL1000 heads on GL1200

#1

Post by mr.hotrod »

Hello everyone, I'm rather new to the forums but I've been working on a GL1200 streetfighter adjacent. I had some questions regarding the GL1000 head swap onto the GL1200 block.

1. I understand that the heads are a direct bolt on regarding the block face. Mechanically I'm wondering if the GL1200 timing gears will fit onto the 1000 cams, as I've got a complete set of heads but no timing gears.

2. How does one handle ignition with this swap since the ignition unit is points and cam driven? I don't see anything that appears ignition related on the GL1200 heads, so would I be able to retain the GL1200 ignition system?

3. I also wondered about carburetor solutions for this swap, since CV carbs are picky about airflow would the larger valves, ports, and higher lift cams cause me issue if I were to use the GL1200 carburetors I already have?

Thanks in advance,
Evan.
1986 Honda GL1200 Aspencade
1986 Honda GL1200 Aspencade
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Re: GL1000 heads on GL1200

#2

Post by Rat »

Welcome to the 'Wingdom.

Several folk have done this, they’ll be along shortly … I hope

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Whiskerfish
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Re: GL1000 heads on GL1200

#3

Post by Whiskerfish »

Below is a search for ericheath posts. He has done more on this than anyone else here that I know of. Scroll down through there and you will see many discussions on the 1000 heads on 1200 engines

search.php?st=0&sk=t&sd=d&sr=topics&aut ... =firstpost
"Agreement is not a requirement for Respect" CDR Michael Smith USN (Ret) 2017
"The book is wrong, this whole Conclusion is Fallacious" River Tam
2008 GL1800 IIIA "TH3DOG"
1975/6/7/8/9 Arthur Fulmer Dressed Road bike
1975 Naked Noisy and Nasty in town bike
and a whole garage full of possibilities!!

Psst. oh and by the way CHANGE YOUR BELTS!!!!
redglbx
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Re: GL1000 heads on GL1200

#4

Post by redglbx »

Evan,
Not sure about the timing gears but if I remember right the 1200 belts have one more tooth than the 1000/1100 motors, I think the 1200 has a taller block that should require longer belts to work. You could lay the pulleys on each other to check them but I suspect (don’t know) that they are the same, just longer belts, but again I’m not sure.

On the ignition, I see you list an 86 aspencade, if this is the motor you are using it has the ignition on the front and I would just use the stock setup. For the ignition stub on the lh cam you can either just cut the stub off (just use the 1200 block off plate) or as it is on my 78 with an 1100 motor in it it has the points housing bolted to the head but with nothing in it, it even has the points wire run to it to look oe but again it’s just show because my bike runs the 1100 ignition on the back of the motor, which in my opinion is much better & more accurate than the 75-79 cam driven ignition.

On the carbs, I would use a set of 76-77 carbs because they are the largest and flow the most stock. If you use the 1200 carbs I would just leave the 1200 heads/cams in place and use the money saved for gas & tires. My .02
Red 1976 oe owner
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1980 CBX , in the que, to fix the ignorant heavy handed owner
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ericheath
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Re: GL1000 heads on GL1200

#5

Post by ericheath »

Disclaimer: I slept at a Holiday Inn Express and that’s where I got all my knowledge.

1 the heads bolt on using the same head bolts and bottom 6mm bolt. The 1000 heads have a smaller diameter but nearly the same volume. The 1200 oil orifice has a larger inner diameter to allow greater flow for 1200 hydraulics, but are interchangeable. Most go with 1200 orifice for more volume. Not sure if it’s needed for 1200 heads. Need to use a 1200 head gasket. Water jacket elbows on top match up.

The big issue is doing something to allow the larger intake valve of the 1000 (38mm) to not hit the piston face which is setup for the 1200 intake valve (36mm) It doesn’t take much, probably a 1mm larger “fly cut.”


Timing pulleys all interchange. The 1200 and some 1100 pulleys were lighter. They are the ones with spokes rather than holes from outside to center.

2. Either ignition will work.

3. I have run each set. For me 1200 carbs were best overall and gave me the best mpg and that was with a 1000 final drive, but 1000 carbs weren’t bad. As for the higher lift cams. I personally think that is bogus. The early cams themselves do have higher lift off the base circle, but the 1200 rocker arms had a greater mechanical advantage and move the valves at least as much as the 1000 or 1100 cams and rockers. I’ve got pics here somewhere.
C171004C-4798-4128-A8A9-3D708C57E656.jpeg
C171004C-4798-4128-A8A9-3D708C57E656.jpeg (252.81 KiB) Viewed 532 times
I believe the 1200 had considerably more exhaust lift via the cam/rocker arm ratio which probably aids in filling.

The only advantages I see with the 1000/1100 head cam swaps are the larger intake valves and the fact that they are solid lifter probably allowing a higher redline.

The 1200 carbs had venturies as large as the 1000’s but necked down to a smaller intake runner and port. Theory is they create more speed of the incoming and exiting charges which ends up with better filling capacity. The 1000/1100 carbs are too narrow to bolt up but can be cheated to work provided your rubber on the intake runners are decent.
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Whatever I suggest here should be given ample time for a moderator to delicately correct. I apologize in advance.
77 WING, 1200 engine with 77 heads, cams, gl1100 foot pegs, Magna V65 front end, 764A carbs, [-gone Suzuki M109 monoshock--, replaced with gl1100 shocks] gl 1200 swing arm, gl1500 final drive, wheel and rear brakes Valkyrie seat, Meanstreak tank, Sportster pipes, Power Arc ignition off crank.
77 Wing. black
83 Wing, in pieces
"Continuing education is important even if the subject matter is fairly useless (as in this case)."---Greg Foresi
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Re: GL1000 heads on GL1200

#6

Post by Whiskerfish »

Interesting observations!!!
"Agreement is not a requirement for Respect" CDR Michael Smith USN (Ret) 2017
"The book is wrong, this whole Conclusion is Fallacious" River Tam
2008 GL1800 IIIA "TH3DOG"
1975/6/7/8/9 Arthur Fulmer Dressed Road bike
1975 Naked Noisy and Nasty in town bike
and a whole garage full of possibilities!!

Psst. oh and by the way CHANGE YOUR BELTS!!!!
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CYBORG
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Re: GL1000 heads on GL1200

#7

Post by CYBORG »

I fail to see the advantage. I have both a 1000 and a 1200. And a 1000 frame with a 1200 engine. The reliability, and less maintence on the 1200, stock, the way Honda built it, to me, is an advantage. The 1200 can be made faster by eliminating a lot of excess weight that is not needed on a "fast bike". And is easier to do.
1978 custom GL1000
1977 custom with 1200 engine
1985 gl1200
Shadowjack
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Re: GL1000 heads on GL1200

#8

Post by Shadowjack »

Both of the stock 1200 Interstates I've had would just about suck the headlight out of my well-running 77 1000. Which is why there's a 1200 engine in a 75 naked frame here. 20% more displacement shows.
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Re: GL1000 heads on GL1200

#9

Post by CYBORG »

Shadowjack wrote: Fri Sep 30, 2022 8:44 am Both of the stock 1200 Interstates I've had would just about suck the headlight out of my well-running 77 1000. Which is why there's a 1200 engine in a 75 naked frame here. 20% more displacement shows.
I agree. And the instalation of a single rear shock improves the handling 100%
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1985 gl1200
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flyin900
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Re: GL1000 heads on GL1200

#10

Post by flyin900 »

I have both a 81 GL1100 and a 84 GL1200 both naked from the factory and I had a 1976 GL1000 now with a new owner. I have to say the GL1200 motor stock in the naked bike is pretty quick and definitely faster than the naked GL1100. The 1976 GL1000 seemed fast at the time, yet it has been a few years now since I owned that one, so the jury is out.

I agree that stripping the GL1200 of all the Tupperware and misc parts and then go from there is a better way to at least start the project. :-D
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1966 CL77 - Honda 305cc - Dual purpose - "Gentleman's Scrambler" was a period moniker.
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1978 CB550K - Very original bike with only 7499 Km. from new - light cleanup and refresh done.
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ericheath
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Re: GL1000 heads on GL1200

#11

Post by ericheath »

Stuffing a 1200 into a 1000 or 1100 is pretty easy, however I would suggest moving up to better forks. A 1200 front end is a fairly easy bolt on. I always wanted to try a 1200 in an 1100 frame with its final drive ratio.
Whatever I suggest here should be given ample time for a moderator to delicately correct. I apologize in advance.
77 WING, 1200 engine with 77 heads, cams, gl1100 foot pegs, Magna V65 front end, 764A carbs, [-gone Suzuki M109 monoshock--, replaced with gl1100 shocks] gl 1200 swing arm, gl1500 final drive, wheel and rear brakes Valkyrie seat, Meanstreak tank, Sportster pipes, Power Arc ignition off crank.
77 Wing. black
83 Wing, in pieces
"Continuing education is important even if the subject matter is fairly useless (as in this case)."---Greg Foresi
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Re: GL1000 heads on GL1200

#12

Post by CYBORG »

I use the 1000 final drive (77 frame and swing arm). I re-inforced the swing arm. And used the 1200 front forks in the 77 frame. Works well.
1978 custom GL1000
1977 custom with 1200 engine
1985 gl1200
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Re: GL1000 heads on GL1200

#13

Post by Shadowjack »

I swapped an 1100 swing arm and final drive to the 1000 frame when I changed the engine, specifically because I didn't want the 1000 final ratio. I would not recommend going this way, because you have to mate the long 1100 rear driveshaft to the short 1000 front yoke, with all the issues that changing the U-joint entails. Plus have new swingarm pivots made. And do something about the right lower shock mount. Oh, and it needed longer shocks. Just put the 1200 engine in an 1100 frame to begin with.
mr.hotrod
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Re: GL1000 heads on GL1200

#14

Post by mr.hotrod »

Thank you all for the input, gives me a good start to planning the project since I don't intend to tear the bike down till winter.

Evan
1986 Honda GL1200 Aspencade
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