Gl1100 block with 1000 head

[ericheath]

I don’t think most people can feel the difference. If you read the article cited above from Old Fogey, there is a little concern that setting the 75 ignition timing at 10 degrees BTDC might yield a dangerous amount of fully advanced timing. The 75-77 advance mechanisms advanced timing to 37.5 degrees. (32.5 past initial setting) Setting the initial timing at 10 BTDC would increase full advance to 42.5 degrees. (45.5 on an 80-81 if using the marks) If you aren’t too crazy it’s probably okay. The suggestion was to use the 78-79 advance mechanism because it has 5 degrees less advance built in to it keeping you in the safe zone. Google total advanced timing and without further controls and safeguards, 38 degrees total advance seems to be consensus of safe amounts.

My hybrid 1200 has timing at 10 degrees BTDC which with 77 heads and cams and advancer would advance to 42.5 BTDC and was ready to use a 78-79 advance mechanism, but ended up going with a different ignition system. It currently advances spark to 42 degrees BTDC but controls its advance until 5000 rpm and above.

(It’s virtually the same as C5)

[Sidecar Bob]

I don't know for sure but the cams are timed to the crank the same way whichever heads you use so I think it should work with 1000 heads. On the other hand the compression might be different and I am not sure if that would affect the optimum timing.

[ericheath]

All of my posts are about ignition timing, not cam timing.

[Sidecar Bob]

Right. I installed '77 1000 cams in my '82 1100's heads and timed them normally (the pulleys are keyed to the cams and if you use the marks on the pulleys they should be right). Then I set the ignition timing per the Dyna S instructions for installing it on a 1000 but using the timing marks on the 1100 flywheel.

I believe that the timing advance I am using is the one that came with the '79 engine but I am not certain because I didn't know there was a difference between the years when I put the '79 engine into my '77 bike (& later into the '83) so there is a small chance that I might have used the advancer from the '77.

As I said, it seems to run as it should. Is there anything I should be concerned about?

[ericheath]

The advancer will have a 431 stamped into it if it’s a 78-79.

I couldn’t tell any real difference. I revved the snot out of it. I did feel that at ten degrees advanced at idle, it may have been a little popping, but that could have been my carbs too. I thought idle was better at 5 degrees, but not much else was different. I messed a lot with the carbs back then.

The problem with mechanical advance is, unless you use a light, you never know if the springs still have there spring. The 431’s have little rubber? bumpers on the stops to help them last, I assume. I got a set from Cyborg, but before I got around to putting them on I decided to try the Power Arc.

[Sidecar Bob]

The bike is in cold storage but even if it wasn't I probably wouldn't look anyway because I'd have to take the Dyna out to see it and then I'd have to set the timing again and if it is running OK it would sort of defeat the purpose of having a set it and forget it setup

[karachishop]

So finally pull the heads apart on the 1975. I dont know how to post pictures.
So I have a few questions.
1) 1975 heads have head gasket leak. It was full of water and oil. I did the valves about 4 years ago. Should I do them again or just cleans and put new seals.
2) 1981 1100 motor is a running motor. No leaks. Can I just put 1975 or 1976 cams in the 1100 heads.
3) if I used the 1981 1100 motor. How to remove and seal the ignition area.
I will have more questions but that's what I can think of right now.

[Sidecar Bob]

Water in the cylinder is usually caused by a blown head gasket.

The 1000 cams will fit in the 1100 heads but you need to modify either the head or the points housing to make it fit. I removed the parts that drive the ignition from the 1100 engine and covered the opening with a plate. Have a look through my New Engine thread (link in my signature) to see what I did.

BTW: Nobody has mentioned the issue of gearing here yet. The final drive ratios of the 1100 and the 1100 are different but their overall gearing (at least in the lower gears) is pretty close to the same, so the gear ratios in the transmissions of the models had to be different. This means that the if you use one model's transmission and the other model's final drive it will produce overall gearing significantly different from stock.

I learned this when I put Mr.H together with a 1000 engine and most everything else from an 1100 and discovered that the overall gearing was significantly higher; In my case first gear was a bit higher than 2nd was on the stock 1000, which meant that since I spend most of my time in high gear at 80+ Km/h the RPM was significantly lower and so was the fuel consumption.
(This was great on 2 wheels but not suitable for the extra load of the sidecar, which is why I eventually changed to an 1100 engine & transmission).

If you are planning to use this engine with the 1000 final drive the effect on your overall gearing should be the opposite. I expect that 2nd gear would be a bit lower than first was on your stock machine and 5th would be somewhere between 3rd and 4th on a stock one. You could entirely stop using 1st gear but the RPM on the highway would be enough higher that it would noticeably increase fuel consumption, not to mention feeling a bit more buzzy.

[karachishop]

Thank you sidecar bob. Your info helps alot.

[ericheath]

Here’s a spreadsheet with the differences. The big one is the secondary gearing on the 81 which went from 0.825 in the 1000 to 0.973 in the 80-82 models. This affects all the other gears so even though first is the same, it won’t be the same as a 1000 with a 1000 final drive. The 1100 in a 1000 bike will be quicker geared in first by roughly 17% in the transmission and the 3.40:1 in the 1000 final drive vs 3.091:1 adds even more. Which is why several guys here who have done it liked dropping 1100’s into 1000’s. Along with the extra 100cc of punch, it got off the line easier. Fifth gear is slightly taller geared in the 1100, but with the secondary reduction factored in, I think they’re pretty close to the same. The 83 year had totally different gearing as well. It has a quicker first and taller fifth gear but it’s secondary reduction switched again to in the middle of the other two. Then there were rear tire changes. 82-83 went to 16” rear wheels away from 17” wheels of the earlier years.

Confused yet??

As to mpg, I believe that will be operator, right wrist controlled for the most part. Quite a few report similar mpg to 1000 models with 1100 or 1200’s in the 1000 frame with the 1000 final drive. Others here have put 1100 swingarm and final drives on to 1000 bikes lower rpm for cruising and improve mpg. They did grunt more taking off.

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Wingrider has a thread of blocking off the ignition with a plate similar to sidecar bob, but on an 84, 1200 which had the same rear ignition setup.

Good luck, I look forward to following your build and learning how to post pics- hint hint.