NGWClub®, Inc.

This subject comes up fairly often, so I thought I'd put together what I know about it to maybe keep from having to write the same responses over and over. Being that I bent a rod on my bike last year from Hydrolocking, I am prepping an 87 motor to take its place. I'm hoping it doesn't start a debate about whether to swap heads or not, just showing how I am doing it. This will work with 1000 heads or 1100 heads. There are three cam profiles to pick from. The 75-77 1000 is most aggressive and a bit more lift, a very little, the 78-79 is least aggressive, and the 1100 is right in the middle. All three have the same size valves, 38mm intakes, 32 mm exhausts. Using 75-79 cams will allow easy installation of C5 if you choose.

The 1200 motor came with significant improvements to the block, crank, journals, an extra 5 mm stroke, but only 0.5 mm diameter to the pistons. It also came with a smaller intake valve at 36mm and smaller intake runners and carb Venturi outlet. Cam profile is similar to the 1100's.

A few have done the swap to see what gains could be made using the bigger valves and aggressive early cams. No data but butt data that I'm aware of. I did it based mostly on the rave reviews of papabear, I think. He had a Honda mechanic friend who had done it and his family allowed him to buy the bike when he passed away. He claimed it was a screamer. Luckily for me Steve, superskypilot, at Saunders did it first to see if it was possible. Read the 69+ page at Saunders if you like. He found that you don't just bolt the parts on. If he hadn't shown that, I'm sure I would have bent all my intake valves.

I'm of the opinion that this is the most bolt on horsepower you can get short of efi and forced induction. All Honda parts.

Start with any 1200 engine minus the heads. 84 models have different ignition and starters and won't bolt in to 1000 frames without some mods either to the frame or the ignition on the back. 85-87 drop right in, but may need a love tap or two on the frame member near the top of the stator.

If using a 1000 or 1100 final drive, the rear cover must be removed and the 1200 final output shaft replaced with one of the others. I think both will work. The 1000 or 1100 propellor shaft will go on the 1200 output shaft, but the 1200 output has no groove for the snapring for the 1000-1100's and those who have tried to go without it, have had the shaft come off in operation. Might be ugly if it happened in a corner.

Another big difference in the early motors and the late motors is that the early 1000-1100 motors had pistons which came up near the top edge of the block, but not past it, while the 1200's come up 0.010"-0.020" past the top of the block. Bolt a head onto a 1000-1100 without a headgasket and it will turn over, but bolt it to a 1200 without a head gasket and it will hit. This combined with the bigger valves and greater lift requires something to be done. If I had all the money Robin has, I think I would sink the valves. Have a shop cut the valve seats deeper. I think there's enough room in the seats to do that. But the other factor is the geometry changed a little in the angle the the valves are set in relationship to the piston.

So the other options are to notch the pistons. Steve at Saunders- well-- he has skill ----and brazed a cutter onto the edge of a sacrificial intake valve. Then put the valve in the head and cut the notch 0.060"- 0.080" deeper--as I recall. I didn't have a valve to waste so I used the double-faced tape and wet/dry sandpaper to do it.

There are several ways to check your depth, but using sandpaper, I wasn't able to conclusively say I had enough clearance or not. I slathered grease in the piston recess to minimize the chance of grit getting anywhere bad, but the truth is, it could get pushed in by the rings and score a wall pretty easily. As to depth, I checked it afterwards and tried to cut them all the same.

More to come. Anyone who wants to correct me on any errors, please do, so I can edit it and look smart.

This time I tried a different tack on the valve reliefs. I took an old valve and used a hacksaw to cut score marks across its face to use it as a cutter. The first cut looked like it worked well, but subsequent efforts made it a waste of time compared to the sandpaper method, except for the fact that the only debris to possibly get in the rings is aluminum and less likely by far to do damage.

My rule of thumb for these is to cut the relief to about halfway to the "IN" marks, a little further than the above photo. So yesterday, after buying impatient with the slotted intake version, resorted to the sandpaper trick to finish.

Today I decided to check clearances. The last time I did this, 2012 or 2013, I used the clay that HVAC technicians use. It tended to stick to both sides and I wasn't real confident in my results. This time I got some kids modelling clay from Dollarama and it worked pretty nice. I don't have a good pick of the current cuts, but you can see the two sides of the clay, then the measurements. On the intake side, I have 0.120" at least, and on the exhaust 0.150" at least. I pinched the calipers into the mold a little.

Note the skinny little ring that squeezed out on the outside between the piston and the gasket.

Hoping this gives direction to anyone else who has the bug to try something different. I forgot to mention that the heads I am using have been shaved 0.025" already. I know of two who have trusted their steady hands and used a grinder to cut the notches freehand. Don't slip.

I am debating with myself getting 0.032" gaskets this time and I have taken almost 0.010" off the block so this time I will be close to 0.040" shaved. Best I can figure it will be about 10.5:1 compression.

I'm hoping to have multi spark ignition for this also with multiple curves for timing. Looking for one to read off the crank.

I'll try to remember to snap pics of the heads. Their combustion chambers have nearly the same volumes. The 1200 has the same shape and opening at the space between the gasket and the start of the combustion chamber. Weird, you would think it would be 3- 3.5 mm larger in diameter. The 1200 has two bulges that help with swirl in the chamber, it also has a dished exhaust valve, while the 1000 has a flat valve which accounts for almost a whole cc less volume. I believe the 1000 piston has more dome giving it the slight edge in compression ratio. The 1200 dome is almost flat compared to the 1000. Another oddity to me is that the 1200 had bigger valve reliefs on the exhaust than the intake.

"If using a 1000 or 1100 final drive, the rear cover must be removed and the 1200 final output shaft replaced with one of the others. I think both will work. The 1000 or 1100 propellor shaft will go on the 1200 output shaft, but the 1200 output has no groove for the snapring for the 1000-1100's and those who have tried to go without it, have had the shaft come off in operation. Might be ugly if it happened in a corner. "

I read this paragraph in your post, Eric, and think I have a bit of information re: the retention of a propellor shaft onto a non-snapring configuration final output shaft.
First, though, I believe the GL1000 and GL1100 both utilize a different ujoint yolk splines count on their respective final output shafts. I may be wrong.
Whether the GL1100 and GL1200 yoke splines' counts are identical or not, I have no idea.

A 1980 CB900 Custom propellor shaft's driven yoke slides onto a non-snapring final output shaft, and its placement is maintained there by a coil compression spring which is inserted into the propellor shaft coupler before the swingarm flange and final drive assembly are fastened together. The smaller diameter coiled end of the compression spring bears upon the flat washer face directly under the driven pinion retaining nut. The larger end of the same compression spring is seated around the snapring which retains the propellor shaft into the coupler.
Seemingly, that must be the same method the GL1200 would utilize for the same purpose, as well? On my trike, I utilized the stock CB900 Custom compression spring into the GL1000 propellor shaft coupler (actually the longer CB900 Custom coupler was used with my unmodified GL1000 propellor shaft) for the same purpose on my unmodified GL1000 engine, and it performed swimmingly, with no identifiable problems, for 15,000 miles.

I am unsure on that , Cliff, but I know that one attempt to use the 1000 propellor shaft on the 1200 output shaft came off. Not sure if the spring can be utilized or not, but I don't think so. I will get a 1200 prop shaft this weekend. I'm hoping to mate it with a 1500 final drive. I believe the number of splines on 10-11-12's are the same. The length and ujoints were different on them. Not sure also about swapping just the joints, but I think it's a "no go."

Ahhhhhhh......ok. I just went 'shopping' on eBay to examine the 1100 and 1200 final drive systems' components and now understand the 1100 final output has a snap ring groove, and the 1200 propellor shaft is completely different, when compared to a GL1000, GL1100 and the very similar CB900 Custom systems' components design.

Thinking back several years ago, OldFogey had corrected my assertion that the GL1000 and GL1100 propellor shafts utilized different spline count yokes. He'd also told me, as you had, the differences are in their respective shafts' overall physical dimensions.
So that proves, yes, if I keep my eyes and ears open I'll learn something new, everyday!

If you had my money you'd be on welfare.

Thanks Eric! This thread should save me from asking a bunch of questions in the not to distant future.

Hopefully someone else does it who can run it at a strip or on a Dyno to see what gains are really there. The weather here still needs to warm up here.

Eric, I can't say for certain, but I do not believe my 84 engine has the bigger exhaust valve reliefs...of what is left, they appear to be the same. You may recall that I got a tad worried that the exhaust wouldn't clear on mine, so I massaged the Pistons on both reliefs.

Now that you mention it, this is of the 87, and I haven't compared the ones on my 85 and a quick look to my photo archive makes them look to be the same size on the 85 model too.

It almost looks as though you could flip a set of 87 Pistons upside-down to use early heads. More work than I'd care to do and you'd think Honda did it for a benefit: maybe helps remove exhaust faster. Wonder what 86 models were like?

I don't have any information on them but you are assuming the valve angles for both inlet and exhaust to be the same. If they are not, that might explain the disparity.

I think I recall reading that the 1000 valves faces came in further from parallel to the piston face than 1200's by a few degrees. It's surprising to me that the chamber volumes were nearly the same.