Rickman CR900 "GS" engine choice poll - big bore GS550-741/789cc vs GS750-894cc

[Chuck78]

Also..... If the wife saw a different GS engine than the familiar ones all over my shop, it wouldn't take long for her to snoop at the crankcase serial # or the 998cc cast designation on the block to see how big of an engine I'm running! When I mentioned the Rickman was modified with GS1100E engine mounts, she immediately raised her voice and told me that's faster/bigger than anyone needs!

 

[Chuck78]

I think with these Yoshimura Road and Track cams and a good lobe centerline timing, the 894cc will be able to hang in 3rd gear very well while canyon carving, as you made the gs1000 3rd gear reference.
The 920cc gs750 when the cams were set on 104 lobe centers approximately was incredibly torquey to the point that I was involuntarily lifting the front end off the ground exiting corners at just over half throttle at 4000-4500 rpm on some mid summer rides, & I sorta accidentally induced a neverending 2nd gear 10000rpm 200'+ uphill burnout on Avon RoadRiders... the power was just off the hook. Much more effort/pressure needed to kickstart the engine. Timed to 109 2nd half of summer, it would rev far beyond redline with great power, but the low mids were just not there.
A lot can be gained with cam timing. That was all with stock gs750 cams which are fairly massive duration, around 280 degrees, but only about .304" lift if I recall correctly. I think I could get close to that performance level out of the 789cc GS 550 base using a mix match of 2 megacycle cams profiles to get the same specs as the Yoshimura Road & Track cams that I'm going to be running now. I still need to get a bathroom scale set up to weigh these engines, as it seems to me that the 550 engine may be a good 40 pounds lighter. I think I could get the Rickman's down to a mere 430-430lbs with the 789cc gs550/650/750 build. that would make it quite an incredible Canyon Carver, much much better on the tight roads than any GS 1000 engine and frame configuration.

I am able to manage a 485 lb 920 cc GS 750 engine and frame configuration quite well in the twisties as is, but a more flickable bike with a swing arm as short as the Rickman would be even better. I am throwing my 750 with a GS 1100 swing arm, which is quite long, into the tightest of turns quite well as it stands now. the crispness of a stiffer lighter Rickman frame and a bike that is even lighter then my severely dieted 750 engine/frame 920cc build can only be even better. Even with 20 pounds or so less weight, a big difference in handling is noticed. The 550 engine would make it super flickable for a medium to higher powered vintage 4 cylinder bike

 

[Chuck78]

GS550 engine with starter - 143lbs no carbs.
GS750 engine with starter - 178lbs no carbs...

GS550 is 35 lbs lighter, 2" narrower, 1" shorter front to rear, same height as GS750. 136lbs if I do the starter delete & starter gears & starter clutch gear delete. Pretty tempting...

Also I could keep the engine forward using the gs1100e front mounts, and have an extra inch in the rear. This can be used to substantially update the rear suspension geometry to make the bike exit turns at rapid acceleration without changing the suspension geometry for the worse due to weight transfer and squatting on the rear end under power... I could get some cromoly 1"x1.5" box tubing and add a vertical brace attached to the frame rails and Rickman swingarm mount plate, move the swingarm pivot forward 1.75", and run a Zephyr ZR550 box aluminum 20.5" swingarm at the same wheelbase as the original Rickman... longer swingarm with same wheelbase keeps the swingarm angle more constant to improve the anti-squat tendencies so you can exit turns under much harder acceleration without getting the swingarm near horizontal, at which point the power/acceleration will drastically compress the rear end, killing your steering head fork angle and making you run wide in the turn or wreck... might as well go all out if I am already doing some bronze welding on the frame...

Modern bikes have this design tendency to run the longest swingarm possible by making the gearboxes compacted and taller rather than longer, so the rear of the engine is more forward than older engines in order to run a longer swingarm with a more forward located pivot as to not increase wheelbase...

 

[Agemax]

you only got your 750 down to 485lb? i got my Gs1000 down to 484lb, fully wet.

 

[Fjbj40]

I got my 1000 down to 471 lbs wet.

 

[Chuck78]

you only got your 750 down to 785lb? i got my Gs1000 down to 484lb, fully wet.

I haven't weighed it for quite some time, only guesstimating. It w as 500 lbs full tank several years ago. When I had the vm29 smoothbores on it, it was probably actually 480lbs. After they got stolen, 475lbs!

I have the stock seat, stock tail panel trunk and taillight, full turn signals& marker lights, L model chrome steel headlight bezel, still have stock battery box & starter relay that's used for a junction block connection and nothing else (no starter!), side covers, all tabs on frame intact, and GS forks. Modern forks of larger diameter are likely lighter. Comparing a gr650 steering stem to a 1999 vtr1000f superhawk, the old suzuki piece is barely hollow.... the Superhawk is thin walled in comparison...

 

[limeex2]

If you're comparing a GS1000 to your Rickman framed 894; that's a completely different animal. A Rickman framed GS1000 would likely be lighter than a GS750-based motor in that same frame. The beauty of a 1000cc motor is that you can stick in 3rd gear and carve the canyons all day long and never have to shift. You can pass uphill in 5th without downshifting; even when riding 2-up.

This is a great thread! I agree with Rudy. With the skills and knowledge you possess, and that I can only dream about, that if I was sticking that much $$$ and effort into modding a 550 or a 750 motor,I would mod a GS1000 motor then work on removing weight and centralizing/lowering the center of gravity. I love big bores. Not trying to hijack the thread but please tell us about the VTR forks vs Bandit forks.

 

[tkent02]

We had an RX7 with a used engine right off a race track. Don't know what was in it but it was the real deal. When you got on it the thing sounded like a whole herd of ****ed off bumblebees up your ass.

I'd do the big 550, but that's just me. I like them.

 

[Buffalo Bill]

I'm not gonna weigh in on the part choices because I'm not qualified, but you have convinced me the 550 lower case is the right choice.
For you it's the engineering challenge, go with that.
Some others here prefer the same old easy choice (GS1000), boring.

 

[tkent02]

I'm not gonna weigh in on the part choices because I'm not qualified, but you have convinced me the 550 lower case is the right choice.
For you it's the engineering challenge, go with that.
Some others here prefer the same old easy choice (GS1000), boring.

I think that's probably the first time we have ever agreed on anything.

 

[Chuck78]

I know the 750's quite well and have lots of spares, and the 900CC 750 would be extremely powerful, more than enough torque on a solo seat performance built non-production model based build... the 789cc hemi 550 would likely be quite powerful enough. Really the ultimate would be habe some 67mm gs650 custom pistons made, which if that were more readily available, would really be a serious contender for horsepower vs the 894 750... the 67mm hemi 750 798cc pistons are readily available here tho, so it's a no brainer for now, could look into the gs650-789cc slugs in the future if I wanted just a head&piston swap.

You are exactly right about the engineering challenge there! Honestly I think I will make a long motor mount plate for the lower left side that would accomodated the 750, 1000, 1100, 1150 engines with multiple bolt on mounts for each middle (lower) mount differences between all those models. The 750/1000/1100/1150 front and rear mounts seem to be all the same. The 550 would require a bolt on adapter plate on the rear mounts to come 1" forward.

If I wasn't so familar with & stocked up on 750 engines, the tscc 1100/1150 would be the no brainer, but honestly the lighter GS550 with pods & pipe is sufficiently fast up to 95mph or so. Revving up the 750 above 4500/5500 rpm, pods & pipe, is just simply a rocket, plenty of too end. What a 900/1000/1100 build gets you is far more low/mid torque without having to attract attention revving it. When you do rev those engines under heavy throttle, they clearly are every bit of a vintage superbike power and some of the fastest vehicles on the road.

 

[Chuck78]

35 lbs less & 2" narrower on the 550-789cc prospect is the biggest plus that makes it quite a contender for this build, however... but the 894cc is still alluring. 35 lbs is A LOT, that's like 5hp for free in weight savings, plus LOTS of added cornering ability and more agile handling... I think I may go for both engines since I want to set up the frame to accept a multitude of various GS engine mount locations...

The VTR1000F Superhawk forks run common 296mm Honda rotors that are available in the same bolt pattern as GS hubs, if wanting to run stock GS wire spoke hubs c this is a huge plus. 94-97 vfr750's are similar, better calipers for wire spoke clearance. Both aRe cartridge 41mm forks, and are taller than most modern forks, nearly the same as gs1000 forks. Steering stem is nearly as tall as a GS as well the superhawk/Firestorm has adjustable rebound and preload. Dampening stock is so-so, Racetech and Daugherty both offer full performance cartridge setups for them. 20mm axle requires machined adapters to run gs wheels, or custom spacers and larger i.d. hub bearings with a 17" wheel gsxr speedo adapter if not adapting the GS axle.

 

[Chuck78]

"The VTR1000 forks work nicely in terms of length on a GS1000. I used those forks with the stock calipers and a CBR600F2 wheel. Triples are CBR600 lower with a custom aluminum top clamp. In retrospect I could have probably bolted on a Bandit 600 triple clamp assembly"

-Jim aka DiamondJ's bike, superhawk forks/brakes.

Mine with gsxr1000 6 piston calipers on bench and Rickman fender mocked up:



OhioCafeRacers Greg's Dunstall GS1000 with VTR1000F Superhawk forks (mild rebuild thread on here, more info on dotheton.com or caferacers.net):

Superhawk owners complain about the stock springs and cartridge dampening, but there are a few homebrew mods to improve them. The cartridge kits available from Daugherty and Racetech fully transform them to the most compliant and awesome dampening available.

These vtr1000f forks are near stock GS1000 height with a useable steering stem length (a hair shorter that a GS750 8v stem) in a nice quality triple clamp yoke set, and the VTR1000F has externally adjustable preload and rebound, and 296mm rotor spec (many many honda floating rotors available that fit GS hubs) with a fairly universal 62mm spacing modern caliper mounting setup!

The Bandit 1200 forks are 775mm same as a GS1000 height. I looked up two of the older gsf1200 Bandit specs 95/96-2000, & they run dual 310mm rotors, so 2 years of CBR900RR 310mm 6 bolt 78mm bolt circle rotors (98-99???) can be run on GS hubs and spaced appropriately to work with those years of Bandit brakes. The Bandit rotors are 5 bolt, did not look up center diameter specs.

Bandit steering stems are too long and need a gs1100e stem pressed in place, or need machined down in height. 89 gsxr1000 k triples work with them, or one GSR member is running ghe lower triple clamp from an RF900R and the upper triple clamp from the Bandit 1200 with a very minor bit of fab work to get them working great. Other 80's gsxr triples may also work.


Aside from the early bandit 1200 forks, 94-97 vfr750 (sliding 2 piston calipers, more clearance for GS wire spokes if used), all vtr1000f superhawk/firestorms, and 93-94 gsxr1000 are the good right side up modern forks to swap onto vintage bikes if you care about ground clearance, geometry, and proper handling/suspension setup, they are the tallest of the options for modern fork conversions. Reading vfr750 forum threads about fork upgrades is a good way to dig up information on which modern forks are taller to fit our vintage bikes, since the vfr's run the same height range of forks...

Edit - also, the last year of CBR600F2 and all years of CBR600F3 have another excellent 41mm cartridge fork option with sliding 2 piston calipers (more clearance for GS wire spokes if used). CBR600F4 & CBR600F4i (fuel injected and different wheels/rotors) are an EXCELLENT 43mm choice, and they are one of only 4 forks that I have considered viable that have adjustable compression dampening. Usually, rebound is far more critical to have adjustability on, but the compression is another bonus.

Also, as I have learned, the Honda forks seem to generally run the calipers more outboard, so if you are running wire spokes or wider spoke mag wheels, you don;t need as wide of triples to clear opposed piston calipers far enough from the spokes. 6 piston calipers have smaller piston bores, so they have more clearance due to the spokes angling inward toward the rim, but 6 pistons require more frequent maintenance (cleaning the exposed portion of the pistons).

The Kawasaki ZRX forks that I looked at (1100 and 1200) both had adjustable compression and 310mm rotors, nice forks indeed. the heaviest of the 4 I compared, but a lot of that was in the heavy steel triples. the Yamaha R6 conventional RSU forks were the lightest, adjustable compression and 320mm rotors (have to mod some Ducati rotors to fit), but I saw a pair of those crashed in the salvage yard, and the stanchions were very thin...


The F4, VTR1000, Bandit, and RF900R forks all run opposed piston calipers. The Suzuki's use more period correct looking brake mounting points, but you either need some modern mags ( some of those honda's look fairly period appropriate in design) or custom wider billet triples (contact Weiss Racing - $425) to clear wire spokes and other wider spoked wheels.

 

[Chuck78]

By the way, I think the style of Honda 17" mags running on both those GS1000's are simply some of THE BEST looking modern wheels I have seen in terms of looking APPROPRIATE on a vintage bike, big bonus.

 

[Buffalo Bill]

I think that's probably the first time we have ever agreed on anything.

Nah, many more times.

 

[Buffalo Bill]

Just one engineering thing I suggest, cut and weld the frame so the forks have a steep rake like a GSXR (24?-26? maybe?). That easy rider GS rake is so lame.

 

[Chuck78]

Just one engineering thing I suggest, cut and weld the frame so the forks have a steep rake like a GSXR (24?-26? maybe?). That easy rider GS rake is so lame.

Rickman CR900 (Betor Fork):.............Suzuki GS750:
Wheelbase .......59.8"............................58.7"
Caster ...............62?...............................63?
Trail .................. 2.67" (68mm).............4.21" (107mm)
Steering Angle ..___?..............................40?

Another spec from a CB750 website, likely this uses the other of the two Rickman forks available:

Chassis Dimensions
Wheelbase: 57.1-59.1" / 1450-1500mm (depending on swing arm)
Rake: 62?
Trail: 3.54" / 90mm


So I am assuming that stating 62? caster would be the reference from horizontal as bicycle head tube angle is referenced, making the Rickman 28? rake and the GS750 27?. Not sure what the 40? steering angle spec listed for the 750 is.

It looks as if the lazier steering on a stock GS may be due to the large amount of trail...??? It is always said that an 18" front wheel swap makes them handle much better, less trail, slight bit steeper rake, right? The Rickman's are criticized as not having steep enough rake, but with less trail

Looking at the swingarm angle on a cr900 with the original shocks, it's not near steep enough to give enough antisquat on comfortable sporty springs, but due to the short swingarm, you can't make the swingarm angle too steep, as that will cause acceleration to try and lift the rear end more under acceleration out of turns. I'd like to put approximately 1" longer shocks on it to help with antisquat and also as a side effect increasing rake slightly, and also drop the triples on the forks slightly to gain about a degree more steeper rake. That should put it slightly closer to modern spec.
Once the bike is set up better and tested, I can have custom Billet triples made in the offset that I need for the best trail.

Sounds like I'll want to take that 28? rake and steepen it back to 27? or 26? if possible by raising the rear end primarily, dropping the front slightly. If I dropped the front too much, I would kill the swingarm angle. With this in mind, it seems that if I consider adding an additional box tube for a more forward swingarm pivot to run a longer zr550 or gs1100e swingarm, I might consider raising the swingarm pivot a slight bit higher, or in tuner fashion with a cue from Rickman chain adjusters and some fancy modern Supersport bikes with eccentric adjustable swingarm pivot geometries, I could make a slotted vertical track pivot mount with aluminum block spacers that lock in the up&down position of the swingarm pivot bolt....

Chopping the frame up front is beyond the limit of my tooling and extent of work I want to do, especially considering the amount of additional bracing that the previous builder has brazed onto the front end after the frame was repaired.... it'd be a MAJOR undertaking at this point. If I received an all stock frame with the head tube joint cracked and unrepaired, it'd be more likely.

I supposed I could unbraze the head tube only (major job) and jig the bike up extensively in front of my drill press, and shave off material from everything angling in more by 2mm or so by the bottom, and bronze weld it back in again after extensive measuring and jigging... LOTSA WORK, holy smokes...

Elevated/forward relocated gs1100e swingarm pivot, longer shocks, dropped front end height, less offset in triples to correct the trail sounds like the easier plan...

 

[limeex2]

Now you really have my attention! Oh wait its the coffee. Thanks for the info on the forks. What is the braced swing arm off of? Those CBR wheels do look great. I could be talked into trading my spokes for better brakes and 17" wheels
Imo the 6-pot calipers look nice but 4-pots grab better,less caliper flex. I just went through this on my ZRX. With modern forks and a wheel or disc set-up that has more spoke to caliper distance,that would open up choices for calipers,like new radials. There are brackets available on e-bay for this. This is the direction I will go on my next project,an ES. I want modern suspension,brakes,tires/wheels which I am starting to accumulate. Trippivot,its on to the next dream...

 

[Chuck78]

Not sure where Jim's braced swinger is from, metmachex or calfab etc? OhioCafeRacers Greg later welded the bracing from a CBR900RR swingarm onto the bottom of that GS1100E swingarm, however:


And I stumbled on another photo of Jim's bike in Greg G's photo album, as well as another GS1000 that is running GS forks with the salty_monk twinpot mod and the same swingarm:

 

[limeex2]

Pulled the forks of my 97 Triumph Sprint this morning for service. Hum...these look long enough for a GS. Yes,length no problem,other rough measurements close enough to spark my curiosity. I have a spare Sprint with a complete front end.Race Tech,braided lines and straight. Best of all its my garage not ebay. What measurements or specs would you need to see if this worth pursuing? That last pic of the red GS looks like a ZRX swingarm? Sorry if I am hijacking your thread.