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

[rudeman]

I voted for the 894cc motor. But if the GS1000 motor was an option I would've voted for it instead. That 894 may make some ponies but I would venture to say that is isn't nearly as driveable as a stock 1000. Install a set of smoothbores and tuned header of your choice and you'll have a runner. I would actually prefer a 1980 GS1000 motor with CV carbs. Get those CVs dialed in and it will surely run.

[Chuck78]

Have you looked at the right hand side footpeg and brake lever to see if they are designed to fold out of the way and clear the kick lever you hold so dear? In the photo showing the Rickman Kawasaki the kick lever is removed, and it appears that the lever, if present, would whack the peg/brake lever if anyone attempted to use it.

Generally all rearsets on kicker motor bikes require some sort of modification of one or both to get good clearance. I will probably be making similar rearsets out of late model sport bike parts as the shifter setup I have is a mismatch of the many different styles of Rickman CR rearsets... I only can run the reverse pattern lever that is like a stock gs splined lever flipped, yet I have a 2nd foot pedal that is made to pivot off the CR rearset and use him joint linkages like the GS550 uses...
May make a lighter tubular cromoly kicker arm as well. A few of them actually, for all 3 bikes.

I'll see if Rice Paddy will sell me a GS1000 engine they have that sat with the spark plugs out for months, for motor mount t configuration and to toy with the gs750 kicker engine with 750 head and 1000 crank/cylinders... then I could set the frame up with universally adaptable GS mounts for 8v 550 hrbrids, 750, 1000, & 1100/1150 mounts...

[Chuck78]

That 894 may make some ponies but I would venture to say that is isn't nearly as driveable as a stock 1000

Well honestly I think a GS550 with k&n filter(s), aftermarket 4-1 exhaust, & rejetted is a fun fast & of course streetable engine! Cams are conservative lift but big duration. 750 stock is lacking that low end grunt but great above 4300-4500 rpm & REALLY moves like a vintage rocket 5500-10000 with k&n+4-1. I'm not going too high on camshaft duration, and may advance the lobe centers of the Yoshimura/Megacycle cams a slight bit & run a more tame exhaust cam to give it better low end and midrange (less overlap, less power consumed by pushing harder/further on 4 more valve springs).

I am trying to consider that I am building a 475cc extremely lightweight 330lb GS425 racer, so that will be my feather weight twisties corner burning flick able machine, so another big engine would fit in well, but 800 vs 900cc's are both going to be fast, especially considering the weight of the bike is A LOT less than a stock GS, as well as the rider (I'm 155lbs). 7lbs=1hp I've heard, so a 789cc gs550/650/750 franken-Rickman at 445 lbs +165lb rider w/gear may very well give a stock pods&pipe gs1000 with 195lb rider+gear a chance of a view of it's taillight & still be fun on the street.

Advancing the cams slightly will give it a better street feel, and still won't take much from the "alerting every police officer within 2 miles" 6000-10000rpm power. If I race it, I can set the cams to 109-111 lobe centers, keep them 106-108 on the street.

I think I'm springing for a set of Yoshimura "Road&Track" spec cams, which is like the .380 lift megacycle intake and .354" megacycle exhaust grind basically. For the 894cc or my 920cc daily rider if I go 789cc gs550.

I'll look into Wiseco 844's fitting the 650 block with 750 sleeves as well, that would be 835cc's & 10.1:1. Getting up that high makes me wonder about the rotating assembly still being balanced well enough. That's why I thought I may draw the line at 789cc. Although a GS650E crank may be balanced better for this if it were an issue.

Lots of fun options, don't worry Ed, I will have lots of free time on my hands this summer to wrench on all this and satisfy my extreme tinkering curiosities... wife's joining this tour as an occupation:
http://www.americanwallofdeath.com so I'll have a lot of free evenings to wrench all summer...

[Rensdw]

Interestring stuff Chuck, I'm looking forward to whatever you are going to build, especially the GS425 build since I am doing something similair.

I like lightweight bikes, the numbers are not there when it come to pure HP but it is so much fun! and if you keep the top speed low the acceleration (within legal limits) is better then most stock liter bikes (ok, maybe not the modern ones)
My dreambike is a 130-140 kilo 75+RWHP bike for uphill riding in the French/Austrian/Italian alps, my Ducati 748S is a blast there, but so ****** expensive when you drop it and a bit too heavy for slow speed cornering (200 kilo's)

My build will probably be around 150 kilo's (330LBS) and I'll be lucky to make 70 horsepower, but it's getting close, just a matter of putting some more money into it haha.

I have the same "kickstarter disease" BTW, don't know why but it is a must have, pushing a button just seems too easy lol

[rudeman]

...7lbs=1hp I've heard, so a 789cc gs550/650/750 franken-Rickman at 445 lbs +165lb rider w/gear may very well give a stock pods&pipe gs1000 with 195lb rider+gear a chance of a view of it's taillight & still be fun on the street.

...

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.

[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.