Big Bore CBX Motors

[Ken Elmore]

Hello Everybody,

Let's try a post for the new site and see what happens (these smilies are pretty cool).

I have a 1980 custom project going with the theme "Black & Chrome." I think that this bike needs a big bore engine of some kind with 6 into 6 pipes to achieve diminished social respectablity. I have read a couple articles on various CBX big bore kits, including the one in our "Tech Tips." Does anyone out there have any first hand knowledge or good opinions on this type of adventure?

I am thinking of this money pit: JE or Arias 1163 pistons (opinions?), knife-edged & balanced crank, Falicon or Carrillo rods, aftermarket valves (suggestions?), Cams? 79/80/82 (I have all 3) or something aftermarket?, German Kawi alternator, and so on.... :twisted:

The mission is maximum torque and mid-range power for this motor--not peak horsepower numbers!!! Does anyone have any suggestions? There is a huge amount knowledge in the ICOA and I would hate to reinvent the wheel--I recently discovered that they are in fact round And, No, Mark, this will not be a turbo--I would find some way to burn my leg on that big pipe any way This bike will also have a modified swingarm to allow a 18X4.25 (maybe a 18X5.50) tire on a chromed 5 spoke forge Alum. wheel with upgraded brakes.

Let's crank up the discussion! Who/where in the US would be a good shop for the machining/various engine work? Don't be bashful--plug your friends as long as they do good work. I think I would like to have this assembled by a pro (1 done correctly. 2 finished before I am too old to ride it). Let's talk the pros & cons (& opinions with details) of various parts and combinations of parts.

You guys can also mention what a bad apple I am for messing with a sacred motor and CBX in general. My goal is to take a mediocre/rusting 1980 and turn it into another beautiful X with factory and tasteful custom parts--looking great at an upcoming rally near you. I am not attacking a perfect, low-mileage bike with a cutting torch--so relax. Let's get a good Big Bore discussion going for this section of our great new board.

Thanks to all of you who have worked very hard on the website improvements.

See some of you guys soon at the DV gathering.

Keep rolling forward, Ken

[SS]

Hi Ken:

your plan sounds great, I am soon (later this month) to have some simular things done on my 82.
NO ! Not the big bore, but all the stage III stuff. Kerker 6-2, K&N's, and Dynojet the carbs.
The swing arm will be extended and the rear wheel will be a VTR 1000 5.5" with (170/60ZR17), with F-2 17' front wheel (110/80ZR17).
New chain, and sprockets (gearing change).
All that said, Jim is a gentleman, and all around nice guy, that I have asked to do my build up. His name is Jim Zemanek, owner of Cincycycles, I have seen some of his work, and he is a first class gentleman, that does A-1 professional work, at reasonable $'s. I live outside of Memphis, TN, and it's a 10 hour haul to his shop in Cincinatti, OH. But I have grandkids in Cincy, and that's all the excuse I needed.

This may be a bit to far to travel for you, but I regard this fellow very highly.

BTW: I just returned from a nice 85 mile ride in upper Mississippi near Tunica, MS the weathers is 70 deg. & cloudy.

ss

If you would like to discuss your potential mod's with Jim (513-753-9500), I'm sure he would give you some insite (he has done several big bore's and customized bikes) I belive he has build some with as much as 150 HP.

[Land_Shark]

Ken, that '80 will certainly be a beauty when it's done. In my opinion a bike which is so far gone to require a complete ground-up restoration will look just as good 'customized' as those original 'mint' ones and in most cases many improvements can be made. I'm currently in the process of restoring a '79 (two years and lots of cash gone by) and I'm shooting for a similar look - black but with lots of polished aluminum and perhaps a bit of chrome here and there. I've always thought a well-polished aluminum part beats out chrome every time . I'm also in possession of a complete '99 'Busa inverted-fork front end and also the rear wheel w/brake assembly. My bike had a Panther racing swing-arm installed previously which has more than enough room for that massive 6" rear meat but I obviously have concerns regarding my chain clearance once the bike is back together. As far as the big-bore kit - after lots of questions and research I decided on the Wiseco forged kits mostly because they weigh the same as stock and I'm using stock (although brand-new) connecting rods. Also they are truly things of beauty and I'd almost consider buying another set to put on the mantle-piece
Of course I've got the requisite Dynojet Stage III's, Dyno ignition, and pretty much anything else out of Tim's catalog .
I have a question for anyone who happens to read this post - regarding the fitting of off-size wheels and sprockets to the 'X. Since the 'Busa wheels are so much smaller (although wider) I wonder if anyone has any experience in determining proper gearing with such a setup, or if this is more a trial-and-error process. I've heard of and seen many conversions utilizing GSX-R forks and wheels and I'm hoping to get some feedback on the gearing changes that were required. Many thanks in advance!

[EMS]

Ken:
I think SS pointed you into a good direction, to someone who has done some big bore conversions. We did a massive reconstruction of a CBX a couple of years ago. We did a single sided swingarm, inverted forks and a custom frame but left the engine alone, mainly because the bike ended up in Germany and the authorities are really a..l over there concerning engine mods. Insurance premiums and vehicle taxes hinge on horsepower and displacement. The thing still runs over there and I think there may be some pictures of it on the German CBX web-site. Again, like with so many things in life, don't lose sight of your goal and what you want to accomplish with your modification. You seem to have a good idea what you want. As long as you don't up the horses significantly at higher rpms, I don't think you will need to do a lot with the crank and the rods. I always thought the Carillos, for example, were quite a waste of money in a non-competition engine. The straight six is pretty well balanced the way it is and the crank and the rods can take a little more. As horsepower is a function of torque and engine rpm, an increase in torque will also increase your hp at low and midrange rpm. Now remember, an increase in displacement without rework of the combustion chamber will raise your compression ratio significantly. Ignition modification is a must, maybe even special fuel. If you want to maintain street rideability, you may find some limitations in modifying the motor.
Sounds like a fun project. And it is definitely more interesting than letting the bike waste away or part it out.
Everything seems to be in Ohio. There are some local guys in the Akron/Cleveland area who used to race CBX-engine machines, called
Phoenix-Cycle. I don't have their number right now, because they moved their shop a while ago, but I will get it for you and you can call them too and pick their brains.

[sr71cbx]

Hi Ken,
I've got some experience in that area,I used to run a 1270cc normally-aspirated engine in my '79 X,before the turbo bug bit me.It used Carrillo rods and stock crank with an Arias 71mm 11:1 comp.piston & sleeve kit,copper head & base gaskets,ARP 10mm studs(of which I have a couple sets left),Precision Machine "Black Diamond" stainless stellited valves w/HD valve springs & titanium retainers in a ported head,and 79 cams to round out the whole package.A Barnett clutch with gorilla springs from a GS1150 dragbike put the power to the ground and the oil pump relief was shimmed to put out 80 psi for reliable hi-RPM usage.The fire got lit by the usual Dyna S ignition w/422 advancer and green coils with Taylor wires to a set of NGK D9EV wiretip plugs.Exhaust chores were handled by a Winning Performance 6:1 header with oversize collector to get the gases out and carb mods included Stage 3 K&N individual air cleaners and my own jetting.Oil cooling chores are handled with a 13 row Earl's automotive oil cooler and -10 braided steel lines.This engine also used way less oil than a stock CBX engine,and returned 32 mpg if you kept out of the throttle!It also ran quite nicely on pump gas even with the somewhat higher compression due to stock dome height on the pistons.
This engine will be reborn in the Team Tyrannosaurus-X roadrace bike later this year,it has a powerband from 3,000 RPM all the way to 12,700 RPM and,when it was in my bike,would blister the 1/4 mi.in 10.90's to 11 flat with stock gearing.Power wheelies are real easy to do with a motor this big!
Why did I take it out?It had noisy pistons,Arias slugs are stout but you can hear them 10 blocks away on a cold startup,even with .004 clearance.I would recommend JE pistons if I were to do it over again.
So there you have it,Ken.All of the others who posted had some very good things to say also,and,like you say,it costs big $$$ to do!Good luck on your project and we're all here to help!!
Take care & ride safe,
--------Mark Miller#0938

[banjobill]

Hi all,
This one for the big bore guys, Infact it could not be the fault at all but what do you think,My engine has a 1300 big bore kit on it,and when cold it spins over no problem, starts up and off we go, but when the engine is hot after a run say,you switch off and when restarting the motor turns over real slow just as though the battery is flat,and will not start,until it has cooled down.
I've tried different stages of engine temperatures and the hotter it is the tighter it seems to get.
I think its because the bores are so thin and are wearing oval in shape making them tight in places.

What do ya think?
cheers.

[Supersix]

I've tried different stages of engine temperatures and the hotter it is the tighter it seems to get.
I think its because the bores are so thin and are wearing oval in shape making them tight in places.

What do ya think?
cheers.

Hi "banjobill" and all,
think your probleme is not the big Pistons...
It,s a well knowing problems with the startermotors from the CBX and the CB 1100 F/R.
Resold all Points in your Starter and give him new carbonbrushes...
They will workbetter as new..

Regards

[EMS]

Bill: I will dare to say what I think but some may disagree with me:
In my humble opinion, you do not have a problem with binding in your engine.
I would say that if your motor's cylinders would deform enough that you would recognize this in your starter performance, the engine would seize. You should also recognize this while you're riding and especially at engine idle. The increased friction should stall the motor.
I think you have an electrical problem. Remember: Electric wiring increases its resistance significantly when it gets hot. I am willing to point at your starter. You may want to have this thing checked. Then again.. Everything is possible

[Guest]

Thanks lads,
The strange thing is that when cold it spins over at normal speed. You may be right, In the dull and distant past I heard that a modified cx500 starter was the way to go because of its increased torque, I shall try and sort the starter before I look at the expensive stuff.
Thanks again.

[xneric]

I agree with the rest that it's an electrical problem. My bet is on the battery. The starter requires more current when it's hot which a bad battery can't supply. I had a car that did the same thing. Have a load test performed on the battery.

Eric

[banjobill]

Hi all,
I've got two new batteries fitted to the bike and when hot I've even tried jump starting it with my cars battery and it just manages then. When the starter button is released you can hear the starter motor spin at full pelt, just as though the engine is hard to turn?

confused?

[Ken Elmore]

Hi Guys,

Since this board ate 2 of my posts today when I tried to edit them :twisted: this will be short!

Arias lists 2 pistons: a 68mm 1163cc piston @10:1 and a 69mm 1198cc unit with unlisted compression. My question is how high can the CBX compression go and still run on premium pump gas. I do not want to build a motor that needs special fuel that cannot be found in BFE on a ride Also do the Big Bore motors seriously erode gas mileage or is this more related to a heavy right hand?

I want to hear from the CBX motorheads in this crowd.

Thanks, Roll it on, Ken

[Guest]

Hi Guys,

Since this board ate 2 of my posts today when I tried to edit them :twisted: this will be short!

Arias lists 2 pistons: a 68mm 1163cc piston @10:1 and a 69mm 1198cc unit with unlisted compression. My question is how high can the CBX compression go and still run on premium pump gas. I do not want to build a motor that needs special fuel that cannot be found in BFE on a ride Also do the Big Bore motors seriously erode gas mileage or is this more related to a heavy right hand?

I want to hear from the CBX motorheads in this crowd.

Thanks, Roll it on, Ken

10.5 to 1 is about the limit for pump gas,your main concern is heat dissipation in a high compression air cooled motor.Use a bigger oil cooler and jet the bike on the rich side.

cbxsix

[sr71cbx]

Hi Ken & everyone,
cbxsix,the previous posting,hit it pretty much on the head,install a 13 row cooler from Earl's Supply and this pulls down your oil temp noticeably in a short time on the hiway.I use one on my turbo X and it pulls the oil temp down from about 250 deg.in traffic to 210 deg.on the road in about 15-20 minutes or so.This is on a warm day too.
Compression ratios are a toss-up,I feel,I used 11:1 compression(as noted in my earlier post)with the 1270cc engine for 2 years in street & strip use and the only time I experienced any noticeable detonation was after sitting in traffic trying to get into Sturgis,S.D.during bike week up there on a 95 degree day.It has a lot to do with dome design and engine mods too.Ken,if you're looking for a good bottom/midrange engine,use a touch lower compression ratio as cbxsix recommended.It should run happily on pump premium either way without any trouble. :)
Hope this helps,take care & ride safe,
-----------Mark Miller#0938

[Dave Krager #5383]

I am sort of partial to the earls 10 row it offers tons of cooling and seems to have a better overall fit on the bike allowing you to re-use your stock length oil lines and not have to get fancy figuring out a solution for the tach cable getting in the way. Even with this setup I had to grind a notch in the oil cooler frame to keep the tach cable from binding.