Topic: Chro-Moly frame?

[Bodi]

I put a lot of miles on a early Bonneville 650, I think it was a 1970 - first year with the flat sidecovers? It was a sweet handling machine and could run away from any Japanese bike of the day on a twisty road - until something rattled off or broke. And you had to be careful starting out as the rear tire would get oily rolling through the puddle of oil leakage and/or gas from the carb overflow after "tickling". Japanese bikes dominated because they were cheaper, virtually maintenance free, and easy starting - not because they handled better. Plus you got better acceleration from a stoplight with a cheap 250 2-stroke than almost any Brit machine, and the 250 could wheelie like mad.

[hcritz]

Hey Guys...
I too spent a LOT of time on a Bonneville...for it's day, it was a really nice handling bike. I think I wore the sidewalls of the tires out as quickly as the bottoms. Lots of sparks from dragging the pipes and stand at crazy angles and It never once dumped me. Of course I'm an old geezer now and wouldn't even think of riding that hard now...but The CB would be very unhappy being thrown around like that!
BUT...it was always broken...the Lucas Zener Diode would always fail and seconds later all the lights would get VERY bright and then VERY dark...that invariably  happend at night when you were a LONG way from home. Finally got a Motorola diode that was used in England...never went out again!<G> Mine didn't have a battery...just two big capacitors under the seat so there was nothing to soak up the excess voltage.
I rode a 71 just the other day...and I was amazed at how rough and archaic it was...No where as smooth and sophisticated as the CB...but it still had that nimble feeling that inspired some really fast runs through the twisties many years ago.
For the riding I do today...I'll take the CB anytime...but still have a big soft spot for my Bonneville!

[eldar]

I am not saying the 750 is a better handling bike. I am saying that it more to do with the rider than the bike. But then you all are talking about the earlier 750s. I don't ever get the wobbles the 76 and pre bikes get. The 77-78 bikes had the front end changed some which apparently eliminates this wobble. I also do not have tapered bearings in it.  The 77-78 also have more rear suspension travel, at least according to the specs hosted on our site here. You might call these subtle changes but then no one ever makes a huge change.  I also do not notice any flew really either, so maybe the later frames are different and not as susceptible to as much flex.  I feel very confident on my bike. I went from a 100 enduro to years of barely any riding, to this bike and it felt like home.

Another thing a person needs to consider is the brit industry and seen seemed to be heavily cafe at the time, the american front, which this bike was designed for, was not.

[mlinder]

Reduce the weight of the cb750 by a hundred pounds and you'll likely get similar handling to the brit bikes of the same era.
Of course, the weight distribution is a bit better on the brit bikes as well, with the center of gravity being a bit lower.
Remember, ina  1g turn (though we aren't getting that on one of these) the bike (and rider) weigh twice as much, so the frame has a lot more to deal with.
A few well placed gussets and such should cure the frame flex quite a bit, but then you start running into swing arm flex, spoke/wheel flex, tire slippage, etc. When you cure one flex, it puts that much more strain on the other things that flex.
Lose weight, increase cornering performance.

[Geeto67]

I am not saying the 750 is a better handling bike. I am saying that it more to do with the rider than the bike. But then you all are talking about the earlier 750s. I don't ever get the wobbles the 76 and pre bikes get. The 77-78 bikes had the front end changed some which apparently eliminates this wobble. I also do not have tapered bearings in it.  The 77-78 also have more rear suspension travel, at least according to the specs hosted on our site here. You might call these subtle changes but then no one ever makes a huge change.  I also do not notice any flew really either, so maybe the later frames are different and not as susceptible to as much flex.  I feel very confident on my bike. I went from a 100 enduro to years of barely any riding, to this bike and it felt like home.

Another thing a person needs to consider is the brit industry and seen seemed to be heavily cafe at the time, the american front, which this bike was designed for, was not.

Your '78 with a wet weight of 510 lbs+ is not even in the same league as a well tuned brit bike in terms of performance and handeling. Maybe you won't get the 100+ mph death wobble but you are not going to get the lean angles or flickability a brit bike will (cb750s are largely too wide). Your K8 may be "stable" but with all that extra tonnage it is probably one of the worst handeling too, not that you'll ever ride agressive enough on the street to notice (not that 90% will ever ride that agressive on the street - but there is always that 10% who have scraped the engine case side in a turn and lived to tell )

they cafe'd the crap out of cb750s just as much as any brit bike here in the states and it still wouldn't make it handle.

the old joke with kawasaki is they did not get a proper test track until the 1970s. Before that their test track had been the runway at the kawasaki aircraft mfg facility. Supposedly all the 60's and early 70's kwackers were tested on this runway. whether this is true or not is speculation but the runway did exist and they did not have an oval test track until the advent of the Z1 era.

[eldar]

I dont know geeto, I doubt any of the earlier 750s handle any better than mine does. I never said it would compete with a brit, the bikes were designed for different styles of riding.  I am saying that maybe the improvments done to suspension and possibly the frame, allow it to perform better than the earlier 750s. I dont have an earlier 750 and you dont have a later. So neither of us can say. most here that do have both, have an earlier K and a later F and you cant quite compare the 2. I will say that comstar wheels are better than spokes though on flexing.  As for scraping the case, I got case guards!  I would like to know what EXACTLY makes the 78 weight more. The tank is a bit larger but that can only account for maybe a pound. Engines are mostly identical so that should not do much, maybe a few ounces so it must be framework.

[mlinder]

Eldar, I'm not sure why the later k's weigh so much.
The 69 (that i have) apparently weighed in at 470ish lbs wet. After that, the weight increased by quite a bit, and I don't know why.
I've had no speed wobble so far (knock on wood), but, the steeper the rake, the more likely you'll get wobble. Is the geometry of the 78 different?

[mlinder]

By the way, a slight increase in rear shock height will get you more clearance on these 750's than your tires can realistically handle, assuming they are not racing slicks.

[eldar]

16.6mm was the rear travel increase. Which is a significant amount really. 4.2 inches is how much longer the K8 is than the k5/6. Caster on the 78 is 62 degrees and the k5/6 is 63. That seems small but when you look at racing, they make changes in increments or degrees and it can have a large impact. Trail on the 78 is 115mm and the k5 is 95. So there are a number of changes. But again, unless a preson is able to ride both side by side, it is hard to compare them. Most of the articles written were about the  early 750s, 76 and earlier. The 77/78 did not get much press coverage. The mags decided they did not liek the change in the looks and then so did other people and thus the 77/78 did not get much coverage. Looks aside, I feel the 77/78 are superiour to any of the other 750s aside from the 69 maybe. I know some one is going to say some crack about their accel or top speed but I have no issue with either and the 77/78 motors are very similar to the 75 F which could beat the 71-76K bikes. throw on a 530 chain instead of the 630 and that right there probably makes a big difference. So many cut down the 77/78 cause of weight and looks yet their performance is almost identical to an F2. The overall height of the k8 is less than the k5/6. So I think the swingarm is different and that is what accounts for the greater suspension travel. There are quite a few changes really, all small in most cases but you would have to go to the model specs to check it out. Ultimately though, I doubt I will ever find the limit of my bike. I dont want to. I dont want to get hurt and I dont want to hurt my bike. I have plenty of fun just riding. If I wanted to corner carve, I would get a rocket

I do however like the vented sidecovers from the 69!

[mlinder]

4.2" is a huge increase in wheelbase. This will drastically improve high speed stability, but turn in and handling will suffer. BMW did the same to their r75's halfway through '72.
I'm confident I can get my 69 down to 430 lbs wet pretty easily, and it should make some pretty significant performance changes.

[eldar]

I bet it would, just dont whack something you need! I could probably drop quite a bit of weight off my bike too. I have a big ol sissy bar I could lose but then I would need to find a normal grab bar but then if I lost the center stand, I would not need the grab bar! Dropping to a 530 chain would also lose quitea bit of weight. I bet I would lose up to 20 pounds just from those 3 things. Maybe someday I will get to pull my bike apart all the way and then photo my frame to compare to an earlier frame, I would almost bet there is some additional bracing going on.  Even better, I would love to get the exact length of all the members and make a new frame out of stronger steel, I could use less and drop more weight that way too. That would be a pretty long running upgrade though, to make.   

I will tell you though, when I dropped my fairing, the ride changed dramatically! That sucker had to be 30 pounds!

[c_kyle]

I'm confident I can get my 69 down to 430 lbs wet pretty easily, and it should make some pretty significant performance changes.

What do you have planned to drop weight (on the bike ?

[rhinoracer]

I believe you can knock several pounds off the bike for less $$ just by changing to an aluminum rear wheel and spool and disc brake, plus it's unsprung weight.

If you want trick, add your chromoly frame and Ti headers and muffler.

[mlinder]

I'm confident I can get my 69 down to 430 lbs wet pretty easily, and it should make some pretty significant performance changes.

What do you have planned to drop weight (on the bike ?

Fenders (rear removed, front bobbed), seat (make a fiberglass one), remove speedo, remove center stand, remove all plastic, smaller, lighter battery, led brake light, and since I don't use the starter button, starter.
To go further, you could get a very light aftermarket set of headers and exhaust, and as rhinoracer said, you could certainly go lighter wheels.
You could take it even further. Lightweight engine parts, fiberglass tank, removal off all unneeded tabs and bits on the frame.
All of these together would make an EXTREMELY light bike.

[eldar]

So you are looking at quite radical changes then.  Lighter bat is certainly a good one though since you are going kick start. Main reason for the bat we have is the starter.

I guess I dont know your area but around here, I would keep a rear fender, however a fiberglass one should work well and save some weight. Are you sure you want to dump the speedo though. Maybe jsut get a small one or is this a racer you are doing?
  You can also get some new coils, they will be smaller than the old ones. Would be one more bit.

[Sam Green Racing]

With refference to what Scott (Rookster) said about the CRs being built in the UK in co-operation with Honda, well it was allmost correct.
I have just spent the best part of an hour, talking to the guy Steve Murray who was responsible for the development of those first CR750s that went on to win the Bol d or endurance race in 1969.
He was also the mechanic to the three UK riders at Daytona in 1970 and was the back up rider should any off them get injured.
Steve was unable to confirm that the Daytona bikes did in fact have chrome molly tube frames. The info that I had saying that they did, came from a book some years ago.
The four Daytona bikes were built in Japan in the RSC department and were crated to Honda USA just before the race.
The normal run of the mill CR750 frame was partly assembled on the same production line as the road going CB750, and then finished off in the RSC department.
That leaves us no closer to the chromoly Daytona frames, did they...didn't they,..books can be wrong .

Sam.

[mlinder]

It's just for fun. It may see a track day or two, but won't be purpose built for it.

I want to make it as well running and light as I can, see just how quick and fun I can get it with stock engine (though I am going to dyna-s).
I won't be going to the extremes of super high dollar light exhaust and such, as it isn't a racer.
I'm a bit loath to chop anything of a 69 frame, as well. Also, the bit of frame that holds the passenger pegs also holds the stock exhaust, so don;t really want to have to rig something for it.
Anyway, after that, I'll do engine stuff.
Cheaper to take stuff off/build my own lighter stuff right now than to hop up the engine. Also can still ride it when I'm just taking #$%* off.
When both are done though, should be a quick scoot. Hell, it's quick now.

[eldar]

Thats the problem. What do you do so you dont destroy anything. I would say if you are going to mods things and it is un-reversable, maybe pick up another part to mod so you can keep your original. If that is a big deal to you.

[mlinder]

Only thing I probably won't change is the frame. Everything else is fair game

[chung]

I have a small cup where I put all the pieces that I cut from one CB750K frame. The cup alone weighs maybe 5-6 pounds. And that doesn't include the weight of what was bolted to the brackets; Center Stand, muffler, battery box etc. The head pipes on a CB350K weigh almost as much as a cast iron manifold on a V8 Chevy.

The second front disc brake had to weigh 10 pounds. Sounds like nothing? But it all adds up.

I weighed an RD350 of mine @ 245lbs with a head and tail light and a license plate. No small feat I was grinding off all of the bolt that stuck out past the nut.

10 pounds is easy to loose at first but you can only throw away so much stuff like gauges, elect start ect. pretty soon you are looking at the extra 1/4 inch of bolt sticking out there doing nothing. Then it's grams rather than pounds that you're counting.

There is a point to all this.... there is a cheap was to adjust your power to weight ratio.

[mlinder]

Agreed. I think seat, fenders, starter, centerstand, lighter battery, loss of all unneeded bodywork, passenger pegs, tail light, should free up an enormous amount of weight. After that, it will be much rougher going.
430lbs wet is ok with me though.

[eurban]

Eldar, I'm not sure why the later k's weigh so much.
The 69 (that i have) apparently weighed in at 470ish lbs wet. After that, the weight increased by quite a bit, and I don't know why.
I've had no speed wobble so far (knock on wood), but, the steeper the rake, the more likely you'll get wobble. Is the geometry of the 78 different?

470LBs wet??  Period mag reviews show anywhere from 499Lbs with a half tank of gas to 526lbs from Cycles 1977 review of the 77K and F where they comment that the 77F weighed in at 553lbs, 27lbs more the the first 750 and 10lbs more than the 77K.  Stock 750s never came anywhere close to 470lbs wet!

[mlinder]

Eldar, I'm not sure why the later k's weigh so much.
The 69 (that i have) apparently weighed in at 470ish lbs wet. After that, the weight increased by quite a bit, and I don't know why.
I've had no speed wobble so far (knock on wood), but, the steeper the rake, the more likely you'll get wobble. Is the geometry of the 78 different?

470LBs wet??  Period mag reviews show anywhere from 499Lbs with a half tank of gas to 526lbs from Cycles 1977 review of the 77K and F where they comment that the 77F weighed in at 553lbs, 27lbs more the the first 750 and 10lbs more than the 77K.  Stock 750s never came anywhere close to 470lbs wet!

Most things Ive seen for the 69 K0 are 460 to 480 lbs wet.
Everything after that blimped up after that... I'll check some literature and see what I find.

[eurban]

More info, how about John Wyatt's book, the  "Original Honda 750"  he quotes some specs from Motorcycle Sport magazine when the 69 was first ridden . . ."The Honda is a heavy bike - 517lb (wet)"  My guess is that the motorcycle press actually weighed the bikes rather than believing Honda's specs although I can't find an official Honda spec.  Figure at the end of the SOHC 750 run the F model had gained (from the 69) about 30lbs and that the K had gained about 20.  Not to burn your Sandcast nostalgia buzz but I think your bike is heavier than you think.  And if you believe the period mag reviews, it is actually slower (acceleration wise) than the porky "end of the run bikes" as well.  . . . .

[Geeto67]

More info, how about John Wyatt's book, the  "Original Honda 750"  he quotes some specs from Motorcycle Sport magazine when the 69 was first ridden . . ."The Honda is a heavy bike - 517lb (wet)"  My guess is that the motorcycle press actually weighed the bikes rather than believing Honda's specs although I can't find an official Honda spec.  Figure at the end of the SOHC 750 run the F model had gained (from the 69) about 30lbs and that the K had gained about 20.  Not to burn your Sandcast nostalgia buzz but I think your bike is heavier than you think.  And if you believe the period mag reviews, it is actually slower (acceleration wise) than the porky "end of the run bikes" as well.  . . . .

a lot of that weight difference can be attributed to gasoline. Honda listed the bike's spec wet weight as with all other fluids but gas. Most magazines will weight the bike with a full tank of gas, and at 6lbs per gallon that is a good 20 lbs right there. Plus the magazine will use truck scales while honda has it's own calibrated bike scale and it is possible to get some variation.

What is heavier on a K8? well for starters the frame is heavier. Exhaust, seat, Tank, carbs, countershaft - you name it. even negligable weights can add up to lbs (as my father used to say nickles and dimes add up to dollars). The fact it has a longer wheel base and more trail indicates it is a more stable ride in a straight line but has less cornering ability. The bike is less flickable (roll side to side) because of the added weight.

I have two 78 Fs, one stripped down and one stocker. The stripped down one is easily more flickable (maneurvable) than the stocker because I have 100+ less lbs to fight  in changing direction. However overall cornering prowess it is probably only marginally better than my stocker.