1975 CB750 K5

Thinking of moving to a '75 Honda 750 with 13K miles and would like to
know what good and bad points to look for with this model.

 

Hold on there Matt, you're really climbing the scale on
the "state of the art" meter. <g>

So, let's see, depending on the bike's anniversary, it's
around 30 years old. At 13K miles, that looks like about
430+ miles a year. No sense in burin' up the road, I guess.

However, I suspect that rather than a linear 430 MPY, the bike was used more
consistently in its early years,
and then parked/abandoned(I'm only guessing) later.

If it's had long periods of inactivity, I would be looking
at bad tires, possible battery leakage/damage, and the
presence of rust.

I can't recall the K5, but I had a '73 K3. It was a four
pipe model, and they were notorious for muffler rusting.
Even back then.

I would also be looking at the fuel purity coming out of
the tank, as well as the same respect to the oil. Of course,
these items could have just been cleaned/changed. Might
want to drain a float bowl or two and check the gas there.

Carefully check all rubber condition(front fork covers, if
they exist, air intake tunnels, etc.). Put the bike on the
centerstand, fire it up, put it in some gear, and let spin the
rear wheel. Check the wheel for true. Run up the engine
and check for exhaust smoking. Listen to the chain for
and excessive noise or binding sounds. Listen to the engine for unusual
noises. My K3 was a single OHC.
Don't know when the DOHC models came about. It
might have a noisy camchain. Obviously, look for any
oil leaks, and if it's liquid cooled, and coolant leaks.

The check list is endless....


Gary

 

Beyond the usual caveats when buying *any* old bike...

The bike itself, by modern standards, is utter crap. It's massively
heavy, requires enormous effort to ride any distance above about 80mph,
and has truly terrifying brakes.

It's detuned and slow. Expect 110mph top speed, or thereabouts (whatever
the speedo says).

I mean, there's a mount for an extra caliper on the 'other' fork leg,
and Honda didn't fit one as standard. It's like saying: :"We know the
brakes are crap, but if you want decent ones, you pay the extra, boy."
Harley tried something similar with their 'aftermarket' brakes, which
actually worked, unlike the ones they fitted as OE.

The throttle is heavy. The suspension is crude and the whole chassis is,
to be honest, completely at odds with the engine performance. It can't
cope above, again, about 80.

The lights are dire, the carbs need re-synchronising every 3000 miles,
and the chain would disgrace a modern 125 and needs adjustment every 500
miles and replacement every 5000. If neglected, it has a distressing
tendency to part, and in extreme cases, this takes out the crankcases.

The spokes in the rear wheel are not up to the abuse of the 60-odd bhp
engine and loosen off or snap, with interesting consequences for the
rear tyre.

The high bars make the thing impossible to ride for any distance above
(yep!) 80mph. There's a pattern emerging here, you know.

And yet......

It looks fantastic, if it still has a genuine 4 into 4 exhaust. It makes
a lovely noise. It's reliable and easily maintained. And it is an utter,
utter classic.

In short, it's great for riding around below (guess what speed?). It
turns heads. It has soul.

 

If I was going to buy a 4-stroke I-4 built in 1975, I would look for a
Kawasaki KZ-1000. It's a much better engineered motorcycle. It wouldn't
matter if I had to pay more money for it.

I'm not much impressed with Honda's early I-4's. The center of gravity
is too high for the wheelbase. You can't remove the cylinder head
without pulling the engine out of the frame (unless you take a hacksaw
and cut the lower steering head braces out of the frame).

 

Gary Walker wrote:

Errmmmmm, if you aren't sure whether a K5 is air or liquid cooled, SOHC
or DOHC, it might be better not to offer advice at all.....

I ought to add - parts availability for the engines is till good. Even
the OE 4/4 exhausts are available. Trim and cosmetic parts, like side
panels and so forth, can be nightmares to source. It all depends on how
original it is, and how original one wants it to be, I suppose.

You're right about the four cans rusting, mind. They all did that.
Squirting a load of oil down the silencers helped.

That reminds me: recently I bought an utterly immaculate Honda CB125S,
all original, clean as you will ever find, 1972 vintage. The OE exhaust
was still in superb condition (it had been dry stored in a heated
building). I discovered that these exhausts are now utterly
unobtainable, and that not even pattern ones have the right style of
silencer.

So I recently bought a pattern system for a pushrod CG125 (which bolts
straight on) and replaced the OE system wit this. The OE exhaust has
had a pint of oil poured into it, and swilled around, and the faultless
chrome has been coated in grease. It's sealed in a plastic bag, hanging
in my garage, and when/if I sell the bike, it'll go back on.

 

Well, not recalling a bike's manufacture history event is a
lot different from not knowing of the that history. Did you see any text in
my suggestion(s) that would make you believe I don't know what I'm talking
about?

 

Oh, the general advice applicable to old bikes is great - agree
totally. But the answer to your question is, when it comes to this
specific model, "Yes".

 

I can recall the K5, my buddy had about a 1971 K1, and that was
totalled in a crash with a taxi cab, so he made the insurance company
buy him the K5 or he would sue them for the injuries sustained in the
accident.

Hey, a CB750 could be bought for as little as $1750 in those days of
the Carter Recession. Such a deal! Everybody bought 'em, even people
who didn't know how to ride...

But this kid I knew was a real operator. He had an XS650 and he let a
guy ride it and the guy hit a brick wall, so he demanded enough money
to get the K1, which was wrecked in the taxi cab accident. Then he had
the K5 for a few months and it was mysteriously stolen and he wound up
with a Volkwagen. Yamaha to VW in less than a year. Hmmmm....

CB750F was in 1979. There may have been 1978 DOHC's, check
www.partsfish.com

 

Actually, that was a problem that dogged *all* CB750s until the F2 and
K7 came along with beefed-up O-ring chains.

Damn nearly happened to me - it popped the spring link on the weedy
chain, lost the sideplate, and the two halves of the link wre just
opening out when I decided to stop for fuel and give the chain a lube at
the same time =:O

 

What are the details and mechanism of crankcase damage when the chain
breaks?

 

The chain breaks a hole in the crankcases around the countershaft
sprocket.
The sand cast cases certainly can't be heliarc welded, and the die cast
cases probably can't be repaired either.

By comparison, Kawasaki's 900cc Z-1 and the KZ-1000 are built like
brick houses...

 

Could I replace the chain and sprockets with stouter parts? Maybe some
previous owner has done that already?

 

I don't know if the chain and sprockets from the later models will fit.
I don't see why they shouldn't, but it's not a conversion I've ever seen
done.

 

I ride a K5 as a daily driver (well, I did until the base gasket
started
leaking. Can't show up at work with my right pantleg oil-soaked, so
it's
parked for the moment). I've got a Tsubaki 530 O-ring chain on it, and
aftermarket sprockets. No problems with the install.

I agree on the brakes, weight, and looks comments, too. I ride it
because
I like the "classicness" of the bike, and don't mind working on old
bikes.

80 mph is about the top you'll want to ride it without a windscreen.

You'll want to look at www.vjmc.org, and wherever SOHC is hanging out
now, I
think it's www.sohc.net.

It's a fun bike, IMO. Far from perfect, just fun.

 

I think that's fair....

I've owned most of the SOHC Honda fours at one time or another. The
very best, from a riding point of view, was the CB650 (believe it or
not). Faster than all but the very fastest 750s, and handled and braked
infinitely better.

The 550s are a good compromise, but they're really thirsty, except for
the four-piper K.

I've still got a 400, which is (IMHO) the best of the lot. It
completely outhandles all the others (with the possible exception of
the 650), is smoother than the others, more economical, and looks just
fantastic (again IMHO). However, it's a finicky little bike, and
requires more frequent maintenance, especially oil changes and carb
balancing. And it doesn't suit the large rider.

Never ridden a 350, nor a 500.

 

Add a can of radiator stop leak in your crankcase next oil change. I
guarantee it will stop leaking. <G>

Just kidding, folks. DON'T DO AS I SUGGESTED.

I actually heard of a woman doing that to her leaking automatic
transmission. No, I didn't suggest it, either.

Ed Cregger

 

I still want to get my hands on a gray market 250cc inline four. I'd pull
the mufflers and then revel in the sound of the little four cylinder revving
up to 17k before shifting. That should make the hair stand up on (among
other things) for any red blooded engine enthusiast/freak, such as myself.

Ed Cregger