Topic: CB750 k4, the long restoration

[theDQG]

Hi all,

My name is Arthur and I'm not exactly new to this board, I existed in another incarnation a long time ago, a different username and a different cb750 which is now riding the big highway in the sky.

Just picked up a k4 which I'll restore to as new as possible.

One confusion I'm having is that this k4 has what seems to be a planet blue metallic scheme, but that only existed on 1975 models, correct?

Maybe sporting a 1975 tank? The side covers are an obvious mismatch.

[theDQG]

Before I can start restoration, I want to address a problem that popped up. When I picked up this model it was in good running condition, but then on my first long ride, the idiot light went on only during idle. It goes out as soon as I twist the throttle, even momentarily.

I did this a few more times, and the result was the same, every time, so nothing wrong with the idiot light itself.

Unscrewed tappet covers #1 & #4, entire head was drenched in oil, and splattered as soon as I gunned the engine, so the oil is getting to the top end just fine.

So with the input of this board, I'd like to come up with a checklist of things to go through, as far as trying to diagnose what the problem is.

Some possibilities I've been thinking of:

-bad sensor
-clogged oil strainer
- shrunk o-rings on oil pump

However, I did some research and it seems that the first thing I should do is install an oil pressure gauge..

[JMS28411 I'm no Spring Chicken]

Remove oil sensor wire, clean re-connect wire to sensor, remove indicator bulb from socket, clean base and re-install bulb.
New oil & oil filter if not already done.

[PeWe]

Tank and headlight ears look later, like K6.
No petcock on right side indicate the later tank that has it on left side. Separate holes for headlight bolt and blinker.

[theDQG]

Thanks for the input.

I have ordered a Marshall oil pressure gauge and will install it.

I have not had a chance to get to the bike, but when I do, my checklist at this point will be to:

1) clean/reconnect wire to sensor
2) clean/reinstall bulb
3) change oil, install new filter (would have to do this anyway if I am to install the oil pressure gauge?)
4) while oil is out, inspect oil pump for any sign of wear or damage. (should I just replace the o-rings, regardless?)

[MauiK3]

The oil gauge should go on the right side of the engine on the blanked port above the points. You only need to remove the blank and install the gauge.
Side covers appear to be K-1.
Steve

[theDQG]

Finally got everything in the mail, including the oil pressure gauge (Marshall)- going to work on the bike tomorrow.

Question: Do I apply blue loctite to the gauge, and the elbow, but use teflon tape for the adapter (where it screws into the oil galley). Correct? Please correct me if I'm wrong.

[theDQG]

bump

EDIT: Found it, had to do some digging on this forum- from a post: "blue loctite on the threads, teflon tape on the gauge threads."

[theDQG]

Got a bit done today- drained oil, removed oil filter and pan.

Going to get a new oil filter bolt with larger head- the old one is just about done.

Installed the marshall oil pressure gauge without any problem.

Pulled the oil pump to replace the three O-rings, but when I pulled it, a substantial amount of oil came pouring out. Is this normal?

Inspected screen- there were minimal metal shavings. Going to clean it off before installing again.

[700504]

Got a bit done today- drained oil, removed oil filter and pan.

Going to get a new oil filter bolt with larger head- the old one is just about done.

Installed the marshall oil pressure gauge without any problem.

Pulled the oil pump to replace the three O-rings, but when I pulled it, a substantial amount of oil came pouring out. Is this normal?

Inspected screen- there were minimal metal shavings. Going to clean it off before installing again.

Yes normal, but when you re-install it you'll want to dip it in oil and crank it by hand first; this will remove air pockets. Then you'll want to put the bike on it's side stand and slowly dribble oil in the galley where you installed your gauge. It's also not a bad idea to put a little in the valve inspection covers to insure proper lubrication on start up.

[700504]

Finally got everything in the mail, including the oil pressure gauge (Marshall)- going to work on the bike tomorrow.

Question: Do I apply blue loctite to the gauge, and the elbow, but use teflon tape for the adapter (where it screws into the oil galley). Correct? Please correct me if I'm wrong.

I just used teflon on the gauge (but mine also has a recessed o-ring on the adapter so nothing needed there), and i used thread seal paste on elbow.

[theDQG]

Thanks for the heads up 700... I'll be sure to remember that.

Comparing O-rings for the dowels (#14 on the exploded dia). New one on left. Old one on the right is flat and stretched.

Edit: since this stupid pic, for some reason, was posted sideways, I should say, the top is the worn one and the bottom is the new o-ring.

[theDQG]

Well, I did all the mods, replaced o-rings on oil pump, primed it and installed it, new gasket for pan, installed that. No leaking, but the red light still comes on.

Took her out for a test ride- the red light still comes on. Oil gauge reads 80 psi cold, goes to 70 when hot and hitting 4k rpm, then goes down to 30 at idle.

The problem is, there is a definite relationship between oil pressure, rpm and the red light. Every time I go from idle to speed, the oil gauge always goes from 30 psi to around 70, then when I come back down to idle, the gauge drops to 30 psi and the red light comes on.

However, I should mention that when I took the oil pump out, there was no gasket between oil pump and engine. Should there be one?

I'm also thinking I should get Elan's oil pump refresh kit.

[SOHC4 Cafe Racer Fan]

I'm also thinking I should get Elan's oil pump refresh kit.

Good insurance.

[disco]

30 psi oil pressure at idle is good. I'd say your oil pressure switch is RS.

[theDQG]

30 psi oil pressure at idle is good. I'd say your oil pressure switch is RS.

That's what I was starting to think, because everything else checks out just fine. Thanks for confirming my growing suspicion.

[theDQG]

Just got a new oil pressure switch. Any particular trick in replacing the old one without taking too much of the bike apart? Any info appreciated, thanks!

[seanbarney41]

I recently changed one.  They are tough to get at.  Honda probably had a special socket for it.  I removed the bottom of the airbox and the timing chain tensioner.  Interestingly, there were different socket sizes between the one I pulled off and the one I grabbed off a parts engine.  I think I had to resort to using a pipe wrench on the old leaky and bigger sized one.  The replacement smaller one went on fine with an appropriate sized deep well 10 pt.  I used a dab of blue loctite on these threads as well.

[theDQG]

Thanks, Sean. I'll tackle it sometimes over this weekend and follow your advice.

Got some goodies from vintagecb750 and had some time, yesterday to do some replacing- the tacky right bar switches had to go-  wires were coming apart and the throttle cables were not routed correctly and had kinks in them- before and after pictures below:

[theDQG]

Next up, the LH switches, but I can't figure out the purpose of what appears to be two ground wires going in, right ahead of where the mirror screws in. Anyone know?

[Jimray23]

Its a clutch safety switch. Most people just do away with them. Honda put them on there as a safety so you had to pull clutch before you start your bike.

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Jim
I really don't see why people ask for advice if their not going to take the advice given.

[PeWe]

3 O-rings between oil pump and case.


Skickat från min iPhone med Tapatalk

[theDQG]

The slow OEM'ing continues.

Got the speedo/tach replaced with replicas from vintage750.

Got a tuneup done and was told that compression showed an average of 130 PSI, within 10% of each other which I believe is the lower end of what is "acceptable." Does this warrant a teardown of the engine at some point?

I finally got a proper 1974 tank with the petcock on the right side and am having it sandblasted, then sent out to petesponies for painting, along with new side covers and correct decals.

[Stev-o]

Its a clutch safety switch. Most people just do away with them.

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I really shouldnt give advice cuz it's not always good!

Really?   If you have it, keep the clutch safety switch, it may save the bike from going down one day.

[seanbarney41]

Its a clutch safety switch. Most people just do away with them.

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I really shouldnt give advice cuz it's not always good!

Really?   If you have it, keep the clutch safety switch, it may save the bike from going down one day.

yup, the bike probly won't go down if it does not start