Author Topic: 1978 CB750K — Post 836 OIL PRESSURE - not good (Read 248179 times)

SKTP · « **Reply #950 on:** April 19, 2016, 10:38:51 PM »

Figured out that there's a short somewhere in the electronic area I pulled it all loose and the starter works again....no to narrow down the exact location.

SKTP · « **Reply #951 on:** April 20, 2016, 08:53:26 AM »

Ok...is the oil pressure dash light suppose to be on (no pressure) then go off (pressure), or the opposite (for the indicator light)?

seanbarney41 · « **Reply #952 on:** April 20, 2016, 09:30:38 AM »

Below 5psi on, above 5 psi off

RAFster122s · « **Reply #953 on:** April 20, 2016, 06:22:51 PM »

The oil pressure switch seems to have a ground issue giving it power through a circuit sharing the power?
I am guessing something it the headlamp bucket is not connected correctly. I don't think you have a bad oil pressure switch but it could be. Do you have easy access to another you could substitute. I don't know how to test it in the pressurized state without jury rigging something with it out of the bike using a pressurized fluid bottle (could be pressurized with an air pump/hand pump in a fluid reservoir.)

Restoration Fan · « **Reply #954 on:** April 20, 2016, 07:44:59 PM »

Check to ensure that the wire from the oil pressure switch isn't being pinched as it runs inside of the interior by the starter.

SKTP · « **Reply #955 on:** April 21, 2016, 06:48:54 AM »

is there another way to know I have oil pressure? Right now I'm thinking that my oil tank staying full is an ok indicator of oil pressure? Hop full sort this all out over the weekend

knowsnothing · « **Reply #956 on:** April 21, 2016, 08:11:22 AM »

Quote from: SKTP on April 21, 2016, 06:48:54 AM

is there another way to know I have oil pressure? Right now I'm thinking that my oil tank staying full is an ok indicator of oil pressure? Hop full sort this all out over the weekend

Take the tappet covers off and see if the oil is making it to the head. You can also run one of those oil pressure gauges.

MCRider · « **Reply #957 on:** April 21, 2016, 08:40:18 AM »

Quote from: knowsnothing on April 21, 2016, 08:11:22 AM

Quote from: SKTP on April 21, 2016, 06:48:54 AM
is there another way to know I have oil pressure? Right now I'm thinking that my oil tank staying full is an ok indicator of oil pressure? Hop full sort this all out over the weekend

Take the tappet covers off and see if the oil is making it to the head. You can also run one of those oil pressure gauges.

In particular, put it on the centerstand and remove the #1 and #4 exhaust tappet covers. Oil should splash out of both. Be prepared to cut it off or put the covers on. IT can make a mess rather quickly.

The oil pres gauge is nice to have, but it won't tell you if there is pressure to the head. Only the crank.

RandyBMC · « **Reply #958 on:** April 23, 2016, 12:59:07 PM »

You are making great progress. I'm trying to catch up!

On the carbs, for our '78s, there are no clips for the jet needles. I see you mentioning the shims. How does that work? Any diagram or video link would help. To do it, do the carbs come off the rear stay and stay plate? I didn't disassemble mine to that point, just did the jets and set the float heights (and cleaned it all up). I also rebuilt the accelerator pump.

Thanks for any help! Keep up the updates - I'm watching and appreciate it!!

SKTP · « **Reply #959 on:** April 25, 2016, 10:20:02 AM »

Sorry RandyBMC I sent my carbs out to be rebuilt by member James Hale <harisuluv@gmail.com>

as for the bike update:

Drove 8 miles Saturday night. Seems to be running well. Still hard to start. Need to get a timing light.

Oil pressure: I took a tappit cover off while running...oil everywhere...so that is a good thing. I spent a bunch of time tracing my oil pressure wire and I believe it is pinched/shorting between the alternator-side connection and the switch. I also tried bypassing the short by hooking the switch directly to the indicator light with a temporary out-side wire and the light never went out. So I think I have a short and a not functioning switch. That seems too connected to be true...but I do not see what else it could be? If I disconnect the blue/red at the alternator the indicator goes out. If I disconnect the wire at the switch, the light stays on.

It sadly leaks a little right from where I thought it might

SKTP · « **Reply #960 on:** May 02, 2016, 10:24:52 AM »

UPDATE

So I had the wires plugged in totally wrong AND the oil-pressure switch was shot. I had the oil pressure switch (that appeared to be WHITE, pulled into the regulator)....and the white regulator (that appears as stained brown (I thought could blue/red into the switch)...well now that is sorted and I have a working oil pressure switch and the bike seems to start more easily...picture below is now correct

In #$%*ty news...it leaks...I am guessing that because I didn't have the jugs surface resurfaced? It has an MLS gasket and the head surface resurfaced only...I am thinking of trying the cotton-rope ghetto solution? Any thoughts on this? After doing this twice, I am not as worried about taking the engine out and trying the head gasket again (not mls this time?) but I'd like to just ride it a while first

Quote from: lrutt on August 23, 2012, 04:43:16 AM

1/4" cotton rope from Ace hardware really does the trick once it's cleaned up in there. Been running that on my 78 750 for 3 years now, replace yearly, no problem. Oil doesn't leak out past the rope. Just jam it in there with a screw driver. You can't even tell it's there unless you really look for it.

The bikes runs well and the transmission works...neutral is difficult to find, but possible

How soon do you usually do your first oil change after a rebuild? 100 miles? 1 tank of gas?

SOHC4 Cafe Racer Fan · « **Reply #961 on:** May 02, 2016, 11:02:13 AM »

Chris,

I would give the bike a good break-in for about 250 miles. Ride it under a load -- Long Beach has plenty of hills to do it on -- keeping the revs in the mid-range. After that, change the oil and adjust the valves.

754 · « **Reply #962 on:** May 02, 2016, 12:33:53 PM »

Do you have a frame kit ? way less work to change gaskets with the kit.. Bike looks great..

SOHC4 Cafe Racer Fan · « **Reply #963 on:** May 02, 2016, 01:38:03 PM »

Quote from: 754 on May 02, 2016, 12:33:53 PM

Do you have a frame kit ? way less work to change gaskets with the kit.. Bike looks great..

If not, Frank has a great weld-less kit available.

SKTP · « **Reply #964 on:** May 23, 2016, 10:44:31 AM »

Rode it a bunch yesterday...I bought $4 cotton rope and jammed it around the head gasket...zero leaks + confirmation that it is the head gasket leaking and not the pucks

I am just going to ride it and see how this rope/tampon holds up

In the meantime I plan on cleaning up my wiring, getting a tune-up/tires and I might add a tank-stripe

But I am happy and there's no oil on my pants!

SOHC4 Cafe Racer Fan · « **Reply #965 on:** May 23, 2016, 11:00:14 AM »

Beautiful, Chris.

RAFster122s · « **Reply #966 on:** May 25, 2016, 11:39:09 PM »

You do know how to get the oil out of the pants, right...
Lestoil works well...plus there lots of other solutions if you can't find that.
David

SOHC4 Cafe Racer Fan · « **Reply #967 on:** May 26, 2016, 09:12:36 AM »

Quote from: RAF122S on May 25, 2016, 11:39:09 PM

You do know how to get the oil out of the pants, right...
Lestoil works well...plus there lots of other solutions if you can't find that.
David

That's why I wrench in black Dickies

seanbarney41 · « **Reply #968 on:** May 26, 2016, 10:25:43 AM »

done the rope trick for tens of thousands...+1 on the black pants

SOHC4 Cafe Racer Fan · « **Reply #969 on:** May 26, 2016, 10:41:38 AM »

Quote from: CB750 Cafe Racer Fan on May 26, 2016, 09:12:36 AM

Quote from: RAF122S on May 25, 2016, 11:39:09 PM
You do know how to get the oil out of the pants, right...
Lestoil works well...plus there lots of other solutions if you can't find that.
David

That's why I wrench in black Dickies

Of course, that doesn't help so much for riding. The rope should for now.

SOHC4 Cafe Racer Fan · « **Reply #970 on:** June 01, 2016, 09:18:20 AM »

Hi Chris,

Your bike has been nominated for Bike of the Month July 2016. PLEASE go to the nomination thread (http://forums.sohc4.net/index.php/topic,158101.0.html) and post that you "accept" the nomination before June 15!

I'm looking forward to seeing you on the roads around Long Beach!

Don

SKTP · « **Reply #971 on:** June 01, 2016, 11:08:23 AM »

Thanks for the nomination...

In bike progress news...I put license plate LEDs very similar to these (I forget what brand I have)

https://www.amazon.com/Rupse-White-Motorcycle-License-Plate/dp/B008RIEQXY/ref=pd_sim_263_4?ie=UTF8&dpID=41Tk53IAozL&dpSrc=sims&preST=_AC_UL160_SR160%2C160_&refRID=M65A0288RCPB5P5D2EQJ

And now both have burned out? Do I need some sort of resistor?

SKTP · « **Reply #972 on:** June 11, 2016, 03:47:09 PM »

What a different s proper tune-up makes! 150psi compression across the cylinders. Timing set properly, carbs synced...new firk oil. Feels so much better and I have some piece of mind.

seanbarney41 · « **Reply #973 on:** June 11, 2016, 10:57:45 PM »

yep, now ride it

SKTP · « **Reply #974 on:** June 13, 2016, 11:28:36 AM »

Newport beach

Backyard photoshoot

News:

Author Topic: 1978 CB750K — Post 836 OIL PRESSURE - not good (Read 248179 times)