Topic: cb750 motor seizing up

[joe750]

Ok guys ive got a serious problem...
I went out to start up my '72 cb750k today and while warming up it started to die and then shut off suddenly and it made a screaching sound from the motor right before it completely died.
My heart sank. I had 60 psi oil pressure on the gauge at the oil galley plug.
I tried to turn it over with the kick starter and it was too hard.

I ended up turning the crankshaft and it turned like it normally should. No popping or squeaking or any strange noises. Also no more resistance than normal.

I checked to see if the camshaft was getting oil and it looked less than normal so i poured a little in the tappet covers and proceded to start it again.

It started right up and ran perfect and then about a minute later, the same thing happened.

So i stopped to prevent further damage.

Its like the motor is seizing up and killing it.
Has anyone had this happen or know of a cause?
Could it be the lack of oil in the valve cover?

[ekpent]

Its not unusual at all for the cam to seize up in the holders with lack of oil from a plugged oil jet. May want to drop the oil pan or filter housing to look for some fresh metal.Doesn't sound good.

[lucky]

What proof do you have that it is seizing up?

It would not have had  time to even get hot yet.
You may have a problem but it is not from overheating.

[Xnavylfr]

Most times if you don't get enough oil on the cam, then it will sound like a mouse squeal before it FINALLY locks and usually breaks the camshaft.

Pull all the tappet covers and have the bike sitting level, start it an check for a good splash of oil in EACH tappet cover. The oil jet in the heads have real small holes and can plug easy... The SQUEAL you mention sounds like a cam seizing to me.

Xnavylfr(CHUCK)

Also if you have a HEAD GASKET leak , the air trying to escape will make a squeal sound.

[Black 750K8]

Joe When you could not turn it over by hand how much time went by before you could turn it over?
 How did you turn over the crankshaft?

What proof do you have that it is seizing up?

It would not have had  time to even get hot yet.
You may have a problem but it is not from overheating.

Lucky
 How do you know how much time went by? Do you mean the whole engine would not be hot enough or just the cam? I do not think a cam with not enough oil would take much time and the bottom end would just be warm but not hot. I am new at this and I am just asking to learn.
Thanks in advance

[Xnavylfr]

It doesn't take much time for a cam to lock and when they do I've seen them twisted in half. The cam locking up sounds like a fan belt slipping on a pulley. The head gasket sounds more like a pressure cooker when it just starts to release steam.


Xnavylfr(CHUCK)

[joe750]

Xnavylfr it did sound just like a belt slipping on a pulley.
Might have been a bad idea but I started it again today to see if I could see any oil splash through the tappet cover holes and there is none. Not even a little:-\ and it ran for 2 - 3 minutes.

Shined the pen light in to check things out and Ioticed a little rtv sealant that had been squeezed through on the inside of the valve cover. I'm guessing the p.o. used this and I can blame him for my blocked oil jets (Im concluding that's the problem)

I guess its out with the motor now to tear into it and unblock these oil passages