Topic: Cognito moto oil tank problems

[Kambo1987]

Hi everyone I have a question for you regarding a cb750 sohc oil tank. I have had a cognito moto oil tank installed on my bike and then ran into some trouble. The website states that the oil tank holds 3 quarts and my engine builder thinks this is not enough for the bike to run properly. Has anyone here had there tank installed and had it running with no problems. My guy seems to think the standard one runs around a. Gallon and the difference in size has caused the engine to run dry. Can anyone give me some advice on this.

[DaveBarbier]

This posts is saying the capacity for the 750 oil tank is about 3 qts. Seems like the CM tank is right there with stock capacity.

http://forums.sohc4.net/index.php?topic=57098.0

The engine doesn’t use over 3qts when it’s running so it won’t go dry.

[DaveBarbier]

Is your bike experiencing any issues? You said your engine builder said it, “has caused the engine to run dry”. Are you saying your engine has an oiling problem currently?

[calj737]

Its a dry sump motor 

[70CB750]

Oil tank for K0 is 3 quarts.  Meaning that when you change oil in 1970 CB750 it will take 3Q to fill the oil tank to the top line of the dipstick.

Later models use about 3 and half quarts of oil in the same situation.

[Jerry Rxman Griffin aka MuthaF'er]

If the tank is "running dry" then you need to replace the stopper valve in the pump

[madmtnmotors]

"caused the engine to run dry"

What do you base this observation on? You'll have to be more specific. If you ran the engine dry it would do all sorts of terrible things and likely seize.

[Bodi]

A 3qt tank is plenty large enough.
The system works by taking oil from the tank into the oil pump, pumping it up to 40-60psi to lubricate the engine. The oil does its work and then drips/runs/dribbles to the bottom of the engine sump. From there another "scavenger" oil pump sends it back to the tank. The scavenger pump is about twice the size of the pressure pump... if the tank drains down into the sump while sitting, that pump can drain the sump and refill the tank long before there's any engine damage from lack of oil.
What your engine builder is saying is BS. But like the others, I wonder what happened with your motor? It smells like this guy is trying to blame some engine damage (probably his fault) on your choice of oil tank.

[rotortiller]

It smells like this guy is trying to blame some engine damage (probably his fault) on your choice of oil tank.

Funny I smelled the same thing all the way up north LOL    

Hope the oil lines were on correctly.

[calj737]

First, there's no "standing issue" with those tanks from a design or operation perspective. Perhaps, he or the Prior Owner installed it incorrectly (reversed the hoses?), but that would be a "User error" not a product issue.

You bought the bike, but it needed an engine rebuild?
He rebuilt the engine, but the tappets needed adjustment? That ticking sound was oil starvation to the top end. Doesn't sound as though he "rebuilt" it very well... He likely didn't clean the oil passages and either he or the PO used sealant where they should not have and it has clogged the oil pump and/or galleys.

Sounds to me as though you just screwed by your engine rebuilder.  Might be worth getting a new motor and finding a new mechanic.

[DANFROMOZ]

Yeh that's a pain fella, I hope this guys gonna do the right thing and at least give you your money back on the labour, no use paying for someone blowing up your motor you could of done that yourself for free....

[DaveBarbier]

Damn, I also feel you’re getting had by the engine builder. How did you find him? Was he recommended to you? Does he know these old SOHC4’s?

The big thing is when you asked what the noise is after the engine rebuild and he said it was the tappets. Why weren’t they adjusted after the rebuild? Or maybe they were correctly adjusted and you’re just not familiar with the ‘sewing machine’ noise they make?

I would say what Cal said as it sounds like he used a sealant where he shouldn’t have or used too much and it got into an oil jet and clogged things up. Very easy to do if you don’t know what you’re doing.

What I would do: stop giving him money and take everything you have away from him. Find a new engine or open this one up again and re-rebuild it yourself. Engines here in the states aren’t that expensive. Maybe a couple hundred bucks max. If you find a runner, you can pop it in in a day and get to riding pretty quickly. We can all help answer questions.

I’m also curious who came to the conclusion this needed and engine rebuild when you had it shipped to you and why.

Can you post photos of the engine/bike before and after rebuild? Or maybe the internal engine parts? Just trying to see if we can find anything fishy. For example, if we see red RTV between the head and cylinders post rebuild then we likely have our answer.

Good luck!

[DaveBarbier]

Just to reiterate, there is no known issue with these oil tanks.

[madmtnmotors]

I would find a used engine to get the bike back on the road and then do a "forensic" rebuild on your current engine. You'll likely have a very difficult time getting the shop/mechanic to get it right, even if they are willing to try, especially after failing so miserably the first time. Likely RTV silicone or other flotsam has plugged one or more oil passages. Sorry to hear about your trouble, good luck with whatever you decide.

[Kambo1987]

Thank you everyone for your help I'll let you know what happens.

[Xander^]

i have the cognito moto oil tank also... no dip stick in it though.. how do you gauge your oil? my aftermarket speedo also does NOT have an oil light. any suggestions?

[Hodmi]

I too have a Cognito moto oil tank.   I wish they had a dipstick, but I use a small flashlight to see inside the tank to check the level.
The tank holds plenty of oil, but you should check it after running the bike for a bit.   When I first ran mine after doing a bunch of engine work, the tank drained a lot as there wasn't much oil left in the engine.  I topped it up to a little below the return line and then everything has been fine.