GTR AND GTO CHECK VALVES.

[reed]

GTR AND GTO CHECK VALVES.
Its worth having a look at the check valve assembly part number 1502-9000 X 2.
They are on top of the motor, take them out and very carefully blow air though them.
One of mine was blocked less oil going into the engine not a good thing.
I am replacing mine,Richard sell them etc.
Thanks.
Steve. 

Thanks.
Steve.

[deisher6]

Steve:
What is the scoop on these.  From the schematic it looks like a bolt with a hole in it.  I have the air cleaner off, should I just take them off and blow them out?  When I was riding last summer I set the oil pump to pump a little more advanced than the recommended setting and I had "plenty" of oil going to the cylinders. 

I was going to back it off when I reset the carburetors after replacing the carburetor rubbers.
Thanks.
regards charlie

[BS Mechanic]

In a two stroke engine, the crankcase goes through negative pressure while the piston is going up, and positive pressure when the piston goes down.  The GTR/GTO need one way check valves where the oil lines enter the crankcase to prevent backpressure during the crankcase compression cycle from pushing oil back into the oil lines. 

Inside each valve is a small steel ball with a spring keeping it seated.  This lets the pump push oil into the crankcase but keeps backpressure from pushing the oil backwards into the tubes when crankcase pressure is positive. 

The 175/200 doesn't need the check valves because the oil is injected between the carburetor and the disk valve.  In that location the pressure is always negative.  The negative pressure always tends to suck the oil into the airstream, so there is no need for check valves.

[reed]

deisher6
The spring inside on the check valve was weak and on the other side was blocked.
So what i did is i replaced them, they have been in there for thirty years +
We are very Lucky that we can still buy them new about 40.00 from Richard.
In my 36 years as a motorcycle mechanic its the small things that can course the
Most problems.
Thanks.
Steve.
PS There was some damage to the piston and crankshaft i am going to rebuild in the near future!

[reed]

Bob
Good post on the check valve very informative.
Thanks.
Steve.

[OldSwartout]

The 175/200 doesn't need the check valves because the oil is injected between the carburetor and the disk valve.  In that location the pressure is always negative.  The negative pressure always tends to suck the oil into the airstream, so there is no need for check valves.

The 175/200 did use check valves in the outlet lines like the 350.  There were oil line connectors after 16B that had a check valve in them, then after 16V, the check valves were added to the pump itself in the union bolt holes. I'm assuming the very early ones didn't have check valves. See service letter BSG-0029.

The check valves in the all the bikes may have been there to prevent crankcase pressure from pushing the oil back, but at one time it was explained to me that they also kept the crankcase vacuum from pulling more oil than desired.  At this point, I don't really know, but they certainly do need to be working correctly.

Even the 90/100 has check valves in the oil pump. Unlike the bigger bikes, they have a check ball in both the inlet and outlet lines.

[BS Mechanic]

You're right, all I've got to look at in person is an old 175 book.   

The 350 check valves only allow flow toward the engine, and do provide some resistance, which the pump must overcome.  Probably also keeps the flow uniform, controlled only by the pump.

Did the 175/350 location for the injection point move in later models?  Looks like it's in the carburator inlet, right before the rotary valve on the original version.

[deisher6]

Thank you all for the good scoop.  I will pull them out carefully and visually look at them.  It would be nice if there were some sort of test and standard to judge their functioning.

Again Thanks
regards charlie

[reed]

deisher6,
On the check valves they are 20.00 each from Richard.
My engine and Richards engine i am replacing the check
Valves,it the little things can do the most damage.
Thanks.
Steve.