Air bubbles in T350 right side oil line

[joethebike]

An old topic often blamed on check valves but my issue does not seem connected with that cause.
Last year I replaced the seals in my T350 pump but ever since I have been plagued by air bubbles in the right side delivery pipe. After reading the forum posts I changed the complete right side oil delivery line 3 times with spares but the bubbles persisted.
If the motor was run in the shed with the pump lever held in the full on position bubbles would clear from the line with strong pulses from the pump pushing all air out and into the engine, but if going for a ride of about 20 km with the pump operating normally by the time I arrived back in the shed air bubbles would again be in the line.
The bubbles would originate directly out of the pumps right side port and proceed down through the line to the engine.

I assume it can't be the check valves (3 sets tried) and in any case the bubbles originate directly from the oil pump and move through to the engine. And why does it pump oil without bubbles on full stroke but with bubbles on variable stroke?

A second pump has been installed and it works without bubbles but why the rebuilt pump has bubbles only out of the right side port is a mystery.

[dollydog]

clutching at straws here really, but did you use the same nylon washers on the banjo bolts every time, but not with the new pump?
cheers, dd.

[joethebike]

I have a lot of nylon washers, tried some as a possible leak cause (you would think that oil under pressure would leak externally from a split washer rather than let it suck air) but when replacing the pump just used the same washers that were used on the "bubbly" pump. It would be interesting to know if the pump has a common piston providing oil under pressure before branching internally to both outlets.

[jabcb]

The T500 shop manual has a pretty good explanation of how the oil pump works. The T305 shop manual has a few diagnostic steps.

The shop manuals are here: https://www.oldjapanesebikes.com//mraxl ... /index.php
Select T/GT500 Shop under Shop Manuals, select Engine under Contents, and then go to page 31.
Select T305 Service Manual, and select Posi-Force.

The pump feeds one cylinder at a time.

Suzuki no longer sells those nylon washers. Instead they sell aluminum crush washers that can be even more problematic.
I’ve had good results with stat-o-seal washers.

[Vintageman]

The T500 shop manual has a pretty good explanation of how the oil pump works. The T305 shop manual has a few diagnostic steps.

Nice.


I have seen the shaft surface on the pump worn and changing its seal won't fix air leak.

Hi-Jack (quiz)

What is different about Gt250, T350 and T500 pump? they are different (flow rates) If I recall. I tore down a T350 vs GT250 and and nothing was obvious for example not geared differently. It might be the cam shape or the size of roller on the bolt for cam. Don't know... I have couple I can't tell what is what anymore