Browse Category: Oil pump

Mounting the oil pump

For about two months ago I tested several oil pumps in the test jig I made. I decided to go for the early version of oil pumps with suction. That was the one giving best result when idling. I got scared about the others giving little or noting at low throttle.

All o-rings were replaced and the same with the nylon spacers.

The 50 years old plastic and the oil-lines are very fragile, and I didn’t do much to clean or make it look nice. I knew it all worked since I had it in the test jig with good results. To drive the plastic base all the way down I prefitted the screws for holding the oil pump.

Torque settings for the banjo bolts is difficult to find. I did some investigation back in 2016 when rebuilding my GT750A and found a number of 2,5Nm. That’s lower than I today have on my smallest wrench. At that time I stole a key from my work, but this time I used common sense and was gentle to the bolts.

By using a syringe I was able to inject the oil all the way to the end of the pipes.

I have the original screws for mounting the oil pump, but I went for 5mm bolts with hex head instead. Much more easy to mount and the screw are not visible when the covers are on.


Oil pump

This post will be about the oil pump, for both the GT750 and GT380, old and new models.

The information below is my understanding based on testing and iformation given to me. If something is wrong, please let me know and I will updatate my blog.

Some basic informations:

As the picture above shows we have an early model of the pump using one extra piston for suction. On later models the gravity from the oil tank above the thank do the job, and Suzuki decided to make it more simple with only two pistons.

Note! Never,ever go away from using the oil pump and only mix oil into the fuel, if so the crankshaft will not be lubericated.

Are all pumps interchangeable ? Yes, all of the GT380 to GT750, old and later models, but there are some differences. Later models for GT750 using the vacuum carbs have a different arm connecting the throttle cable, see the picture below:

The punch mark and alignment marks are at different location (order) on J-K (GT750 models and all GT380 models) compare to the latest GT750 models. The alignment procedures are also differnt, see the picture above and the service manual.

Test setup:

The speed of the pump is controlled by a DC motor and most of the parts are 3D-printed.

The shaft running the pump is made of brass and locked in position by two ball bearings.

Lesson learned after the testing:

At normal operation the cylinders get more oil compare to the crankshaft, but one important observation:

At the first punch mark there are almost no oil coming to the cylinders, only to the crank. On my test with two later models with only two pistons and no suctions, this was the case. A bit scary to watch. On the early model with three pistons and suctions I got a bit of oil to the pistons at the first punch mark as well, but no much. As soon as I increased the throttle it all worked as normal. Most of the oil to the cylinders and less to the crankshaft.

In the video below the pump is running between the first and second punch mark.

On my GT750 the oil consumption is close to 100ml per. 100 km, as it should be. In test above the rpm of the pump is 1hz ( 60 rpm) and refer to the engine that will be about 4000 rpm. The consumption from the test looks very much the same as I see on my GT750, but the 3-piston pump with suction gives a bit more.


I ordered new gasket from E-bay, but to start the testing I made my own by scanning the old one and cut new with my laser cutter:

Seems to work fine. Since I have paid the money for new ones, I might swap the gaskets when they arrives.

Copy from the manual: