Suzuki 2 Strokes

Hello, I am assembling my GT750 engine which I purchased from a guy in the UK 8 years ago, it is close to TR750 specs with C/R gearbox, 3mm cylinder spacer, ported, etc.
I am now thinking of which way to go with the lubrication:
It seems to be common advice to keep the oil pump for better lubrication of the crank main bearings. I usually prefer premix on my RD500 track engines since I simply know exactly what what mixture it runs - in case of oil pumps I can hardly determine the oil:gas ratio.

Did some of you try to combine both methods - like using the oil pump to feed the bearings only, and pre-mix for the pistons?

thanks for any feedback

best regards

Wolfgang

I believe the TRs ran the oil pump locked at minimal delivery and also ran pre-mix in the tank. I have never had problems with Suzuki oil pumps. I run a near-TR engine and I run the pump as normal.


Lane

Hello Wolfgang,

I run a TR500 replica in a spanish race series and have removed the pump and run premix 3% and I have never had any problem with the engine. On the 500 you have to modify the crank when you decide to run premix only and not sure if its the same on the 750?

My reason for doing so is that I know what I am mixing and its going in the tank and with the pump I never feel 100% confident

cheers

Eamonn

Suspensionking wrote:Hello Wolfgang,

I run a TR500 replica in a spanish race series and have removed the pump and run premix 3% and I have never had any problem with the engine. On the 500 you have to modify the crank when you decide to run premix only and not sure if its the same on the 750?

My reason for doing so is that I know what I am mixing and its going in the tank and with the pump I never feel 100% confident

cheers

Eamonn

A little off topic but Eamonn, is it possible to send me the details of the crankcase mod as I am considering doing the same thing to my T500 racer?

Hello Wolfgang

sure I will check with the person who build my engine to make sure I give you correct information.

Eamonn

^To delete oil injection I did the following: (outside bearings) bored hole from bottom of transfers to factory oil supply passage, removed the slingers & replace with equivalent shim thickness,new seals with assembly lube,plugged all four injection inlets wth Loctited set screws, removed tach/pump drive and plated off. Two inside bearings are fed from transmission, so no change there. I use an electronic tach,32/1 Maxima M premix.

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Jimroid wrote:^To delete oil injection I did the following: (outside bearings) bored hole from bottom of transfers to factory oil supply passage, removed the slingers & replace with equivalent shim thickness,new seals with assembly lube,plugged all four injection inlets wth Loctited set screws, removed tach/pump drive and plated off. Two inside bearings are fed from transmission, so no change there. I use an electronic tach,32/1 Maxima M premix.

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Thanks Jim. I'm guessing that the alignment of the hole you bore is pretty critical to make sure it joins up with the original passage from the pump line, did you just eyeball it or are there some fancy measurements?

I'll have to look at my pictures from when I did it.There was nothing real fancy,but it will come back to me when I look at the pictures.

Wolfgang, the oiling system on a Gt750 street bike is relatively sophisticated but not too hard to replace.

First are the oil slingers on the main bearings. The OEM system pumps a very small amount of oil to the main bearings and there it is slung outwards by centrifugal force into the outer ring of the oil slingers. From there it moves through the big end pins to be released into the big end bearing.

If the oil pump is removed, it is essential to remove the outer ring from those oil slingers. With the crank apart, grind off the outer ring and leave a "washer" to take up the end play. They should really not cover the ball race any more - just as wide as the inner race. That leaves a large space between the bearing and crank wheels that will allow oil mist into the bearing.

Oil mist from pre-mix can just be allowed to come into the crankcase and swirl around. Yamaha twins (RD and TZ) have a 6mm hole drilled into the floor of the transfer port to allow oil mist separate out and be forced down to the top of the main bearings just to one side of the bearing.

Twisted ports on a GT750 make that difficult to replicate but not impossible. As far as I know, TR750 motors kept the oil pump on low and TR main bearings are similar to a TR500 with bearing and seals in an outer sleeve, so they must have allowed that oil feed to get to the side of the main bearing in the same way as it does on a stock GT750 or TZ Yamaha. Jimroid is correct that if you were to drill a 4-6mm hole from the transfer port floor into the oil feed passage you will be OK. Aim to rill that hole to exit where the stock oil feed hole exits right beside the main bearings.

The position is not critical and as long as it exits by the main bearing, it is not critical where it is. The stock oil feed banjo holes should all be sealed.

Use a god oil such as a Silkolene (Fuchs) and mix it rich. 30:1 to 40:1 is a good place to start.

ChrisK wrote:

Jimroid wrote:^To delete oil injection I did the following: (outside bearings) bored hole from bottom of transfers to factory oil supply passage, removed the slingers & replace with equivalent shim thickness,new seals with assembly lube,plugged all four injection inlets wth Loctited set screws, removed tach/pump drive and plated off. Two inside bearings are fed from transmission, so no change there. I use an electronic tach,32/1 Maxima M premix.

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Thanks Jim. I'm guessing that the alignment of the hole you bore is pretty critical to make sure it joins up with the original passage from the pump line, did you just eyeball it or are there some fancy measurements?

I like this topic Thinking of removing the oil pump on my 500. I would much rather use premix then I know exactly what I'm getting.