Vortex ROK GP - changing Balance Shaft oil

Does anyone have a guide or video on how to change the oil in the Vortex ROK GP?

How frequently does the oil need to be changed?


It’s a 2 cycle engine, there is no oil in the engine. Only the oil that you mix with your fuel.

@Rapid1 That is incorrect. It does have gear oil to lubricate the balance shaft that should be changed regularly.

@Jgbedford, the drain plug will be on the side closest to the engine. Depending on how new your engine is, it’ll either have a clear sight glass in it or be just a regular solid aluminum plug. There’s also a 5mm bolt that’s lower on the engine that you can drain any extra oil out of if it all doesn’t come out of the main drain plug.

You can either fill it through the drain plug by tipping the motor on it’s side or through another plug that’s on the top of the case right next to the exhaust. I want to say it’s 100cc of 75w90 but I’m not 100% sure off the top of my head. I would change it at least after every race weekend. That way you can keep fresh oil in it and also keep track if you start seeing metal shavings.

Drain plug is red, fill plug is blue.


Sorry, thought he was talking about crankcase oil. It’s a question I often hear on 2 cycle engines.


Here is a link to our engine documents https://rokcupusa.com/rules/rok-cup-engines/, you will find the info you need under in the owners manual. As for how often, this is probably the least expansive maintenance item next to cleaning your engine, for me I would do it ever 2 track days, or every race weekend, for sure you can go longer but if nothing else you will make sure the fill levels are correct. Thanks for purchasing Vortex

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Thank you @CourterZT,

I see the plug, but can you identify the 5mm bolt you refer to?

Is it as simple as removing the plug, letting it drain, and refiilling through the fill plug after reinserting the drain plug? This can be done from a kart stand and does not require the motor to be removed from the chassis, right?

I appreciate the help!

Hi @Garett_Potter,

I appreciate the link to the manuals, thank you.

I see the type and amount of oil, I must be missing something - I don’t see where the manual specifically shows how to change the oil.


The bolt is almost directly below the drain plug, just slightly to the right.

Yep, it can be done on the kart it’s just a slight pain to get to. I normally remove the engine just to make it easier and give everything a thorough clean but it’s not necessary.

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Hi Everyone, sorry with Covid-19 I never got back to my kart until today - I wanted to get it all ready for the summer, hopefully I will be able to get out and use it soon.

I can’t find a drain plug on the side. I took some pictures while it was off of the chasis. I ended up holding the motor upside down for a few minutes, the oil that dripped out (and there wasn’t very much of it) was pretty discoloured.

Hopefully there is an easier way to change the oil if I’m going to start doing it more often.

The one directly in the center of your second picture is the one that should drain (at least it used to). It seems like they also got rid of the sight glass/plug which is odd. If you pull that bolt out you should be able to get some oil to come out still. Unfortunately ROK’s seem to consume gear oil so that’s why it’s so important to keep up on changing it.

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Hey @CourterZT, I did take the crank cover bolts off and one had a copper washer, the bottom middle one as you indicated (maybe this is the drain plug?). I haven’t run the motor all winter, and it was still a cool day in Canada, maybe I didn’t have enough patience to drain it out that way. I’ll have to try that bolt again after a few sessions on a warmer day when we are allowed to go back out and start karting… for now, I managed to get it all back to gether and rev it in the driveway to impress my neighbours ;).

As mentioned, the oil I did get out from turning it upside down was very discoloured (bad me… the sport is new to me and I didn’t realize it reuqired frequent changing). Maybe the drain plug on the bottom of the motor has some sediment collect over the winter preventing it from draining.

I appreciate the help - I got another 75 CC back in there, so I am ready to go when the tracks open back up.

Hey @Jgbedford, do you mind telling me what gear oil you used in your case? The best I could find in writing is in the ROK GP Manual they call for 40W90 oil… I can’t seem to find it anywhere and I’m questioning if its a typo…

Thanks for your help!

It’s impossible to find, I’ve looked everywhere. It drove me crazy! In the end I used motul trans-oil 10w-30 and never had any issues.

Thanks for your help! 10W30 it is.


Hi @Bakaboo -

I run Fuchs Silkolene gear oil SAE 90.

When I drained it last, it was really thick so I let it drip for a few hours.

I believe I bought this at Goodwood Kartways.

Never had any issues after 2 seasons so far.

Hope this helps!