KTM Owners Forum banner
  • Hey everyone! Enter your ride HERE to be a part of this month's Bike of the Month Challenge!

1 - 6 of 6 Posts

·
Registered
Joined
·
10 Posts
Discussion Starter #1
Had a problem with my oil pump idler gear recently. It’s plastic and was causing a whiring noise. It was so tight on its shaft that I had to prise it off with a heel bar. Fitted a new one and the noise has gone. My concern is the cause. So I have checked the oil pressure. Manual says 13 psi at 1600 rpm and 36 psi at 6k. Mine is 20 at idle and 75 at 6k and if you hit the limiter it’s over a 100psi. I have checked the relief valve and spring length and all seems good. My question is, is this normal or have I got a problem that has caused the failure of the idler gear. Do these plastic gears swell for any reason.
 

·
Registered
Joined
·
903 Posts
There has certainly been an issue with the plastic idler gears on the 250 and 350 motors. They have either chewed up the teeth or warped or both. A mate of mine had one go at about 24 hours and it needed everything from the crank up due to oil starvation.
The cure from KTM was a different plastic material that isn't prone to the same problem. I don't know if the same has happened on the 450s.
I an no expert but an oil pressure reading so much higher than standard suggests to me that there is a blockage somewhere in the lubrication circuit and parts of the engine are getting no oil. Bits of plastic debris may be blocking the oil ways and/or nozzles.
If the idler wheel was damaged then make sure that you account for all the missing material. Check the oil filter screen and all the oil ways.
 

·
Registered
Joined
·
10 Posts
Discussion Starter #3
Hi, thank you for your comments.

The gear was not damaged it was just very tight on its shaft. Getting oil to the top end jet. I also did the first piston change recently at 500 hours and was still in factory spec with no evidence of a blocked piston cooling jet. The bike runs fine, it’s just niggling as to the reason why the gear went so tight after being faultless for nearly 500 hours.
 

·
Registered
Joined
·
10 Posts
Discussion Starter #4 (Edited)
Got an update on the oil pressure issue for future reference.
A very good friend of mine gave me his 2016 450 exc for a test. He runs the same oil and got the following results. 20 psi at idle and a maximum of 70 psi on the limiter. I think this is acceptable for reference. With this in mind I tried a lower rate spring on mine and was getting 10 psi at idle but as soon as I started building up the rpm to about 3k the oil pressure just flicked from 30 psi and went off the scale/ over 100 psi. This was not what I was expecting considering I was getting 75 psi at 6k with a stronger spring on mine. After doing some research on the lubrication system I found that the bypass from the relief valve is ported to the suction side of the pump. In the picture you can see the ball/ valve in its seated position. In the next picture you can see the ball/ valve in a possible bypass position where it can partially block the port back to the suction side of the pump. To me this explains the reason for the excessive pressure build up as the ball/ valve is partially blocking the oil it’s trying to relieve. With this in mind I tried another experiment. The original spring ends are not perfectly square and positioned the spring so that when compressed it bent away from the relief port and so that the ball would deflected away too. After doing this I fired the bike up and hey presto oil pressure limited to 70psi on the limiter.
So back to the initial problem with gear. Has this spring moved over a period of time or has the ball worn/ formed a seat against the port to the pump and then caused an overload situation on the pump drive train and overheated the bearing path on the idler gear, it’s possible. I think I’m going to look at a different style of valve to replace the ball bearing 841BD0EF-2333-4640-A94F-D3A620CB9900.jpeg AD0DCB8D-4E80-4578-9917-4E485AA4AD3E.jpeg
 

·
Registered
Joined
·
10 Posts
Discussion Starter #5
Another update..... contacted KTM to let them know what I had found, got a response back today saying that, “ they were sorry to hear about my troubles and if I wished to take it to a dealer, I could pay for an inspection to be carried out”.

Ok so I don’t need to do that because I know what the problem is, I just wanted to let them know....

I’ve made a new valve and give it a go. It was better but required a bit more work. After a modification to the valve I’m really happy with the result. The first picture is mk1 second picture is mk2. Getting 20psi at idle and 50 psi on the limiter.



6B605CBE-EDDA-40BF-82BD-543306F971CC.jpeg D8DC733B-7B20-4153-8F36-EC14FC3854DC.jpeg 8C8E53CF-1B37-452D-B089-091F444879D0.jpeg
 
1 - 6 of 6 Posts
Top