KTM 250sxf tensioner

Related:
Create New Tag

3/13/2018 4:21 PM

I pulled apart a 2016 KTM 250SX-F with 73.1 hours. Replaced piston and cam chain.
Tensioner does not seem to hold chain tight enough to keep it from jumping on the intake cam gear when I test spin the motor. Could the tensioner just be wore out and will not work upon re assembly? Did I fail to set something right? Should we look at an aftermarket manual tensioner?

|

3/13/2018 7:30 PM

I would be looking at the chain guides as being worn. Also look at the crank chain gear for wear.
I would stay away from the manual tensioner.

Paw Paw

|

3/13/2018 8:36 PM

Did you put the tensioner in the ready position before re- installing, and then release the tensioner?

|

3/15/2018 3:32 PM

I've heard of some people having issues with the oem tensioner, I put a dirt tricks tensioner in mine and I'm at 81hrs all working great. But I would check the chain guide as well to make sure it's not worn out

|

3/15/2018 4:04 PM

Okay on the guides, I replaced the one that the tensioner presses on. I put a new chain on, always do that when I put a top end in just kind of habit .Yes I preset the tensioner using the dime and nickel method to get it down to that first click. I put it in the engine and presses in on it to set it. However, when I go to turn the engine to check for everything to spin right, the chain will jump on the intake cam gear. It's like it does not press on the chain enough.

|

3/15/2018 4:39 PM

Have you inspected the cam and crank gears? If worn the cam chain will run up them and cause what you are talking about.

Paw Paw

|

3/15/2018 5:29 PM

I would take the tensioner back out and reset it. What you describe sounds like what the service manual describes when its not set properly before installation.

Speaking about setting the tensioner, service manual says, This function is necessary to ensure sufficient timing chain tension even at low oil pressures. So if not set properly it sounds like it could jump.

Tensioners have been known to go bad, but it was much more prevalent on earlier generations. You hardly ever hear about it now on sites like KTM Talk where it used to come up from time to time previously. Especially considering how many more KTM/Husky 250/350s are out there now.

|

3/15/2018 7:43 PM

Paw Paw 271 wrote:

Have you inspected the cam and crank gears? If worn the cam chain will run up them and cause what you are talking about.

Paw ...more

It is a new chain. Read my post.

|

3/15/2018 7:47 PM
Edited Date/Time: 3/15/2018 7:47 PM

MX915 wrote:

I would take the tensioner back out and reset it. What you describe sounds like what the service manual describes when its not ...more

To trip the tensioner I just press in on the access hole, correct. I tried 8-10 times. I even left it all the way out and pressed it in. It will collapse to about half and chain is not tight. I guess I will just order a new OE part. Maybe it was wore, and it just failed when I reset it.

|

3/15/2018 8:29 PM

I highly recommend a dirt tricks tensioner

|

3/15/2018 8:33 PM
Edited Date/Time: 3/15/2018 8:33 PM

ktm-5 wrote:

I highly recommend a dirt tricks tensioner

Ok, I'll check into one of those. Thanks.

|

3/15/2018 9:52 PM
Edited Date/Time: 3/15/2018 9:58 PM

I made the tool you need to do the job you need to do

Setting the adjuster is a pain.
You must use something to just catch the small lip while you push down, it should click all the way closed.

Now the hard part. I figured out how to make the tool to release the adjuster while it's inside the cylinder.

Both the outside and inside need to be pushed at the same time to release the stupid thing.

I can post a picture of the tool tomorrow.

Basically the tool is just two push pins, but the inside pin sticks out about 2mm.

Imagine you pushed a Popsicle out about 2mm, make a small tool that fits in the hole, with a inner pin and give it a quick hard push. I hated learning about how that thing worked.

below video shows how to set it correctly, I used a washer that barley fit, just touching the small chrome lip while pushing down.

|

3/16/2018 6:27 PM

Paw Paw 271 wrote:

Have you inspected the cam and crank gears? If worn the cam chain will run up them and cause what you are talking about.

Paw ...more

Truckdriver wrote:

It is a new chain. Read my post.

I read your post, but no where have you stated you have inspected the cam and crank gears. If the gears are worn, even a new cam chain will jump as the chain spacing and the gear tooth spacing will not be the same. It is just like have a new drive chain being run on old sprockets.

Good luck to you, but I am done with you after telling me to "read your post".

Paw Paw

|

3/16/2018 6:33 PM

You don't need any special tools to release it, just stick a screwdriver down in front of the chain push the chain against the guide and the tensioner will release.

|

3/17/2018 8:50 AM

MX915 wrote:

I would take the tensioner back out and reset it. What you describe sounds like what the service manual describes when its not ...more

Truckdriver wrote:

To trip the tensioner I just press in on the access hole, correct. I tried 8-10 times. I even left it all the way out and ...more

Paw Paw is one of the smartest guys on here and is trying to help you. I would listen to what he is saying as I have seen him properly diagnose a lot of bikes correct just by asking simple questions.

|

3/17/2018 9:14 AM

You're doing it correct. But you need to crank engine with spark plug out to build oil pressure.

|

3/17/2018 9:14 AM

Paw Paw 271 wrote:

Have you inspected the cam and crank gears? If worn the cam chain will run up them and cause what you are talking about.

Paw ...more

Truckdriver wrote:

It is a new chain. Read my post.

Paw Paw 271 wrote:

I read your post, but no where have you stated you have inspected the cam and crank gears. If the gears are worn, even a new ...more

Sorry. I have no new cams to compare to. I can't believe the gears would wear out that fast. The gear on the balance shaft looked fine. I always looks for damage. I ordered a new tensioner.

|

3/17/2018 9:19 AM

williamsmotowerx wrote:

You're doing it correct. But you need to crank engine with spark plug out to build oil pressure.

Is there a way to build pressure before I try to turn motor over. It's still on the bench. I am I unable to even try to turn the engine over with a socket on the crank. I can get the motor to turn until the intake cam starts to touch the rocker arm. As soon as there is some pressure against the camshaft the chain will try to jump over the gear. So I guess I need to figure a way to put more pressure on the Chain initially? I tried to soak the adjuster and some extra oil and compress it in and out while doing that. I still can't get it to hold the chain tight enough to even begin to try to turn the motor over. So I cannot see how it would function even if I tried to put the motor in the bike and kick it over with the starter a bunch of times to try to build oil pressure. It won't even hold the chain tight enough for one motor Revolution let alone multiple. Really has me baffled.

|

3/17/2018 9:33 AM

Did you take the cam bridge off also? If so does the cam rotate freely when bridge is torqued down? I know when I did my first top end and reinstalled it the cam's would not spin freely

|

3/17/2018 12:58 PM

You can jumper wire starter directly on bench. Suggestion above is also very valid, assembled, cam chain tensioner out, rock cams back and forth. If they're tight, cam caps need to be sanded. No explanation for why they get tight other than heat, cold cycle changes dimensions. I've only seen KTM 250's do this.
You can take allen plug out, use oil squiter can on check valve to pressurize

|

3/17/2018 1:54 PM

ktm-5 wrote:

Did you take the cam bridge off also? If so does the cam rotate freely when bridge is torqued down? I know when I did my first ...more

Yes, had bridge out to remove cams, to remove chain to do the top end. Like I mentioned before, I always do a fresh cam chain, slider, valve seals when I do a topend. Your right there, might as well solve any issues while you got it apart. But I will pull chain off and see how the cams spin. They seem to move fine.

|

3/17/2018 2:00 PM

williamsmotowerx wrote:

You can jumper wire starter directly on bench. Suggestion above is also very valid, assembled, cam chain tensioner out, rock ...more

I wondered how to pre pressure the system. Great will tackle that early tomorrow. Got stuck driving today. Thanks. I think I will just pull the whole thing back apart and try all the suggestions as I assemble it again. I could have missed something first time. I will post photos of all the parts I case someone could spot an issue too. Really wishing I would have passed on this. Give me my Japanese bikes!!

|

3/17/2018 4:42 PM

To me it sounds like you are not re-setting the cam chain tensioner properly. It's quite a pain but very easy to do once you figure it out. You must place something like a coin or around that thickness on the edge of the tensioner, and then press down and it will lock into a certain position. If you don't use the coin, the tensioner will compress too far, and when you go to install it and pop it back out, it will not be in the right position. If you could get a copy of the service manual it explains it perfectly. I work for Husky, when I did my 2016 FC250 top end I played with this. Lots of guys just install the dirt tricks tensioner because they're afraid to install it incorrectly.

|

3/17/2018 6:01 PM

Either you didn't reset the tensioner correctly or you didn't release it correctly. Both of those will create the issue you are having..

|