Timing chain question

[TrentMember]

When doing my rebuild I noticed that my timing chain had some issues so I’m going to replace it. First question is do I need to dump the oil so that I can view the tdc notch or should I just find the master link unlink it and join the new chain then run it around by turning the cam with a wrench then join it once it gets back to the same spot.

I get the feeling its probably safer just to dump the oil into a clean container so that I can be sure that its at tdc with the cams in the corresponding position but I’m interested if it’s over kill.

Also just to note the symptoms, I noticed when I checked the valves that the marks on the cam gears were lining up a touch lower than they should and when I did the rebuild I cranked the motor by hand without the valve cover on and noticed that the chain was lifting on the exhaust cam gear every other stroke. It was far from jumping but with the tensioner operating normally obviously this wasn’t right. Waking up this morning I’m starting to question if I didn’t put the cam gear in correctly but I don’t think I could have gotten it wrong since it has a locking ring and the bridges torqued down spot on.

Cheers.

p.s I reckon I’ll just about have a brand new bike after this!

[Bruce CurtisMember]

What does the manual say to do Mr ABlue?

Different engines require different techniques, is it an endless chain (no joining link) standard double row, single row?.

personally I would just do as you’ve said and thread it through using the old one as aleader, but there maybe some hidden traps, like in some older 4Ts you had to wind it backwards slightly after installation to engage the tensioner correctly.

BC

[TrentMember]

I know the trick with the ktm tensioner and that’s seperate to the chain. I couldn’t find any detail in the manual because it only approaches assembly from scratch so the side covers and timing idler gear are all off.

I’ll have a chat with the guys at the shop I suppose – if it is an endless chain I guess that’ll mean a fair bit more work.
This is what it looks like though IIRC.

[PaulMember]

AB, the shop probably has a joining tool for cam chains so dont go an pull the whole thing apart just yet, you may not even have to take the head off to replace the chain.

[TrentMember]

Yeah I got distracted picking it up yesterday because it looked like they were closing up so I’ll probably just take the bike back down to them and pay for them to do it while I wait.

[GregMember]

Dont KTM timing cams have a master link, like a chain joiner link. I can remember bailing KTM rat out last year last minute around Christmas because he needed one for his bike

If that’s the case very easy to do a cam chain replacement I would have thought

TB

[drewMember]

hey AB, by the time you get it all sorted, you’ll be a late second or early third year apprentice :blush:

[TrentMember]

I’ve had some good teachers! I figure if I got the sack for spending too much time working on my bike I’d have a decent shot at getting a job turning wrenches

I didn’t buy my bike to learn how to work on it but I do admit I usually enjoy it. I only hope at some stage in the near future I can retire my mechanic skills and just ride knowing I have them should I need to call on them! To be fair on my bike though I have to point out that I did have a fair few posts about fixing my brother’s bike so mine has generally been ok.

Work I’ve done:
water pump seal (failed and what a nightmare getting it off!)
new piston and rings (maintenance)
bled brakes and new pads (maint + bike had empty m/c from prev owner)
valve checks (preventitive maintenance)
New sprockets and chain (stripped front and then changed others as maintenance)
Pivot pegs and KTM handlebar damping mounts.
New rear wheel bearings (needed help getting spacers out as I didn’t have a drift)

Work I’ve had done:
oil drain bolt (inherited from prev owner)
spark lead (failed)
new cylinder (inherited from prev owner)
new clutch m/c (I broke it )
new battery (strange one that too because it didn’t have the stock battery carrier in it so I just went with the smaller battery.
forks revalved and tuned

Now the cam chain and I need to do the fork seals but was advised here to have someone do that i think

[TrentMember]

Spoke with the ktm guys quickly then and it sounds like its an endless chain so it’ll mean pulling the clutch cover off and looping the chain from the timing shaft.

Quick look so far: drop coolant and oil. Remove inside clutch cover. Drop chain down from valve gallery and loop onto cam gears. slide chain onto timing valve twin wheel. Reassemble.

I have a feeling I need to replace the clutch cover gasket but they’ve told me that it’s not required so I’ll check that. Looking at it now it would’ve been a lot easier to remove the water pump seal by pushing it out from the inside!

[TrentMember]

Got the hard bits done last night – actually I should say the unknown bits because it wasn’t hard just a tad time consuming and that was partly because I don’t have a 21mm spanner so I have to remove 3 of the engine mounts and tilt the engine back to get a socket onto the cam chain tensioner. Here’s a run-down in case anyone needs it later.

Drained the fluids – pulled the water pump off – lifted the valve cover – locked it into tdc – mopped up all the extra oil that came out of that hole! – removed lower engine mounts and loosened top mount and tilted motor back to get socket onto the chain tensioner bolt and remove it – remove the upper cam bridge and cams – remove rear brake m/c and lever to make room for cover coming off- remove 12 off inside clutch cover bolts and take cover off – stare in awe and all the bits you’ve never seen before! – Gasket was cactus so I had to peel it all off and I gave the cover a bit of a clean up to make sure it was all gone – it was quickly suggested that I mightn’t need a new gasket but this was definitely not the case!

Meow I had to work out how the chain came off and I figured that maybe just the timing gear twin wheel would come out but since it was in a tight position and the chain was still on it couldn’t so I bit the bullet and slipped the timing chain idler shaft out nice and easy then removed the chain guide for more room and the twin wheel then just lifted out.

So that had it removed and it was all easy so far though it required a leap of faith – next step was to get the new one on. I wouldn’t say it was difficult but by yourself it is tricky to get the twin wheel back onto the slack chain. I used some pretty pink ribbon to suspend the chain from the frame and with a bit of fiddling I got the twin wheel on in the right position. There are marks on two teeth on the primary gear and the twin wheel has a mark on one tooth that has to sit in between them – I assume this is another check so you know you’re at TDC since the gears are symmetrical so I wouldn’t expect putting it in a different slot would affect its operation. With the twin wheel in place you lift a stop disk and slide the shaft back into position and ensure the woodruff key is lined up so it goes in easy.

That’s where I’m up to now.

Now I just replace the rear chain guide and loctite that back into place reinstall the cams / bridges and loop the chain on the gears as you install them and make certain that the marks are at 9 and 3 o’clock being valves closed. With that done install the new clutch gasket and replace the cover then reinstall the water pump. Now install the chain tensioner and release the lock. If you don’t know how to do this be sure to ask because it is crucial and the process must be followed correctly! I think I’ll probably turn the motor by hand and make certain that the chain is seated then replace the valve cover and fluids before starting her up and smiling. This should only take about an hour tonight including taking the time to torque all bolts to the specs and loctiting where necessary.

There was more in it than I would’ve expected but it was good garage time I reckon.

[GregMember]

AB what year model is the KTM250 and how much work has it done? Nice work by the way you have done a hell of a job mate

TB

[TrentMember]

2007 model built in aug 06 with about 4300kms – I bought it with 2600 and it was a mess then but I didn’t know any better. I know they have a bit of a rep but I blame my problems with it on the previous owner not the bike.

Thanks for the help everyone and I have to give a rap to KTM newcastle too I ask them almost as many questions as I do you blokes and they’re always willing to give advice even though it does them out of work.

Either mine or my brother’s bike will probably be up for sale soon – I’ve decided I’m keeping mine for a little longer but he’s not riding his so we’ll pick one and sell it. Either bike should be a good buy since mine’s almost new now and his has always been strong as an ox. For a 250 4t that is

[TrentMember]

Sheeez! all back together fine but now its not cold starting well! I’ll check the valves again tomorrow when I get back from wollongong but they should be fine. I can’t understand it because it cold started fine before I changed the chain

[Anonymous]

that sucks. i’d say sell it and buy a 2t. but with all the money and time you put into that bike, you may want to keep it to get it all back.

[Anonymous]

Good write-up AB, you’re becoming quite the mechanic

Keep the write-ups coming they are a good technical resoutce for anyone else that has the same issue.

I hope you get the cold starting problem sorted.

[Author]

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