Finding TDC and Camshaft timing marks (WR250)

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neeklondon
125cc L Plates
Posts: 13
Joined: Sun Feb 02, 2014 11:13 am

Finding TDC and Camshaft timing marks (WR250)

Postby neeklondon » Mon Jan 15, 2018 6:58 pm

Hi,

I've not been out on the lanes for about a year, so my WR 250F (07) has been sat idle in the garage for a long time.

Of course it doesn't start now, so I'm giving it some love. Prior to this, it would start well from magic electric button and kick when warm - starting cold was always a bit of a pain - now it just doesn't want to start period. I suspect this is probably due to sparkplug / fuel / carb issues, so I'll remove and clean the carb.

Anyway...I've never had the topend off before, so thought I would work on my mechanic skills and give it a go. My plan before hitting the lanes again is to probably replace the piston rings (and maybe piston) as it's was burning a small bit of oil previously.

I got the top off and noted that the intake valves are out of spec - not a problem as I can sort that, but I guess this is strongly related to it having issues starting when cold ;)

What I did note was a couple of problems (perhaps related):

1 - When the timing mark on the motor is aligned (at TDC), the intake valve dot is not exactly parallel to the head-gasket - it's about half a tooth out (the dot appears higher).

Is this something to worry about? I thought if the cam timing was off I would have had horrendous issues prior to this (starting / running / things going bang?).

I'm not sure whether I would need to re-time this (i.e look at moving the cam 1 tooth around). It was certainly on the compression stroke as I used the straw-in-the-sparkplug-hole-trick.

2 - Something that concerns me more (but might be normal) is that again, when at TDC via the timing-mark (I use the "I" notch, not the "H"), if I pop a straw in the sparkplug hole, I notice that it doesn't seem to be the 'true' TDC. i.e. I can turn the motor a small amount more and then the straw tops out - the problem with this is that I go past the timing-mark notch by about 10mm (hopefully that makes sense).

Could both of these issues be related to a worn cam-chain? As part of this project, that was going to be my next step - to remove it and check for kinks / stretch.

Thanks to anyone who can offer some widsom :)
Last edited by neeklondon on Mon Jan 15, 2018 7:00 pm, edited 1 time in total.

smokinrider
250cc Trail Rider
Posts: 80
Joined: Sat May 07, 2016 7:46 pm

Re: Finding TDC and Camshaft timing marks (WR250)

Postby smokinrider » Mon Jan 15, 2018 11:13 pm

using your straw method find true tdc by rocking piston up and down till youre happy youre on the money.
then check your timing marks again. If not on them, you could try a tooth either way. (only wind over by hand to avoid any damage if valves open on to the piston. and stop and investigate if anything feels like its come to a dead stop on something. don't just force it past) you also want ideally to come up to tdc rotating the crank the usual firing rotation so the cam chain slack is taken up by the tensioner.

if you still cant get it on the money then id say new cam chain, adjuster and cam chain guides.

ps make sure you are looking at the right marks on the cams and that the piston is on the right stroke. usually tdc on the compression stroke, Both valves on the rock. remember 1 full rotation of the crank is half a cam rotation, so timing marks that are supposed to be on the inside edges between 2 cams would be on the outside edge of the 2 cams 1 rotation later. this used to confuse me on my 310. as they always almost lined up. 1 turn later and they are in the right place.
Last edited by smokinrider on Mon Jan 15, 2018 11:16 pm, edited 1 time in total.

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neeklondon
125cc L Plates
Posts: 13
Joined: Sun Feb 02, 2014 11:13 am

Re: Finding TDC and Camshaft timing marks (WR250)

Postby neeklondon » Tue Jan 16, 2018 8:17 am

Ok thanks for the reply - I'll recheck it on the weekend (can't wait for lighter evenings!).

Something else that I've considered is that it may be 1 tooth off...seems like some people like to fiddle with the timing and mod it to the YZ spec...I like everything stock..but this bike has unknown history (to me) :)

Billy
woz bus pass
Posts: 1631
Joined: Tue Dec 04, 2012 7:49 pm

Re: Finding TDC and Camshaft timing marks (WR250)

Postby Billy » Tue Jan 16, 2018 11:08 pm

Why not let sausage fingers have a look at it and save yourself a whole lot of grief (Luke B).


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