A forum for owners of Yamaha TTR250 trail and enduro bikes!

Shanemhi · Member

93 ttr250 not starting....help please

JOHNYBOY · Super Guru

when you say it spins faster was there any nasty noises from it when it stops or when you are trying to start it now sounds like cam chain broke or possible jumped a tooth or two but you would have heard a noise

hanzo · Senior Member

Hi Shane are you sure that the starter motor is meshing properly with starter gears ie that your not missing teeth from splines .Hopefully you haven't ignored a failing sprag clutch and all the starter gear components are in order .next stop after that is to check cams are lined up correctly and valve clearance are in spec.does the bike have a kicker ???

katana · Senior Member

If you haven't yet drained this bit, it will send oily foam into your airbox home.spin.net.au/pcpgoodies/photos/dirt_bike/Airbox1.jpg

hanzo · Senior Member

Check the stickies section for Brian's guide to cylinder head removal for pics of cam positions and tdc guide you've got fuel and spark so could be a timing issue so long as the starter side is all good .Think if it was compression you would have noticed before now .I wondering if you have stripped the spline on starter due to a failing sprag clutch

Shanemhi · Member

I didn't notice any nasty noises,I will check the threads you've posted ,I'm pretty new to this so have no idea what a sprag clutch fail is or what the signs are.many that for our replies much appreciated

hanzo · Senior Member

It's difficult to say Shane without going through the simple things first you could take the starter cover off and see if there's any signs of anything untoward like metal swarf in there a five minute job.drop the plug out stick your thumb over the hole crank the bike see if it blows your thumb off not very scientific but give you indication how much compression there .A failing sprag will have given you quite a loud bang when you kill the engine as it kicks back against the starter gears it's a common fault on the ttr

hanzo · Senior Member

Don't worry too much about the mayo in airbox as katana post it probably just wants draining just moisture and oil mist and pretty common

Shanemhi · Member

Ok ,many thanks for your replies I will have a look in the morning
Much appreciated

TTRfan · Super Guru

Welcome to the forum Shane!

As Hanzo suggests, it is a quick job to whip the starter gear cover off to check the starter pinion and starter gear are (hopefully!) in good shape.

See here - the first picture in the pictorial guide is of the starter gear cover.

You don't need to drain the oil for this but make sure you use a good fitting Allen socket if you still have the original small-headed screws fitted as they can be a tad reluctant to undo

Worth changing them over to these at some stage if you are keeping the TTR wink

If you are taking the plug out to do a "thumb test" of the compression then make sure there is no dirt or grit lurking around the plughole to drop in to the combustion chamber.

The chap you bought the TTR from said he had replaced the piston and rings so, if the compression is found to be low then firstly check the valve timing and clearances are OK and that the cams haven't jumped the chain and maybe bent the valves. If that is all in order then it sounds like the head will have to come off to check the valves, clean and lap them back in - preferably with new valve stem oil seals.

Brian

Shanemhi · Member

Thanks,
Ok, so I've removed starter motor cover and everything looks fine, the thumb test I couldn't feel any compression ,tried bumping it in second and the engine rotation feels normal and even had a couple of pops!!

I spoke to PO and he said he changed piston and rings and installed a good second hand crank 700 miles ago ,the he dropped it in a puddle and drowned it !!when he got back it was smoking so he pulled it apart again and piston had warn a little on the outside but the ring grooves were fine so changed rings and did timing chain at same time,the crank was still ok ,apparently the gearbox looked fine inside and he re shimmed the cams,also the sprag clutch he thinks was changed 3500 miles ago,but he did notice the starter brushes were worn(but I guess if motors spinning fine then that's ok for now ??)

Shane

TTRfan · Super Guru

If there is no compression then, unfortunately, it sounds as though you are going to have to take the head off to see what's happening. However, just in case, check the valve clearances when you have the cam cover off as that may give you a clue.

hanzo · Senior Member

Think you're going to have to get head off Shane as Brian suggests something on the timing side sounds amiss have you checked all connections to carb make sure you've got no splits in carburettor boot where it joins the cylinder head make sure you've got a good airtight seal

Shanemhi · Member

exhaust:less than 0.05+0.38
Inlet:0.15+0.24

So I'm guessing I need to re shim them ?
Would this explain no compression ?
I've posted a some pics just in case I've missed something obvious !!
Again many thanks for any help

mossproof · Super Guru

Bite the bullet - pull the head off

If there is some clearance on the valves, then ASSUMING THEY ARE SEATING PROPERLY I don't think this would cause enough loss of compression.
With the head off you can:
1: Check the valves are seating properly by putting the head on the bench upside down and put some diesel or kero into the combustion dish (make sure the spark plug is in!) If a valve is stuck open or not seating/burnt out etc you will see fluid coming out of one of the ports (inlet or exhaust)
2: Inspect the piston for holes (!)
3: Inspect the bore for glazing or scratches/damage
4: Inspect the rings for damage
5: Inspect the head gasket for damage.
Good luck,
Simon.