GS250T fades, stalls then won't turn over

[rwms71]

Hi All

Not sure where to list that as it could be in several categories.

i was given the above as a non runner, having been stood for 15+ years, so I did a full strip down and rebuild of everything including carbs, engine etc. I have done lots of checking of the electrics due to various issues getting the bike to star at all, as the were ground probs, starter button probs, timing probs, valve clearance probs, all of which were rectified one by one.... So I have had the bike running twice and the same thing happened, as follows;

it started fine and runs for about 5 minutes, then the revs fade and it dies and when I hit the starter button it acts as if the battery is flat, it turns over slower and for shorter periods of time until I just get the solenoid click. I checked the battery and it reads 13V. I left it over night and it fired up again as normal but the same thing happened. I thought the starter was bad, but as it fired up fine after the first incident it feels like the engine seized so the starter can't spin. I wondered if oil is not circulating round the engine too.. I am going to try again in the morning and if it is still stuck will try putting a wrench on the crank to see if it can be freed..

Any thoughts on the cause as need fresh eyes as I am convinced everything should be perfect having checked and rechecked every bit of this bike..

thanks

richard

 

[Guest]

It's been a day and no replies to your post.

I'm only guessing, but your thoughts about oil circulation seem like a good place to start, if only from the point that damage could occur. That said,if the thing got to the point of almost seizing then there will probably be internal damage to repair. It's a plain bearing engine and they don't like to go five minutes without oil.

Presumably, the red oil pressure light went out when it started. That means the pump is pumping, but it doesn't mean that oil is getting to the engine; only that it's leaving the pump. I haven't done this to a GSX motor, but I think that if you loosen one of the chrome bolts that are rocker pivots, oil will dribble when it's running. Hopefully someone who has done this or who has a better way to check will chime in.

You could also remove the valve cover and start it up and see that way. Messy, perhaps. If you aren't getting flow than the next move would be to remove the oil pan and see whether the pickup screen is plugged- usually from silicone gasket goo from some repair.

It only takes one bearing somewhere to stop an engine turning and there's no real way to find out which one without taking it apart. It would also be wise to take the ignition cover off and use a 17mm wrench on the crank to see whether it turns easily when cold and then gets tight after running a bit.

You did remember to fill it with oil?? of course you did, silly me.

Anyway, good luck with it and keep us posted. And what all did you do to the engine since you got it?

 

[tkent02]

i was given the above as a non runner, having been stood for 15+ years, so I did a full strip down and rebuild of everything including carbs, engine etc.

Strip down and rebuild of engine? You had the whole engine apart?

 

[Guest]

I think I,d use a car battery to jump start it while your getting it sorted because even a new bike battery wont last long , also rig up a temp fuel tank, fuel taps & vacuum pipes & diaphragms can cause problems

 

[Gorminrider]

Reading that original post, it sounds like it's running out of gas. and then, also the battery is being worn down by repeated starts-might be on its way out.

You could just remove the plugs and crank the engine. If it seizes or slows- well, back to oil maybe...maybe test further by squirting oil into the plug holes. A car battery can help if you have one lying about and will take a funky mc battery out of the mix.
BUT:
Restriction in fuel tap or carburetor float/ inlet valving..these issues are more common than oil circulation issues....Maybe gas tap is failing..... turn your tap to Prime and see if that helps...and/or remove fuel line and check fuel flow by sucking on the vacuum outlet...then to save removing carbs test the carb inlet valving by removing bowl drain screws and ensure fuel flows steadily into a container MORE than the bowls capacity- a judgement call but it might tell you the inlets and floats are at least free flowing...ie: not just a drip.....drip.....drip that is refilling the bowls overnight...
I am Making the usual assumptions that your carb maintenance checked for shop-manual specs per float level but maybe did not involve an actual bench test of turning the carb upside down and blowing through the inlet to test needles etc...

 

[rwms71]

Ok, to try answer some questions.

I stripped the bike to its nuts and bolts, sanded to metal all painted bits and repainted it all. The engine was too, so all bearings and seals replaced, new gaskets, anything worn was replaced, new Pistons, rings etc, honed. New cam chain guides, all peripherals overhauled; tensioner, carbs, starter motor, new brake piston and seals, pads, new chain and sprockets ,new wiring loom, replaced some switch gear, new air and oil filters. New battery, and solenoid and cables . Petcock cleaned and new rubbers, tank treated with POR-15 kit as had some pin holes by the badge, even stripped the petrol cap and cleaned...

oil light goes off once it started. The starter motor spins fine when bench tested using the new battery and I keep it charged, so is reading 12.9 to 13.4 V

the crank will turn when I put a wrench on it but it is a bit stiff.. Not sure how easy it should be to turn..

I checked the float heights on the bench when stripped with a micrometer and the carbs have been checked twice...

I tried the tap on prime too and seem to get good flow.

 

[Guest]

I,d forget anything to do with oil or seizing, these engines are pretty tough & bulletproof, theres alot of compression there so they are quite hard to turn over, that's why I say use a car battery at 1st till you get it sorted.have you done the cam timing yet? I got mine 1 tooth out at 1st & it was a bastard to start & ran bad, its easy to get wrong so double check,the problem arises when aligning the pin along the line of the cylinder head, as you clamp the cams down. Mine was in the wrong position, not the nr of teeth.

 

[rwms71]

Yes, cam timing was done and done again as I did a partial strip down to recheck valve clearances as first time I was lining up the mark on the atu to the wrong mark on the casing so re-did it. The bike ran quite well for the 5-10 minutes it ran for. The second time it broke down I was half a mile from home, so that was a fun push home.. (first time it died at the house while I was trying to set the idle revs)

 

[Guest]

The available crankshaft bearings come in four different colour coded sizes with a range of about .0012; i.e. .0003 increments. Considering that the specified clearance is between about .001 and .002, if you got the wrong bearings it could be,well, interesting. Did you Plastigage everything before you final assembled it? The same applies to the counterbalance shaft.

 

[rwms71]

I did not have a plastigage but worked out the bearings to get from the codes/numbers stamped on the casing and shafts.

 

[Guest]

It has to be fuel related ! If it ran reasonably well for 5/10 mins. Have you tried easy start squirted in air box, if it starts every time with that, then I,m sure its fuel. Take your tank off & attach a funnel direct into the carbs, use fresh fuel & check again. Did you change o rings on mixture screws , what are the carb to air box boots like ?

 

[rwms71]

The symptoms of it fading and stalling do sound like fuel starvation, but the starter should still spin when trying to start it. The starter turns feebly for a few tries before I just get the solenoid click. Off the bike it spins fine and the battery powers it ok, so it is like there is too much resistance from the starter clutch/engine/gears???

 

[tkent02]

Just curious what you set your ring end gaps to and how you did it?

 

[rwms71]

Do you mean degrees round the piston? I set them as per the Haynes manual. I used some old feeler gauges to ease them on, slid them round into position then fed them in to the cylinder.

 

[tkent02]

No, I mean how large is the gap? If there's no gap the engine won't turn, I did this once a long time ago. Locked up solid.

I'm thinking that possibly there is a tiny gap, so it turns when it's cold. When the piston and rings warm up they expand until there is no gap, and the engine stop turning.

Usually you have to file the ends of the rings to get the gaps correct.

 

[rwms71]

I see what you mean now. I can't remember if I checked this or not. I just checked the manual and the end gap (fitted) are
top........ 0.10 to 0.25 mm service limit 0.70 mm
second... 0.10 to 0.30 mm service limit 0.70 mm

0.10 mm is really small, that enough? I am fairly sure the rings did not touch when on the piston.. So should not when in the cylinder?

 

[Guest]

If you hold the end of the crank it should push/pull in and out a bit- say about ten thou - quite easily. If it won't do the same when it's hot, then the crank is tightening up. It will have less endplay when hot because the cases expand outwards against the thrust bearings, but there should be some play always. It's a long shot, but a free and easy test.