DR250 piston hitting spark plug
Posted November 24, 2008 - 06:44 AM
Posted November 24, 2008 - 11:55 AM
Posted November 24, 2008 - 02:30 PM
1) please make sure its the right plug
2) NO PLUG GAP IS 0.035mm?!!??!?! 0.8 is more realistic
3) buy a new plug, unless the plug has visible SMASH marks on it, id say the electrode is weak
4) if you have the correct plug and the head hasnt been skimmed, there is no way it is physically possible for the piston to hit the plug, i would say the electrode is weak, and the spark plug washers are lowering the compression ratio to a level which is weak enough to create a weak enough combustion to not bend your weak plug.
5) sorry to be so harsh but you really shouldnt be working on a bike if you believe a plug gap should be 0.035mm. thats miniscule.
Posted November 24, 2008 - 02:44 PM
Posted November 25, 2008 - 05:19 AM
Posted November 25, 2008 - 05:34 AM
Posted November 25, 2008 - 06:04 AM
when gapped right the tip is almost 90 degrees from the top of the plug. after i run the plug its bent down to about 45 deg.
I am confused, the way that sentence reads in my head, makes it sound like the arm of the plug is sticking straight up? Obviously this is not correct as .035" is closer to the width of thicker construction paper. Could you take a picture perhaps of the plug before/after running?
If you are indeed gapping this plug correctly, I would say that the head needs to be pulled. There is just no other way around it, and sadly may be the easiest solution. Let us know what you find.
*EDIT - Sorry I didn't not drink my morning coffee fast enough. I understand what you mean now by 90 degree's
Posted November 25, 2008 - 07:02 AM
Whats the history with this thing?
Posted November 25, 2008 - 07:47 AM
I don't know anything about the DR250 but if you are lazy (no insult intended ) and just want to keep it as is you should be able to find a plug having a shorter reach and simliar heat rating. Or use another crush washer or two.
wondering why you started fooling with the tune anyway, was it pinging? Maybe it has a high compression piston. Have you done a compression test?
Posted November 25, 2008 - 08:18 AM
Try to get a good quality photo of the plug before & after & down the plug hole with piston at TDC or (ideally) with the head off.
The suggestion of a compression test is about the best non-invasive way to find out if it's a modded motor & I'd do that & compare with standard figures before going any further.
P.S. I hope I don't need to tell you this but nevertheless I will just in case-: When you get the problem sorted fit a new plug regardless of whether the one you have is right as the action of bending/re-bending/bending yet again will have fatigued the electrode & the last thing you want is that breaking off & jamming down the side of the piston.
Posted November 25, 2008 - 05:01 PM
If it is carbon, swing by the drugstore and pick up some 90% (not 70% or 75%!) rubbing alcohol and some long cotton swabs. The alcohol will melt the deposits away with almost no effort. You can pour some into the plug hole and leave it in there for a while too.
Posted November 25, 2008 - 10:00 PM
Until he tells us the plug number that he's using, I remain skeptical...
Posted November 26, 2008 - 05:45 AM
Posted November 26, 2008 - 06:09 AM
Posted November 26, 2008 - 08:21 AM
BUT! I've been wrong before.
Posted November 26, 2008 - 10:20 AM
If it's not carbon and the engine isn't making any bad noise when running, then I'm with Thumpzuki.. it's had to have had machine work done..
I just thought of something else... if someone stripped the plug hole in the head and fixed it with an insert... maybe the insert has screwed down into the head too far? That should have been obvious when you looked, but if you're not looking for it....
Posted November 27, 2008 - 06:55 AM
Good suggestion - check for a plug thread repair.
Seems like the interference is about .015". That's less than one crush washer.
0.015" interference isn't much when it comes to the electrode - the piston is moving pretty slow close to TDC and the contact just pushes the electrode away.
I still have the feeling the topend might have been altered somewhere along the way. Valves are the concern - it is bad for the piston to interfer with those. In the end it would be good to see it there is evidence of that. If there is then the valve stems are likely bent and the seating and guides are on their way out. A compression check would be very interesting.
Take it to the Dealer??? I don't know - so some half trained mechanic with a hangover adds a crush washer and charges two hours labor? I'd do the work myself, know for sure what's going on, and save the money.