DR250 piston hitting spark plug

[texas-dr]

it is obvious that if the correct spark-plug with the proper gap

is being installed and the piston is hitting the spark-plug enough that the

electrode gap is being closed- there is an issue with the engine.

the head is going to have to come off to see if either the head or cylinder

has been milled,,,, or if a wrong piston has been installed.

more than likely someone didnt understand the close tolerances and probably milled the head.

if the spark-plug is properly gapped and the piston hits it enough to close the gap,,,,,, COME-ON guys, thats a serious problem.

yea you can put a couple of extra washers under the spark-plug LOL LOL

what are you going to do to protect the valves ?????

just hope its not revved enough to float a valve - that will get his attention.

if the bike is worth keeping i would rather see him cash-up for a used-head instead of blowing the thing up, which will happen if a valve bends due to hitting the piston.

[Older and Slower]

Head gasket thickness, or missing? A missing head gasket should be obvious, but i used to run my RD350 with out head gaskets (o-ringed heads) to increase compression. Did the same thing with an H2 750. If he has a set of calipers with a depth gauge, he could compare plug seat height from piston crown at TDC against another bike? Just a couple of suggestions.

Cheers.

[Bob Onit]

These are all great suggestions but are still all guesses at this point

I had asked Max things about the history of the bike in an earlier post such as , did this just start happening? Is the bike new to you? whats the history with this thing? But didn't get any answers yet.

If he had just bought the bike it may very well have had the head milled and maybe it does takes a shorter plug, if he has owned it for a while and this just started then theres a problem.

It's tough to diagnose something without knowing if any alterations have been made or how long the problem has been going on for.

[KnotHead]

If anyone has his phone number, call him and tell him to put down the turkey leg and get cracking on that bike! There's a bunch of people waiting for him to figure it out and post up with his findings!

[BSR-1]

If anyone has his phone number, call him and tell him to put down the turkey leg and get cracking on that bike! There's a bunch of people waiting for him to figure it out and post up with his findings!

the first thing I checked was to see where he was at but he's too far away for me to help.

[Thumpzuki]

Well this threads going nowhere if we don't get answers to even the basic questions. For all we know it could have been doing this for years with a previous owner who never checked the gap & could be anything from the list of suggestions so far. Heck it could even be worn main or big end bearings, nothing was mentioned to suggest the bottom of the motor's not knocking it's ass off...

Hope it's something simple like a missing/incorrect head or base gasket though, let's have some more details please...

[maxbowersox]

Ok sorry about the delay, Yes the bike is new to me, I thought I had answered that one. But wow! there are so many possibilities of what it could be. I have had so much advice which I appreciate. I do also have a spare engine for this bike but the condition of it is unknown, so comparisons between the two are useless(almost). BUT, I use to work at a bike shop and a friend of mine is the main mechanic there. So I currently have the bike at his house. I like to work on my stuff myself, but I am not above getting help when I need it, as long a as I trust the person, which I do. Hopefully I will get an answer today or tomorrow. He is also going to help with the jetting, I suspect he will have to get the plug issue solved first. Sorry to keep you waiting. Here is a list so far of what people have told me( I think) : shaved head, no gaskets, wrong plug, rethreaded spark plug hole in the head, Carbon on the piston, wrong piston, bad rod bearings, piston installed backwards, weak spark plug, and probably more. Well see what it is! Hopefully soon, I had to just stand around and watch my son ride this weekend.

[texas-dr]

may we have a drum roll please

as the drama builds......

God hurry, renee is a monster with anticipation !!!!!!!

[bikepilot1]

Just to add to the list, if someone got crazy and put a 350cc crank in to stroke it they may have milled the head to provide clearance and it may now require a short plug. I know on my wife's stroker KX a short plug is required and when I installed the plug the bike is supposed to take the piston closed the gap (got the bike used, just thought someone had the wrong plug in it, no idea it was stroked). I measured the stroke and sure enough it was longer than stock. Called up the only shop that really strokes these things and they explained the thing about milling the head for clearance for the stroker kit and the subsequent need for a short plug.

good luck

[ProCycle]

I just had my DR350 apart to install a 440 big bore kit. The 350 is the same basic motor as the DR250. I measured about 7/8" between the end of the plug and the piston at TDC. I don't think it could possibly be that much carbon.

I know on the 2-valve DR200 motor the intake valve comes pretty close to the spark plug electrode. When we put big valves in the DRZ125 we have to index the plug to avoid the intake valve hitting the ground electrode. I can't imaging tis being the case on a DR250 though.

[maxbowersox]

Yeah, that sounds reasonable. I pretty much abandond the carbon on the piston a while back. That was just one of the Ideas people had for me, He said the only way it could be carbon was if it had a shorter plug for a long time(enough to let the carbon build up) and then I went and threw the right plug in it. I am also trying to get ahold of the previous owner and granting him amnesty to tell me everything he knows about the engine. The bike is still at my mechanic friends house now I should have it back in a couple of days, and ill let everyone know.

[bikepilot1]

I just had my DR350 apart to install a 440 big bore kit. The 350 is the same basic motor as the DR250. I measured about 7/8" between the end of the plug and the piston at TDC. I don't think it could possibly be that much carbon.

I know on the 2-valve DR200 motor the intake valve comes pretty close to the spark plug electrode. When we put big valves in the DRZ125 we have to index the plug to avoid the intake valve hitting the ground electrode. I can't imaging tis being the case on a DR250 though.?

For what its worth there will be less space on the 250 as it has a raised center dome rather than a flat top piston like the 350 (it is higher compression). The 250 piston profile is pretty much the same as the high compression wiseco piston for the 350. Still, there should be quite a bit of clearance.

I'd triple check that its the right plug:)

good luck!

[BSR-1]

it's been over a week, is there any update?

[texas-dr]

hhhmmmmmmmmmmm

[Icelander-DR650]

MAX!!! We want answers ?

[texas-dr]

the roar of silence is deafening ?

[BSR-1]

the roar of silence is deafening ?

is that what I was hearing????

[maxbowersox]

Ok, I heard from the mechanic today, He got the jetting right, and set the valves. He used a micro sized inspection light to look in the cylinder through the plug hole. There is definitely some debris in the cylinder. He confirmed the right plug and good compression so we cannot figure out what would be broken in the cylinder. It doesnt seem to be loose and floating around. So he thinks it must have embedded itself in the piston or head. So the only thing left to do is pull the cylender head. I will get the bike back tomorrow night and pull the head off, probably this week end and let everyone know.

[texas-dr]

Renee says "someone put a wrong spark-plug in it (too long) and it hit the piston and broke off.

the broken piece off the old spark-plug is hitting the new one."

she is a smart girl....

[BSR-1]

So the only thing left to do is pull the cylender head.

POSTED BY BSR-1 DATED 11/24:

"you could pull the top end off to see?"

I could have saved you 3 weeks & a trip to the mechanic.

P.S. I think Renee would agree!