Piston/vaulve smaking the plug??
 

2nd time I have removed a plug and what appears that the piston is taping or hitting the top of spark plug. This hasn't happened until I rev. the engine over the 10k rpm range. I just have a 155cc BB in it. But wondering if maybe gasket to thin? Or is it getting hit by the vaulve when gets in higher rpm range? Kind of hard to see, but got taped where the plug Elec. goes into it's turn. Anyone come across same issue?

Can't see it hitting just when you rev it. If it were hitting I would think it would hit all the time.

Is there a possibility you're getting something in the cylinder? Is your air cleaner nice and secure?

Yes, it's good and secure. And I agree with you, should be doing it all the time, rather then just when I hit the higher rpms. Why I'm scratching my head.

you got the right plug? NGK-CR7HS. plug should have a 12.7mm (1/2") reach.
I don't see the crush washer on that plug. If your using it without the washer it is most likely protruding to far into the cylinder thus making contact with the piston.

i'd pull the head and see what's making contact. either a valve or the piston is going to have damage on it from the contact. good call by CKAU, (wasn't there when i posted) think he's spotted the issue if you've been running w/o the washer.

I'm running a Trail Tech. The temp sensor replaces the washer. It's brand new. But doesn't mean it cant be the issue. (good call btw) However, still leaves the question why only at the higher rpm's? And yes, correct spark plug.

things happen in engines that sort of go against what you'd think. at high revs you can get a hair more piston travel. great example of this is when someone buys a "little old lady only drove it to church on sundays" car, drives it hard once and kills it when the rings hit the rock hard oil ridge at the top of their travel.

I have a TrailTech also, but I still run my temp sensor below the crush ring. Has anyone else heard of or done this?

from that picture it doesn't look like it hit the valve.

From what I understand that is the normal thing to do. The sensor replaces the washer. However, the washer does look thinker then the sensor. But since the washer compresses, it could be fine. So you have no performance difference while using the sensor, and the washer?

It makes since that there could be a slightly more movement in the displacement when the rpm's get in the higher rpm range. The dog has been in the shed most the winter while working on it. So been running and tuning it while on jake stands. (no load) So actual driving with 200lbs, I might not even get into that high of RPM's. However, guess there is a few things I can try. replace the sparkplug without using the sensor, and with the correct washer. See if same issue is there. Also, give good test run while i'm in it. See if issue is still there. But i dont want to get rid of the sensor. I'm not sure where I can get a 10mm washer thin enough to clear the problem. But still stay within its normal hight.

It seems like it's smacking the plug, even when I have my fat azz in it. :)
So i put the washer back on spark plug, with the heat sensor. I gave it a good pre-run on jack stands. top 47 mph, @ 11,900 Rpms. And it didn't smack the plug. So looks like i'm getting full performance with the washer. But still will half to see what it does when there is a load on it. interesting note: same time I did the pre-run on the stands, put in a new Iridium spark plug I got that day. max mph went up 1.1 mph and rpms went up around 200. (over stock spark plug)

glad to hear its not smacking the plug anymore, that's good results of 1.1mph gain just for a spark plug. If always been a fan have cooper spark plugs as I use them in my mustang, and put them in my gy6 engines and it is a noticeable difference now im curious if the iridium plug will have a difference on the gy6 over the copper plug. I cut my washer off my spark plug now I wonder if I should put a plug back in with a washer guess only one way to find out.

I would keep an eye on it. And if it is doing it, you wont hear it. I was just doing some spark plug checks and came across it. I even checked the gap in the spark plug every time it did it. And did not move it. So just really wierd.
I haven't seen any reviews saying anyone having the same issue. So could be just me. :cussing:

Did you install the 155cc kit?

What kit was it if so? Flat top or domed (high compression)

Was the head shaved at all?

You might want to not keep revving it that high. The valve springs aren't that strong and valve float does occur in these. Which results in bent valves from kissing the piston.

excellent point xlint, if he doesn't have the upgraded valve springs the valves could be traveling to far and be causing them to hit the plug.

yes, got the 58.5 BBk. came with piston, Jug, matching head with vaulve and spings already assembled. decribtion was high compression piston. High quailty.
"RACING BIG PORTS 58.5MM CYLINDER HEAD AND 1 RACING CAMSHAFT" I got the A12.
The piston was a flat top. everything went on pretty good. And havent had any issues leaking. However, I will not deal with them again. In the end got what I paid for. Took way to long. next time will go with BD. cost a little more. but dont half to deal with stupidity. I couldn't tell you if it has a higher range spring in them or not. Main thing I did notice, was that the ports was noteably bigger. It works for now, until I save up for a bigger one. 175cc stroker. ;)

I would ask them if the head has the upgraded valve springs. You could wind up damaging a lot.

I will see what I can find out. the washer seems to help. And it dont normally run at that high of rpms. loaded might hit 10k rpms

OK. high compression flat top piston. I have to think the head is smaller in size, or they gave you a pretty thin head gasket to get "high compression"

I would have to think there's some sort of debris inside the combustion chamber to close the spark plug gap, or the plug is reaching too far into the head/combustion chamber. (which may be the case since you removed the plug gasket).

I should be able to get it out this weekend, and give it a good run. As long as it's not hitting the plug, and I'm not losing power with the washer on, with the sensor. Then would just half to say, the sensor is not thick enough to replace the washer. And you could be right also, it could be a thinner gasket to get the higher compression. To the point there is no wiggle room. And once I removed the washer, and replaced with the sensor, it's setting to far in. At least im hoping this is the case. Thanks guys.