Sanding top of piston....?

[Buggyracer28]

Well, sounds crazy.... Heres my story. I am almost positive a little spec or 2 of dirt got in through my carb, which scratched a little of my con rod which came up through the sides of the piston (? microscopic) then getting stuck at the top of the piston and denting (extremely small) the top of the piston which IS THE REASON (finally) that is killing my glow plugs....

NOW, The piston and con rod are FINE. The top of the piston is just kinda ruff with minor indents on top. I tried just straight buffing it out with the dremel and it helped, but there are still some little bumps. If i sanded the top of the piston with maybe 600 grit sand paper, then buffed the top out evenly, will my piston life another day? The con rod is fine, just minor scratches (think ipod nano). If this does work, it will save me $79.99 + shipping. Worse case scenario I'm thinking i might need a pinch which is ALOT cheaper... If its worth trying, i have nothing to loose. If I didn't think it was salvageable I wouldnt ask. I can take pics if it helps.

 

[Monkey Wrench]

Before you sand it, have you tried using Mother's Metal Polish and a Dremel tool? I did the same thing to my .15FE and after I polished it, it was smoother than butter and ran great!

 

[Got Nitro?]

I wouldn't use 600,i would go with something finer,like 800 or 1000,sure it's gonna take awhile,but it will look nicer,probablly should water sand it,dry sanding could be bad.

 

[olds97_lss]

Man... I don't know... that's a touchy thing to be sanding. Think about it, it's peak travel speed has to be rediculous. It goes up and down for every turn of the crank. Most engines peak RPM is above 30,000. Any unevenness you create will cause a wobble which could damage the piston a lot more than a few pits in the top of it.

The most I've done is clean the top of the piston with a q-tip and DA.

 

[Buggyracer28]

Before you sand it, have you tried using Mother's Metal Polish and a Dremel tool? I did the same thing to my .15FE and after I polished it, it was smoother than butter and ran great!

Sounds great! I gotta get some of that. Where can I get it?

Olds, I wouldnt do anything about this if I liked burning glowplugs and running for 30 seconds. So, something has to at least be done to it. There has to be an end to this. I will try as hard as I can to get it perfect. Monkey's plan is sounding extremely good.

 

[Buggyracer28]

Well, it turns out my dad had a CRAP LOAD of polishing stuff, so I just used some of his. I just got finished putting the engine back together and it seriously seems like it has more compression than before! Its nuts! Well, I'm goin to the LHS tomorrow to pick up some glowplugs so I can test it tomorrow. Ill tell ya how it goes.

BTW, polishing it made it look alot better, but not 100%. Still looks good though.

 

[niggle]

Unless the underside of the head/button is also dented I doubt that this is caused by grit.

Marking of the top of the piston is quite normal, IMHO. In extreme cases it can be a sign of detonation, in which case make sure you have the right glow plug and number of shims for the % nitro content in your fuel.

This being the case, you can polish the top of the piston but the marks will reappear very soon.

 

[Buggyracer28]

I have 2 shims, should I go 1 more?

 

[supercharged]

you should see the dents in my .46 piston and underhead from the rear engine bearing breaking up the pieces of metal between the ballbearings came out of the bearing and severely scratched most of the internals

 

[rocknbil]

Just a FYI, remember the plug coils? It's more likely a red-hot speck of coil is what's dinging up your piston. Think about it, how could a speck of dust get past your carb and leave no visible marks but get into the combustion chamber and leave visible marks?

I have 2 shims, should I go 1 more?

Is this the stock configuration or have you added shims, what % of nitro are you running? Been kinda watching your issue, and this is new information - if you've varied the compression ratio from stock this could very well be why you're blowing plugs. (?)

I don't know how good you are at tweaking engines, so if you've seen this stuff already, it was worth a shot. The below info is for boats, it's very old but still relevant because a nitro engine is a nitro engine, and the concepts are the same:
Compression Ratio
How to set Head Clearance (Squish Band)

 

[Buggyracer28]

Thanks for the info bil. I bought 3 OS A3 glowplugs today because I knew they would break and didnt want twaste my money. 2 of them already died in a matter of seconds. THEY BREAK WHEN the engine reaches a certain rpm. Then the engine makes a sound like it doesn't like whats happening, then the plug breaks.

I fixed the no running without the ignitor problem, drives great at low rpm, but once I try getting the speed up, *click*.

I guess its just time for a new piston/sleeve Ill be selling my ntc3

 

[Plaidfish]

sounds like detonation to me too...I've polished mills out and had no issues.....sleeve/piston heads/ports....never had any issues from giving it a good polishing up.....

 

[Buggyracer28]

I tried getting more shims today at the lhs, but the stupid guy was just a complete retard.... (i dont want to get into that one) The side of the piston at one part looks like it got burnt or something (metal burning ) and same with the same part of the sleeve... THAT is my guess at where the dirt got in. When I take out the glow plug it leaves pieces of metal or something at the bottom of the button and on the glowplug near the opening. I think that is what is pushing the coil in and breaking it. sometimes it gets caught inside the coil making it not light up.

I think i have decided to just get a new piston and sleeve. I dont have enough money and i can't earn enough money for all the glow plugs that i am/will break. Its just too much pressure...

btw, on top of this my dad just ran over my mbx-5....................................