Help

[anthony_marquart]

While working on switching my .12 to water cooled I found that my head button is stuck to the sleeve. I also found 2 things.

1. The piston and button have a little damage on the opposing surfaces. I did have the coil of 2 plugs "disappear". Could this be the culprit? Should I just take a little scotch brite to them and clean up the surfaces? It's only on the outer band of the parts, (squish band) maybe too tight of clearance?

2. ONLY the center of the piston of the piston has any scorching on it. the quish band area is still shinny except for the few little dents.

I put the piston and head in the freezer hoping the head will shrink enough to get it loose... Any other suggestions?

BTW,.. Anyone have a .12 to run in INDY?... I'd love to make a class..

 

[BB Mods's]

Bake the motor @ 350*f for 1 hour.

 

[Mike Hughes]

Bake the motor @ 350*f for 1 hour.

That won't help. The aluminum will expaned before the brass does. It will just make it as tight as it is now. I think you will have to take a small wooden dowel into the sleeve from the bottom and give it a good hit with a hammer. Holding the sleeve in your hand tightly. Make sure it does not get away from you IE hitting the floor. You may have to clean it up with some high grit sand paper 400-600 to get it to fit again. You can use the sand paper to clean up the squish band also.

Mike

 

[Glenn Quarles]

What Mike says. I have a small screwdriver handle that fits perfectly in the sleeve when I need to tap one out.

Glenn

 

[jetpack]

The marks your seeing on the piston and head could be caused from too lean of mixture (pre-detonation), and also can explain the blown plugs.

 

[anthony_marquart]

When I've seen what I thought was pitting from detonation it was over the entire surface of the piston top. This is just under the squish band.

Will I see the pitting from detonation only in this area?

Also I only see scorching in the center of the piston and a little toward the exhaust side. Is this normal?

I actually am not loosing plugs anymore. Not sure why, maybe the engine is actually broken in now.

The marks your seeing on the piston and head could be caused from too lean of mixture (pre-detonation), and also can explain the blown plugs.

 

[steve wood]

if the head and piston doesn't show detonation on the little motors it ain't workin

 

[anthony_marquart]

Would it be over the entire piston top surface if it were detonation?

if the head and piston doesn't show detonation on the little motors it ain't workin

 

[DON MAHER]

if the head and piston doesn't show detonation on the little motors it ain't workin

This has to be one of the most misleading statements I have have seen on IW in a long time!!! :angry:

Detonation does not help performace, it hinders it!!!!! If it did Mark Grim's 110mph record setting .21 cmb would have been covered with it. IT WAS NOT!!

Don

 

[anthony_marquart]

Is this a stupid question? I can't seem to get even an "I don't know"...

Does the pitting caused by detonation always cover the entire piston top surface? If there are only marks in the squish band is it likely caused by plug wire debris or could it be detonation marks only in that area?

if the head and piston doesn't show detonation on the little motors it ain't workin

This has to be one of the most misleading statements I have have seen on IW in a long time!!! :angry:

Detonation does not help performace, it hinders it!!!!! If it did Mark Grim's 110mph record setting .21 cmb would have been covered with it. IT WAS NOT!!

Don

 

[jetpack]

Plug wire would not leave much of a mark. When a plug blows, the engine stops within a few strokes until the broken element clears the chamber. It is more likely a detonation pattern. Pre-detonation occurs where the clearance is the smallest. I would clean up the marks as best as possible without hurting anything. Leaving them in will cause hot spots, and lead to easier pre-detonation the next time the engine is run.

I would add a couple of head shims and work on increasing the compression a step at a time. As soon as you blow a plug that is short lived, back up and add a shim or start backing off the nitro content.

Too much compression will mimic a lean mixture somewhat, even with a properly tuned carb.

I think you caught it early.

 

[steve wood]

if the head and piston doesn't show detonation on the little motors it ain't workin

This has to be one of the most misleading statements I have have seen on IW in a long time!!! :angry:

Detonation does not help performace, it hinders it!!!!! If it did Mark Grim's 110mph record setting .21 cmb would have been covered with it. IT WAS NOT!!

Don

i have never seen a 21 that runs right without at least a light sandblast over the entire head button. this is on a heat racing engine that is run hard for many, many laps, and run too lean also. i could see where a straight away set up may not do this

 

[Terry Keeley]

if the head and piston doesn't show detonation on the little motors it ain't workin

This has to be one of the most misleading statements I have have seen on IW in a long time!!! :angry:

Detonation does not help performace, it hinders it!!!!! If it did Mark Grim's 110mph record setting .21 cmb would have been covered with it. IT WAS NOT!!

Don

i have never seen a 21 that runs right without at least a light sandblast over the entire head button. this is on a heat racing engine that is run hard for many, many laps, and run too lean also. i could see where a straight away set up may not do this

I agree, purdy easy to go "over center" on the little motors. Plug wires (or what's left of them) usually embed themselves in the squish band area and leave much bigger marks than the light blasting of detonation.

I imagine that running a motor with bits of plug wire embedded in the squish band would make the pre-ignition/detonation issue worse as the charge might ignite there instead of at the plug... :unsure:

 

[Matthew Hughes]

If you are seeing it all around the head button and not in the bowl area than you might have a negative head clearance. This would explain the reason the head is stuck in the sleeve. The piston has mushroom the head button ever so slightly causing it to get stuck. It may have been too tight to begin with or your rod length has grown from bearing wear or bushing wear. It does not take much when you have the button down at .004.

Mike

 

[tnrcboatracer]

I thought that the brass had a higher CTE than the aluminum (especially the high silicon AL). Hence heating the ass'y will make the button fit looser, not tighter. Otherwise whenever out motors heated up, hte pistons would stick. I'll have to check my Mark's handbook.

 

[DON MAHER]

Is this a stupid question? I can't seem to get even an "I don't know"...
Does the pitting caused by detonation always cover the entire piston top surface? If there are only marks in the squish band is it likely caused by plug wire debris or could it be detonation marks only in that area?

if the head and piston doesn't show detonation on the little motors it ain't workin

This has to be one of the most misleading statements I have have seen on IW in a long time!!! :angry:

Detonation does not help performace, it hinders it!!!!! If it did Mark Grim's 110mph record setting .21 cmb would have been covered with it. IT WAS NOT!!

Don

Anthony, Detonation does not always cover the entire surface. Most of the time detonation starts at the ex. port and works back into the chamber.Heavy detonation can cause the edge of the head button to expand & become very sharp , same w/piston.This will cause the piston to wear at the ex port very fast, if not corrected.

Don

 

[moparbarn]

I thought that the brass had a higher CTE than the aluminum (especially the high silicon AL). Hence heating the ass'y will make the button fit looser, not tighter. Otherwise whenever out motors heated up, hte pistons would stick. I'll have to check my Mark's handbook.

think you're right, jon. same reason cylinders have "pinch" when they're cold, but much less when hot .

 

[jetpack]

Here's a good link with excellent pictures and descriptions on combustion chamber appearance which I though would be helpful. It is probably the best site I've found yet with this type of question.

RC cars have become pretty popular and there's been a lot written about them. It's more popular than boat racing, and there's tons of rookies involved (youngsters) which always have problems. It's a good area to feed from with engine questions. If anyone knows about burning up engines, it would be these guys. :blink:

Combustion Chamber Pictures

 

[anthony_marquart]

Well I learned two things from that.

1. my engine has gotten hot. The plugs have been a little dark on the bottom. I though a greyish, slightly pulled plug was perfect...

2. The damage on my button and pistion is from some foriegn debris. It doesn't look at all like the pitting shown there. It looks like it tried to chew up a plug wire!

So I will clean it up and add a shim just in case..

Luckily the piston and sleeve fit looks perfect,.. no other damage can be seen..