New button is turning black...why??

[Sean Bowf]

OK...went to the pond with the new button in the .18 GO engine. Probably ran 10 or 12 runs. Started with an x440 and a longer pipe length, wound up with a Y535 and a shorter pipe length. We ran out of time and were making some speed gains just prior to leaving. Last thing I was doing was making it richer, and was gaining speed. So, I take it I was running too lean. It was never too hot to touch the cooling jacket. When I got the engine home and tore it down, I noticed the plug inside the combustion chamber was black (still looks new on the outside), and the button was turning black. The top of the piston also has a black ring that is inside the squish band (so silver/gray where the squish band is at). The plug was brand new (OD #9) when this day of running started (and the button was also brand new).

I would think the black (carbon deposit?) would be an indication that I was running way too rich. But, since I was gaining speed by making the engine richer just prior to leaving, I would not think that is the case. What else can cause this?? Note in the pic below, that the element in the plug is a frosted silver/gray in color.

The stock button also was pretty dark when I took it off the engine to start trying mods, but it had A LOT more runs on it.

I am running a 40% red max fuel blend.

Button has a flat squish on the outer 50% of it, and a 1.5 degree angle on the inner half.

Sean

 

[jetpack]

That I would call a lean condition masked by a rich setting at the end.

Your element is frosted, maybe some pitting on the plug surface.

You started adding more fuel at the end while it was still burning hot and caused the black deposits as you went richer, but the element and surface finish of your plug tells me at one time this engine ran lean.

Is the piston crown still smooth or is there any pitting? Lets see the piston too.

I think something is happening too fast in the chamber.

Second attempt I would try richer like you had been going.

The squish band surface finish is scallopped which will slow down the travel of the volume into the bubble and also promote pre-ignition. Scalloping is used to add turbulance to the mixture before it gets compressed into the bubble, but maybe too heavy to add any benifit and just cause pre-ignition problems, so maybe recut or polish that out.

A sharp edge leading into the bubble area will promote pre-ignition also but save softening that corner as a last step because it does add power to leave that sharp.

 

[Sean Bowf]

No problem showing the top of the piston Jetpack, but realize this engine has had a gallon or two through it testing...so I don't know what is recent, and what is not on the piston. See attachment.

I will have to try to get a clearer picture later. Engine is in the boat still right now.

Sean

 

[Sean Bowf]

This one might be a bit clearer. Looks like I smudged the top of the piston with my finger at some time.

Sean

 

[jetpack]

Well one thing for sure I dont think you hurt anything.

Sounds like what you described with your setup your engine is hungry for more RPM's so keep backing off with the needle I guess.

Clean things up, start rich and see what happens???

The frosted element worries me along with the coarse finish on the plug bottom.

Here's a factory shaped head button similar to yours. The edge leading to the chamber looks rounded but there is actually another flat angle added there, it was softened by me from cleaning and it is a tick softer than stock and that is why it looks more like a radius than another angle.

 

[Geraghty]

OK...went to the pond with the new button in the .18 GO engine. Probably ran 10 or 12 runs. Started with an x440 and a longer pipe length, wound up with a Y535 and a shorter pipe length. We ran out of time and were making some speed gains just prior to leaving. Last thing I was doing was making it richer, and was gaining speed. So, I take it I was running too lean. It was never too hot to touch the cooling jacket. When I got the engine home and tore it down, I noticed the plug inside the combustion chamber was black (still looks new on the outside), and the button was turning black. The top of the piston also has a black ring that is inside the squish band (so silver/gray where the squish band is at). The plug was brand new (OD #9) when this day of running started (and the button was also brand new).

I would think the black (carbon deposit?) would be an indication that I was running way too rich. But, since I was gaining speed by making the engine richer just prior to leaving, I would not think that is the case. What else can cause this?? Note in the pic below, that the element in the plug is a frosted silver/gray in color.

The stock button also was pretty dark when I took it off the engine to start trying mods, but it had A LOT more runs on it.

I am running a 40% red max fuel blend.

Button has a flat squish on the outer 50% of it, and a 1.5 degree angle on the inner half.

Sean

The discoloration is a residual varnish from the castor in the fuel....a frosted glo-plug with no wire deformation is perfect....there is nothing wrong......go enjoy your boat......

 

[jetpack]

Look to the lower left of the threaded hole at the 8 oclock. I cant tell but looks almost like a piece of glow plug wire in the varnish. Is that a reflection maybe.

Is that a torn machine finish on the bottom of the plug or is that pitting? I cant see it being as contaminates.

 

[Sean Bowf]

Thanks Geraghty for the input.

Jetpack, I have seen folks make different comments about intake path, etc, for smoothness, and try to stay out of the discussions...but here goes. I see a lot of folks polish up a lot of the intake patch (crank, channels, etc) on their engines. Being an old motor head, I had always heard this was not a good thing to do (car motors). It would make the fuel stick to the intake channels of the manifold, head, etc, instead of staying in the air mixed up. Not sure if what I had heard back then was ever true...but I always have that stuck in my head.

Now today, where they inject fuel right behind the intake valve in an engine, folks polish intake channels, etc, in their engines to make the air flow better. I can see where this would also be a good thing.

But...my thought is that once the fuel is mixed with the air, the surfaces that it passes should NOT be smooth. This is just my opinion, I have no testing to back anything. I have heard that having the squish to bowl corner too sharp can cause problems (holds heat and cause detonation I think was the reason). But have not heard anything about the surface of the combustion chamber.

I have also heard that you want turbulence in the combustion chamber on these engines, again, to keep the fuel/air mixed up with an even mixture.

Now, all that said, what would be the advantages and disadvantage of one over the other?? I have no problem smoothing out the squish band...the bowl is already pretty smooth, but I can polish that too. I just wonder if it would be a good thing or a bad thing.

Sean

 

[jetpack]

I agree with intake channels not being polished and should have some type of finish other than a gloss because I'm sure you have already seen how water acts on a polished surface verses a grit type finish. The grit finish sponges the water away, the gloss makes it pool. I would think with a grit finish in intake tracks would prevent any type of collection of vapor and making its own droplet.

Combustion chambers however are different because a grit finish would promote hot spots to form. Best to have a reflective finish there I seem to think, and carbon has to work harder to form barnicals that only incourage more carbon.

Stay away from any type of hard carbon varnish because it stops heat transfer pretty well.

Keeping the fuel mix takes on a new tack as it comes to compressing it as it is not so much the surface finish that keeps it rolling as much as it is the transformation of the air that's about to be compressed up into the dome and thats where the proper squish band shapes come in at a certain respect.

I think with the right mixture you won't see too much more of the dark stuff, and go soft with compression for now and see how she burns with a clean head.

 

[Sean Bowf]

Did you notice the top of the piston?? The first picture I posted of it...you can see the tool marks on it too...that is the factory finish on it.

Sean

 

[Jerry Wyss]

Do you know what your bubble volume is? along with "headspace" and depth to the plug face.

From clear the H over here I'd say it looks like too much volume,, probably too much "H/S"

and too cold of a plug. Being black like that from the first few runs is not normal. It tells me you have an inefficient combustion burn.

The button looks like it's been cut with a carbide tool. High Speed Steel is all thats necessary for aluminum and they ain't that hard to shape.

Lapping the fit where the the button seats on top of the sleeve flange will help too.

 

[Sean Bowf]

Do you know what your bubble volume is? along with "headspace" and depth to the plug face.

From clear the H over here I'd say it looks like too much volume,, probably too much "H/S"

and too cold of a plug. Being black like that from the first few runs is not normal. It tells me you have an inefficient combustion burn.

The button looks like it's been cut with a carbide tool. High Speed Steel is all thats necessary for aluminum and they ain't that hard to shape.

Lapping the fit where the the button seats on top of the sleeve flange will help too.

Volume is .23CC, head clearance is .007, depth from squish to plug face is about .120. CR was 8.8 to 1. This is down from the stock CR of 10.4 to 1. Original head button had a volume of .11CC and head clearance of .022, and it also turned black. Wanted to get the head volume larger, to get the CR down and get some more RPM out of the engine...no??

This engine had a stock exhaust timing of 157, which is why the volume is so large (to get the CR down). I adjusted it to 171, but have not had a chance to run it yet...and with the cold front coming through this week, it might be a couple weeks before I get the chance. If I raise the exhaust timing any more, the blow down will be higher than 30...

Yes it was cut with a carbide bit. Figured buy once and never have to buy again. Don't remember how I did that one, but now I am putting the carbide bit in my tool post and using it like any other tool.

Sean

 

[mtruex]

sean,

i bet the engine was very rich to the ear when it ran the best like you have it? i will say that the volume sounds very excessive for an 18 engine, most .21s dont even come out of the box with that much head volume.. im sure you have low ex timing and that is why you made the button so big, but by lowering compression in a low timed engine you took the torque away from the engine trying to get more rpm when in fact you wont get more rpm because of the low timing..i would recomend getting the timing up in the engine, 125-128 intake and 175-180 ex (this is a bit conservative to start) and then make your head button from there.. 10.1cr would be a good conservative start on that and you can fine tune from there with ex timing and button volume..im guessing this engine is for a miss vegas?

 

[Sean Bowf]

The engine is in a MV, but mainly just trying to learn from it.

Out of the box it had A LOT of torque and no RPM. I got my best speeds from an X440, but the speeds were still pretty slow. After putting the new button on I gained a couple MPH over the X440 while using a Y535 (the normal prop I use on a MV). It can still turn the x440, just not as well.

I guess I need to figure out if there is a way I can make shims for under the sleeve. As I mentioned in my last post, I took the exhaust timing to 171 but have not had a chance to run it since. Without either cutting the transfer ports higher, or raising the sleeve, this is about as high as it can go without making my blow down higher than 30. To get to 180, I would need to raise the sleeve about .020

Be curious to take what i learn from messing with this engine, and applying it to the CMB .21 LS I have in a mono.

Sean

 

[Jerry Wyss]

The engine is in a MV, but mainly just trying to learn from it.

Out of the box it had A LOT of torque and no RPM. I got my best speeds from an X440, but the speeds were still pretty slow. After putting the new button on I gained a couple MPH over the X440 while using a Y535 (the normal prop I use on a MV). It can still turn the x440, just not as well.

I guess I need to figure out if there is a way I can make shims for under the sleeve. As I mentioned in my last post, I took the exhaust timing to 171 but have not had a chance to run it since. Without either cutting the transfer ports higher, or raising the sleeve, this is about as high as it can go without making my blow down higher than 30. To get to 180, I would need to raise the sleeve about .020

Be curious to take what i learn from messing with this engine, and applying it to the CMB .21 LS I have in a mono.

Sean

Raising the sleeve .020" is pretty common with low timed buggy engines. I've been using buggy/car engines on the thunder tiger o/b lower for years. I have also cut all the ports

in a buggy sleeve with a diamond bit dremmel. Tedious work that, and I do it only on the

cheaper brands.

The .21 LS likely has a large volume button too, but I would bet everything else is more than good.

 

[Sean Bowf]

How are you making the shims to go under the sleeve Jerry?? Or are you buying them some place?

Sean

 

[Jerry Wyss]

How are you making the shims to go under the sleeve Jerry?? Or are you buying them some place?

Sean

I had a guy make me up about 800 on a wire machine for 21 size engines in .001 , .003 and .005" sizes.

I really don't know what a "wire machine" is but the outcome was pretty slick.

The man that made them is Steve Deryck,, he's the guy that was developing

a machine to cut props,, some here may remember him.

You can, if your engine comes with any thick aluminum head shims, take out part of the center to make them fit around

the sleeve. I took the center out of a couple thunder tiger .010" aluminum head shims that went under the sleeve

flange of a O.S.30VG-P-X. I have modified so many engines that I end up with a pile of headshims. You have to improvise a little bit now an then.

I'm not sure what size an .18 sleeve is,, not sure if anything I have will suffice.

Some guys turn .020" off the top of the piston,, basically will do the same thing.

 

[Sean Bowf]

Yes, I have an aluminum shim that is about .0115 thick that came from the engine (there is also a brass one that is .0075, so the two together are .019).

The thing that I had thought was to get a nail clipper and reach over the outer rim to clip away the inner rim until it fit over the sleeve. I just figured there has to be an easy way to make shims that I don't know of.

Sean

 

[Jerry Wyss]

Yes, I have an aluminum shim that is about .0115 thick that came from the engine (there is also a brass one that is .0075, so the two together are .019).

The thing that I had thought was to get a nail clipper and reach over the outer rim to clip away the inner rim until it fit over the sleeve. I just figured there has to be an easy way to make shims that I don't know of.

Sean

The way I did it you prolly wouldn't want to do with a brass shim, the two aluminum shims were enough.

I held the outside of the shim near the ends of three fingers.

I ran a Dremel with a spiral carbide cutter bit on the inside and ran it like a

squirrel cage. It was tedious and having the right friction and speed to take material off without burning hide clear thru was a mini battle. :lol:

 

[tnrcboatracer]

Check out Wood's R/C Boat Products (http://woodrcboatproducts.com). Steve makes sleeve shims for popular engines. I have some for my MAC 21.