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Old 12-16-2005, 01:10 PM   #556
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Quote:
Originally Posted by stefan
The problem is not the heat, but the adhesion to the metal. Most silicones do not withstand our fuel.
i think the adhesion of silicone to a smooth, oil free, dirt free, metal surface is pretty good (peel strength is 3kg/cm, using 1 in. x 8 in. stainless steel screen at 180 pull angle), but who know exactly what is going to happen when the crank is spinning at 35K+ rpm with a non-symmetrical, elastic mass at the center, as least i don't.

i had used RTV filling on the crank for the pass two years (about 35 engines) and had only one failure, that is a pretty good track record, i think. the one that failed recently is a crank from a JP engine, the area where the RTV filling would go is very rough, comparing to other cranks.

i agree on the tip that the bonding surface must be oil/dirt free for the RTV to have a good adhesion, but i don't quit agree on the surface condition. i think the smoother the surface is, the better for the RTV to stick. i guess mybe if the suface is smooth, the edges of the RTV can do a better job on keeping the fuel out. once the fuel get under the edge, it will degrade the adhesion quickly and propagate to the rest of the bonding surface.

i am no expert on engines, just sharing what i had tried. so if i were dead wrong on the subject, please just ignore me.
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Old 12-19-2005, 02:50 AM   #557
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Hi all!

I've been reading this thread for a while now, and I've been trying to do some work in a Mega ZX21 crankshaft. I already have the RTV silicone, but no matter what I try, I just can't drill the crankshaft (correct me if I'm wrong, but all crankshafts with the orange stuff are drilled in order to make them lighter, right?). I've tried with a lathe and a drilling bit, but it just scratches the surface....
How do you guys (Grinder) do it?

Thanks for you help!
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Old 12-19-2005, 04:50 AM   #558
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Quote:
Originally Posted by areal
Hi all!

I've been reading this thread for a while now, and I've been trying to do some work in a Mega ZX21 crankshaft. I already have the RTV silicone, but no matter what I try, I just can't drill the crankshaft (correct me if I'm wrong, but all crankshafts with the orange stuff are drilled in order to make them lighter, right?). I've tried with a lathe and a drilling bit, but it just scratches the surface....
How do you guys (Grinder) do it?

Thanks for you help!
That part I am going to keep a secret. It took me a long time to figure out how to remove material while keeping the steel cool. It is not as simple as one may think. A drill bit will scratch the surface, but that is about it. Grinding stones heat up the steel and are not true everytime. I use a milling mahine, and some home made mounts to secure the pieces before milling. This creates a perfect bore everytime. One little hint: Look into what types of bits milling machines use to cut hardened steel, and cooling systems. If the crankshaft steel is not kept cool it will swell, that creates more problems.
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Old 12-19-2005, 07:08 AM   #559
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I already knew it was going to be difficult to get a straight answer
Nevertheless your tips and tricks showed me the way!
Thanks!!!

PS: If I eventually manage to drill the crankshaft, I'll let you know
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Old 12-19-2005, 07:43 AM   #560
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Quote:
Originally Posted by areal
I already knew it was going to be difficult to get a straight answer
Nevertheless your tips and tricks showed me the way!
Thanks!!!

PS: If I eventually manage to drill the crankshaft, I'll let you know
Also be carefull, a crooked hole can make for a very unbalanced crankshaft.
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Old 12-19-2005, 10:17 AM   #561
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I'll try to keep that in mind...
Thanks once again!
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Old 12-19-2005, 06:23 PM   #562
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Hey Uriah:

Its Edgar from PR. Wew are going to have an event on March, I would like to invite you and Eddie.

Please let me know where to contact you guys

edgarj@coqui.net.

Thanks
Edgar
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Old 12-19-2005, 09:37 PM   #563
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I've got Permatex RTV Red High temp silicone 26B. On the oackage, it says that it is not safe for the silicone to come into contact with gasoline. Does this also rule out methanol and Nitro?

If so, what is the permatex part number for the correct silicone?

Regards
NJ
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Old 12-19-2005, 10:22 PM   #564
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Drilling a hole on the crankshaft, and on anything heat treated, will very hard to do anyway you try it.

What you need is a CARBIDE drill bit or endmill. You need to use very good cutting oil, we use All Purpose TapMagic at the shop, straight, not diluted. You dont want to use a lot of RPMs, a the most 500rpms. You need to keep pulling the tool out of the hole that you're drilling, cut a little and pull it out, cut a little bit more, pull it out etc. You have to keep blowing the chips ou t of the hole too, otherwise you keep re-cutting them and this wears the bit faster. Go easy on it. As far as mounting everything, the milling machine is much better, like Uriah said, on the milling machine everything will be solidly mounted and the hole will be straight, or straighter, than on a drill press.

You can take it to a local machine shop, but a lot of people are afraid of drilling or milling anything heat treated, we have expirience with it because we do a lot of molds that require heat treated components. Sometimes we break a high speed steel drill bits and we have drill them out, and thats how we do it.
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Old 12-20-2005, 02:47 AM   #565
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Hmmmm....
I guess I'll try it first on some old crankshafts!!!

Thanks for all your advices!
By the way - Merry Xrmas to all
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Old 12-20-2005, 06:52 PM   #566
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Awesome!



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Old 12-20-2005, 07:27 PM   #567
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I also forgot to mention that if the bottom of the intake passage (the 7mm round hole on the crank) is not flat at the bottom, you will need to go in there with a bigger flat nose carbide endmill, provably 1/4", to make the bottom flat. If its at an angle the drill bit wont bite, it will bend and break. I hope you know what I mean by this.
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Old 12-20-2005, 09:01 PM   #568
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I have a JP X12, when I took the engine apart I noticed that the bore thru the crank is the same size all the way thru it except for the end right where the counter weight is. It looks to be something in the casting of the crankshaft. The hole that the fuel comes thru gets smaller by about 1mm. Does this sound normal? If not can I smooth it out with a dremel? Anyone have any thoughts on this one?
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Old 12-20-2005, 10:56 PM   #569
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I saw on and ad somewhere that the new Nova engines come that way. It accelerates the fuel mixture, and gives it more pressure. I dont know where I saw it, but I did, and it was recently.
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Old 12-21-2005, 02:55 AM   #570
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Quote:
Originally Posted by nitrodude
I also forgot to mention that if the bottom of the intake passage (the 7mm round hole on the crank) is not flat at the bottom, you will need to go in there with a bigger flat nose carbide endmill, provably 1/4", to make the bottom flat. If its at an angle the drill bit wont bite, it will bend and break. I hope you know what I mean by this.
By bottom you mean the end of the hole?
I don't recall seeing anything like that on any .21 crankshaft...
In fact, I have an old .21 NovaMax crankshaft, which I've taken apart and removed the orange RTV silicone and I'm pretty sure that the bottom of the hole is not flat - but I'll check tomorrow and let you know!

Thanks!
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