Help for a newb?

[BoostedBaja]

I've got a non hemi 212 preddy (filter, jet, header), and I'm gonna get a billet con rod to pair with the cam/ springs I'm gonna order. What is stock length for a non hemi? Do I need anything else for the cam swap? (Don't say flywheel, lol)

 

[bob58o]

3.308"

http://www.arcracing.com/6254-arc-billet-rod-hf-predator-212cc-3-308-std/


Your cam will want something like 32 degrees before top dead center ignition timing.
You need an offset flywheel key 8 degrees (if your cam wants 32).

What is your cam?

You may want to upgrade the carb as well.

 

[Bbqjoe]

Here ya go!
http://bfy.tw/8nUH

 

[bob58o]

I plan on using a black mamba junior with a stock flywheel. I'm well aware of the danger that creates but I rarely push the bike hard, and when I do its for very short periods, seconds at a time.

I have the BMJ with the stock flywheel.
My stock flywheel used to turn 7000 RPM. Not racing for a half hour straight (never tried), but for 15-30 seconds at a time. It has held up so far.

Is there any way I can advance my stock flywheel timing?

Black Mamba Jr wants 32 degrees BTDC. Get a key like this.
http://www.arcracing.com/dj-2172-x-offset-key-for-clone-gx200-gx160/
I have the 8degree key.

And thanks for the reply

You might want to get the longer rod. Buy a Feeler Gauge ($5 at Harbor Freight) and get back to us when you take the head off. No need to waste potential compression with a short rod, when you could get the longer one.

For cheap you could also get a "Hemi" flat top piston.

Since you will be removing the head, might as well get a new thinner gasket too.

 

[BoostedBaja]

How thin of a gasket would you recommend for a stock piston? And what size con rod would you recommend? Would it be the same size for a hemi flat top? Thanks

 

[Bbqjoe]

I may be wrong, But I recently read that most clones are .030 in the hole.
The predator is like .003 from the deck.

http://www.kartpartsdepot.com/product_p/001.htm

 

[bob58o]

I may be wrong, But I recently read that most clones are .030 in the hole.
The predator is like .003 from the deck.

http://www.kartpartsdepot.com/product_p/001.htm

From what I've read, Deck height seems to vary among clones and Predators. This is why I mentioned the feeler gauge and getting back to us when you get the head off.

You Need to Measure...
to Be Sure...
if thinking about a longer rod

My Hemi Predator was 0.024" in the hole. The longer rod put me at 0.004" In the Hole.

---------- Post added at 05:36 PM ---------- Previous post was at 05:23 PM ----------

How thin of a gasket would you recommend for a stock piston? And what size con rod would you recommend? Would it be the same size for a hemi flat top? Thanks

Again, you need to measure.
It depends on how far down your piston sits at top dead center.

If it is 0.003" below the deck, you can use a 0.027" (or bigger) gasket.
If it is 0.020" or more below the deck, you can use a 0.009" (or bigger) gasket.

The flattop has a -0.020" compression height vs the dished piston from the non-hemi.

If wanting a flattop piston...
you should be able to get the longer rod (+0.020") and use and use a 0.027" gasket.
http://www.arcracing.com/dj-1285ph-std-bore-hemi-predator-flat-top-piston-kit/
http://www.arcracing.com/6256-billet-rod-hf-predator-020-3-328/

If using the stock piston, you should be able to get the stock length rod and use a 0.027" gasket.


MEASURE AND GET BACK TO US. If your piston sits more than 0.020" "In the Hole", my recommendations will change.

OR CALL ARC RACING AND ASK FOR JODY.
800-521-3560

 

[Flyinhillbilly]

The hemi piston is .020 shorter than the non hemi version so that opens up a lot of possibilities for mixing and matching parts. Most shoot for about .030 piston to head clearance, but I've ran mine at .017. The piston kissed the head just enough to keep the carbon worn off of it, so I'd say .020 is the bare minimum.

 

[minibiker]

They also have a stock height flat top piston. I used a + .040 rod and a hemi flat top piston which is the same as using a stock height piston with a .020 rod. All non hemi blocks are different I have two one was much deeper in the hole. I used the one that was less in the hole with the + .040 rod and hemi piston and ended up .014 in the hole .

 

[Flyinhillbilly]

Fwiw I'm talking about quench area. Piston to head clearance including the head gasket.

How thin of a gasket would you recommend for a stock piston? And what size con rod would you recommend? Would it be the same size for a hemi flat top? Thanks

The best thing to do is to measure what you have and figure out what combination of parts will get you to where you want to be. Which is .020-.030 inch piston to head clearance. Compression is the key to the kingdom on these things if you're trying to make more power, the right head work and cam will only complement it.

 

[bob58o]

so I'd say .020 is the bare minimum.

I've heard people running 0.020" as well, but I swear I just read a thread about keeping secrets for job security purposes.
Just kidding, I didn't try it so I was being safe with 0.030"

 

[BoostedBaja]

Once again thanks guys. I'm new to this forum and this engine stuff in general so it's nice to have a place that will put up with beginner's crap. Lol

---------- Post added at 06:06 PM ---------- Previous post was at 06:02 PM ----------

So while I'm here, how do I find TDC? Just rotate the engine until the piston is at the top of its rotation? I'd think it wouldn't be that simple since we're dealing in really small measurements.

 

[OzFab]

Once again thanks guys. I'm new to this forum and this engine stuff in general so it's nice to have a place that will put up with beginner's crap. Lol

We deal with more noobs than you care to imagine, some are more "noob" than others; you're doin' ok...

So while I'm here, how do I find TDC? Just rotate the engine until the piston is at the top of its rotation? I'd think it wouldn't be that simple since we're dealing in really small measurements.

Nope, it's that simple...

 

[Bbqjoe]

I believe I've heard of people filling the cylinder with beer cheese soup, minus the popcorn, and rotating the engine. You'll know it's at TDC when the soup stops flowing out.

 

[OzFab]

Ah but, how do you know when you've passed TDC?

A screwdriver in the sparkplug hole is how I was taught...

 

[bob58o]

Ah but, how do you know when you've passed TDC?

A screwdriver in the sparkplug hole is how I was taught...

People told me that, but on my Predator, I could see the piston through the spark plug hole. Easy to see it stop moving up, "pause", then go back down.

---------- Post added at 08:38 PM ---------- Previous post was at 08:33 PM ----------

Even easier with the head off.

 

[OzFab]

Even easier with the head off.

Well, of course but, I'm talking about worst case scenario, without having to pull anything apart...

 

[minibiker]

That's good for setting valve lash but you have to take the head off to measure how deep in the hole you are.

 

[bob58o]

That's good for setting valve lash but you have to take the head off to measure how deep in the hole you are.

I don't know another way.
But I couldn't change a plug last November.
So take all info I give with a grain of salt.