munro1656

Hi glenn
the timing I was aiming for is 180deg on exhaust maybe a touch lower
I was going to run a 0.02" cut at top of piston about 1/4" down thats on the out side then I was going to run a cut on the inside for lightening I think those ball cuts on the piston skirt maybe beificial as well I am assuming they would also help with lurication in the bore? , but the machining that I was reffering to I have seen was taken off the top of the piston and i couldn't figure out the benifit
cheers craig

MrMikeG

Looks good!

glennb2006

hi Craig,

if you look through the post that Larry put a link up to, it details on there the purpose of the piston indentation (Lubrication), also makes mention of the piston size reduction, as well as timing figures. It also shows some of the work that needs to be done to match ports to crankcase.

You are going to be quite extreme on your timing, but no point doing it for little gain (In my opinion).

I believe that weight is removed from the piston by relieving material from under the piston crown as well as the gudgeon pin (AKA Piston Pin) bosses. Not done one on a Zen yet so I don't know how much you can get away with, maybe someone will let the info slip.

I am interested to see your results as I've a Zen here that I am going to have a go at this Winter on the dark evenings. Want to see what I can get out of it.

Glenn

Scott Schneider

Piston mods ... yea, here is a few picture to feed your need for speed [>:]

munro1656

Thats The mod I was talking about earlier in your fist pic you have machined top of piston and I thought that would reduce compression?
In your second pic you have tapered bottom of skirt what is the reason for that?
cheers craig

ryan_t888

Scott, those pictures are great, thanks for sharing. Do you have any different angle shots or photos of modified jugs?

Ryan

Scott Schneider

Again, SEE THIS SITE AND POST ***

http://www.modelgasboats.com/Magazin...e_Porting.html

Response to piston mods ..... First mod is too turn the OUTSIDE diameter down @ .002" (.004" total) about 1/4" down from dome and past ring groove. This allows a HOT piston to expand within a Cool cylinder without seizing.

Next while piston is in the lathe, clean up the squish area so it is no longer the casting profile but an even machined one.
* If you choose to "Flat Top" the piston ? do so next.

The "Flat Top" mod is used on HIGHLY MODIFIED Zenoahs that will run at VERY high RPM, It softens up the torque a tad, but allows engine to over rev better when staged on a rather short pipe.

As for more pictures

*** You asked: tapered bottom of skirt ?? ... tapered the piston pin boss area, as well as thinned the skirt area while lightening, but NO taper ?

Scott Schneider

Being you got me sharing here on RCU

I will share some Zenoah R&D tech of my own design that shows just how far outside the box you can go

Lower end fitted with a FULL circle crank from the RC series Zenoahs, cases also fitted with a 3rd main bearing on PTO side.
* Special adapter needed along with flywheel machining to do the FC crank conversion tho.

munro1656

Thanks everyone for your input every little bit of advice is valuable I must say there is more work that goes into a mod like this than you'd think[sm=spinnyeyes.gif]
I have done a little more work to zen today I have my fingers tightly crossed that I haven't stuffed anything up!

pedro2-5

[sm=tongue_smile.gif]hey craig if you are faster than me you will have to mod my motor for me

munro1656

Mod or sabatage your motor?

ryan_t888

I believe these are the stock timing figures.

Exhaust Duration: - - - - - - - -162 degrees
Transfer Duration: - - - - - - - -125 degrees
Piston Intake Port Duration: - -142 degrees

What do most of you guys mod your engines to?

I don't increase the transfer timing.
My intake timing is increased to about 145-150 degrees. I've noticed some people choose to skirt the piston while others prefer to open the intake port on the lower edge.
I have always preferred exhaust timing in the 172-178 degree range.

The stock Piston is about 29 grams. My piston is about 23 grams currently. If you can get in to the low 20's, there should be a decent enough improvement.

Ryan

munro1656

Thanks ryan
do you have any pics of your work to post the next step for me is piston i'd llike to see what you've done to achieve 23gr
chers craig

ryan_t888

Sorry Craig, I would love to post pictures but I will not have a camera for a few weeks. I will definitely post pics if I can get a hold of cam.

Ryan

munro1656

Hi all
I did some work on piston today so I think all mods are done and I think i'm ready for reassembly. Would there be any benefit in leaving off the jug gasket?
here's todays pics
cheers craig

glennb2006

Looking good, what weight did you get the piston down to?

Glenn

munro1656

Hi glenn
I managed to get it down to 24.59gr (checked with my old mans digital scales for measuring powder for amunition) maybe I could have gone a bit more but wasn't sure of thickneses
cheers craig

MistralK

Nobody runs the full shoulder crankshaft like the G230 one? It can increase high RPM..

munro1656

??? please explain I have never seen a 230 crankshaft so give it to me simple! what are you trying to say?

MistralK

I mean this one..combineted with lighter piston it takes more revs..

ryan_t888

Craig

Did you take material off from inside the piston? When you are looking inside the piston there are knobs from the casting process, these can come off. Make sure you leave the center indent alone though. I also took a tiny layer off the top of the piston to smooth out the finish, and I tapered the cut out section near the piston pin.

As for the jug, do you know any of your new timing marks? I would also place a gasket in there as there must be some material to fill the voids in between the machined surfaces. You can get thin gaskets from americanrcboats. This will increase compression, increase piston port timing and decrease exhaust port timing compared to a thicker gasket.

How are going to get the piston and ring back in the cylinder? What is the method you will use?

Ryan

munro1656

Ryan
As far as new timing marks are concerned I can only go by what I have read and heard cause I'm not exactly a pro at this I have used measurement to acheive what I believe to be correct Lets hope I'm rite As for as the piston goes I put it the lathe to start with and took a cut from the inside skirt area then with die grinder took some further material out from inside I removed a couple of nobs but had left others then just removed casting marks and smoothed over the rest and I didn't remove the centre nob only smoothed over it. As far as getting the piston back in I have a piece of shim here that I will lube up and hose clamp to piston then install basically the same as ring compressor that is used in automotive assembly
The pics are from just after I finished with course bur they haven't been cleaned up yet if you could see any area where I could go further let me Know It's not together yet!

cheers craig

glennb2006

Another couple of grams to go there and you will be in region, under the crown and around the bosses should find it for you.

Glenn

munro1656

I managed to scrap off 1 more gram today maybe if I had a cross sectional diagram of a piston I could find were I could get more with out jepardising strength my hat really goes off to you guys that make it sound so easy to get your piston in the low 20's grams. I think that's it for motor so it'll go back together this weekend then i'll work on intake manifold

MrMikeG

You can measure the outside down to the ring groove, then measure the inside and you can see how far you can go. Just watch out for the piston pin.

20 gram piston