Anyone Do Their Own Porting?

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, and others.
MonsterAir said:
Expecting a parts delivery tomorrow for my new/used rig, so I figured I'd pull the motor tonight and clean, re-ring and replace gaskets. Well look what I found! How do ya suppose that happened lol.


No deep scoring in the cylinder so I'm lost on how something like this would happen and talk about chitty oil. The last owner did not take care of this thing well.
Click to expand...
Broken strap on the spark plug? doesn't look to be real bad damage, and a bit of carbon on the top of the piston doesn't necessarily mean bad oil.
 
john addinall said:
when fitting a 2mm stroke crank in your motor, the piston stroke goes up with 1mm and down stroke by 1mm.
1mm equals +- 8 deg. so your exh will go up with 8 deg but your inlet will open up 8 deg later. on the marine motors we use 1mm copper base gasket when building 2mm stroker motor.
Click to expand...
Duhh on my part LOL, ya +/- 1 mm hence the 1mm gaskets they sell
 
john addinall said:
hi gents. i am also new to gas cars and like to do my own port work. i am racing gas boats and modify my own motors. this is new ball game for me and i really look forward to mod my first baja motor. i read many guys like to used thinner gaskets or want to stroke motors, but by doing that you change the timings on the motor. funny that timing nrs are not mentioned anywhere, why? top secret detail? by swoping cranks and gaskets intake and exchaust timing change, and this is only the start by mod motors. thanks for a brilliant forum. i still have much to learn.
Click to expand...
if you are in the gas boats thing, this link below might be of your help in porting:
RCMK Engine Modification
Engine Porting
buzzkill said:
Duhh on my part LOL, ya +/- 1 mm hence the 1mm gaskets they sell
Click to expand...
correct.
stroker crank means the same stock length of conrod but the pin on the "bigger" end is drilled 1mm outer vs original stock position. hence the conrod moves a little further to the outside... because of which you have to trim the crank case.
my understanding is that +2mm stroker means 1mm gain at TDC and another 1mm at the BDC.
IF you use a 1mm base gasket to accommodate the +2mm stroker crank, you need to trim the ports to restore the stock timing values.
IF you cut the squish band to accommodate the +2mm stroker crank, you do NOT need to trim the ports because they keep the stock timing values. (because the port windows relative position to the stroke won't change, BUT you need to cut the combustion chamber too to restore the stock compression rate)

again, it is just my understanding... (hope it's right)
 
Last edited:
szaki75 said:
if you are in the gas boats thing, this link below might be of your help in porting:
RCMK Engine Modification
Engine Porting

correct.
stroker crank means the same stock length of conrod but the pin on the "bigger" end is drilled 1mm outer vs original stock position. hence the conrod moves a little further to the outside... because of which you have to trim the crank case.
my understanding is that +2mm stroker means 1mm gain at TDC and another 1mm at the BDC.
IF you use a 1mm base gasket to accommodate the +2mm stroker crank, you need to trim the ports to restore the stock timing values.
IF you cut the squish band to accommodate the +2mm stroker crank, you do NOT need to trim the ports because they keep the stock timing values. (because the port windows relative position to the stroke won't change, BUT you need to cut the combustion chamber too to restore the stock compression rate)

again, it is just my understanding... (hope it's right)
Click to expand...
That's about how I figured as well. The "factory ported" cylinders don't change timing numbers a bit.
 
Well to throw a wrench in the mix. I didn't need to mod the crank case to fit my stroker. I guess the case mod is only for the 32cc?
 
yes, G320RC needs the crankcase mod
+2mm (30mm) Stroker Crankshaft for Zenoah G320RC Engine - dd404b

“Note: The lower rod of the +2mm crankshaft (since it sits 1mm lower than the stock rod location) makes it slightly rub on the stock Zenoah G320RC crankcase. Before using this crankshaft, it is essential that you remove a small amount of crankcase material to free up space so the rod does not hit”
 
i can understand the +3mm stroke with this crank. (1,5mm gain at both TDC and BDC)
STROKER CRANKSHAFT +3MM
1607800927589.webp
...but what is the sense to extend the rod when it has NO effect on the stroke? the +5mm is just shifting the piston travel upwards and you have to use one of those bloody thick base spacers and screw the port duration.

someone could enlighten me please, because i'd really want to understand.. :unsure:
 
szaki75 said:
if you are in the gas boats thing, this link below might be of your help in porting:
RCMK Engine Modification
Engine Porting

correct.
stroker crank means the same stock length of conrod but the pin on the "bigger" end is drilled 1mm outer vs original stock position. hence the conrod moves a little further to the outside... because of which you have to trim the crank case.
my understanding is that +2mm stroker means 1mm gain at TDC and another 1mm at the BDC.
IF you use a 1mm base gasket to accommodate the +2mm stroker crank, you need to trim the ports to restore the stock timing values.
IF you cut the squish band to accommodate the +2mm stroker crank, you do NOT need to trim the ports because they keep the stock timing values. (because the port windows relative position to the stroke won't change, BUT you need to cut the combustion chamber too to restore the stock compression rate)

again, it is just my understanding... (hope it's right)
Click to expand...
Some good info right there??
 
My understanding is that long rods change the angle of piston and help increase rpms. I'm looking into +3mm stuffed crank with a 5mm long rod. More torque and more rpm. Not sure if it's offered for the 32cc engine though.

I'll probably have to have a custom head made up. I've also been wanting to try a balanced crank, anyone run one of them?
 
MonsterAir said:
My understanding is that long rods change the angle of piston and help increase rpms. I'm looking into +3mm stuffed crank with a 5mm long rod. More torque and more rpm. Not sure if it's offered for the 32cc engine though.

I'll probably have to have a custom head made up. I've also been wanting to try a balanced crank, anyone run one of them?
Click to expand...
If you change the angle of the piston you need an oblong cylinder !
 
after some reading, i've found the following regarding rod length:

- long connecting rods have reduced angles during movement, generating less lateral thrust and friction (less wear) on the cylinder walls.
- short connecting rods reducing the masses that move in both alternating and rotary motion. The result is a net advantage in terms of performance, but a somewhat reduced duration and a need for expensive surface treatments on the cylinder walls to mitigate the effect of increased lateral thrust

i mute now, ciao... :sleep:
 
You typically see short rods in high rpm set ups, long rod motors don't seem to get the rpm, but have much more torque. Think about it this way, long rod, more room to push on the power stroke, = more torque. Short rods don't have the leverage advantage of long rods, but because of this they excell in high rpm running.
 
Ya know that was what I thought originally but a lot of what I'm reading says it reduces friction which in turn would increase rpm, no? The 3+ and 5+ rod motors I have seen (listed online) were speed run motors so there has to be some type of rpm increase there I would think.

I also vaguely remember the long rods are prone to breaking under high torque situations.... It's been so long I'm trying to catch up to where I left off 5yrs ago. lol
 
MonsterAir said:
Ya know that was what I thought originally but a lot of what I'm reading says it reduces friction which in turn would increase rpm, no? The 3+ and 5+ rod motors I have seen (listed online) were speed run motors so there has to be some type of rpm increase there I would think.

I also vaguely remember the long rods are prone to breaking under high torque situations.... It's been so long I'm trying to catch up to where I left off 5yrs ago. lol
Click to expand...
with higher torque you can gear up !
 
MonsterAir said:
Ya know that was what I thought originally but a lot of what I'm reading says it reduces friction which in turn would increase rpm, no? The 3+ and 5+ rod motors I have seen (listed online) were speed run motors so there has to be some type of rpm increase there I would think.

I also vaguely remember the long rods are prone to breaking under high torque situations.... It's been so long I'm trying to catch up to where I left off 5yrs ago. lol
Click to expand...
Idk, poor design of the rod or material? Cant think of a too much torque being a major issue in one of these engine. I've heard of rods stretching and hitting the head, but I think that was a heat stress issue, or something like that.
 
Back
Top