GW's Motorized
Well-Known Member
Can you post some pictures of that?
Correcting transfer angles, bearing upgrade, and case stuffing
- Thread starter Jayraye39
- Start date
Jayraye39
Well-Known Member
- Local time
- 5:07 PM
- Joined
- Jul 13, 2021
- Messages
- 851
GW's Motorized
Well-Known Member
That's a really good idea, thanks.
Chainlube
Well-Known Member
No need to compromise your piston, when another base gasket combined with some deck treatment can fix the timing.
Jayraye39
Well-Known Member
- Local time
- 5:07 PM
- Joined
- Jul 13, 2021
- Messages
- 851
ive already decked my jug. the piston in the pics just isnt TDC. Wouldnt another base gasket lower my compression? I mainly ramped the piston not so much for transfer duration but mainly for fuel direction. But the added duration did give me a top end boost.
Jayraye39
Well-Known Member
- Local time
- 5:07 PM
- Joined
- Jul 13, 2021
- Messages
- 851
I actually think the best way to correct timing or port duration is to modify the piston crown because its easily correctable and you dont sacrifice anything. if you correct the jug and ports for better timing. you take a chance of ruining your jug then you have to start over port and match a new jug. not ideal.
If I add more base gaskets. I sacrifice some cylinder compression and risk having too much transfer and exhaust duration. But by ramping the piston you change duration and timing by how steep and how mutch material you take off of the crown.
Also If you took off too much material or your duration and timing was was to much. all you have to do is swap out a piston and try again. the only sacrifice with the piston crown mod is that you might have a slightly less effective squish band. which on these motors really isnt a big power producing factor. The piston crown mod will always be #1 for me.
If I add more base gaskets. I sacrifice some cylinder compression and risk having too much transfer and exhaust duration. But by ramping the piston you change duration and timing by how steep and how mutch material you take off of the crown.
Also If you took off too much material or your duration and timing was was to much. all you have to do is swap out a piston and try again. the only sacrifice with the piston crown mod is that you might have a slightly less effective squish band. which on these motors really isnt a big power producing factor. The piston crown mod will always be #1 for me.
Wevil Knievel
Active Member
- Local time
- 2:07 PM
- Joined
- Apr 5, 2021
- Messages
- 208
Do you have any suggestions for how much to take off?
I realize that each engine is unto itself and it depends upon the port work that is done and all of that but for the average China Doll motor, what would you suggest?
If I may ask...
Jayraye39
Well-Known Member
- Local time
- 5:07 PM
- Joined
- Jul 13, 2021
- Messages
- 851
Not sure on the exact measurements. As I did it by eye little bit at a time and ran it until I found the peak performace.
What i ended up with was about half of the crown thickness. so say the thickness to the first ring is 1/4in. I took the Transfer ramps down to 1/8 in crown thickness.
For higher rpms the exhaust ramp is not ground far back into the piston like the transfers. I found the best results for the exhaust ramp was to just file the very edge 1mm down and 1mm back tward center of piston.
For best overal performace of the crown mod your gonna want to retard your spark timing on the magnet and keyway. That is if you havnt already
