building from scratch, all new parts

[danlandberg]

I'm building a GT5 38 mm stroke and 47 mm bore. There was DIY engine kits a few years back. I haven't seen them lately so I had to go through many sights and vendors to obtain all the parts to rebuild one engine and build one from scratch. The PK80 I'm running now does not have enough bottom end power to pull my trailer due to the open transfer port design. So far I have done (on the new build) port matching on the transfer ports and cleaned up all obstructions in the cylinder ports plus advanced the intake timing by removing the intake port obstruction (lower piston skirt). What my question is, What can I do to increase low to mid range torque and power? Buying from all the different places has created more tedious time consuming work for me, but I want the build to be mine and know everything about it.
My GT5 had 15 to 20 thousands side to side end play at the crank.. after having to use emery cloth to turn down the clutch shaft for the bearings to fit on the new parts I also had to enlarge the small bevel gear , large clutch gear and the 415 drive sprocket. The taper was to large in outside DIA, to allow the gears and sprocket to seat enough to stat the nuts on the threads. What is the crank end play save to be at? Mine has 0 by feel, but turns freely. Any help on gaining low to mid HP and torque would be helpful. THANKS. This forum is very helpful, and I do what I can with what I have to work with.

 

[Greg58]

I have gained low to mid range power with a expansion chamber, mine has a longer head pipe that moves the power band lower, the shorter head pipe design give more top end.

 

[danlandberg]

I realize the header length is a determining factor on low to mid and top RPM range. I just don't want something like a poo poo pipe. Way to long of a header pipe.

 

[danlandberg]

Maybe I'll go with a SBP chamber, have a little more control of the headed pipe length.

 

[danlandberg]

THIS IS THE START OF THIS NEW BUILD

 

[FNTPuck]

A G5 cylinder will bolt right on to a PK80 without the issues a zeda triple40 would have and it has steel sleeve, closed transfers with divider, and great ports out of the box for only like $35.

I'd start with that and then do some light portwork, match the transfers, and mill it down for compression and it will have TONS of tq. I have one on my build and even with a too large KX85 pipe it rips down low.

 

[Greg58]

This is the pipe I run, it’s the best I’ve found for a 48cc. I hear the Mz pipe is very good on 66-69cc engines.

 

[gary55]

I'm building a GT5 38 mm stroke and 47 mm bore. There was DIY engine kits a few years back. I haven't seen them lately so I had to go through many sights and vendors to obtain all the parts to rebuild one engine and build one from scratch. The PK80 I'm running now does not have enough bottom end power to pull my trailer due to the open transfer port design. So far I have done (on the new build) port matching on the transfer ports and cleaned up all obstructions in the cylinder ports plus advanced the intake timing by removing the intake port obstruction (lower piston skirt). What my question is, What can I do to increase low to mid range torque and power? Buying from all the different places has created more tedious time consuming work for me, but I want the build to be mine and know everything about it.
My GT5 had 15 to 20 thousands side to side end play at the crank.. after having to use emery cloth to turn down the clutch shaft for the bearings to fit on the new parts I also had to enlarge the small bevel gear , large clutch gear and the 415 drive sprocket. The taper was to large in outside DIA, to allow the gears and sprocket to seat enough to stat the nuts on the threads. What is the crank end play save to be at? Mine has 0 by feel, but turns freely. Any help on gaining low to mid HP and torque would be helpful. THANKS. This forum is very helpful, and I do what I can with what I have to work with.

Certainly a good pipe will help. The other things that will help aside from port work is a 6cc head and adjusting the squish gap to .8mm. The added compression makes a world of difference in low end torque and hill climbing ability.

 

[danlandberg]

The GT 5 Pro racing engine would pull the trailer pretty good. The PK 80 does not have enough bottom end power to pull the trailer loaded with groceries with out peddling you a$$ off to get it moving and sliding the clutch. This engine kit came with to many problems from day 1. The clutch didn't work, the small bevel gear screw wobbled and was cross threaded at the factory. Must have been assembled on a Monday by a guy with a SAKE' hangover.
That's why I'm building a GT 5 engine for my work horse bike. I may put the PK 80 on the aluminum engine ready frame.

 

[danlandberg]

Where is a good place to get a MZ pipe?