cRanbrook build

JerboaJohn

Well-Known Member
Joined
Jul 29, 2018
Messages
1,272
oh yeah,,
like I have these extra jugs I'm gonna try adding extra boost ports, but external tubes from case to cylinder. seems easier to me to drill a hole and just touch up the entry to the cylinder than grind a channel in the wall.
ya gotta experiment! many ways to skin a cat
 


Spare_Parts

Well-Known Member
Joined
Nov 29, 2017
Messages
2,024
I was thinking along the same lines for a bit. Haven't looked at cheap jugs in a while though. Do have a 2018 jlzeda cylinder that never was finished. The transfers need so much work. Would like to try on a cheap one for proof of concept.

Going to order a little cross slide to see what the drill press thinks of side loading burrs. Might dance around or might be fine. Would be nice to cut in ports on a machine. The vice will still be useful for drilling.
 

FNTPuck

Well-Known Member
Joined
Jul 2, 2018
Messages
677
I think its been mentioned here but fair warning m y G5 steel sleeve put the piston way down 1.9mm inside the hole without gasket(!). Had to do a belt sand milling and dropped it down to .5mm in the hole with a .5mm (after compression) copper gasket for a total of 1mm squish. This is the recommended ~.5mm target plus .5mm extra for any rod stretch and expansion while hot...on 80cc dirt bikes its estimated to be only .3mm stretch but I added another .2 "just in case" and rounded up to .5mm.

Basically cut the squish in less than half - more TQ, way better performance :).
 

Spare_Parts

Well-Known Member
Joined
Nov 29, 2017
Messages
2,024
Wow, that far down? I use a single 0.5mm base gasket, 0.4mm head gasket, Fred 6cc head and took 1.2mm off the deck to get 0.65mm squish. Maybe the batches of these cylinders vary but all 3 sent here have been within a couple of hundredths of a millimeter. Guess the cases could vary as well and since zms was using CDH and Zeda you never know. Almost forgot, at least 2 different strokes for cranks @39.5 and 40mm. Was there also a 39? Guess this is why each engine has to be hand built.
 

FNTPuck

Well-Known Member
Joined
Jul 2, 2018
Messages
677
Wow, that far down? I use a single 0.5mm base gasket, 0.4mm head gasket, Fred 6cc head and took 1.2mm off the deck to get 0.65mm squish. Maybe the batches of these cylinders vary but all 3 sent here have been within a couple of hundredths of a millimeter. Guess the cases could vary as well and since zms was using CDH and Zeda you never know. Almost forgot, at least 2 different strokes for cranks @39.5 and 40mm. Was there also a 39? Guess this is why each engine has to be hand built.
Yea was like 2.6mm squish with the stock alu gasket LOL. I ran it anyway since I already had it together and it still did over 45mph on my short neighborhood test lap but was noticeably soft down low and didn't like to accelerate from a slow roll without pedaling. Once I took off 1.4mm from the top of the jug though it picked up a TON of TQ and 8 whole mph(!) up top on the same stretch of road. In all fairness it may have maxed out higher before so probably not a FULL 8mph, but I didn't take it on any long roads before narrowing the squish to top it out since I knew it wasn't making the power it should have so didn't really care - it was barely pulling anymore once it hit mid 40s so wasn't too much left in it if anything.

My head is 6ccs as well, but has no real squish band since its from a 50cc moped and needed some mods to work. I sanded it down to remove the stock (too small) squish band than took an old piston with sand paper glued to it, put a bolt through it and welded a rod to the bolt, then mounted to a drill in a vice and shaped the chamber myself to the 47mm piston so it won't hit the piston with the single gasket anymore. That's why I kept the squish at relatively wide 1mm since I'm scared to take it much lower without a proper squish band on the head. It works great, lots of compression, and cools better than the chinese CNC head I ran before. 53mph isn't anything crazy but its not bad for a simple piston port no reed budget setup on stock 36t sprocket!
 
Top