High compression head

Tyler6357

Well-Known Member
Mar 15, 2012
1,285
288
83
Santa Barbara, CA
I removed one of the base gaskets and tested squish again making sure this time the solder was in line with the wrist pin it actually stopped the piston this time. I tested it twice my solder originally measures 1.45mm but the squished parts are measuring about 1.30 so does that mean my squish is 0.15mm?
Alright, 1.3mm is equal to 0.051" and you want about .03", therefore you have 0.02" to go or 0.508 mm more. You need to get it to 0.762 mm which equals .03". Since your squish is less than .006" the head should have shown a little improvement if you had taken off the extra base gasket.
 

Tyler6357

Well-Known Member
Mar 15, 2012
1,285
288
83
Santa Barbara, CA
If you come out at .04" or something very close, you could put it back together and ride your bike with only 1 base gasket and see if you notice any performance increase. You can always lower your squish a little more if you want.
 
Last edited:
  • Like
Reactions: Lone Wolf

Lone Wolf

Member
Jul 28, 2021
31
37
18
61
If you come out at .04" or something very close, you could put it back together and ride your bike with only 1 base gasket and see if you notice any performance increase. You can always lower your squish a little more if you want.
Once you get the head set up correctly, if it is still not fast enough for you, another inexpensive way to increase your speed is a sprocket with a lower tooth count. I am going with a 32 tooth rear sprocket. I am installing it tomorrow. I will let you know how it turns out. Well, actually later today.
 

Larry Trotter

Active Member
Nov 26, 2017
341
152
43
74
No. Your squish is about .050 inches now so you only have.020 to remove to meet your goal of .030 inches.
 

Chris7420

Member
Jul 23, 2021
50
21
8
21
No. Your squish is about .050 inches now so you only have.020 to remove to meet your goal of .030 inches.
I’m a little confused on how you determine the squish. So you measure the squished piece of solder and the overall measurement is you’re squish? I thought you measure before and after squishing it and the difference is the squish
 

Chris7420

Member
Jul 23, 2021
50
21
8
21
I’m a little confused on how you determine the squish. So you measure the squished piece of solder and the overall measurement is you’re squish? I thought you measure before and after squishing it and the difference is the squish
So my goal is to get the squished piece of solder to measure 0.03”/0.762mm if I understand correctly?
 

Lone Wolf

Member
Jul 28, 2021
31
37
18
61
So my goal is to get the squished piece of solder to measure 0.03”/0.762mm if I understand correctly?
When you are measuring squish, you are measuring the gap between the piston and the head when your piston is at top dead center. You only have to measure the solder after the you squish it, and you measure it at the thinnest point, which should be close to the out side edge of the cylinder.
 
  • Like
Reactions: Tyler6357

Tyler6357

Well-Known Member
Mar 15, 2012
1,285
288
83
Santa Barbara, CA
I’m a little confused on how you determine the squish. So you measure the squished piece of solder and the overall measurement is you’re squish? I thought you measure before and after squishing it and the difference is the squish
After you compress the solder you remove the pieces and measure the smallest point on any of the pieces of solder. The smallest measurement you get is the squish, it's the spot that's most compressed you could say.
 
  • Like
Reactions: Lone Wolf

Chris7420

Member
Jul 23, 2021
50
21
8
21
After you compress the solder you remove the pieces and measure the smallest point on any of the pieces of solder. The smallest measurement you get is the squish, it's the spot that's most compressed you could say.
Okay I wasn’t sure cause you’d think it would change depending what size of solder you use wouldn’t it? But anyways I sanded the head some more and retested and the squished solder measures right about 0.76mm. It seems to run a little better and compression is now at 110psi
 
  • Like
Reactions: Tyler6357

Chris7420

Member
Jul 23, 2021
50
21
8
21
Once you get the head set up correctly, if it is still not fast enough for you, another inexpensive way to increase your speed is a sprocket with a lower tooth count. I am going with a 32 tooth rear sprocket. I am installing it tomorrow. I will let you know how it turns out. Well, actually later today.
Let me know how the 32t sprocket works. I’m definitely interested, I’ve considered it before but am worried that it would make it so you really have to pedal to get the bike going with a small sprocket like that.
 

Tyler6357

Well-Known Member
Mar 15, 2012
1,285
288
83
Santa Barbara, CA
Okay I wasn’t sure cause you’d think it would change depending what size of solder you use wouldn’t it? But anyways I sanded the head some more and retested and the squished solder measures right about 0.76mm. It seems to run a little better and compression is now at 110psi
You should be able to wind it up a little more at the top end, I think removing that extra base gasket helped the compression too. It's hard to believe they would put 2 base gaskets on, oh wait...... no it's not.
 

Tyler6357

Well-Known Member
Mar 15, 2012
1,285
288
83
Santa Barbara, CA
Let me know how the 32t sprocket works. I’m definitely interested, I’ve considered it before but am worried that it would make it so you really have to pedal to get the bike going with a small sprocket like that.
You will notice it going up a steep hill, you have to peddle to keep your RPMs up
 

Lone Wolf

Member
Jul 28, 2021
31
37
18
61
Let me know how the 32t sprocket works. I’m definitely interested, I’ve considered it before but am worried that it would make it so you really have to pedal to get the bike going with a small sprocket like that.
Will do, it might be a couple of days.
 

mapbike

Well-Known Member
Mar 14, 2010
5,460
57
48
Central Texas
yep.... Ive done over 50 mph on one of my bike running a ( Puch 70cc hi hi ) which is said to have the wrong angle squish band for these engines and Ive also had engines that will do 40 mph+ running ild style stock straight plug heads that dont have a squish band at all in them.

With theae little engines, rhe most common performance level that most will ever acheve will have liitle to nothing to do with whether or not they have "proper squish"

correct port timing, better balance of the crankshaft, free flowing exhaust (stock exhaust if used needs flange matched closely as possible the gasket and port) wa to much back pressure on exhaust kills the power and tip speed of these engines even when all else is in good order, correctly jetted carb and some minor port and piston work that will ensure a good free flow of furl mix in and exhaust out.

If stick exhaust is used I recommend adding extra holes in the end cap to allow exhaust to get out easier, Ive seen engines gain 5+mph and get the ability to pull hills that they would barely pull previous to adding extra holes, these engines need veey little back pressure to run good when all elae is right.

I want to emphasize the right PORT TIMING & CORRECT CARB JETTING.

No matter what someone does to their engine, if these two aspects aren't right, its never gonna live up to its potential.

A very bad crank balance is a big performance limiter also.

If someone has whats referred tp as the "half breed" engine geometry, no matter what head they use, the compression will always be on the low side unless they deck about .060" of the jug/cyl. port timing is weird on them also. rod marking ZAE50 is a quick identifier of these engines or used to be.





I never not once tested for (squish).....Lol bikes ran fine
 
  • Like
Reactions: Venice Motor Bikes

mapbike

Well-Known Member
Mar 14, 2010
5,460
57
48
Central Texas
I see some great info here on measuring the squish band clearance which is definitely a positive to have right when all else is correct, but squish alone though will net you zero noticeable performance gains if all else isn't right in my experience.

Port timing, Carb tuning and proper exhaust flow are key to making these little china girls run at their most capable level.

My best running engines have always run with very little back pressure.

personal top speed of 52 mph was done with basically a straight pipe exhaust.

gearing can be an issue also, some engines will hmgive you a faster top speed with a 40T rather than a 32T

The engine has to be capable of pulling the smaller sprocket and if it isn't, its finna be a complete dawg..
 
  • Like
Reactions: Venice Motor Bikes

Lone Wolf

Member
Jul 28, 2021
31
37
18
61
Let me know how the 32t sprocket works. I’m definitely interested, I’ve considered it before but am worried that it would make it so you really have to pedal to get the bike going with a small sprocket like that.
It took me a little longer than expected, but I got all of my current upgrades done, including the 32 tooth sprocket. it is awesome. I decked my head down to .039", installed a pull starter, ceramic High temp clutch pads, 4 liter gas tank, and a 32 tooth sprocket. All of this gained 10 mph for me. It is slightly slower taking off from a dead stop, it still can do that without pedaling. This is a good thing because the pull starter is in the way, and I can't pedal this bike until I get some wide cranks. It does 25 mph up a 30 to 35 degree incline, which is 7 mph more than before. So the guy that said you would have trouble going up hill was incorrect. It does a steady 40 mph on flat ground, 10 mph more than before. Going down that same 30 to 35 degree hill, I hit 50 mph, again 10 mph more. Basically I gained everywhere except low speed acceleration. Which was only a slight loss of performance. My suggestion for you on the 32 tooth sprocket is "go for it" I think you will like the improvements you will get.
 

Lone Wolf

Member
Jul 28, 2021
31
37
18
61
At 50 you have a death wish.
Nah. I'm just a crazy old biker who misses his Honda Shadow. I did a 100 mph on that a few times. I'm not done with this bike yet. I'm still getting a reed valve, a better exhaust, and a BBR Stage 2 racing CDI. I also am going to get a degree wheel so I can do a proper port and polish. This one isn't even the biggest one. I have an all aluminum bike with a built in gas tank that I can pick up with one hand. I'm putting a 212cc Predator motor from Harbor Freight on that one.