Tons of compression

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After adding a third tranfer port, arrow reed valve with keihin carburetor, reed piston mod, decked for a .70mm squish band, sickbike expansion chamber, a 6cc fred head and a jaguar cdi my compression is around 180 (so my compression tester reads). How do i lower my compression without compromising my squish band. I have crazy torque and with my sickbike shifter kit my top end is nice too. I don't want to lose any power. Any suggestions?
 
Open the combustion chamber bowl up, add another base gasket, or add another head gasket. Any or all. This is the ideal order to the solution but try another base gasket first. Cheap and quick.

Up to 2mm squish will still keep much of its effect. Many stock engines run 2.5mm squish.
 
180 is nothing crazy, I've personally run 200+ with the only ill effect being the cost of higher octane fuel. you've already got the jag cdi, I would suggest using a colder spark plug with a smaller gap and more oil than you think you need to keep the chrome plating happy.

you could also cut out the transfer walls to cut down crankcase compression a bit, with the side effect of giving you more top end power but sacrificing low end, that'll drop your dynamic compression ratio a surprising amount. a .1 decrease in crankcase compression ratio will equate to about a 15 PSI drop in compression assuming all my assumptions about which china girl you're running are correct
 
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squish clearance isn't the same on all sizes of engines because the final number that matters is squish velocity. Larger engines have more area being squished and so need larger squish clearances to maintain the same correct squish velocity.
You can read more on the subject and download my free squish velocity calculator at http://www.dragonfly75.com/moto/sqVelocity.html
 
180 is nothing crazy, I've personally run 200+ with the only ill effect being the cost of higher octane fuel. you've already got the jag cdi, I would suggest using a colder spark plug with a smaller gap and more oil than you think you need to keep the chrome plating happy.

you could also cut out the transfer walls to cut down crankcase compression a bit, with the side effect of giving you more top end power but sacrificing low end, that'll drop your dynamic compression ratio a surprising amount. a .1 decrease in crankcase compression ratio will equate to about a 15 PSI drop in compression assuming all my assumptions about which china girl you're running are correct
Hey more about cutting the transfer port walls out, I was asked to work on a 47cc motor recently, it was for a pit bike of some sort, I was tearing it down and saw it had no transfer port walls. Thought it was an interesting look. Couldn't figure why they did that other than simplicity.

If I were to cut the transfer walls out, but backfill the ports with jb weld to bring the compression back up would that change things or better or worse? Using a Reed valve too, also note the other motor comes with a Reed as well, and connects to the crank case, doesn't use the cylinder or piston to time or control intake, also doesn't expose raw fuel and air to a preheat like our cylinders can tend to do. Only useful feature that seems to have on our motor is the heat being transferred from the intake to the carb is an automatic carb defroster for those winter months.
 
you'd want to not reduce the width of the transfer channel. don't use JBWeld. no difference will be felt by the small decrease in crankcase compression.
without that wall there is a zone of "interference" near the side edges of the piston which limits that width by air pressure/turbulence.
I don't think it's a good modification.
 
Hey more about cutting the transfer port walls out, I was asked to work on a 47cc motor recently, it was for a pit bike of some sort, I was tearing it down and saw it had no transfer port walls. Thought it was an interesting look. Couldn't figure why they did that other than simplicity.

If I were to cut the transfer walls out, but backfill the ports with jb weld to bring the compression back up would that change things or better or worse? Using a Reed valve too, also note the other motor comes with a Reed as well, and connects to the crank case, doesn't use the cylinder or piston to time or control intake, also doesn't expose raw fuel and air to a preheat like our cylinders can tend to do. Only useful feature that seems to have on our motor is the heat being transferred from the intake to the carb is an automatic carb defroster for those winter months.
there's no reason to cut the transfer walls out if you're just going to narrow up the ports again. transfer walls are good, but if you need more transfer volume in a small area (or simpler production) then removing them isn't the end of the world.
 
Interesting. Thank you.

Still searching my head on cast iron cylinder vs a pro coated nikasil coating.

Only I also find threads mentioning finely balanced cranks, perfect mods and types of oil brining about motors that last them a year and a half without too much issue.

Course my luck tends to sway the opposite? Do everything to the T without error and everything goes to hell. Just slap some wd-40 on that b**ch and throw a bit of dirt on it and what do ya know, it works like new. Wtf.

Seriously explain.
 
I had main bearings fail in under 48 hours twice in a row, 3 different times. Yes this is magic but wait there's more!

Hey replace every seal and gasket with brand new bona-fide true-blue gaskets and seals and it just doesn't do s**t. Use a cereal box or old notebook for a gasket, and put a torn up burnt seal under that mag and what do ya know, it runs faster than that guy that sang that song about that guy who's name was Lola. Unless he was into that kinda thing then bad example, you get the point but wait there's even more!

Disect that motor and install any part on any other motor and guess what it runs?!? Yet no single part new installed to the old motor makes it run.?

osYeNnnnnnn;
Peanut brittle.
 
"Well, I'm not dumb but I can't understand
Why she walk like a woman and talk like a man
Oh my Lola, lo lo lo lo Lola, lo lo lo lo Lola"

Whew, Frank, kinda scary thought for a Sunday morning.
Just the kinda thought that keeps a single guy drinking responsibly!
Never know what ya might drag home if you don't keep your wits about you...

Cast Iron vs Nikasil:
Lived with them both, in 4-strokes and 2 strokes. My Blasters are both actually, one with a KTM engine.
Anyone living with cast iron is counting the over-bores. Counting down until none are left. Always looking for the next size piston.
Last oversize is the end of life...
Cheap pistons, oil and air cleaner bring it all the sooner, as do bearing and ring failures, quickly wiping out overbore re-life chances.
Original Nikasil is thin, like our chrome flashing on our China Girls. It is what you get with any bought Nikasil cylinder.
Rebuilder Nikasil is layers of plating, tough as nails. Will stand surprising abuse, like blown piston skirts, but not bearing bits.
If you had a China Girl cylinder that was a wonder of porting power, a good Nikasil plating would keep it forever.
Good oil and air cleaner, you could throw a $9 piston in it and $30 of rings every 5 years or 20,000 miles.
No kidding.

Everything to a "T" and it still fails?
My paying job is to install complicated production machinery and get it to run as fast as possible, as long as possible.
All things have a life cycle, all failures have a reason. Most are predictable if you know the factors involved.
When things fail unexpectedly, there is a learning opportunity. Why?
If you are not honest with yourself about the reasons, you will never learn a thing, and will repeat the mistakes.
"Cheap Chinese metal" is a cop-out. Bolts strip or break because you overloaded them. Chrome comes off for a reason.
Everything to a "T" implies impeccable quality control as opposed to "assemble and hope".

Quality Control:
I did a 2 year college course on this topic, could talk at length about any minute detail, but in the end it gets down to a balance of quality vs cost. How much do you want to pay for? So when you build your own engine are you doing the quality control? The inspection? The blueprinting? The quality testing?
Did you:
Dial the crank in to check for run-out or misalignment?
Check for fit on the bearings and install them without putting the load across the rolling elements?
Check for proper bearing side loads and clearance after assembly?
Leak test the whole assembly with pressure to test sealing?
Do a plug chop to assure proper mixture?

Usually not, because most of us want that low $$$ value point but forget it comes with an increasing failure cost.

My thoughts for a Sunday morning...
 
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