Base Spacer

Chad_Broski

Chad_Broski

Active Member
Raise your cylinder, and thereby your port durations, with a spacer. This should increase power, just remember to take off the same amount from the top so you don't increase your squish clearance [by more than 1% of the total stroke]. Remember to do some calculations and measure the ports beforehand so you know where you're at and where you're going. This is by no means a substitute for a good port job, but it will increase power. And it is much less work, and much less hard.
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- 2STROKE STUFFING

All I would like to know is: 'does this really work?'. I would love to hear some thought and advice.
Thanks. (^)
 
I would also like to know 'if it does work, what adjustment will I have to make to maximize efficiency/power gain (besides porting, which I am already aware that I will have to do that eventually)?'
 
If you add a spacer to raise the ports you have to deck the cylinder the same amount to get the compression back to where it was, you’ll also need to check the piston skirt at the intake port at top dead center to see if you need to trim the piston.
 
Remember that raising the ports will help top end but will hurt low end, I have a 49mm bore engine that runs great at the top but is weak at low speeds.
 
This is a must read if you’re modifying a two stroke.
image.jpg
 
Also look for Graham Bells book on two strokes, i downloaded both and use them when porting. A lot is way over my head but it gives you a working knowledge of the process.
 
Greg58 said:
Remember that raising the ports will help top end but will hurt low end, I have a 49mm bore engine that runs great at the top but is weak at low speeds.
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Fascinating
Also, just wondering, if "raising the ports will help top end but will hurt low end", then is the reverse true also? As in if I lower the ports, will it help low end but will hurt top end? I am not really that worried about top speeds RN, I preferably just want low end torque. If you can answer this I will have one last question. Thanks for the recommendations!
 
You can try rtv instead of the base gasket, you’ll need to check the squish clearance to make sure the piston has enough clearance.
 
I have found a work around of sort with a expansion chamber, I went by the books above to set the port timing on a grubee 48cc, then added the chamber and a silencer to help control back pressure. I got improvement in top end and bottom end torque. I have 128 degrees of transfer duration which Graham says will produce 8000-9000 rpm, I’ve got 8200+ from mine.
 
Awesome, what are the specs?
I would share mine but it's just bone stock (nothing special), and it sputters lots of oil all over the engine and bike frame, and since it's so dusty where I live, the bike has shifted colors from a matte black to a light brown, lol.
 
Wow, now I have so much more questions. First off, what is the average connecting rod length of the standard cheap china 2 stroke "80cc" engine? Are the rod length's universally the same for all these off-brand models? I am trying to find the maximum piston acceleration that the piston rings can handle by using this equation: G max = (N2*L/2189)*(1+1/2A). But I need A, which is "the ratio of connecting rod length, between centers, to stroke" but I don't know the rod's length. Also what are the piston ring sizes and do they vary from kit to kit, or no?
 
All I go by is which piston the engine uses, type A is a low pin piston, the pin is located 15/16 up from the bottom. Type B or high pin piston has the pin at 1-1/6 up. The rings are 47mm on a standard engine, I buy rings in bulk, usually five sets at a time. I have a 66cc 38mm stroke and a 69cc 40mm stroke and both take the same piston. If you’re replacing a piston you need to measure to see what you need.
 
My 49mm bore engine is a 75cc, it was a 47mm bore 69cc. I got the iron sleeve piston and cylinder from eBay.
 
Greg58 said:
All I go by is which piston the engine uses, type A is a low pin piston, the pin is located 15/16 up from the bottom. Type B or high pin piston has the pin at 1-1/6 up.
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Okay, guess I will have to take apart the engine to measure the connecting rod,

Greg58 said:
I have a ... 69cc 40mm stroke
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Same as mine.

Greg58 said:
This is how I check port timing.
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That seems to be very useful, where did you find it at, or did you have it printed off?
 
I printed the wheel and glued it to a dvd, it is accurate enough for what I’m doing. Both of mine use the type B piston, the 40mm stroke I converted to the 49mm iron sleeve.
 
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