Author Topic: Bumping up compression?  (Read 522 times)

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Offline eriksat1

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Bumping up compression?
« on: March 06, 2014, 10:50:32 am »
If you remove the cylinder base gasket then check the squish to get more compression doesn't that change the port timing?

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Offline KilliansRedLeo

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Re: Bumping up compression?
« Reply #1 on: March 06, 2014, 10:52:15 am »
It does but only a tiny bit, sometimes not even enough to make a measurable difference. There are a whole bunch of factors that can also be impacted.

Have a look here:
http://chainsawrepair.createaforum.com/ported-saws/clearances-math-squish-gasket-thickness-base-cut-squish-cut-free-port/

And here:
http://chainsawrepair.createaforum.com/ported-saws/two-stroke-basics/
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Offline sharkey

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Re: Bumping up compression?
« Reply #2 on: March 06, 2014, 11:25:27 am »
I do not advocate running w/o a base gasket.  There are dis-similar metals involved that expand and contract at different rates when heated.  Most crankcases are magnesium and most cylinders are aluminum. 

If you toast an expensive older or unobtainable cylinder because you used Permatex without the gasket, dont cry. 

If you want to boost compression take the time to do it correctly.     

Offline KilliansRedLeo

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Re: Bumping up compression?
« Reply #3 on: March 06, 2014, 11:28:47 am »
I do not advocate running w/o a base gasket.  There are dis-similar metals involved that expand and contract at different rates when heated.  Most crankcases are magnesium and most cylinders are aluminum. 

If you toast an expensive older or unobtainable cylinder because you used Permatex without the gasket, dont cry. 

If you want to boost compression take the time to do it correctly.     

Good advice as usual, plus you don't have to scrape off the goo at a later date!
"When the people fear the government...you have tyranny....When the government fears the people....you have liberty"

Thomas Jefferson
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Offline 660magnum

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Re: Bumping up compression?
« Reply #4 on: March 06, 2014, 11:39:52 am »
What I've seen of the Yamabond type sealers on older setups has a positive impulse in my mind.

The anaerobic sealers as I have seen them applied correctly have offered some isolation between the metals and is not so difficult to remove.

But I have seen other crap (usually silicone RTV) used that made a nightmare out of the area where the parts joined.

I have also seen the proper anaerobic sealer used improperly (Might I say impatiently) that made a mess out of the situation with the sealer all squished inside the crankcase.

The suitable areas for sealer use is limited.

 
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Offline KilliansRedLeo

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Re: Bumping up compression?
« Reply #5 on: March 06, 2014, 12:02:38 pm »
I use a small (cheap, throw away) brush like those used by kids to paint plastic models to get a nice even coat on the bottom of the cylinder. Or as said before I ask my wife to do it. If they can put eye make-up on while driving to work, they can do a great job on the cylinders.
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Offline 660magnum

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Re: Bumping up compression?
« Reply #6 on: March 06, 2014, 12:08:24 pm »
+1
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Offline eriksat1

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Re: Bumping up compression?
« Reply #7 on: March 06, 2014, 02:54:13 pm »
So what is the correct way to do it? Have the base of the cylinder machined down so you get the squish you want along with a gasket? Do they make different thickness gaskets?

Offline KilliansRedLeo

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Re: Bumping up compression?
« Reply #8 on: March 06, 2014, 03:26:57 pm »
Yes that is next to the most accurate and most expensive way, it is also irreversible, once done, no more playing around! You must also know the compressed gasket thickness in order to get the squish right. It is because of this that saw builders normally shoot for a nominal squish of between 0.020 & 0.030 and as close to 0.020 as they can, they can get much closer to 0.020 if they eliminate the base gasket. In the case of a work saw vs. a all-out race saw a couple of thousandths makes little or no difference, only the stopwatch will notice, bad race technique will sometimes negate any advantage gained.

Paper gaskets in this country come in different thicknesses as does annealed 110 copper shim stock but you must cut your own.
"When the people fear the government...you have tyranny....When the government fears the people....you have liberty"

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Offline 660magnum

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Re: Bumping up compression?
« Reply #9 on: March 06, 2014, 03:34:13 pm »
This increased compression story has not changed any on chainsaw engines in the last 30 years that I have been messing with them. The squish was .020 then too.
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