Author Topic: Grooving the cylinder  (Read 336 times)

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Offline joe_indi

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Re: Grooving the cylinder
« Reply #10 on: March 15, 2015, 01:14:19 pm »
..............

please show some photos after it was run.

.......................


Okay "Another Joe" :)
I will see what I can do, maybe after a week or so .

Joe

Offline joe_indi

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Re: Grooving the cylinder
« Reply #11 on: March 20, 2015, 01:13:03 pm »
The customer came in today. This is how it looks after 10 days. I am not too happy, nor is the customer. The saw is drinking fuel! I replaced the piston.  :'(
Maybe the grooves were too wide and deep, which lowered the compression too much.
I will give another try.........when I can afford to waste another piston 

Offline 1manband

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Re: Grooving the cylinder
« Reply #12 on: March 20, 2015, 07:37:06 pm »
looks like the motor was running very cold?  is the underside of the piston clean (cold) or carboned up?

is the coil ok?

......not the picture i was hoping to see.  bummer.
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Offline Al Smith

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Re: Grooving the cylinder
« Reply #13 on: March 20, 2015, 09:50:15 pm »
I think it's apples and oranges compairing automotive engines to two cycles .I've got a couple of raised dome 3.5 and 3.7 liter Ford pistons in the garage .They have valve clearance cut outs on the dome .Basically a wedge design combustion chambered head not hemi .

In my way of thinking cut outs as  discribed would just be a place to collect carbon,a potential hotspot .

Offline joe_indi

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Re: Grooving the cylinder
« Reply #14 on: March 21, 2015, 12:29:12 am »
looks like the motor was running very cold?  is the underside of the piston clean (cold) or carboned up?

is the coil ok?

......not the picture i was hoping to see.  bummer.
It seemed to be running hotter. Dry carbon on cylinder top and piston top. The user said it had no 'muscle' in deep cuts.The engine was just putting out smoke. The saw was  fine otherwise. With the new piston it runs well.
This grooved piston also was brand new.
One thing I recall is that idling the exhaust sound was very subdued, like what you get from a saw with poor compression. That is why I think those grooves that I cut might have been too big for this piston.
I look at this from another viewpoint, to lower compression on MS460 I add an extra cylinder gasket (0.3mm thick each) just that extra gasket changes the saw so much especially at idle and mid range.
That is why I think the grooves were too big.The saw lost too much of compression.

Offline 1manband

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Re: Grooving the cylinder
« Reply #15 on: March 21, 2015, 05:02:20 am »
charging up the battery in my camera.  hope this may be of help on determining if it was due possible compression loss.
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Offline 1manband

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Re: Grooving the cylinder
« Reply #16 on: March 21, 2015, 10:11:59 am »
.
Just some basic stuff.  Photos to follow.

Rough 3 dollar way (approximate way) to determine how much volume you have removed from the piston crown or port or head or whatever the frig you are doing:

using an odd shape to demonstrate here:  3/8 inch nut

get and use a buret if you need more accuracy to the 0.2 cc standard.

1.  Obtain a suitable size syringe for what you are doing.  (60Ml one shown).  Pharmacy should have them.
2.  Food coloring.
3.  Remove plunger.
4.  Add food coloring/water mix into the syringe.
5.  Read the level.  (To the meniscus..... bottom of the curve).  Write it down.
6.  Put the aluminum shavings; or clay or silly putty which you have carefully used to fill a void;
into the syringe.
7.  Read the level.  Write it down.
8.  This obviously is the change in cc's.

A +/-1cc change is approximately equal to a 1.7 change in compression ratio in these tiny motors.

Some folks rely on compression gauges.  My thinking is different than most about most things motor.

Please realize that this does not show anything to do with finding the Trapped Compression Ratio......which is the only thing that is of importance in any 2 stroke motor, imo.

*Since the density of aluminum = 2.69 grams per 1cc.  One could also weigh the piston, cylinder, or whatever before and after whittling to get an idea of the volume removed from each port separately.*

hope it helps someone.
-joe
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Offline 1manband

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Re: Grooving the cylinder
« Reply #17 on: March 21, 2015, 10:13:48 am »
.
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Offline 1manband

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Re: Grooving the cylinder
« Reply #18 on: March 21, 2015, 10:17:53 am »
dang it.  have to resize photos.  brb.

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Offline aclarke

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Re: Grooving the cylinder
« Reply #19 on: March 21, 2015, 10:54:03 am »
Joe, Great info!!   Thanks

 

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