Chainsaw Repair
How To Basics - Carb Fixes + Mods - IPL and Service Manuals => How To Basics and Fixes => Topic started by: joe_indi on March 10, 2015, 06:17:52 am
-
We have been thrashing this subject of grooving on cylinder heads on an automobile forum. Yesterday a member posted these links. I had a MS460 come in today for a piston replacement. It seemed a golden opportunity to try a bit of grooving. So, after getting the necessary assent from the customer to use his saw as I guinea pig, I got down to it and faced my first hurdle, how to groove the cylinder head!
The customer started getting some anxious moments seeing my attempts and was on the verge of withdrawing his assent when I got the bright idea of grooving the piston top instead.
5 minutes later I was tightening down the cylinder.
Started the saw up and waited for it to warm up and gave the new piston to run a bit.
I checked for any changes.
Since I had no test instruments I had to go by my senses.
When throttling the sound at the air intake is more pronounced.
A hint of a deeper note at the exhaust.
Feels as if mid range has increased.
I had to move the H screw out a bit beyond 1 turn to get a four stroking at full rev.
The L screw also needed to be turned out a bit more to get a smoother idle.
I was able to take a couple of snaps of the piston before and after the grooving.
Unfortunately the customer was not in a mood to take a video of the running saw with my Blackberry.
I am on a slow connection right now. I will upload the images later. (I have uploaded the images
I will try to get a video later.
http://www.somender-singh.com/ (http://www.somender-singh.com/)
https://www.youtube.com/watch?v=5YbcOhiwmkE (https://www.youtube.com/watch?v=5YbcOhiwmkE)
-
Seems like it would impede flame travel across the piston? Then again maybe I am thinking into it to much.
-
This is only beneficial for low RPM (low velocity) and will hurt performance as you get to higher RPM where turbulence already exists due to the high velocity (E.G higher Reynolds number).
-
With a Hemi type head seen on many chainsaws the "swirling motion" (turbulence) is created when the fuel/mix enters the chamber in a vertical swirling motion if I'm not mistaken.
Not sure how the piston grooves would help that?
The Indian guy , Somender Singh has been cutting grooves on key portions of heads to improve burning of stagnant areas in combustion chambers for years with apparent dyno proven results. I tried this on a few saws and didn't feel any difference. Lol
-
With a Hemi type head seen on many chainsaws the "swirling motion" (turbulence) is created when the fuel/mix enters the chamber in a vertical swirling motion if I'm not mistaken.
Not sure how the piston grooves would help that?
The Indian guy , Somender Singh has been cutting grooves on key portions of heads to improve burning of stagnant areas in combustion chambers for years with apparent dyno proven results. I tried this on a few saws and didn't feel any difference. Lol
As I had mentioned in my post, the grooves are to be cut on the head, not on the piston. Since I had no tools handy to cut grooves on the head through the restricted space of the cylinder I tried these grooves instead on the piston.
But I dont know if the grooves on the piston give results similar to grooves on the head.
Joe
-
Some detailed dyno reports of Singh grooves on a 3 cylinder Suzuki (geo metro) engine. Looks like improvements under some conditions, and stock is better under others.
www.herningg.com/singh
-
the piston crown is also the floor of the combustion chamber.
not a fan of sharp edges on the piston though, hot spots. (old school). maybe if it was ceramic coated?
there was a company that manufactured race pistons years ago with raised pattern 'grooves/ribs' that is no longer around(?)
will look around for a photo. edit: http://www.autoserviceworld.com/issues/image.aspx?src=/daily_images/117003-49057.jpg&size=170
^what scarr wrote.
please show some photos after it was run.
cool experiment joe!
-(another) joe
-
the piston crown is also the floor of the combustion chamber.
not a fan of sharp edges on the piston though, hot spots. (old school). maybe if it was ceramic coated?
there was a company that manufactured race pistons years ago with raised pattern 'grooves/ribs' that is no longer around(?)
will look around for a photo. edit: http://www.autoserviceworld.com/issues/image.aspx?src=/daily_images/117003-49057.jpg&size=170
^what scarr wrote.
please show some photos after it was run.
cool experiment joe!
-(another) joe
Those cut outs in that piston are valve reliefs.
-
will look around for a photo. edit: http://www.autoserviceworld.com/issues/image.aspx?src=/daily_images/117003-49057.jpg&size=170
Just fixing pic
(http://www.autoserviceworld.com/issues/image.aspx?src=/daily_images/117003-49057.jpg&size=170)
-
the piston crown is also the floor of the combustion chamber.
not a fan of sharp edges on the piston though, hot spots. (old school). maybe if it was ceramic coated?
there was a company that manufactured race pistons years ago with raised pattern 'grooves/ribs' that is no longer around(?)
will look around for a photo. edit: http://www.autoserviceworld.com/issues/image.aspx?src=/daily_images/117003-49057.jpg&size=170
^what scarr wrote.
please show some photos after it was run.
cool experiment joe!
-(another) joe
Those cut outs in that piston are valve reliefs.
little ones. have never seen or heard of them made for 2 strokes. would guess that they would not be effective.
have to see if i saved some pics off the web of "yin/yang" pistons (don't know what they were called) on my old laptop, a few different designs of smokey's idea (?) by some other folks.
the pic above looks like it's only 1/2 swirl?
edit:
could not find the photo. think the drawing of smokes piston in a patent looks a bit different from the photo of them i saw. (the ramps lead to flat spot on the photo. drawings do not seem to show this). brain cells dying off. https://encrypted.google.com/patents/US4467752
ironic thing is that smokey seems to have been quoted that it didn't quite work after he built a flow bench. don't know if this is true.
-
..............
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
-
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
-
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.
-
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 .
-
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.
-
charging up the battery in my camera. hope this may be of help on determining if it was due possible compression loss.
-
.
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
-
.
-
dang it. have to resize photos. brb.
-
Joe, Great info!! Thanks
-
Joe,
In my case, the grooves on the piston, wouldnt it be a shortcut/easier method to fill the syringe with water, top up the grooves to piston top height and read off how many ccs of water is on the piston?
Maybe kerosene instead of water?
Joe (from India) ;D
-
Joe,
In my case, the grooves on the piston, wouldnt it be a shortcut/easier method to fill the syringe with water, top up the grooves to piston top height and read off how many ccs of water is on the piston?
Maybe kerosene instead of water?
Joe (from India) ;D
very true, good point. the difference in methods, is mainly in accuracy. we are talking about maybe 10 to 15 very small drops of liquid = 1cc.
if the top surface of what you will need to find the volume of is flat, it's standard practice to use a glass plate with the method you describe. "CCing heads."
suggested using clay or silly putty, because it would work for many different kinds of situations where surface is irregular or crowned etc.
liquids leave a depressed cup type of shape on the top surface. the wider the area is that you will be measuring.... leaves a deeper depression. reason for using clay or glass below.
it all depends on what you are trying to accomplish.
-joe
-
It's more common to use plexiglass or lexan to CC heads since you can cut and drill it much easier than glass.
-
You are trying to tell me about the inaccuracy in using a liquid because of the surface tension which would not give an accurate level, ok I understand.
Could you tell me what happens if the squish area is increased beyond limits?
-
Excessive squish velocity will transfer too much heat from the gas to the head/piston and could detonate fuel mix. Excessive velocity would also degrade any cooling effect provided from latent transfer of fuel droplets under squish area. There are some interesting GP bike head designs that incorporate several corners or sharp edges in the combustion chamber where an eddy of trapped fuel/air droplets improve cooling.
-
...the same thing that happens when squish is set to the bare minimum....just more of it.
the further away the fuel is from the plug, the longer amount of time it takes for the burn. inefficient.
depends on fuel mix quality, purpose, and load the motor will mainly see in operation.
-
Excessive squish velocity will transfer too much heat from the gas to the head/piston and could detonate fuel mix. Excessive velocity would also degrade any cooling effect provided from latent transfer of fuel droplets under squish area. There are some interesting GP bike head designs that incorporate several corners or sharp edges in the combustion chamber where an eddy of trapped fuel/air droplets improve cooling.
the diameter of these tiny pistons used chainsaw motors already give about 30 m/s velocity in the chamber, which is better than fine... just as they come from the factory.
-
I agree. Lots of folks over the years have taken the squish down into the teens in an effort to increase compression without realizing the squish velocity is excesssive.
-
I agree. Lots of folks over the years have taken the squish down into the teens in an effort to increase compression without realizing the squish velocity is excesssive.
...
-
Joe, what are your thoughts on why saw mfgs use a flat squish in lieu of tapered squish band?
Adam
-
Joe, what are your thoughts on why saw mfgs use a flat squish in lieu of tapered squish band?
Adam
imo, depends on chamber design. the further away...flatter is better, near side more angular.
suspect that is because they want to time the curl of waves to hit in unison at the plug... for shorter burn time while promoting good scavenging efficiency.
easy way to tell is that a poorer design requires more initial ignition advance to compensate whatever is causing an overly rich or overly lean condition in the chamber.
45-60 degrees of crank angle typically to burn all the fuel. more efficient with lesser degrees, more power can be extracted while the piston is closer to tdc while the chamber volume is the smallest. better to have a majority of crank angle burn degrees pushing on the down stroke than upstroke i would imagine.