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Post by MCS on Jan 7, 2009 21:12:48 GMT -5
Zip, Since the last time this was discussed, I've given it some more thought. Homelite cylinders are chrome lined aluminum - there is no cast iron sleeve. Honing a cylinder like this would remove the chrome lining and essentially destroy the unit. You cannot run cast iron rings on an aluminum cylinder. I have three Homelite service manual and I haven't run across anything that talks about honing so I think you did the right thing. A new cylinder with a new piston and rings should seal up quite well without a lot of break-in. Perceived compression when cranking with the starter rope will be affected somewhat by the diameter of the fully filled rope pulley. I do know that the Homelite service manuals give a compression value but my manuals are at the lake cabin so I can't look it up right now. But this does bring up an interesting subject. Why did Homelite start adding compression relief valves? I have a Super EZ and a 150. The 150 cranks easier than the SEZ with the compression relief closed. Do the XP saws, which are similar to the C line, have compression relief? Put a gauge in that C and tell us what it reads. Be sure to lock the trigger open so you get a good charge.
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Post by MCS on Jan 7, 2009 22:13:50 GMT -5
This is from the David Bradley that is in a posting on this board. Notice the cylinder construction.
CYLINDER BORE: 2.0 in. (50.8 mm) PISTON STROKE: 1.5 in. (38 mm) CYLINDER TYPE: Aluminum with cast iron sleeve
This can be honed
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Post by lesorubcheek on Jan 8, 2009 15:33:13 GMT -5
Do the XP saws, which are similar to the C line, have compression relief? None of the 6 cube saws (XP-1000, 1020, later 1050 etc) had a decomp, but the larger 2100 series did and I'm pretty sure the 2000 series which presded it did as well. Dan
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Post by mikevan on Jan 8, 2009 16:10:15 GMT -5
Maybe the de-comp valve was a 'homeowner helper' type of thing? A 3 or 3.5 c.i. saw doesn't really need one, just my opinion.
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Post by billg on Jan 9, 2009 2:25:48 GMT -5
I belive on the SEZ it was timing
Bill
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Post by chainsawwhisperer on Jan 9, 2009 7:26:01 GMT -5
Zipper, I have always heard that you do not need to (and shouldn't) hone a plated (chrome) cylinder. But If a person chooses to do so it must be done quickly and with the right size ball hone, so as not to ruin the plating. I do not know if this holds true for other plated or bonded bores, but, I would assume so. If it were me I would not hone it.
A7ec, I have an AH-47 engine apart right now, from a D/B, I was surprised to see that the cylinder has an iron bore. There is some strange engineering in that cylinder, but then again it's 50 years old.
SEZ with compression release, On 'Othersite' there is a current thread, showing a Dyke's ring from a SEZ. Homelite calls it a 'head land ring' enabling the saw to produce more power. From what I gathered reading that thread, the SEZ had far greater compression than other comparable saws, thus requiring the compression release. Someone then wrote that that may be why that saw can (which is 40cc) can pull full 3/8 chain.
BillG, Timing?? Do you mean port and ignition timing? Or just when it went to market? CSW
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Post by MCS on Jan 9, 2009 10:35:18 GMT -5
OK Everyone here is Homelite's documented position on honing cylinders. Read about 2/3rd the way down in the center column. Amen
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Post by lesorubcheek on Jan 9, 2009 10:56:49 GMT -5
OK Everyone here is Homelite's documented position on honing cylinders. Read about 2/3rd the way down in the center column. Amen That's a nice clip for the question of a used cylinder, but Oldzip's orignal question was around a new cylinder wasn't it? I've wondered about this also. I have a some NOS cylinders lying around and a few of them just don't seem to be smooth as they should be. Almost like a light paint overspray or something inside them. The only new cylinder I've used on my saws so far was for a 925. I used some 600 grit with light oil and gave it a light sanding just because it didn't really feel right. I've yet to read any Homelite documents that talk about the use of a new cylinder on a saw and if there's any needed preparation for it. Dan
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Post by MCS on Jan 9, 2009 11:32:26 GMT -5
Well, the way I read it is just the way it is printed. Reading both sentences I see this, "Install a new cylinder and don't hone it." ;D
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Post by lesorubcheek on Jan 9, 2009 20:20:45 GMT -5
This is indeed the fun stuff! I'm certainly in agreement with ya'll that honing probably isn't the best thing to do, whether its a new or used cylinder. I gotta dig out a cylinder and see if a pic can illustrate this sorta painted look that I was talking about. Also, A7, I hope I didn't sound too mean with my previous reply. I just re-read it and I sounded sorta rude there. Again, that article you posted is great material and about the only thing I've ever seen that addresses this question in any way. I just gave ya a karma bump for it anyways.
Dan
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Post by MCS on Jan 10, 2009 12:38:25 GMT -5
Zip, I will agree that 100psi is pretty low since the saw has a new jug, piston, and rings. In the chart I put up in Tip and Tricks, for every saw, 90psi was the value where it is time to replace parts. Since you have all new parts I don't believe ring break-in is the whole reason for your low compression but you said you put oil in the cylinder and the compression came up. That in itself indicates something isn't quite right. In my profession, I am an expert troubleshooter. I get called in to help on problems that others have struggled with and have not been able to resolve. I have uncovered many problems where new parts were defective or installed incorrectly, wrong part installed, and problems were the other techs, just plain screwed something up. So, let's go through some things and I don't want to convey any feeling that are negative. Two cycle engines are pretty basic - no valves, cams and timing chains. Good compression is the result of the full volume of the cylinder, that which is from when the piston closes the ports to the top of the stroke, being compressed into the volume of the cylinder dome. The only place for leakage is past the piston and rings. Your compression gauge should hold the reading as you crank with the throttle open. Step 1 Make sure you aren't trying to fix something that isn't broken! You have a compression gauge so check a couple other saws just as a bench mark. I don't have a value specifically for the C9 but since the SXL is 130-155, I see no reason that the C9 wouldn't be somewhere around 150psi. How does the C9 compare to the ZIP? Step 2 Take the muffler off and look. Sometimes eyes are the best thing to find problems. Step 3 Squirt a little oil in the cylinder and take another reading. If there is a big change, something is wrong with the rings or side clearances. Step 4 Time to pull the jug and review everything inside. But before you do that, use a piece of wire and insert it in the spark plug hole. Turn the crank until the piston is all the way down and mark the wire with a sharpie, then do the same with the piston at the top of the stroke. Before I type more, I'll wait for the results.
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Post by chainsawwhisperer on Jan 10, 2009 21:34:33 GMT -5
Zip, I was thinking. might the new piston be slightly different than the old one? What I mean is maybe one was a flat top and one is a domed top?, or maybe somehow the pin hight is different? Also, how thick is your base gasket? All this is assuming that your compression IS low and it's not a faulty gauge. The compression will come up as the rings wear in but how much is anybody's guess. I might be cutting wood tomorrow at my FILs The weathers got us froze out of the duck hunting. Everything is pretty much locked with ice, the boat ramps and most of the shore blinds
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Post by chainsawwhisperer on Jan 11, 2009 17:14:35 GMT -5
Zip, you might want to check your ring end gap, and just for S& G's check your squish. I am glad to hear that the compression seems like it's coming up, Hopefully, you will not have to do any thing but run it, and break it in. CSW
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Post by chainsawwhisperer on Jan 12, 2009 13:27:20 GMT -5
Zip, this link explains the process. The idea is to tighten up the squish area to about .017 thou., by not using a base gasket or milling the cylinder. This will force more of the unburnt fuel/air charge into the actual combustion chamber, where it can be used, plus it will raise compression. I am unclear weather the benefit is from the increase in usable F/A charge, or the increase in compression, or both. www.arboristsite.com/showthread.php?t=77961&highlight=measuring+squishI need to hit the Gordon Jennings book again.
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Post by OBR on Jan 12, 2009 19:04:58 GMT -5
csw, one thing on squish...when u drop the cylinder you need to raise the ports to keep the same timing, otherwise you'll slow your saw down but should have an increase in torque. With engines theres always a trade off. Also, are you sure it increases the volume of the charge, because the piston still displaces the same volume in the crankcase? but it does increase the compression in the combustion chamber, as you said.
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Post by chainsawwhisperer on Jan 12, 2009 20:23:35 GMT -5
OBR, I forgot to mention that, thanks. Reducing the squish area, does not increase the 'volume' of the charge. What it does do is increase the percentage of usable charge in the combustion chamber. Hypothetically, 100% of the charge goes into the cylinder (VE is more like 75%), if you mathematically figure out the ratio of squish area to combustion area you will find that the squish area makes up about 5-7% of the area. If your original squish band is .040 and you then drop it to .020, now your squish band is only 2.5-3.5% of the total area. You have added 2.5-3.5% to your "usable" charge. You have to remember that the charge in the squish band does not really add to combustion pressure, it mostly protects the ring land. That's not to say that it doesn't burn, but it's potential is wasted when it burns. My way of explaining it may not be the most accurate, and my numbers are hypothetical, but that is the theory behind it. Search for Gordon Jennings 'Two stroke Tuners Handbook" It is by far the most comprehensive tuning book out there.
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Post by MCS on Jan 12, 2009 22:06:29 GMT -5
CSW, OldZip should not worry about measuring squish at this point. With new standard parts and gaskets he should have good compression. If he doesn't, then that is the first thing that needs to be fixed. Altering the squish, or a better term - the top dead center volume of the cylinder - is just a way to tinker with the engine output. It is the same a milling the heads on a car engine. OldZip, get some hours on that C and then get a new compression reading. Just for grins, I went out and did a compression test on an ebay 903 that I have - 150 psi - so I would think with new parts in the C, you should be close to that.
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Post by chainsawwhisperer on Jan 13, 2009 7:28:30 GMT -5
Zip, A7E is right, before you do anything else put some hours on it then retest compression. A7E, I did not mean that Zip should start tinkering with squish volume. I meant to check it to help determine if there was some error when the parts were machined. Yes, I know it's a 'one-in- a-million' chance that the compression is low due to a manufacturing/machining error. But we are still kind of grasping at straws for now. I hope I did not confuse anyone or derail this thread. CSW A7E, you used the word "volume" which is 100% correct, I had used the term "area" which is 100% wrong. (2nd power vs. 3rd power)
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Post by sugarcreeksaws on Jan 15, 2009 15:44:28 GMT -5
Hi OZ, Found this in a 2 cycle racing site for breaking in rings....sounds like a good technique....
"Crank up, keep idle to a max of 1/4 throttle first 2-3 minutes to allow engine to heat up properly. After that rev from idle to half throttle consistently for approx 5 minutes. Shut down and allow it to completely cool down. Crank it up again, allow it to warm up, then rev from idle to 3/4 throttle for approx 5 minutes. Shut down and cool completely. Start again, allow it to warm up rev from idle to wide open for just a few minutes, 2-3 or so. Now run it like you normally would."
I realize you have already started to break in the C-91....I would be willing to bet your compression will come up nicely.
Joe
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Post by MCS on Jan 15, 2009 21:01:33 GMT -5
You just missed a MCS on ebay. Closed at $71.00
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