|
|
Post by karla48 on Dec 17, 2012 15:09:39 GMT -5
Finally got my second Homelite 330 running, I also started on my third re-build. Anyhow just some interresting Info, on the one I just finished. I had spark, I had 110 PSIG of compression with 5 pulls, and had a clean carburator but could not get a pop from the engine. I tried a little carb cleaner directly into the engine but nothing. I tore the engine completely apart inspecting everything, and found both piston rings completely stuck in the piston. Cleaned the cylinder and piston, and replaced the rings, and re-sealed the engine. The engine started on the second pull, and tuned up really nice with some minor tweaks. I didn't check the new compression numbers, and probably should but it definitely has power.
|
|
|
|
Post by tommyhnavix on Dec 17, 2012 15:29:55 GMT -5
Some times when you remove the muffler you can see the rings have like a whitish powder on both sides. These are usually stuck in the piston. I have squirted the acetone, dextron atf 50/50 mix into the cylinder, reinstall the plug and let it soak a while. I pull the rope several time a day as I pass by the saw. All at once you can feel a dramatic rise in compression. Pulling the rope allows the pressure to work the mixture past and behind the rings freeing them up nicely. Every saw I work on gets the muffler off to check for scored piston and cylinder, then compression checked. After compression test I give it about a table spoon dose of the acetone,atf mix and pull the rope about 5 time and let it set. Some times over night. Most of the time there is an increase in compression when retested from freeing up the rings and the cleaning effect. There are a few saws that still need to be disassembled and have new rings installed though. As far as compression goes. In my experience any thing under 110 pounds compression has a lot of wear or stuck rings. It may run but will not cut well because of lack of power under load. 120 pounds is about the minimum but that can very by saw size and pro saw verses consumer grade saw. I like130-140 pounds compression and above. If the saw has no power under load with that kind of compression it's usually not a piston, ring, scored cylinder issue.
Tom
|
|
|
|
Post by karla48 on Dec 17, 2012 15:40:14 GMT -5
Oh, I just checked the compression with the new rings, and its only 120 Psig, but definitely starts on the second pull and runs and sounds great, so Just an update. I was hoping for a little higher compression but I'll have to find some specs on the 330's and see what a really good compression reading would be, any thoughts?
|
|
|
|
Post by karla48 on Dec 17, 2012 16:15:38 GMT -5
Tom, Thanks for your help. I probably should have measured the inside diameter of the cylinder and checked it with my bore micrometer but I didn't, I suspect I have alot of cylinder wear. The cylinder inspected Ok, I did have a little bit of scoring near the exhaust port but below the rings on the piston. Anyhow, Its running! I did find some Spec's for the 330's in one of my service manuals, and they stated about 130-160 Psig with a warm engine. My reading of 120 Psig was with a completely cold engine, Now I have my curiosity If I heat the engine up, and then take an immediate reading, what will it be. Anyhow something to try, just for curiosity! Lol.
|
|
|
|
Post by karla48 on Dec 17, 2012 16:26:38 GMT -5
Oh, I am also wondering If there is a wear in period for the new rings? I have not run the saw very much, maybe a total of 5 minutes. Maybe I should go out and cut some wood for 30 minutes or so, and then check the compression again, something to do on another day. Also Lol.
|
|
|
|
Post by Brian VT on Dec 17, 2012 17:41:24 GMT -5
Search anywhere for "engine break in" or "seating rings".
Lots of different theories from running extra oil to using minimal, or even no oil. Then there's the question of how hard to run it. Again, theories range from babying it to putting a hard load on it.
TONS to read and you'll have to decide what makes more sense to you.
This is generally how I go about it for my dirtbikes (same principle).
Cool down means ALL the way. Engines will hold heat a lot longer than you can tell. I wait 3 hours minimum.
"1st ride of the day 1/4 throttle for 15 min let bike cool down-check bolts for tightness
2nd 1/2 throttle for 15-20 min let bike cool down-check bolts
3rd 3/4 for 15-20 let bike cool down-check bolts
4th -go nuts."
"When breaking in a 2 stroke the most import part of the break in has nothing to do with the rings. it's actually the piston skirt. you hear the people talk about warm up let it cool several times. Well this is correct, however it is to work harden the lower portion of the piston skirt and form fit it to your cylinder. Under high RPM the skirt will flex, and more so when new and prior to work hardening. If over rev'd prior to break in, you can damage the piston, and cause metal blurring. have you ever pulled an engine down, and you see the piston skirt has blurred or torn metal. look at it with a strong magnifier, and you can see the damage. Low RPM's, not riding, just above idle until the engine is completely warm, let it cool completely, do this twice, then ride about 15 minutes without over revving. after that you are good to go."
|
|
|
|
Post by karla48 on Dec 17, 2012 20:11:42 GMT -5
Brian, Thanks for your analogy to a dirt bike, it makes sense. So I guess, I will count today as day 1 with 5 minutes of runtime. Then tomorrow run it for a little longer (maybe 5-10 minutes), and If we get a nice day latter in the week then cut some firewood for 20-30 minutes, That should give it a few heat ups and cool downs. As far as the head bolts - ugh, It would require a complete teardown of the chainsaw to get to the engine bolts, so I think I will leave them alone. I did follow the head gasket sealant directions, which was to apply the sealant, and snug up the bolts, and let dry for an hour, then tighten them the rest of the way, and wait 24 hours which I did too. Anyhow Thanks for the help.
|
|
|
|
Post by karla48 on Dec 18, 2012 11:08:36 GMT -5
Oh, some more data, I ran the engine for 5 minutes today to get the engine warmed up, reving it up a little during that 5 minute period, and then took the compression readings on a warm engine. The compression readings are Now 95 PSIG, which means they went down from the cold readings of 120 PSIG, Does this make sense? It seems opposite of what I expected, I thought I would get a higher reading, Any thoughts ??
|
|
|
|
Post by tommyhnavix on Dec 18, 2012 11:23:05 GMT -5
WOW!! Brian, That is great advice  I think one might be wise to do the same when buying a new piece of equipment also. I like synthetic two cycle mix oil. I use amsoil at 64:1 mix ratio. When I install new rings, cylinder or piston I like to take the saw out and do some light cutting with 32:1 non synthetic mix. I try to run one tank full through the saw and set the carb a little rich to limit the top speed. When the saw goes out the door to the customer I give him one bottle of 32:1 non synthetic for one gallon and tell him to run that through the saw and bring it back to me for final carb adjustments with the oil mix they are using. Also record before and after compression readings. It usually increases a little after a gallon of fuel is run through it. This has worked out pretty well for me. When you work on other peoples saws it's hard to monitor the use they get. Some definatly get used harder than others. The tree service guys I do work for follw my suggestions pretty well because they have seen longer life by breaking them in a little before heavy use. Saves them a lot of money in the long run. I try to encourage the same thing with new saws I sell also. On my own personal saws I try to run a gallon of 32:1 non synthetic mix through them to break in before switching to 64:1 synthetic Amsoil mix. I do it on new ones and overhauled ones. My oldest saw is over 30 years old and still runs and cuts like new. Tom |
|
