bamba
Collector wannabe
Posts: 16
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Post by bamba on Apr 26, 2011 10:40:27 GMT -5
I just happened to look closely at my cylinder while preparing to remove my flywheel to check my condenser. I was able to see and feel vertical scoring along the inside of my C-72 cylinder.
I recalled reading a comment here indicating that there's not much that can be done about it except to replace the cylinder.
Then I come across some comments indicating that the cylinder metal is harder than the ring or the piston and most likely the scoring is actually metal deposits from one or both of these.
I did a bit of checking and I've read that certain acids would dissolve the metal deposits enough to restore the saw to decent working order.
I figure you guys would know the ins/outs associated with dealing with a scored cylinder, and piston.
The scoring is just enough for my fingernail to get caught on it so it's pretty nasty.
I do have the option of bringing the saw back to the guy that sold it to me, but I kinda Luv this big ole girl, and I don't mind fixing her up as long as I don't have to do major surgery.
Thanks in advance
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Post by MCS on Apr 26, 2011 11:10:45 GMT -5
Well, before you get too carried away, have you done a compression check?
The cylinders are chrome plated which makes them very hard and there is really no need to hone them. In fact, a standard hone will do very little to the surface. Homelite didn't recommend honing and all that can be done if the cylinder is really bad is to replace it and the piston.
Believe it or not, some light scoring will have little effect on the saw. The bigger problem would be if the piston rings are stuck and locked in the grooves.
Start with a compression check and let us know the results.
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bamba
Collector wannabe
Posts: 16
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Post by bamba on Apr 26, 2011 11:37:53 GMT -5
This is the same saw (C-72) which has a compression of 120 PSI cold. With this being a separate issue, I figured I should create a new thread. It's encouraging to hear that some light scoring may not have a big effect on the saw. The saw definitely runs, actually it runs GREAT until it get's hot (20min) then it has to cool down before it will perform good again.
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Post by MCS on Apr 26, 2011 12:45:14 GMT -5
Personally, I think your problem is something other than compression. After it warms up, 20 min. as you say, does it stop running to the point where it won't even start and idle?
What exactly does this mean?
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Post by 925fetish on Apr 26, 2011 14:37:12 GMT -5
The piston heats up and grabs the rings so they can't seal the compression in.If you continue to run the saw again and again it will get past repairing and you will have to replace the piston and cylinder.As it stands you might be able to clean the cyl.w/muriatic acid,smooth the piston w/a scotch brite pad,and ream the ring grooves out so they have enough clearance to stay in contact with the cyl. wall after it gets some heat in it.
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Post by tribulation138 on Apr 26, 2011 15:12:32 GMT -5
yea... do comp reading first. ive had saws with 115 and lower that start ok. but under load die or quite after getting really hot. they all has scored engines or bad rings.
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Post by MCS on Apr 26, 2011 17:18:46 GMT -5
ream the ring grooves out so they have enough clearance to stay in contact with the cyl. wall after it gets some heat in it. I hope you are saying to remove any carbon buildup and not increase the width of the groove. bamba, do a compression check when the engine is hot. |
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bamba
Collector wannabe
Posts: 16
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Post by bamba on Apr 26, 2011 17:41:06 GMT -5
After it warms up, 20 min. as you say, does it stop running to the point where it won't even start and idle? then it has to cool down before it will perform good again. Exactly... I still haven't ruled out the condenser though. I've heard symptoms of the condenser failing while hot as well?? Once I find out if the condenser checks out, I'll take a hot compression reading. and I may as well check for healthy spark while hot and not starting. That "hot" compression reading should tell me quite a bit. Wouldn't a new set of rings and a smoothing of the cylinder go a long way towards increasing the compression? My rings are pretty much the same diameter as the piston. I would think they would be just a tad bigger?? |
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bamba
Collector wannabe
Posts: 16
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Post by bamba on Apr 26, 2011 17:44:08 GMT -5
yea... do comp reading first. ive had saws with 115 and lower that start ok. but under load die or quite after getting really hot. they all has scored engines or bad rings. Did you end up replacing the rings... or did you have choose to replace the cylinder? |
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Post by tribulation138 on Apr 26, 2011 18:39:05 GMT -5
yea... do comp reading first. ive had saws with 115 and lower that start ok. but under load die or quite after getting really hot. they all has scored engines or bad rings. Did you end up replacing the rings... or did you have choose to replace the cylinder? depending on the issue. if the cylinder is scored really bad it might not even hold a good compression even with rings. ive also had where the cylinder is fine but the piston is scored not to deep and i put a fresh pair of rings on. The saw ran awesome after that. some saws i tried different combinations to fix. but some saw engines no matter what you do will be just garbage. maybe you might have crank seal leaks also. |
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Post by MCS on Apr 26, 2011 20:09:32 GMT -5
Wouldn't a new set of rings and a smoothing of the cylinder go a long way towards increasing the compression? My rings are pretty much the same diameter as the piston. I would think they would be just a tad bigger?? You didn't say that you had it apart. How does the piston itself look? Yes, if the rings have lost their spring, new ones will probably fix most of the compression. I have an XL-800 that has rings the same size as the bore. I put it together just by pushing the piston and rings into the cylinder. It has about 120# but runs quite well. I put this saw together without new rings for a specific purpose - to see how it would run with low compression. It runs fine, maybe a little weak, but it can keep the RPMs up with a 18"bar so the clutch doesn't slip. On your saw, if the cylinder just has some light scratches, I'd put in new rings an put it together. Make sure you clean any carbon from the bottom of the ring grooves. Take one of the old rings and break it so it can be used as a scraper. Do not remove any aluminum from the edges of the ring groove while you are doing this. |
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Post by MCS on Apr 26, 2011 20:28:59 GMT -5
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Post by 925fetish on Apr 27, 2011 14:29:41 GMT -5
You have to open the ring grooves back up to original size.When the pistin scores around the ring grooves they close up and seize the rings,threfore the rings can't maintain pressure against the cyl.
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bamba
Collector wannabe
Posts: 16
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Post by bamba on May 7, 2011 11:21:00 GMT -5
You have to open the ring grooves back up to original size.When the pistin scores around the ring grooves they close up and seize the rings,threfore the rings can't maintain pressure against the cyl. You mean when I clean out the grooves the piston rings will spring open and make a better seal around the cyl? I'm having a hard time finding someone selling the "set" of rings I need. I've seen people selling a "single" ring but this saw has dual rings. Sooner or later (I think?) I'll find someone selling both rings as a set. Otherwise I'll have to buy 2 individual rings. Hopefully it won't come to that. Thanks for all your help |
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bamba
Collector wannabe
Posts: 16
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Post by bamba on May 7, 2011 14:23:21 GMT -5
You didn't say that you had it apart. How does the piston itself look?
Actually I don't have it taken apart, ..... not that much. I can look through the exhaust port and see some of the scoring on the piston and on the cylinder walls. I've also "lightly" dragged a screwdriver across sections of the cylinder scoring to get an indication of how deep the scratches are.
I did get the flywheel off and using a multimeter checked out the Secondary side of the coil. I found that the spark plug connector inside the boot wasn't connected to the wire securely, and was producing an intermittent connection.
I reconnected it and now I get a healthy 8.3K of resistance from the connector to ground.
The Primary side of the coil tested at 1 ohm, the condenser tested fine , and the breaker points operation tested fine as well. I cleaned a bit of oily residue from around the area, checked the point gap for .015 and reinstalled the assembly
I'm looking forward to getting the flywheel and other stuff back together and cutting some wood sometime tomorrow. I'm also looking forward to getting a compression reading while she's hot. It will be interesting to see if fixing that intermittent spark plug connection improves anything??
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Post by tribulation138 on May 7, 2011 15:47:19 GMT -5
lets us know on the hot comp reading.
and a intermediate spark does goes running difficultly or hard starting.
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Post by mineralman2 on Jan 6, 2024 19:59:43 GMT -5
I know this is a very old thread, but I just wanted to extend my thanks for all the interesting dialog here, particularly the science behind properly-functioning piston rings and the expansion of the different metals in a hot engine. Cool stuff!
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