Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jan 7, 2018 19:12:05 GMT -5
Well much to my disappointment I am posting about a replacement piston and not posting a video of a running C-72 which I had very much anticipated making today. Anyway I went back with new crank bearings and crankcase seals along with new piston and rings. This is all in combination of a new crankcase gasket, new coil wire, new rebuild kit in carburetor, new points and condenser, new intake gaskets (all three) which I thought all this would equal running C-72....WRONG. LOL anyway my trouble now is my new (aftermarket) piston from lil red barn has an issue. Once all assembled I was tightening the sprocket nut when I noticed a drag in the rotation of the crank. So I investigated different things all the way down until I had the cylinder back off. I found that the skirt of the piston is dragging the crankshaft on the down stroke. Now I guess there could be some slack in the rod cap and rollers but I am certain (after loosing hair on my head) that all the rollers made their way back into the rod and rod cap so none are missing. None the less the skirts is dragging. I am going to take both pistons to work with me tomorrow and let the worlds greatest machinist who I happen to work with have them and see what he can do. Its really only a few thousandths difference at most so I am not sure if trimming the skirt is the route I will take but I will at least measure everything best we can prior to doing that. I wonder what the likelihood of finding all those rollers in the rod cap new are, just in case I decide I need them?
|
|
|
|
Post by undee70ss on Jan 7, 2018 21:35:26 GMT -5
You MUST have all the rollers in there, or you will have issues in short order. You can’t have ANY slack in the rod cap. If you are not sure all rollers are there, take it apart and make sure. Use a little grease to keep rollers in place.
Aftermarket parts are sometimes way out of spec, keep us posted after your machinist looks at them.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jan 7, 2018 22:00:47 GMT -5
You MUST have all the rollers in there, or you will have issues in short order. You can’t have ANY slack in the rod cap. If you are not sure all rollers are there, take it apart and make sure. Use a little grease to keep rollers in place. Aftermarket parts are sometimes way out of spec, keep us posted after your machinist looks at them. I will certainly do so. I also found a set of rollers but I am positive I got them all in. I ended up using grease on the umpteenth try and it worked fine. I just figured any slack in there would essentially equal a shorter rod and cause the problem I have now. I figure either the piston is longer or the wrist pin hole is closer to the top which would allow the skirt to be lower |
|
|
|
Post by onlyhomelites on Jan 7, 2018 22:25:05 GMT -5
Man, if it wasn't for no luck, you wouldn't have any at all with the C-72! When she finally runs, it'll be that much sweeter though!
|
|
|
|
Post by dieseltech on Jan 8, 2018 7:06:26 GMT -5
I used a piston from Lil red barn in my C9 without any problems. It must be just a mismachined piston. Good Luck
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jan 8, 2018 7:42:57 GMT -5
Well didn’t take long after looking this morning to find the issue. The aftermarket piston is pretty close to original only it’s diame is .005 smaller. The difference that counts the most is of course visible in the pic with the thickness of the skirt. Shouldn’t take long to correct that though...but as my luck would have it I am back in the market for a set of rings as the new aftermarket rings didn’t survive removal in order to put the piston in the lathe to correct the skirt😕🙄 www.flickr.com/photos/138659658@N05/shares |
|
|
|
Post by sweepleader on Jan 8, 2018 9:56:20 GMT -5
Stick with it, you are doing a great job. You will soon have a saw you love.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jan 8, 2018 12:53:54 GMT -5
Stick with it, you are doing a great job. You will soon have a saw you love. Thank you sir I am certainly looking forward to the soon part |
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jan 8, 2018 15:37:48 GMT -5
Well after contacting little red barn and explaining what happened they are sending me a set of rings for the new piston for free. Overall I am satisfied just have a little concern over the new piston being .005 smaller In diameter. We checked all dimensions on the new piston vs the original and total height was within .003, distance from wrist pin to skirt was the same as well as to the top, and like I said diameter was .005 smaller. I am sure original design had a +/- tolerance I just have no idea if that is within but I am going to try it out anyway. There really is nothing wrong with the original piston it cleaned up good, I removed one keeper from the pin but couldn’t get the other sides keeper out ended up just knocking the pin through. Would that still be usable or would I need to find a replacement keeper for that side of the original piston?
|
|
|
|
Post by 5terrysupersaws on Jan 8, 2018 17:46:37 GMT -5
A good general guide line for piston to cylinder clearance is .001" per inch of bore diameter.In this case a 2" piston should have about .002" clearance.I just verified this spec. on one of my saws using a .002" feeler blade between the piston and cylinder wall,the feeler blade had a slight drag when pulling on it.(Tried a .0025" was too tight).An under size piston of .005" will give a total clearance of .007" ,WAY too much IMHO.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jan 8, 2018 19:13:11 GMT -5
A good general guide line for piston to cylinder clearance is .001" per inch of bore diameter.In this case a 2" piston should have about .002" clearance.I just verified this spec. on one of my saws using a .002" feeler blade between the piston and cylinder wall,the feeler blade had a slight drag when pulling on it.(Tried a .0025" was too tight).An under size piston of .005" will give a total clearance of .007" ,WAY too much IMHO. Thank you I was a little concerned about that. The machinist I mentioned earlier actually told me he thought that was too much also. He said I need to also consider how much wear may be in the cylinder too. |
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jan 9, 2018 7:53:51 GMT -5
After measuring again this morning the replacement piston is the same diameter below the rings as the original. It’s just the very top between the dome and the top ring that is a little under so I am much more comfortable now and confident the piston will be fine after the minor skirt mod. Any tips on installing rings and maintaining them in one piece? I put the first set on with no problem but removing them and the old ones on the original piston I managed to break them quite easily
|
|
|
|
Post by onlyhomelites on Jan 9, 2018 8:22:26 GMT -5
The best method is to use a ring spreader. Short of that, you can do it by hand, just be sure not to try to spread while you have too much height mismatch from side to side. My guess is the breakage occurred when trying to get from the lower groove up to the top of the piston? That's where I have had trouble before. It can be tricky, but if you do it by hand, you've got to spread both ends at the same time and lift it off.  |
|
|
|
Post by sweepleader on Jan 9, 2018 13:16:45 GMT -5
Right up there ^^^, what Leon said.
I should have said what Leon hinted at, do not go 2 grooves in one step. If you are working by hand, move from the top groove off then from the bottom groove to the top groove. Do not bend the ring more than one groove at a time.
|
|
