What we have in this picture is my old Jred 490 cylinder on the right with the matching piston(s), on the left is the one I just received to replace it. As you can see, they are different. I'm a little confused as to why they are so different, can anyone help me out? They appear to be the same size and have the same characteristics (except the windows on the inside), the pistons appear to be the same size too. I'm guessing it will work but wanted to get some feedback and opinions here before I try it.
Calling all Jred heads
- Thread starter sdb153
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No possible way those two cylinders will interchange. One is open transfer port and one is piston port. Totally different engine designs.
outdoorlivin247
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opcorn:
shawn022
ArboristSite Guru
Never seen a 490, but curious. Do you have a pic of the crankcase where the cylinder bolts on?
BTW what part of PA are you from?
BTW what part of PA are you from?
Not sure what the popcorn is all about but...I guess I'll be sending it back. Anyone know what saw it could be from? It's supposed to be a 490. All the holes line up, front handle screw hole in the side of they cylinder matches, two brackets or whatever where the muffler attaches match.
outdoorlivin247
Addicted to ArboristSite
Just kind of watching this...Not smart enough to know for sure...I think it will work as a whole, but you can't use the new piston w/ the old cylinder of vise versa...One is an open transfer the other is closed tranfer...It look like the old one has marks were the case will work w/ the new piston and cylinder...I have a 70E sitting int he garage right now that looks like the new set up...I can take a picture when the wife gets home...
outdoorlivin247
Addicted to ArboristSite
I'm about a half hour or so west of philly.
Yep, that looks just like the 70E in the garage...
Saw Dr.
Junk Collector
Lets dispell a few myths here. BOTH of those are piston port. That is the type of valving for the intake on a saw engine. The other common type is reed valve. The left one is an open transfer style cylinder/piston setup, which is generally lower in performance. The one on the right is a closed transfer setup, and is generally for higher performance. They may interchange. Several saws can use either style top end (Husky 257/262 comes to mind.) The important thing is that you do not try to use a non-windowed piston in a closed port cylinder, or it won't work. You can use a windowed piston in an open port cylinder, but that is usually not done from the factory to save on machining cost.
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shawn022
ArboristSite Guru
We're on the same page here. I think it would work but not 100% sure. The gasket would have to be cut out around the transfers. Hopefully more intelligent and seasoned jreders will come along.
shawn022
ArboristSite Guru
You can use a windowed piston in an open port cylinder
That I did not know. It doesn't mess with the flow?
That I did not know. It doesn't mess with the flow?
Saw Dr.
Junk Collector
There has been a bit of discussion about that on here and other forums. I have done it personally on at least 6 MS-290's I have rebuilt, and they all were SUBSTANTIALLY stronger than stock. Probably because of the increase in compression too, but it worked just fine.
If that 490 cylinder bolts up, and the squish checks out, it will very likely work just fine. The closed port cylinders may not be available anymore. A running open-transfer 490 will cut alot more wood than a closed-transfer saw with a junk top end. I'd bolt it on and run it, if it were mine.
Maybe I'll give that a try. I always have the original piston to fall back on if it doesn't work out. I loved the power prior to toasting it, I'd be disappointed to take a step back in power with the open port design.
outdoorlivin247
Addicted to ArboristSite
So the open window piston creates more crankcase volume to increase compression?..Or am I thinking wrong?...
shawn022
ArboristSite Guru
Thats good info. Guess I'll have to get some pistons back out and start measuring again. Maybe a 920 piston WILL work in a 910.
Saw Dr.
Junk Collector
Those pistons I used in the 290's were higher compression by design. It had nothing to do with the windows. Just a slightly taller crown.
Yes, you can use the original piston in the replacement 490 jug, if the pin to crown and pin to skirt distances are the same, and the squish is acceptable. Be very careful of the ring ends when changing pistons, as sometimes they end up where you don't want, and you'll end up snagging a ring and trashing the piston and jug. I would just run what came with it (the top end kit), unless it is a cheapo chineese one.
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PB
Addicted to ArboristSite
They came both ways, as the IPL's list different part numbers.
shawn022
ArboristSite Guru
And theres you're final answer
Saw Dr.
Junk Collector
I have not tried that, or checked on it, but be certain that a 910 piston will NOT work in a 920 or 930. The windows allow the fuel/air charge to pass through the transfers and on to the top of the piston in a closed transfer system. Without them, no mixture gets into the combustion chamber, and the engine does not run.
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