I'm careful to warm a saw before putting it to work or reving much. Does this thing need to set and idle for 5 minutes or what? Perhaps it simple expands more than the cylinder. That's beyond my pay grade though, lol.
Wiseco Piston Pics and Comments
- Thread starter blsnelling
- Start date
Help Support Arborist Forum:
timberwolf
Addicted to ArboristSite
I think this article covers the issue quite well.
http://www.docstoc.com/docs/14437665/Expansion-coeffficient-of-aluminum-%E2%80%93-Forged-vs-Cast
The main point is the silicon use to improve the castibility of cast pistons and cylinders for that mater also reduces the thermal expansion. Forged pistons simply change in size more with change in temperature and will require a little extra piston clearance and care in the warm up period.
http://www.docstoc.com/docs/14437665/Expansion-coeffficient-of-aluminum-%E2%80%93-Forged-vs-Cast
The main point is the silicon use to improve the castibility of cast pistons and cylinders for that mater also reduces the thermal expansion. Forged pistons simply change in size more with change in temperature and will require a little extra piston clearance and care in the warm up period.
I found this quote in the article interesting.
"Cast pistons give better long term wear in "normal" applications because the excess silicone hardens the surface.".
Sounds to me like a factory cast piston will give a longer service life in a chainsaw. The advange of the forged piston comes into affect under heavy abuse, perhaps as found in boosted applications.
"Cast pistons give better long term wear in "normal" applications because the excess silicone hardens the surface.".
Sounds to me like a factory cast piston will give a longer service life in a chainsaw. The advange of the forged piston comes into affect under heavy abuse, perhaps as found in boosted applications.
So, for this piston, should Brad take a little 1200 grit sandpaper to it until it has proper clearance for the cylinder he has?
Mr. HE
I have some super fine grit. Perhaps I should run my ball hone through the cylinder, giving it a little more oil holding ability, and perhaps ever so slightly enlarging it?
When measuring piston to bore clearance, where do you measure on the piston? There a big variance from crown, to below the rings, to the bottom of the skirt. Clearance at the skirt on this piston was less than .002".
I have sanded in the past when I had really tight pistons. I would fold the sandpaper in a zig-zag pattern and then wrap it around the piston and turn the piston by hand. This basically made an internal flap wheel sander and seemed to work well for taking a very small amount off evenly.
I could take a picture if you need.
Mr. HE
I could take a picture if you need.
Mr. HE
I have sanded in the past when I had really tight pistons. I would fold the sandpaper in a zig-zag pattern and then wrap it around the piston and turn the piston by hand. This basically made an internal flap wheel sander and seemed to work well for taking a very small amount off evenly.
I could take a picture if you need.
Mr. HE
That's exactly what I do too. I got a Golf piston once that was too big for the bore so I spent the better part of an hour hand-sizing it and checking the clearance with a feeler gauge to get it within specs. I think this is the best way of re-sizing a slightly too large piston.
Wiseco pistons have long been known to expand a lot due to the piston skirts and other areas being thicker overall. When I'm building the kart engines I have to spend a lot of time relieving areas inside the pistons to get them to a point where they won't cold seize.
What clearance should I be looking for here on a 54mm bore, and where to measure on the piston?
IMO, I would like to see .003 for that piston.
And check it at the bottom and half way up the skirt.
The crown is always much smaller.
Lee
And check it at the bottom and half way up the skirt.
The crown is always much smaller.
Lee
+1. On the Macs that are just slightly larger in bore diameter I usually shoot for .0035" to .0045" depending on the thickness and height of the piston. On the great big engines I might go a little more. The last West Bend 820 I put together with a Wiseco piston I went .0055" just because of the sheer size of the piston.
Careful measurement with my Brown & Sharpe dial calipers measures the bore at 2.1265". I know that's not the correct measuring device, but that's the best I have.
Here are piston measurements.
Very top edge - 2.116" / .0105" Clearance
Just below bottom ring - 2.120" / .0065"
Middle of skirt - 2.123" / .0035"
Bottom of skirt - 2.122" / .0045"
You can see how much the skirt has already worn.
Here are piston measurements.
Very top edge - 2.116" / .0105" Clearance
Just below bottom ring - 2.120" / .0065"
Middle of skirt - 2.123" / .0035"
Bottom of skirt - 2.122" / .0045"
You can see how much the skirt has already worn.
Last edited:
With dial calipers the part that hits the cylinder
is not sharp but is slightly flat and will give a false reading.
I would use a bore gauge or a good inside micrometer.
Lee
is not sharp but is slightly flat and will give a false reading.
I would use a bore gauge or a good inside micrometer.
Lee
These have a sharp edge, so it should be quite accurate.
My thoughts on this are no it should not go back.
The reason is because not every cylinder is the same size. Brad might have one on the smaller side and that is why his piston is too big. You could get a saw with a cylinder on the larger size and the piston would be just right for you.
Even a factory piston should be checked for size and adjusted down if too large and a larger one used if too small. Usually the a factory piston, being cast and having larger clearences, can just go right in a you'll get away with it.
Mr. HE
I decided to go ahead and give it a quick hone.
Last edited:
indiansprings
Firewood Purveyor
Can't believe the amount of skirt wear, most I've seen for no more than you ran it. Even with the hone job, I'd be afraid of seizure with prolonged sustained cutting. Gonna have to be careful and let the saw warm up as you do before spooling up. Got anyone close with a lathe. Might be able to chuck it up and use a fine emery cloth with a little oil to remove very little material on the crown.
Hmmm. I see what you are saying...but there will be nominal "cold" size for both piston and jug. I would assume that Wiseco have got this right. The problem with these forged pistons is that they seem to expand far faster than the jug. Most people will not be like Brad, they will start up the saw and stick it in some wood - and get a cold seize. If these things need a bit more slop in them when they are cold, then the need to be a scratch narrower than the stock items. The damage to this piston is effectively "the evidence".
Brad may have a narrow jug, he may not - that will need measuring (precisely) as well.
:agree2:
In reality very few people know how to do this and never measure anything, they just pop it in an go. If they are in fact to big I think Baileys is goign to start having problems. Just my thoughts.
My thoughts on this are no it should not go back.
The reason is because not every cylinder is the same size. Brad might have one on the smaller side and that is why his piston is too big. You could get a saw with a cylinder on the larger size and the piston would be just right for you.
Even a factory piston should be checked for size and adjusted down if too large and a larger one used if too small. Usually the a factory piston, being cast and having larger clearences, can just go right in a you'll get away with it.
Mr. HE
In reality very few people know how to do this and never measure anything, they just pop it in an go. If they are in fact to big I think Baileys is goign to start having problems. Just my thoughts.
