Piston clearance?

[lone wolf]

Im thinking Im gonna go ahead and go with a meteor on this one. It seems I could probably get by with this one at .006, but it's at the high end of the spectrum. Grandpa always said "If it's worth doing, its worth doing right"

hey you can email meteor with the q on clearance.

 

[blsnelling]

are you talking about new saws that don't have a lot of time on them im guessing?

Yes. And I find that the bottom of the intake skirt wears smooth right away.

 

[lone wolf]

Im thinking Im gonna go ahead and go with a meteor on this one. It seems I could probably get by with this one at .006, but it's at the high end of the spectrum. Grandpa always said "If it's worth doing, its worth doing right"

if you measured it correct maybe take one more look .

 

[wigglesworth]

if you measured it correct maybe take one more look .

I will measure tonight, as I dont have it here. And emailing Meteor isnt a bad idea.

 

[lone wolf]

hey wiggs i just measured a new i.t.b. meteor piston for a 044 ms 440 and the piston to wall clearance is .oo2 so I would say .002 is what the new piston to
wall would be if you got a new meteor or a slight bit more cause you are using a larger bore correct.

 

[lone wolf]

hey wiggs i just measured a new i.t.b. meteor piston for a 044 ms 440 and the piston to wall clearance is .oo2 so I would say .002 is what the new piston to
wall would be if you got a new meteor or a slight bit more cause you are using a larger bore correct.

btw where did you put the feeler gauge?

 

[Mad Professor]

I've measured up some new OEM Stihl 038M (52mm) and 038S (50mm) cyl assys.

They were between 0.002 and 0.0025 at the skirt.

They have a fair amount of taper so the crown had a lot more clearance.

 

[lone wolf]

I've measured up some new OEM Stihl 038M (52mm) and 038S (50mm) cyl assys.

They were between 0.002 and 0.0025 at the skirt.

They have a fair amount of taper so the crown had a lot more clearance.

what did u measure with

 

[Tzed250]

.


A good rule of thumb is .001" of clearance for every 1.0" inch of bore. This is the opposite of the guideline for interference fits.


.

 

[Fred482]

.


A good rule of thumb is .001" of clearance for every 1.0" inch of bore. This is the opposite of the guideline for interference fits.


.

X2, and the other "thumb" says .004" per 1.0" of bore for ring end gap. These work on most engines, not counting special metallurgy castings/stampings.

 

[wigglesworth]

Updated measurements!!

Ok guys, I borrowed the bore gauge and mic's and here is what I got...

Piston crown= 2.039
Piston 1/4" up the skirt=2.042
Bore=2.046

I also rechecked the bore with the feeler gauges, and I was wrong before. A
.004 will slide in and go all the way to the squish band. A .005 will only go about 1/4" up the skirt before hanging. The feeler gauge's verify that my measurement's are correct in that there is .004 to .0045 gap between the piston skirt and cylinder wall, not .006 like I first mis-measured. I dont think that is that bad, and will probably go ahead and run this piston. What say ye?

 

[Jacob J.]

If it were me, and it usually is, I'd buy a Meteor and be done with it. Save that one as a back-up.

 

[lone wolf]

to loose you should be 2 thou

 

[blsnelling]

Maybe too loose for perfect, but that piston should live a long time. On the other hand, Meteor pistons are cheap.

 

[lone wolf]

Ok guys, I borrowed the bore gauge and mic's and here is what I got...

Piston crown= 2.039
Piston 1/4" up the skirt=2.042
Bore=2.046

I also rechecked the bore with the feeler gauges, and I was wrong before. A
.004 will slide in and go all the way to the squish band. A .005 will only go about 1/4" up the skirt before hanging. The feeler gauge's verify that my measurement's are correct in that there is .004 to .0045 gap between the piston skirt and cylinder wall, not .006 like I first mis-measured. I dont think that is that bad, and will probably go ahead and run this piston. What say ye?

now what is the end gap of the rings?

 

[wigglesworth]

now what is the end gap of the rings?

I got new ring's on the way already. Actually have new rings and OEM clips on the way.

 

[lone wolf]

I got new ring's on the way already. Actually have new rings and OEM clips on the way.

did a rebuild last nite with a new meteor piston the end gap was 9 thou.

 

[timberwolf]

By the sounds of it then the piston has a good bit of life left, but also 1/4 to 1/3 of it's life gone. Unfortunatly that is the best 1/4. The looser the fit the greater the losses in sealing around the ports and more blow-by will result as the piston rocks in the bore potentially unseating the rings. Just little silent power robbers at first.

If you go to the trouble of porting a motor and increasing the bore it is somewhat a shame to throw away some of those gains to save a few bucks on a new aftermarket piston. Also from an hours to dollars prespective I would think the pay back on a new piston would pay for its self times over.

 

[Tzed250]

:agree2:

 

[Mastermind]

Aftermarket pistons are cheap when compared to saws, I'd go with a new one. But what do I know.