Cylinder out of round?

[wigglesworth]

Anybody ever came across a cylinder that was out of round?

I think I found one. Id take a pic, but you couldn't tell anything from a pic. The cylinder looks mint, no scoring scratches or anything like that, but once the piston get's an 1/8" or so above the exhaust port, there is resistance on it, and it will scuff the piston a bit if you push it to the top.

BTW, it's an OEM Husky 55 cylinder. The piston in question is a brand new Espian, that measures perfectly round with my calipers. I wish I had the right tools to measure that deep inside the cylinder.

 

[Axlerod74]

Anybody ever came across a cylinder that was out of round?

I think I found one. Id take a pic, but you couldn't tell anything from a pic. The cylinder looks mint, no scoring scratches or anything like that, but once the piston get's an 1/8" or so above the exhaust port, there is resistance on it, and it will scuff the piston a bit if you push it to the top.

BTW, it's an OEM Husky 55 cylinder. The piston in question is a brand new Espian, that measures perfectly round with my calipers. I wish I had the right tools to measure that deep inside the cylinder.

Any chance the rod could be slightly bent?

 

[wigglesworth]

Any chance the rod could be slightly bent?

Nah, this is while holding the cylinder and piston in my hands.

 

[Axlerod74]

Nah, this is while holding the cylinder and piston in my hands.

Yeah, after I thought about it, it wouldn't make much difference anyway due to the wrist pin.

 

[Stihl-Pioneer]

I have a set of inside micrometers, but they won't do you any good here.
Some outboards allow I believe up to .004 out of round. I am not sure on saws.

 

[THALL10326]

Anybody ever came across a cylinder that was out of round?

I think I found one. Id take a pic, but you couldn't tell anything from a pic. The cylinder looks mint, no scoring scratches or anything like that, but once the piston get's an 1/8" or so above the exhaust port, there is resistance on it, and it will scuff the piston a bit if you push it to the top.

BTW, it's an OEM Husky 55 cylinder. The piston in question is a brand new Espian, that measures perfectly round with my calipers. I wish I had the right tools to measure that deep inside the cylinder.

I had a 026 aftermarket job come in the shop once that was smaller near the top of the cylinder. The piston would not go to the top of the cylinder, it would stick, you couldn't budge it to go to the top, couldn't use it. You sure its out of round or just tighter(smaller) at the top?

 

[wigglesworth]

I had a 026 aftermarket job come in the shop once that was smaller near the top of the cylinder. The piston would not go to the top of the cylinder, it would stick, you couldn't budge it to go to the top, couldn't use it. You sure its out of round or just tighter(smaller) at the top?

Well, the tight spot doesnt go all the way to the top. It will leave 4 or 5 little scuff marks on the piston, spanning from transfer to transfer, just above the exhaust port height. Once again, I am certian the cylinder is clean, free of any aluminum smear or any score marks etc, etc. It's almost like there is a ripple in the cylinder or something?

 

[THALL10326]

Well, the tight spot doesnt go all the way to the top. It will leave 4 or 5 little scuff marks on the piston, spanning from transfer to transfer, just above the exhaust port height. Once again, I am certian the cylinder is clean, free of any aluminum smear or any score marks etc, etc. It's almost like there is a ripple in the cylinder or something?

Thats odd for sure. Cylinder new or used? If its used I guess it worked at one time or another..

 

[teatersroad]

In Gordon Jennings 2-stroke bible I recall he alludes to how pistons at ambient temp are actually conical, and take to being cylindrical at operating temp. Could it be your the fit is tight and noticeable in the fashion you mention because of the 'conical' nature?

Episan allows for 'a' or 'b' sizing when ordering. Do your machine stamps match? For kicks maybe heat the piston and see how it fits.

 

[wigglesworth]

Thats odd for sure. Cylinder new or used? If its used I guess it worked at one time or another..

Used. It had some aluminum transfer on it when I got it, but no damage to the plating that I can see or feel.

 

[frischtr]

In Gordon Jennings 2-stroke bible I recall he alludes to how pistons at ambient temp are actually conical, and take to being cylindrical at operating temp. Could it be your the fit is tight and noticeable in the fashion you mention because of the 'conical' nature?

Episan allows for 'a' or 'b' sizing when ordering. Do your machine stamps match? For kicks maybe heat the piston and see how it fits.

The fit would be tighter at operating temperature, as the piston would swell slightly and the cylinder diameter shrink.

 

[wigglesworth]

In Gordon Jennings 2-stroke bible I recall he alludes to how pistons at ambient temp are actually conical, and take to being cylindrical at operating temp. Could it be your the fit is tight and noticeable in the fashion you mention because of the 'conical' nature?

Episan allows for 'a' or 'b' sizing when ordering. Do your machine stamps match? For kicks maybe heat the piston and see how it fits.

It's an "A" piston, but the jug doesnt specify "A" or "B".

 

[teatersroad]

The fit would be tighter at operating temperature, as the piston would swell slightly and the cylinder diameter shrink.

copy that, but if it were noticeably over tight or more consistent in it's resistance it may point to the piston as the problem.

 

[SPDRMNKY]

maybe not the "right" tools, but...

how about a good straight edge or metal ruler and a small bright flashlight?

lay the ruler down the side (inside), get your glare just right, and you might be able to see your imperfection...

or...

if you can get the cylinder stood on it's head and locked down...make the base level, and then use a combo square to see if your sides (inside) are "straight"

a light touch obviously...

just the first couple thoughts in my noodle...not scientific, but MIGHT give you an answer?

 

[teatersroad]

It's an "A" piston, but the jug doesnt specify "A" or "B".

Pretty sure "A" is the smaller option, so good there. I don't know Stihl, but shouldn't there be a machine stamp dead center on top of the cylinder? If not does that point to cheap aftermarket? You are fitting w/o rings I presume.

just thought, have fun with that head scratcher

 

[wigglesworth]

Pretty sure "A" is the smaller option, so good there. I don't know Stihl, but shouldn't there be a machine stamp dead center on top of the cylinder? If not does that point to cheap aftermarket? You are fitting w/o rings I presume.

just thought, have fun with that head scratcher

It's a Husky cylinder. For sure OEM as well. And yes, no rings.

It's definitely a head scratcher.

 

[teatersroad]

It's a Husky cylinder. For sure OEM as well. And yes, no rings.

It's definitely a head scratcher.

missed the husky ref, had stihl on my mind somehow. open port? you probably mentioned that too though. I would hazard to guess an open port would be more likely to distort, but just a guess. If it's closed port 55, those are coveted and hard to replace.

 

[wigglesworth]

missed the husky ref, had stihl on my mind somehow. open port? you probably mentioned that too though. I would hazard to guess an open port would be more likely to distort, but just a guess. If it's closed port 55, those are coveted and hard to replace.

Yep, open port. It seems the distorted area is right above the exhaust port, spanning from transfer to transfer. I may run a hone thru it, to see if there are any noticible valley's or ridges. Besides, it's junk right now, oh well if I tear it up.

This was going on a saw to sell. New bearings, seals all new intake rubber etc, etc. I guess im in the market now for a cylinder.

 

[Nitroman]

Rather than speculate, take it to a machine shop and have it measured correctly.

 

[shelbythedog]

Certainly a replacement cylinder would be cheaper than buying the tool, but the best way to measure the roundness of a bore is with a bore gauge. Measuring out to .0001" would certainly give you a difinitive answer to your question. In my experience rebuilding automotive 4-strokes it is not uncommon to see bores out of round by .0010-.0020" of an inch and if the piston to wall clearance is tight in your cylinder it could certainly result in a tight spot.

Dial Bore Gages - Sunnen