MS461 Scuffing / scoring the bore intake side

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NickC

ArboristSite Member
Joined
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Location
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First off, as a new member Hi to everyone!

I bought an ms461 that had seen very little use, bar and chain never been off it was factory fresh under the bar. I've owned it a year now and used it rarely. Looking through the exhaust port I can see marking on the plating, I made a brass tipped 'scribe' to have a feel and can't really tell but it doesn't feel scored and notchy, they don't go all the way up the bore. There are a couple of stripes from contact on the piston skirt looking through the carb, but again, not obviously scored as such.

Through the plug hole the exhaust side of the bore is perfect, the piston is too on that side.

A few similar minor 'streaks' in the plating up from the transfer ports.

So I guess I'm asking is this anything to worry about? Is it 'normal'? I did read, but know can't find a thread that said a little scoring on this side is normal, I'm not sure which forum it was. I'm doubtful, I don't think it's normal.

A few observations when I first picked it up -

The mix looked very oily, there was a lot of carbon on the top of the piston which has now gone.
It was, and still is squeaky clean under the filter and into the intake port.
The chain was ruined, the front of the cutters had been bevelled down, I've no idea why but would indicate a lack of operator knowledge.
I don't remember the carb being set lean.

I will admit it has run a bit lean since, but only briefly while trying to get it cutting better after struggling with the chain, threw it in the end, After being led astray by you lot I ported the exhaust and removed the anti tampers, I didn't replace them after trimming the tabs and it drifted in lean while my brother was using it, I heard it 'wailing' but only for a short time in cold temps. It's not your classic lean run looking saw? The compression is good 170-80psi

Due to lack of use it's probably had a bit of slightly stale, but not 'dead' mix

So what's the smart money on?

Intake contamination?
Lean run?
Carbon?
Unsympathetic break in?
Mix?
There is no bevelling on the transfers, I guess due to the small length being quads? I can't see much on the exhaust.

I'm reluctant to pull a 'new' saw apart, but if needed it's an easy enough job for me and I have little a machine shop so can do most things, what worries me about that is being overcome by the desire to get the die grinder out....

Apologies for the length, I'll post a few (poor) images and thanks for any opinions.
















 
Welcome to AS. Generally intake side scuffing is from either debris or water ingestion. With a chain as you describe, I'd suspect debris. Fine particles from a heavily dulled chain made it past the air filter. I'd also suspect that the air filter and air box was cleaned up prior to your purchase.

That said, keep the chain sharp, filter clean, use fresh mix and run it.
 
Since the piston is much softer than the cylinder wall you will not know the full extent of the damage done until the cylinder is pulled off. Many of us will pull a cylinder just for the fun of it, it is not difficult for us but sometimes a daunting project for first timers.
 
I see that often in a saw that’s 100% fine.

Even new saws can have a bit of wear at the bottom of the skirt, even brand new after factory test fire.

I think your fixing something that ain’t broken. Viewing the intake bore through the ex port can give deceiving results. Even if there is some minor scratches on the intake side of the piston, which is the thrust side, I can’t see what it will make worse provided your air filtration is Ok.

Personally, I’d just run the saw.
 
I dont see anything abnormal either, i have looked at brand new never gassed (i think they do run a factory test though) and seen that. The exhaust side looking with a pen light thru spark plug hole is what i normally look at, but piston looks fine too, so i would just clean up air filter and run, choke the saw and use compressed air around air box prior to removing air filter. That is great compression. You are right the beveling is pretty slight on the smaller transfers these days but not much time for those rings to distort. Sounds like the saw found a good home now, congrats.
 
Thanks for the responses, all very much appreciated.

The paranoid, impatient perfectionist in me wants to strip it to inspect, but after a sit down and a cup of tea I realise that if I can just feel the marks with a point and they 'disappear' under a strong focussed light, they can't be scores, so I could strip the saw and scotch pad the marks off (hopefully) only to have them re-appear after a few uses.... Waste of time.

The rest of the bore is like a mirror, the marks on the intake skirt are minor witness marks on the fresh machined finish. I'm confident there hasn't been anything getting past a loose filter. So maybe what I'm seeing here is a bit of bedding in. I've never bought a saw less than 20 years old before!

As an aside, the saw has been my first 'big' saw and a trial, snatching, grabbing and smoking the clutch, wearing me out. Embarrassingly, it took me a long time to figure it out....

As said the chain was butchered, I had to file a lot of material off to get the cutting edge back, having successfully used a Stihl 2-in-1 file on the .325" saws I bought a 3/8" and used that. It has taken the depth gauges or rakers down to 1.0mm / 0.04".... So much for an 'easy file system', it's effectively scrapped the chain! The .325" is ok.
 
Those streaks look like oil smear that will wipe off. If those were marks on the cylinder then the piston would already be trash.
Little vertical black streaks on the cylinder wall and polishing on the bottom edge of the intake side of the piston happen within seconds after firing up a brand new saw from the factory.
 
Well curiosity killed the cat, but I'm glad it overcame me as this is not good...

Bore is ok as expected, the only thing I can see is a cluster of four pits in area of damage.

The piston is worse than I'd hoped, rough. OEM pistons are £104 in the UK!!!!!

Still can't see it's dirty air, there is not a scrap of dust to be seen. The rings feel rough around the pits.

IMG_20190403_200828.jpg IMG_20190403_200718.jpg IMG_20190403_195314.jpg
 
Looking at piston prices I thought I'd have a go and am surprised how well it cleaned up, touched the area with a fine diamond lap to check for highs - weren't any to speak of. Conscious not to remove any material very gently sanded the area with 1200 grit paper and a swipe with some scotch. Checked with a micrometer and the area isn't low as far as I can tell.

The only area left visible is in the close up, can only feel the two pits with your nail.

Still at a loss how this happened, the skirt covers the end of the transfer buy maybe 4-5mm in that area. The piston was heavily carboned when I bought it, thinking about it this started after it's first real hard days work. Is it feasible some loose carbon got into it from the transfer? Speculation of course.

Reckon it's ok? I'll get some new rings.

IMG_20190404_160043.jpg IMG_20190405_104005.jpg
 
Looking at piston prices I thought I'd have a go and am surprised how well it cleaned up, touched the area with a fine diamond lap to check for highs - weren't any to speak of. Conscious not to remove any material very gently sanded the area with 1200 grit paper and a swipe with some scotch. Checked with a micrometer and the area isn't low as far as I can tell.

The only area left visible is in the close up, can only feel the two pits with your nail.

Still at a loss how this happened, the skirt covers the end of the transfer buy maybe 4-5mm in that area. The piston was heavily carboned when I bought it, thinking about it this started after it's first real hard days work. Is it feasible some loose carbon got into it from the transfer? Speculation of course.

Reckon it's ok? I'll get some new rings.

View attachment 728119 View attachment 728120
Probably manufactoring casting flaws.
 
Looking at piston prices I thought I'd have a go and am surprised how well it cleaned up, touched the area with a fine diamond lap to check for highs - weren't any to speak of. Conscious not to remove any material very gently sanded the area with 1200 grit paper and a swipe with some scotch. Checked with a micrometer and the area isn't low as far as I can tell.

The only area left visible is in the close up, can only feel the two pits with your nail.

Still at a loss how this happened, the skirt covers the end of the transfer buy maybe 4-5mm in that area. The piston was heavily carboned when I bought it, thinking about it this started after it's first real hard days work. Is it feasible some loose carbon got into it from the transfer? Speculation of course.

Reckon it's ok? I'll get some new rings.

View attachment 728119 View attachment 728120

It always seems that an ounce of prevention, remove and clean up damage when first discovered, or wait for the pound of damage that is surely to come from just running it. When I first looked at the damage from the pict you posted I figured the damage would only get worse by running it. Good on on you for the ounce of prevention.
 
I have some OEM rings but haven't reasembled it yet, is the finishing (or lack of) normally this bad on the transfers?

And there's a nice cluster of four pits right where the damage is on the piston skirt.

I realize if a piece of material chipped off the transfer and got caught up there would be scoring, could the pits have anything to do with it? Collecting and loosing carbon?

I've seen little pin prick pits, these are like craters, I'm just at a loss how the damage occured as there was no filtration problem that I can detect.

I know I sound paranoid, I am...... And will be pulling the exhaust after every use to see it it's recurring...

IMG_20190411_102600.jpg IMG_20190411_102651.jpg
 
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