Odd Piston Wear

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I Installed some economical pistons after a bore to .040" After about ten kilometres of wear, I pulled the engine apart for unrelated reasons but noticed some odd horizontal wear on the pistons. It looks to be machining marks when the pistons were made. The marks are only on the front and back. I'm thinking these marks are from the rings not being fully seated and started to wear an outer layer of the pistons? I was going to only replace the rings and do a hone, but now I am questioning the pistons themselves. I believe these are Emgos 19145/E040. What are your thoughts on the wear and should I reuse the pistons?


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Cheers
Dan
 
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How much clearance is there between the lower part of the piston skirt at its tightest point and the bore?

Just by the way, you may not have cleaned the honing grit off the bore very well.
 

acadian

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How much clearance is there between the lower part of the piston skirt at its tightest point and the bore?

Just by the way, you may not have cleaned the honing grit off the bore very well.
Seconded, check and then double check the skirt clearance at the lower portion of the bore, front to back, with a good (calibrated) micrometer and bore gauge. When cleaning a freshly honed bore do not use solvent based cleaners, just warm water and soap.
 

SteveA

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Bit of a carborundum here.... :rolleyes: Yes I do know how to spell conundrum! ;) (Edit: It is carborundum I have difficulty with)

If it was honing grit, where is that grit now?

Keep stripping and flush everything?

Pistons should be fine after a bit of a clean up too, and why would you want to put more expensive pistons in it unless you were 100% you knew what the cause was and had eliminated it?
 
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SteveA

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OK, silly question.....were your piston ring clamps 100% clean and did you have to wiggle them around at all fitting or removing?

Isn't it strange the marking is only in the middle third of the piston height on one side?

BTW, you say you are thinking about a hone, but why?

You haven't shown us the bore, but if it is fresh from the borer why would it need a hone?

Unless you already know you don't have enough clearance?
 
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I don't see how it's possible for pistons to get that horizontal scuffing pattern in normal operation. Looks like somebody hit it (them) with a wire brush or similar with a side-to-side motion though can't think why anybody would do that.
 
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I don't see how it's possible for pistons to get that horizontal scuffing pattern in normal operation. Looks like somebody hit it (them) with a wire brush or similar with a side-to-side motion though can't think why anybody would do that.
To take out the vertical scratches!
 
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Cylinders were cleaned after they were honed. When I picked them up from the machine shop, they actually forgot them on the parts washer for a couple hours

I didn’t use ring clamps and no one did any sanding to them. I think perhaps there was particulates in the oil that exposed the production marks.

I’ll have a look at clearances next time I get into the shop.

and I want to do a hone just to make sure that the rings do seat properly. Yes 10km is probably not enough to glaze the cylinder walls, but at this point why take any chances.
 
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I’ll be sure to do a better job cleaning this time. The drain plug screen was pretty nasty as well when I cleaned it out. The whole engine needs a proper cleaning.
 

RoadScholar

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How much clearance is there between the lower part of the piston skirt at its tightest point and the bore?

I think this is a very good question. I'd like to add another: Did you check the end gap of the rings before installing? If the rings are tight and the bore to piston clearance is wide the horizontal scuffing could be piston slap. I wouldn't disagree that there could be a manufacturing glitch, but if you didn't measure/adjust the end gaps and the skirt clearance your issue, from my perspective, will remain in some dark corner of the Twilight Zone.

I compliment you for noticing and bringing this to the right place.

Best.
 
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I always check ring gaps when assembling top ends.

I'll have to have a look at skirt to bore clearances next time i'm in the garage. Thanks for the suggestion. I have my hands full with a 1 year old and a demanding job as a service electrician. Oh and I see on the underside that these are JCC's.

Cheers
Dan
 
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When I have a rebore done I scrub the bore with washing up liquid and a pot scourer to get every last little bit of grit out of the bore
A parts washer is not enough in my opinion
I use hot water, a bar of soap and a sponge.

Dish washing liquid plays Hell with my dermatitis!
 
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mean gene

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My guess is piston slap top on one side of skirt bottom on other side. Can't guess why horizonal marks, as Grandpaul said 'Defies logic".
 
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