Scuffs on Piston Skirt

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Dodge72

Dodge72

Odd one out
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So I got my slant torn apart a few days ago in anticipation of getting the block sent out to check if everything's good. I was prepared to see some damage to #3 due to oil on the spark plug and lower compression than the other cylinders when it was running. (150 in everything, then I think 110-120 in #3) Head has already been rebuilt and shaved .030" and placed back on the car, then the blue smoke happened.

Checked everything, bearings are okay. Camshaft good. Head gasket fine. No obvious broken rings on #3, but #2 piston had this on both sides right next to the wrist pin location:

20190225_202306.jpg


The actual cylinder looks very normal, no scratches or anything. Nothing enough to catch my fingernail on the skirt. Should I be concerned? Get new pistons? I have not been able to check roundness of cylinders yet. Thank you
 
Got too hot. It's done. Needs pistons.
 
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RustyRatRod said:
Got too hot. It's done. Needs pistons.
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Well that makes sense. Overheated the engine previously to where it started to knock and it warped the head. Thanks Rusty! Do you have a recommendation where to get quality pistons?
 
Dodge72 said:
Well that makes sense. Overheated the engine previously to where it started to knock and it warped the head. Thanks Rusty! Do you have a recommendation where to get quality pistons?
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Not really. Any of them will do. They are all the same piston for the 170, 198 and 225 so if it says slant six pistons it's probably right. lol I am going to use the long 198 rods in mine so I am going to run the 2.2 Chrysler 4 cylinder non turbo pistons.

Also, I would strongly recommend you mill that head at least a total of .100". That way it will actually help compression some and add a little power.
 
I was going to go through and measure out the cc's and figure out my compression ratio to plan out the block work and cam. My goal was to get a healthier compression ratio than stock. Might need to wait if I need to bore out the block, or maybe I can just mill it another .070" and figure it out from there.
 
Dodge72 said:
Well that makes sense. Overheated the engine previously to where it started to knock and it warped the head. Thanks Rusty! Do you have a recommendation where to get quality pistons?
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IF that's the only Piston with a Scored skirt (from what I can see) ,& there's no big lip or any lip on the bores other than Carbon, I'd just put in a good used or single NEW correct bore size Piston like a Silver light or Enginetech (rockauto.com no association with) & a fresh set of Ringings (if it wasn't using water prior teardown) Hone the Block , use cast rings or Chrome top if you might run it hot again.
Good luck.Trev.
 
RustyRatRod said:
Also, I would strongly recommend you mill that head at least a total of .100". That way it will actually help compression some and add a little power.
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I respectfully disagree. I would reccommend measuring and milling to get a total CR of 8.5-9.0. The actual amount would depend on usage, and cam used. Milling a total of .100 could get the CR up in the range, where the timing curve will get super critical to stay out of detonation, and premium fuel would be required.
 
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Charrlie_S said:
I respectfully disagree. I would reccommend measuring and milling to get a total CR of 8.5-9.0. The actual amount would depend on usage, and cam used. Milling a total of .100 could get the CR up in the range, where the timing curve will get super critical to stay out of detonation, and premium fuel would be required.
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Agreed, for a streeter or truck doing hauling. We used to take upto 100 thou give or take off a virgin head after I'd ported them & tickled chambers for the circuit.dirt rack racing getting comp right up there around 10:1, depending on head gasket. A total of
060" total cut (with some hardened exh seats & Kline bronze guides for early head,) generally raised the Comp Ratio 1 full point approx & kept you out of detonation & still allowed reasonably quick altered advance curve.
Good point. ( although for the racers for the pre-smog heads there's a ton of meat in those heads for serious miling)
Cheers again.T
 
My Kaw Triple 2 stroke lost the fuel oiler while going 80 down I95, pulling the clutch helped a bit but by the time I was down to 20mph the tire locked up. I let it set for 1/2 hr poured some oil in the plug holes and off I went. Pistons looked just like yours.
 
69FBCuda said:
My Kaw Triple 2 stroke lost the fuel oiler while going 80 down I95, pulling the clutch helped a bit but by the time I was down to 20mph the tire locked up. I let it set for 1/2 hr poured some oil in the plug holes and off I went. Pistons looked just like yours.
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Yep...it's Called "Galling" & funny you should mention the bike - back in the day when running in the new MX'ers or Fitting a New Piston to honed bore, we used to polish off high spots that started to Look like Galling or scoring & it a Map Factory race w/shop manual they even state & printed tear down after a heavier oil mix run in & "Wet sand the high spots down" (I'd already learnt this as a kid saving old Techumseh & B & S minibike eng pistons , if fact you be surprised how many prifessional "bush mechanics" can save an engine/piston by polishing out IF scoring/galling isn't to bad when replacements are know here to be had.
For the threaded I've just posted up 2 screenshots of rockautos Slant pistons avail (they have rings, gaskets, T/chain too for budget 1 stop shopping too)
IF your bores checkout OK & not cracked or needing bore job, get your current 5 pistons magnafluxed crack tested, check for any shrunk skirt & button it back up if as you say can head etc good.
You'll be disappointed if you lay out for full block record as your reringerr will go better.
Set of Gappless middle rings will make a difference added ( see totalseal) Giving away so speed secrets here.
Cheers Trev.
Piston c & p below...
 
AJ/FormS said:
Jus curious;
I agree that #3 piston swoll up, but wondering how it can happen to just that one
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Luck of the Draw ! - that piston caught & slowed you down before the others followed suit, unlike running short of oil. + Some engines with Paired/side-side exh ports tend to run hotter in that area than rest of engine
An old complaint of a good souped Ford Flathead V8.
Count yourself lucky ;-)
 
Charrlie_S said:
I respectfully disagree. I would reccommend measuring and milling to get a total CR of 8.5-9.0. The actual amount would depend on usage, and cam used. Milling a total of .100 could get the CR up in the range, where the timing curve will get super critical to stay out of detonation, and premium fuel would be required.
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OK, that's cool. I was just parroting what I've seen you post before. But I do agree to measure everything.
 
Thank you for all the input! I will be measuring out cc's and doing the math as soon as I get a graduated syringe here. Will the varnish ring at the top of the cylinders affect calculating the compression ratio? I'm gonna need to tell the machine shop guys how much to mill off the block.
 
If you mill the head the pushrods are now too short by the amount that was removed from the head . I have no use for cast pistons . the same for cast rings . Cheap crap IMO.
 
383Scampman said:
If you mill the head the pushrods are now too short by the amount that was removed from the head . I have no use for cast pistons . the same for cast rings . Cheap crap IMO.
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Pushrods may, or may not be too long. It depends on how much milling, and how the tolerances add up. Also depends on the cam base circle. I have run stock push rods with a head milled .125, and had to get shorter pushrods with the head milled .100.
As for cast pistons, unless you are building a pretty stout race slant, cast are fine. I have stock cast pistons in most of my engines. Cast rings are good on used bores (they will seat quicker, but not last as long). I like moly rings, on a new bore/hone.

PS: forged pistons for a slant will cost about $500 or more per set. cast pistons are less then $100/set.
 
383Scampman said:
If you mill the head the pushrods are now too short by the amount that was removed from the head . I have no use for cast pistons . the same for cast rings . Cheap crap IMO.
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I have already shaved the head
.030 and my stock pushrods have worked just fine. I've heard you can cut a bit off and still be okay. It'll depend on how much I cut off of course.

Edit:Oops, beat me to it lol. My cam will not be very radical if at all (Oregon Cam #2106 or #819, not sure yet ). Just upgrading small things to be a very nice driver/cruiser.
 
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Save the pushrods for last, that way you can check them
 
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