Is this the cause of my blowby

General engine tech -- Drag Racing to Circle Track

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simon010
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Re: Is this the cause of my blowby

Post by simon010 » Thu Aug 09, 2018 9:05 pm

the top ring looks like its "shinny" at the gap.

rgds
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Re: Is this the cause of my blowby

Post by AC sports » Fri Aug 10, 2018 5:36 am

It's just the pic mate.
None look to have butted together.
Cheers

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Re: Is this the cause of my blowby

Post by jed » Fri Aug 10, 2018 6:43 am

X2

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Re: Is this the cause of my blowby

Post by Leftcoaster » Fri Aug 10, 2018 9:34 am

The hone cross hatch pattern showing in the OP's second photograph is no where near the universally recommended 60 degrees

Pistons look to be 2 litre Alfa/Lancia 2v DOHC, and the valve cutouts look like they'd trap much of the 5ml of oil injected for the "wet" compression test

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Re: Is this the cause of my blowby

Post by Neal Arnold » Fri Aug 10, 2018 12:55 pm

The cylinder finish is definitely the problem! Picture shows it.

If it was bored and honed then a 320 ball hone. How much was left after bore? What grit stone was used before it was ball honed?

Just doesn't seem right?

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Re: Is this the cause of my blowby

Post by AC sports » Fri Aug 10, 2018 2:50 pm

Looks like the bore was machined 0.02mm undersize in error. Don't ask! Machine shop
error, but mine too for not checking his calibration. He used 2 Mikes. One for the bore gauge one for the pistons. ..and guess what?
Anyway,
I suspect I know the answer to this one, but I'll ask it anyway to hear your opinions & reasons.
Can I use a 240 grit ball hone to take it out the 0.02mm then plateau with a 320 grit ballhone @ the correct angle?

DJ58
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Re: Is this the cause of my blowby

Post by DJ58 » Fri Aug 10, 2018 4:17 pm

Not with a ball hone :( need to have it done with a honing machine to correct size. May need to be bored to next oversize piston to clean up cylinders.


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Re: Is this the cause of my blowby

Post by MTENGINES » Fri Aug 10, 2018 5:07 pm

Leftcoaster wrote:
Fri Aug 10, 2018 9:34 am
The hone cross hatch pattern showing in the OP's second photograph is no where near the universally recommended 60 degrees

Pistons look to be 2 litre Alfa/Lancia 2v DOHC, and the valve cutouts look like they'd trap much of the 5ml of oil injected for the "wet" compression test
60°? Universal?

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Re: Is this the cause of my blowby

Post by MTENGINES » Fri Aug 10, 2018 5:22 pm

Warp Speed wrote:
Tue Aug 07, 2018 7:14 pm
I think that early overheat may have taken it's toll. Unless it was just too tight to begin with.
This

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Re: Is this the cause of my blowby

Post by Biteme » Fri Aug 10, 2018 6:17 pm

Why is there no carbon on 2nd ring just below top rings gap?
1st thing I thought when I saw it was fuel wash through excessive end gap.

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Re: Is this the cause of my blowby

Post by rebelrouser » Fri Aug 10, 2018 6:43 pm

My 2 cents. The scuff marks on the cylinder are due to loading of the skirt, I would check piston to wall clearance. A lot of forged racing pistons now are a very hard alloy, they are prone to scuff walls, especially if high combustion temps make them swell a lot. Many times clearance may need to be adjusted. I would wonder how round the bore actually is, I have freshened engines with excessive blowby, that looked similar to the photos, and when measuring the bore they were not round, many were egg shaped, or had low spots in them, either from poor machining, poor honing, or cylinders walls that just could not take the cylinder pressure. I leak check all my engines on the stand before firing. If they leak too much they come back apart and I find out why. I have had customers give me blocks with machine work done, that leaked 30% or more on the stand. A trip to a good machine shop and a better hone job, fixed most of them.

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Re: Is this the cause of my blowby

Post by af2 » Fri Aug 10, 2018 10:09 pm

MTENGINES wrote:
Fri Aug 10, 2018 5:22 pm
Warp Speed wrote:
Tue Aug 07, 2018 7:14 pm
I think that early overheat may have taken it's toll. Unless it was just too tight to begin with.
This
And that!!!
GURU is only a name.
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Re: Is this the cause of my blowby

Post by Leftcoaster » Sat Aug 11, 2018 11:21 pm

MTENGINES wrote:
Fri Aug 10, 2018 5:07 pm
Leftcoaster wrote:
Fri Aug 10, 2018 9:34 am
The hone cross hatch pattern showing in the OP's second photograph is no where near the universally recommended 60 degrees

Pistons look to be 2 litre Alfa/Lancia 2v DOHC, and the valve cutouts look like they'd trap much of the 5ml of oil injected for the "wet" compression test
60°? Universal?
MT, I was referring to the cross hatch patterns observed on approximately 18 different gasoline and diesel blocks received from engine machine shops - - perhaps there have been dramatic changes these last 20 years?

For what its worth, although the OP hasn't confirmed engine identity, to para phrase what former Hart F1 engine builder and Alfa/Lancia guru Guy Croft of the UK has written re flex hone bore prep after boring and honing

" - - use 10W40 engine oil as lubricant - - 20 secs at 400 to 500 rpm to create a 30 degree cross hatch, then a slower stroke for 10 secs for 45 degrees

- - chrome faced top rings 180 grade silicon carbide - - moly faced 240 grade

- - Total Seal gapless top rings 240 grade, 20 degree hatch - - "

I'm also aware suggestions on previous ST threads run the gamut from similar flex hone finishes to near mirror finishes, with nothing more viscous than WD40 as piston/ring break in oil

At days' end, I'd follow the ring manufacturer's suggestions :?

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