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Blowby - vertical cylinder wall scratches
https://www.slantsix.org/forum/viewtopic.php?t=66726		 Page 1 of 1
Author:  Pierre [ Mon Aug 15, 2022 12:13 am ]
Post subject:  Blowby - vertical cylinder wall scratches
In an effort to curb escaping oil vapor from the valve cover I switched back to a stock baffled unit. Open breather for the intake, Standard brand V180 PCV plumbed directly to the driver side plenum wall of a clifford manifold. Before installing the breather I ran the motor with pvc attached - no suction at the breather hole. Placed a paper towel over it - you can see a puff-suck-puff-suck pattern happening. Without the towel theres a steady faint stream of vapor coming out. Not a huge amount and it's very faint... just seemed like typical oil vapor.

Compression is good - lowest at 160, highest at 185. Leakdown.... not so much. 2 holes at 90+%, one at 85%, 3 at 40-50%. Sigh.

Attached are some boroscope pics. #6 is one of the 90% holes. What's that blotch? The others I got mixed up... I believe #10 is one of the 40% holes. You can see what appears to be deeper vertical mark towards the top. Yes, pics are rotated.

Is it possible these vertical marks are normal and I'm just chasing my tail .... or are any vertical marks a no-no? Reading random opinions online seems they are mixed but agree that any felt by a nail are a no-no. Gut feeling says the heads coming out. Is it normal for leakdown to be this significantly poor but compression good? I repeated the leakdown test a few times to verify it wasn't a testing error.

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Author:  Rick Covalt [ Mon Aug 15, 2022 3:23 am ]
Post subject:  Re: Blowby - vertical cylinder wall scratches
I see the compression Ok (or a little low) and the leakdown bad quite often working in the mower shop. I think the volume of air being moved by the piston is so large it overcomes the "leakage" and it still builds compression. Put the piston at TDC and do the leak down and all the leakage shows up.

If your leakdown test is bad probably the grooves are affecting you. Where do you hear the leakage from? The spot sure looks like rust / corrosion to me.
Author:  Dart270 [ Mon Aug 15, 2022 5:18 am ]
Post subject:  Re: Blowby - vertical cylinder wall scratches
What are you trying to achieve with this motor, and how much oil does it consume (miles/qt)? How many miles do you drive it per year?

Lou
Author:  Pierre [ Mon Aug 15, 2022 10:09 am ]
Post subject:  Re: Blowby - vertical cylinder wall scratches
I don’t think it’s the valves - it sounded like the air was leaking down the crankcase

I only drive it a few thousand miles a year during the summer. I don’t know how many miles on it but it’s low… 10-20-30k range since rebuild. It got one of Docs pump gears initially which ended up spinning on the shaft and loosing pressure. It was gone through a second time but I’m not sure if the bores were remachined or just honed the second time around

The idle was difficult to tune in the efi it was always rough and got worse as it was hot. This was my first higher compression 9:1 I think ) and nonstock cam 210rdp (edit: err, thats not right... believe its rv10 rdp) so I thought it was normal. With the Clifford cover on and a push in breather on the chimney the two short grooves filled up with oil after 300 miles. Cleaned it up, drove a second week with another 300 miles. Grooves filled up again and now it’s starting to come out of the dipstick base. That’s what prompted me to run the leak down instead of just compression. In the two weeks/600 miles it dropped 1/16-1/8 on the dipstick
Author:  Rick Covalt [ Mon Aug 15, 2022 1:33 pm ]
Post subject:  Re: Blowby - vertical cylinder wall scratches
Are you running a PCV valve?
Author:  Dart270 [ Tue Aug 16, 2022 4:24 am ]
Post subject:  Re: Blowby - vertical cylinder wall scratches
Yes, definitely need PCV. What are hot lash settings? If idle gets worse when hot, that is very often tight valves and that will make it idle rough and wear out valves and get poor gas mileage.

Lou
Author:  Pierre [ Tue Aug 16, 2022 7:40 am ]
Post subject:  Re: Blowby - vertical cylinder wall scratches
Yes pcv. With the Clifford cover I was using a pcv with a drilled hole and that removable baffle Dan described in another thread. The removable baffle would always eventually get overrun with oil. I thought it was just from lack of proper baffling. That’s when I switched back to a stock baffled cover.

I haven’t driven it with the stock cover. That’s when I realized the pcv had plenty of vacuum but there was zero felt at the breather hole. I did the leak down then and here I am.
Author:  Pierre [ Tue Aug 16, 2022 2:04 pm ]
Post subject:  Re: Blowby - vertical cylinder wall scratches
I can’t remember where I last left the lash. I believe that cam required more then stock… maybe 15/20 or 20/20. Yeah worse idle when hot may be valve lash but with grooves like that and unbalanced leakdown …. :shock:
Author:  Dart270 [ Wed Aug 17, 2022 7:04 am ]
Post subject:  Re: Blowby - vertical cylinder wall scratches
I would try 0.018" int and 0.025" exh and see if the idle is purrin' at high temp. Then you can tighten it up by 0.002" increments until the idle gets bad again. Yes, you do have some leakdown/comp issues, but personally I would probably not mess with it unless you are going for best MPG and least oil consumption and/or max power. Probably some combination of assembly issues and oil pump failure left you with the scratches, but they may not affect driving much if everything is tuned right??

Just spitballin' here...

Lou
Author:  Pierre [ Wed Aug 17, 2022 8:47 am ]
Post subject:  Re: Blowby - vertical cylinder wall scratches
Yeah it drives ok, the idle is rough but tolerable and I got the tune to where it won’t die hot or cold. The more I seal it up the more it’s leaking though. I filled the oil pan to block rail with silicone as I thought that was leaking all along the passenger side. Then it came out the dipstick base.
Author:  Dart270 [ Thu Aug 18, 2022 7:22 am ]
Post subject:  Re: Blowby - vertical cylinder wall scratches
The idle should be buttery smooth with that cam and compression, assuming sensible ign timing and lash and carb tuning.

I guess if you are building crankcase pressure, then maybe the ring sealing is not good enough?

Lou
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