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Need Advice. First engine build - Lots of Blow By

Spinner

Probationary Member
9
1
Oct 11, 2017
Van Buren, Arkansas
Recently I finished my first engine build here's a quick run down.
Oil port
Balance shaft delete
Scat H beam rods / stock 2g pistons
Ring gaps .020 top and .023 bottom
Block and head are stock otherwise
New valves, guides, and seals.
Maybe 5 miles on build so far.

Here's the issue I'm experiencing quite a bit of blowby and oil seeping through the bolts on the valve cover.
I noticed the PCV was not in great shape.
I do have the PCV as well as the left side port running to a catch can.
Thinking that it may be backing up there somehow I unplugged the line to the can and let the PCV breathe free and still same issue.
I do notice a steady puff, puff, puff of blowby out of the side port on the valve cover sorry I have no other way to measure it.
My initial impression was that I had gapped the rings too large but I am confused since I read this gap is common and even larger gaps still.

Apologies for the wall of text this is the best I can describe it. Again it's my first build so I may be missing something obvious.

Any advice would be great, thanks in advance.
 
Last edited:

DSMPT

DSM Wiseman
1,340
888
Jun 12, 2014
Japan / Mexico, Arizona
Do a leak down test and a compression test. That could narrow down the issue.
.020" and .023" gap shouldn't cause that much blow-by. So I guess you improperly gapped or you have something else that cause it. In addition to the ring gaps, damage on piston ring lands/skirt, bad ring sealing (wrong ring installation, damaged rings, improper cylinder wall preparation) and PTW clearance would be suspicious. How much piston to wall clearance do you have?
 

Spinner

Probationary Member
9
1
Oct 11, 2017
Van Buren, Arkansas
Thanks for the reply. Unfortunately I didn't have the tools to do a piston to wall measurement since the pistons were stock size and the block was stock as well I figured this would be alright I could be way off here it's my first build. I'm almost certain I installed the rings correctly. I will try a compression test soon.
 

1990TSIAWDTALON

Moderator
7,465
3,563
Nov 14, 2013
Independence, Kansas
Good valve guides? We had a car that had bad valve guides so my son put new seals on the head and that fixed it.....for about a week, then wobbly guides wore out the new seals again. Lots of smoke but good motor. Not one I built, one he bought.
 

Spinner

Probationary Member
9
1
Oct 11, 2017
Van Buren, Arkansas
Good valve guides? We had a car that had bad valve guides so my son put new seals on the head and that fixed it.....for about a week, then wobbly guides wore out the new seals again. Lots of smoke but good motor. Not one I built, one he bought.
That's interesting. In my case there's no smoke out the exhaust or anything so I'm pretty sure the guides and seals are fine.
 

DSMPT

DSM Wiseman
1,340
888
Jun 12, 2014
Japan / Mexico, Arizona
I actually have the same issue with great compression and great leak-down numbers. Very odd.
What Marty said above plus, 2nd rings/oil rings/cylinder wall condition and the PTW clearance, piston skirt design are also related to cause of smoke. And this does not affect much the compression test and the leak-down test result as long as if the top rings are working properly.
That's interesting. In my case there's no smoke out the exhaust or anything so I'm pretty sure the guides and seals are fine.
Did you check distortion and taper on cylinders before building the engine? And did you hone properly?
 
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