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Top end confusion

  • Thread starter Thread starter gearhead13
  • Start date Start date
G

gearhead13

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So, I was putting the top end back on my engine, timing the cams etc. I put a spark plug in each cylinder one at a time and turned it by hand and I could feel and hear the difference in compression between the 4 with #1 being the worst. So, I hooked up my compressor to the cylinders one at time with them at tdc and lash checked that it wasnt too tight. I could feel the airflow out of the intake ports on #'s 1, 2 and 3, with #1 being by far the worst and #4 no flow at all.
When I lapped in the valves, I tested the seal by pouring Isopropyl alcohol (just what I had on hand) in the ports and there was very little or no leakage out the valve head side. I have read online that valves take a few hundred miles to fully seat, although if you are real anal about it you would make the seal perfect from first startup. I did valve jobs on my previous engines with the same bit of leakage and got real good compression out of them.
So, I was quite upset about my finding of the air leakage and figured I had slightly bent some intake valves, and ended up ordering new ones ($260).
I took the head off tonight, didnt see any sign of valve/piston contact so I tested seal with the alcohol again and it was right about the same as when I put it together, WTF?
Now I am really confused, I have never hooked up air to cylinders before so I must have really jumped the gun on the new valves.
 
Did you check valve clearances when you put the cams back in?

There is a chance that one or more valves are a bit tight.

This is a situation that will not be evident when the head is sitting on the bench.

.
 
As I stated, I made sure there was plenty of lash.
If I can cancel the order I will.
Two of them are leaking more than I would like them to so I might take them out and lap them some more, But I already lapped the crap out of those two and they still seep a little:confused:
I REALLY didnt expect there to be so much airflow leakage from valves that held fluid so well.
 
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air in the cylinder has always been tricky for me...as in "leak down testing".
if you rock a little one way or the other you will have leaks/intake/exh./oil filler cap.
i know your supposed to move the cyl. to TDC and then put air to it but...more times then not the piston goes down on me and i get leaks "leakage"...yes i know that means it wasn't on TDC but a degree wheel doesn't lie when set up with a positive stop.
i finally started using a helper to roll the engine around and hold it steady and i would look at the gauge.
 
gearhead13 said:
So, I was putting the top end back on my engine, timing the cams etc. I put a spark plug in each cylinder one at a time and turned it by hand and I could feel and hear the difference in compression between the 4 with #1 being the worst.
Click to expand...
This tells me your valves are not sealing. Cancel the valves and send the head to APE for a performance valve job ($230)....plus shipping. Don't even get me started on lapping (sanding) valves.....Billy
 
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