Fixing poor leakdown, Cyl 1 leaks at 50%, rest are cool. |
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Fixing poor leakdown, Cyl 1 leaks at 50%, rest are cool. |
VaccaRabite |
Oct 24 2007, 07:00 AM
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#1
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En Garde! Group: Admin Posts: 13,554 Joined: 15-December 03 From: Dallastown, PA Member No.: 1,435 Region Association: MidAtlantic Region |
So, at the Sterling meet I did a leakdown test on my motor, and found a problem with Cylinder 1. 45% leakdown, but 120 lbs of compression. Was tempted just to let sleeping dogs lie, but pulled the head off.
What was going on was clear as soon as we did that, the head was not totaly sealed to the cylinder, off by a very small amount. Instead of having the head recut, I decided to try and lap the two of them together. So, last night I hand lapped them, using ground graphite to check for even contact. I got good contact after the third round of hand lapping (lap, clean, check). Now I need to get the jug back on the block. I have a ring compressor on the piston, but I can't ficgure out how to get the head back on. Do I have to take the piston head off the rod? If so, how do I get it off. It looks like that tis a spring keeper that needs to be removed. Is there anyhting on the rod the needs to be loosened before I can pull the pin out to remove the piston head? Obviously, if there is a trick to getting the jug back on without pulling off the piston head, I'd like to do that. Zach |
Twystd1 |
Jan 2 2008, 08:53 PM
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#2
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You don't want to know... really..... Group: Members Posts: 2,514 Joined: 12-September 04 From: Newport Beach, California Member No.: 2,743 |
You will also need to know what plateau finish to put on the cylinders for your specific ring pack.
Or hopefully your machinist knows the right finish. Even if you take the piston with you to show the machinist. Does your machinist know what clearance the piston to cylinder should be...???? IMHO... YOU need to know this stuff before you see the machinist. Personally, I have all my cylinders bored and honed in boring jig that is torqued to about 60 Lbs. for boring and 35-40 lbs for honing. (SOMETIMES CALLED A HONING OR TORQUE PLATE) This are basically a 1.5 inch thick plate of aluminum with the center milled out to access the cylinders. There is plate at the top AND the bottom of the cylinders held together by 4 hardened pieces of all thread. Then torqued to a given spec. Before any machining AND measuring takes place. I have different plates for different bores. (Like big bores 101' 103s etc.) If ya want to do this nats ass..... It's a good place to start. And I would think that most GOOD aircooled machinists also do something along those lines. And have the plates available. Cause they aint cheap to make for a one time dealio. (Time consuming) Also... It looks like you are going to incorporate the existing "Used" rings on your pistons. Have your machinist CHECK the rings closely for both circumferential wear and also the top edge of the top 2 rings. If they aren't close to perfect. They MAY not seat well on a new surface. Then again... They may work just fine. I use new rings on fresh cylinders. PERIOD. They are cheap insurance for good leakdown numbers and and low oil consumption. Then again... I'm a nut case that way. Do it right..... ONCE. Clayton Cheers, |
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