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 |
VaccaRabite |
Dec 27 2007, 07:31 PM
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#2
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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 |
I pulled the heads, and then made some spacers out of some 1 inch square tube steel stock i had laying around, and used them to re-tighten the cylinders down. I did not tighten them to spec, as I was concerned about breaking a cooling fin, but I got them to where the cylinders could not move.
I put a level with a good straight edge across the cylinder bank and looked for gap. If the level was square on the #2 cylinder, then there was a bit of gap on the #1 cylinder. This was somewhat expected, all things considering. Using feeler gauges, I measured the gap. Where the bubbles were forming (#1 cylinder, facing the #2 cylinder) there was a .007 inch gap. On the opposite edge (facing the flywheel) was a .005 inch gap. In my leakdown-bubble tests, in the spot with the .005 gap showed no leak (no bubbles). I don't think I can manipulate my calipers accurately enough to measure the lip of the inside of the #1 cylinder. It seems pretty clear to me that the cylinder is either sitting slightly cocked, or is not squared off at the top. I'll have to measure that tomorrow. Zach |
Borderline |
Dec 29 2007, 12:22 PM
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#3
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Senior Member Group: Members Posts: 720 Joined: 8-February 05 From: San Juan Bautista, CA Member No.: 3,577 Region Association: Northern California |
I pulled the heads, and then made some spacers out of some 1 inch square tube steel stock i had laying around, and used them to re-tighten the cylinders down. I did not tighten them to spec, as I was concerned about breaking a cooling fin, but I got them to where the cylinders could not move. I put a level with a good straight edge across the cylinder bank and looked for gap. If the level was square on the #2 cylinder, then there was a bit of gap on the #1 cylinder. This was somewhat expected, all things considering. Using feeler gauges, I measured the gap. Where the bubbles were forming (#1 cylinder, facing the #2 cylinder) there was a .007 inch gap. On the opposite edge (facing the flywheel) was a .005 inch gap. In my leakdown-bubble tests, in the spot with the .005 gap showed no leak (no bubbles). I don't think I can manipulate my calipers accurately enough to measure the lip of the inside of the #1 cylinder. It seems pretty clear to me that the cylinder is either sitting slightly cocked, or is not squared off at the top. I'll have to measure that tomorrow. Zach QUOTE Okay, so I measured deck height today with Josh's help. #1 was the same as #2. I don't have to get my case decked! Its a problem with how the heads were cut. The heads need to be recut, taking as little material off as possible. Zach OK, with the risk of being chastised by the Cap'n, I'll stick in my $.02: How did you come to the conclusion that the head needs machining? You found the problem: the top surfaces of the two cylinders are not even. You found gaps of .007 and .005. Now you have to find out what is causing that variation. Just because the deck hts are the same, doesn't mean the problem is in the head. The top surfaces of the cylinders must be even. I would check both cylinder lengths and check the top ends for flatness. You may need to have the case decked. How did you measure the deck hts? If you want things to be right, you've got to measure everything until you find the source of the problem. The person that assembled the engine may have shortened one cylinder because the deck hts weren't even, not thinking about the heads sealing. You're on the right track, just keep measuring.. Just trying to help. |
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