914 1.7 Knocking Sound -- New Here, First Post, Horrible knocking coming from the motor |
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914 1.7 Knocking Sound -- New Here, First Post, Horrible knocking coming from the motor |
UberElectricEagle |
Sep 20 2009, 07:20 PM
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#1
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atomic Group: Members Posts: 43 Joined: 10-August 09 Member No.: 10,659 Region Association: None |
Greetings. I am new to the Porsche world and I purchased a 1972 914 1.7 about a month ago. It's a pretty nice car over all, but I think the motor, or part of the motor, might be toast.
When I purchased it, it badly needed a muffler. The knocking noise was harder to notice and sounded more like an exhaust leak over the horrible sound of the lack of a working muffler. The car seemed to run decent even with the poor exhaust and the price was good so I bought it. I just wanted a decent car over all that I could drive around for fun on sunny days before the winter gets here. It came with stainless heat exchangers I installed and I installed a really nice dual muffler from Dave at Triad. When I fired it up with the new muffler, I really noticed the knocking when I drove it since the all the exhaust leaks were now sealed up and I wasn't wearing ear plugs. At idle it's not too bad, but once I get going, the knocking is very noticeable. It's odd too, because it's not real consistent under power in motion. To me it sounds like the noise is coming from the #1 cylinder. I think the cylinder is providing no power, because when I take the wire off the cap, there is really no change in performance. (I put a video link of the horrible sound below.) Any advice on where to go from here would be great. My gut feeling is telling me the motor is going to have to come out. If I'm going to do all that, I might as well put a 2.0 liter in or ????? I'd even settle for just a solid running motor with some minor upgrades to make it a little quicker. Any advice on what route to take on a good used motor would be great. I guess A motor that runs on 4 cylinders would be an upgrade. Thanks for your help, a mildly depressed Sam http://www.youtube.com/watch?v=a5JhEd7SUH4...re=channel_page |
VaccaRabite |
Sep 24 2009, 06:44 AM
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#2
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En Garde! Group: Admin Posts: 13,456 Joined: 15-December 03 From: Dallastown, PA Member No.: 1,435 Region Association: MidAtlantic Region |
Your idle jets are clogged for #1. I'd put money on it.
What kind of carbs are they? Weber IDF? Sorry if you posted that info, but I am getting dressed for work and don't have time to re-read the entire thread. Find a good diagram for the type of carbs that you have, and blow out the #1 idle jets with compressed air after giving it a good squirt of carb cleaner. Clean the spark plug. Put everyhting back together and try it again. If you are making 140# compression, I think you are in really good shape there. If you can borrow a leak tester, it is still a good thing to do. I still think its easy/cheap stuff. POSITIVE WAVES! (IMG:style_emoticons/default/smile.gif) When winter comes, consider pulling and rebuilding the carbs. If you have IDFs it will cost you about $70 (shipping included) for the kits and a few hours of your time. Fresh rebuild is ~#150 compression. Over 130 is great compression. 130-100 is happy diving compression. 95-100 is start looking for rebuild parts compression. under 95 - pullit and start over time. Also, you want to have compression in all 4 be ~the same. AND, compression is just 1 part of the story. You really should do leak down too. You can have good compression, but still have crap leakdown. It sounds weird, but I had 115# compression @45% leak on my #1 cylinder. It lead to a full rebuild, as I discovered my case was collapsing at the cylinders and had to be fixed. But, really. 140#, I think you are going to be just fine once you get fuel flowing. Could you take and post a picture of the top end of your engine bay, so we can see your carb set up? Zach |
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