 porsche 914, why am i scared of a knocking engine |
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| dlindzey |
 Dec 10 2020, 07:45 PM
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#1
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repeat offender  Group: Members Posts: 33 Joined: 8-April 14 From: texas Member No.: 17,226 Region Association: Southwest Region  |
looked at a 1.7 the other day
engine rebuilt in 2016 less than 30k miles, fancy pistons seemed like legit job, compressions between 140-150 all cylinders no leak down numbers 2018 or so got rid of the fuel injection system which had recently been rebuilt anyway and went to single carb since then little issues and tune ups, last shop records this year complained about knocks at start up and variable idle often fast for no reason i saw the car and drove it not knowing the above and the engine knocking is obvious even to someone of my mechanical inclination, the idle was too fast as well and the fuel pump was loud would anyone pay top dollar for a car that knocks before you even get it home or is usually a minor thing a decent mechanic can fix--prior shop took a run at it before owner bailed on the car that he had already pumped at least 15k into. so what is the collective wisdom-car looks good but sounds bad |
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Replies(1 - 6)
| yellowporky |
Dec 10 2020, 08:28 PM
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#2
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Member Group: Members Posts: 427 Joined: 18-October 09 From: Martinez, Ca. Member No.: 10,948 Region Association: Northern California |
a knock is not good. factor in $8k for a shop to rebuild the motor and if it still makes sense then you should have a solid known car to enjoy.
And put the fuel injection back on |
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| Spoke |
Dec 10 2020, 09:18 PM
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#3
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Jerry Group: Members Posts: 6,992 Joined: 29-October 04 From: Allentown, PA Member No.: 3,031 Region Association: None 
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Are you looking for a project car to work on or do you want to drive it? For me the rule of thumb is you may not find the car you're looking for locally. I live in PA and found my 914 in Connecticut and my 930 in Denver, CO. Both were worth the trips and auto shipping.
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| KSCarrera |
Dec 11 2020, 03:11 AM
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#4
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Member Group: Members Posts: 310 Joined: 31-January 19 From: UK Member No.: 22,846 Region Association: England |
You say 'fancy pistons' – what do you mean by that? Was it rebuilt with, for example, forged JE pistons, or similar? If so, they have zero-offset wrist pins, which means the piston can rock in the bore when cold, resulting in a slightly alarming 'knock' at start up and idle for the first minutes of running until things get warm. It's a characteristic, not a fault.
If the knock is constant, especially under load, then that's a whole different ballgame... |
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| 930cabman |
Dec 11 2020, 05:59 AM
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#5
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Advanced Member Group: Members Posts: 3,176 Joined: 12-November 20 From: Buffalo Member No.: 24,877 Region Association: North East States
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QUOTE(yellowporky @ Dec 10 2020, 09:28 PM)  a knock is not good. factor in $8k for a shop to rebuild the motor and if it still makes sense then you should have a solid known car to enjoy. And put the fuel injection back on What is the rust factor? Engines/transmissions/suspensions/brakes are all minor repair items when compared with rust buckets |
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| iankarr |
Dec 11 2020, 06:54 AM
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#6
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The wrencher formerly known as Cuddy_K Group: Members Posts: 2,482 Joined: 22-May 15 From: Heber City, UT Member No.: 18,749 Region Association: Intermountain Region
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Knocking / pinging under load is a timing thing that’s easily solved. “Ticking / tapping” sound is probably valves that just need adjustment...or hydraulic lifters needing to fill with oil. Does the noise get better/worse after 10 minutes of driving? Banging noises as if something is hitting something inside the engine which don’t improve are probably more serious.
Regardless, single carb setups are not good. The atomized fuel has too long a path through the runners to work optimally. There could be vacuum leaks causing the inconsistent idle. Please post a clip of the knocking sound and I’m sure the engine gurus here can tell you more... |
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| Superhawk996 |
Dec 11 2020, 07:26 AM
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#7
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914 Guru Group: Members Posts: 5,915 Joined: 25-August 18 From: Woods of N. Idaho Member No.: 22,428 Region Association: Galt's Gulch
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Probably nothing to worry about (IMG:style_emoticons/default/dry.gif) (Sarcasm Alert)
https://www.youtube.com/watch?v=LONT1oboJrs |
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