Crap....Do I need an engine rebuild? - Rennlist Discussion Forums



Crap....Do I need an engine rebuild?

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Old 11-08-2016, 01:15 PM   #1
dreygata
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Default Crap....Do I need an engine rebuild?

Well this hasn't been the best of weekends. On top of some currently un-resolvable issues with a couple motorcycle projects, and my phone taking a really bad fall, my 87 924S developed an engine knock.
After draining the oil, I stuck one of those extendable magnets into the oil pan's drain hole, and pulled out a few metal pieces.
I haven't fully sifted through the oil (which is currently in a couple of perfectly clean plastic shoe boxes), but I'm guessing that my rod bearings are shot.
Not sure what caused it, as the oil level seemed to be within spec, but given that I've had this car maybe one month, who knows.

I'm guessing that I'll be needing to do an engine rebuild unless you guys think something else would work.
An engine rebuild will be the most extensive thing I've taken on, but I've rebuilt a basket case motorcycle so hopefully it's not horribly more difficult.
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Old 11-08-2016, 07:57 PM   #2
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how recently had the engine been running fine before you noticed the knock?
common "scary noise" is the hydraulic lifters draining of oil and making a hell of a racket on first "dry startup"...can take several minutes until they pump up fully and quiet down.

any chance you could take a video/sound recording of the suspect noise?
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Old 11-09-2016, 08:20 PM   #3
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The engine ran fine when I bought it a month ago, drove it 2.5 hours, and then have put around 250-300 miles on it.
Saturday night is when the noise started. I drove it about 15 miles home (mostly at 65 mph interstate speeds) then parked it. It made the noise the entire way home and it seemed to correspond to increasing/decreasing throttle, both with and without the clutch engaged.

I'd have to put the oil back in the car to start it back up, which I'm not going to be able to get around to do until maybe Friday. Even still, the metal bits that I pulled out of the oil pan's drain hole don't leave me with much hope (largest was around 1/4" square). I can try to get a pic of the metal bits sometime Friday as well (phone busted the same day as the car...)
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Old 11-10-2016, 04:19 AM   #4
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Quote:
Originally Posted by dreygata View Post
I'd have to put the oil back in the car to start it back up, which I'm not going to be able to get around to do until maybe Friday.
Don't do that. Spend $40 on some fresh 20w-50 and an OEM filter.
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Old 11-10-2016, 07:15 AM   #5
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Get a pair of electrically insulated gloves and pull the spark plug wires off one at a time to see which cylinder is making the noise. I would start with #2. If the noise goes away you will know which cylinder is at fault. Bearing material isn't magnetic, so you may have other issues going on
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Old 11-10-2016, 11:53 AM   #6
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That's good to know. I'll plan on getting some 20W-50 and filter then listen to see exactly where it's coming from. I'll also run the old oil through some coffee filters to see if anything comes through.
I suppose I can cut open the existing filter as well.
So if bearing material isn't magnetic, what would be? And what sort of things would I be looking for?
What exactly does pulling a plug while the car is running do other than prevent ignition in that cylinder?
I'm new to more in depth car maintenance/repair, so forgive me if my question seem somewhat stupid.
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Old 11-10-2016, 01:41 PM   #7
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Broken valve springs is the most common issue I have seen that would be magnetic. Pulling the spark plug wire takes the load off of the bearing, thus making the noise less noticable, if that is what is going on
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Old 11-10-2016, 06:42 PM   #8
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Valve springs make a hell of a noise in a 944 when they break too...good suggestion.
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Old 11-14-2016, 01:07 PM   #9
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I'll check those out. So to recap, fill with fresh 20W-50 dino oil, new filter, start it up, listen for noise location, pull plugs to see if the noise lessens?
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Old 11-14-2016, 09:05 PM   #10
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If one of the rod bearings are bad, the spark plug removal test will narrow it down. If broken valve springs are at fault, an inspection camera through the 8mm plus in the cam tower may be able to determine which one(s) are broken. Although it may be easier to pull the tower to get up close and personal with the valves/springs
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Old 11-15-2016, 06:59 AM   #11
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Quote:
Originally Posted by dreygata View Post
So to recap, fill with fresh 20W-50 dino oil, new filter, start it up, listen for noise location, pull plugs to see if the noise lessens?
You do not have to pull the plug(s)...just the plug wire(s).

As previously mentioned, unless you are wearing insulated gloves, do not attempt this while the engine is running.
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Old 11-15-2016, 10:23 AM   #12
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The plug wires are what I meant. I have some thick gloves t hat I've used for that purpose before.
I don't have an inspection camera though.

I should have time this weekend to get things looked at. I really appreciate the input
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Old 11-15-2016, 04:47 PM   #13
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Good luck, keep us posted
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