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2G Extremely loud knock, Rough idle and misfire

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SameOldDSM

Proven Member
35
5
Mar 17, 2023
Niles, Michigan
Relatively new to the forums but I'm in need of some help diagnosing what happened to my engine.

Last Sunday I bought a 95 Gsx with a 6 bolt. According to the seller its had a lot of work including a full timing service, new water pump, all previous oil leaks fixed, a turbo service, new head gasket, arp studs and evo springs and retainers.

Drove it 3 hours home and it was perfect except for needing a new battery and whenever it was wide open pushing 20lb of boost it would cut out extremely hard whenever it was above maybe 5k rpm. He kept saying it could be something in the tune, or from the shit battery that he had in it. Keep in mind this guy didn't care about the car like he should have other than the engine and transmission. Cosmetically it's beat, especially in the engine bay.

Drove it around for a while to get better at driving manual and had no issues. Replaced the battery just the other day and somehow it seemed to fix the cutting out at high rpm under boost.

Was feeling good about the car so I took it to work yesterday and it was normal until I left the running lights on after lunch. Battery was a bit dead but it still turned over and started but now it has an extreme misfire and somewhere near the back of the engine there's a super loud clanking sound. I'll try and upload a video of it.

Had a buddy come help me, he suggested we pull the valve cover off right there to check everything up top and it was all in check. Rocker arms were in place, cams looked good even turned it over and had good oil pressure, everything sounded smooth and compression sounded good. We put it back together had it towed home and now I don't know where to start. Figured id get advice from people who have experience before just diving in head first. And keep in mind it was running perfect before shutting if off at lunch.

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Had an extremely similar noise recently and it was my cam gear bolts working loose. I know you said it was all good up top but I missed it the first time I checked, worth double checking.
 
You just reminded me of when I pulled on the timing belt since it's exposed the rear cam gear moved but the front didn't. Not sure if this is normal but I don't remember it happening before when I did the same thing a few days ago. If that's the case could that have damaged my engine internally?


Also I cannot check exact oil pressure yet just could tell it had some since we turned it over with the valve cover off and it was clearly pumping oil. I will be adding an oil pressure gauge soon.
 
I'll see if I can't dig deeper and get the belt off tomorrow, praying it didn't get damaged.

The timing belt? Are you familiar with how to set the timing marks to top dead center? Have you memorized how to properly set belt tension and measure tensioner depth?
 
Did you check torque on the cam gear bolts? You said the intake cam moved while the exhaust cam stayed still. I'm assuming that meant the gear moved independently of the camshaft which would mean that that bolt is loose. Unless I misunderstood.
 
That engine is not running on all cylinders, it sure sounds like rod knock to me, if you have a misfiring cylinder it can become more audible if the bearing was already on its way out. Once again your another person that buys a car the he knows absolutely nothing about, knows for a fact that its not running right and decides to beat on it at 20psi of boost when its breaking up (for a reason) and then wonders why it ends up damaged.
 
Are you sure that the pistons and valves are not contacting? Hard to pin-point with this short video but one thing I should mention is, according to the video it looks like you have wrong valve timing (timing marks off) or/and no compression in cylinders.
When the engine gets off, if the engine is healthy and has the right valve timing, usually the dowel pin on cam gears should be somewhere at 1:30, 4:30, 7:30 or 10:30 o'clock (pistons are in middle of stroke). It shouldn't be exactly at 3, 6, 9 or 12 o'clock. In the video, looks like you have it at exactly 9 o'clock. This makes me think something is not right.
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Pretty positive I smashed my valves unless these marks are somehow normal. Timing belt is tight and the cam gears are not loose. Any idea how this could have happened, and how I'd go about fixing it along with preventing this from happening again?

Also really curious how it ran perfect just before, and the second I started it, it was knocking

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Any idea how this could have happened
Now it's more obvious that the valve timing is wrong. You have the valve timing approxi 30 degree advanced at cam. I think simply you set the timing improperly when you re-installed the timing belt.
 
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Previous owner was the one who had the work done. I've only had the car for a week.🫤
Then the timing belt skipped for some reason, such as the tension too loose etc. Can't see well in the video so I could be wrong but looks like the tensioner pulley's position is not correct.
 
those cuts in the pistons are normal, but the lack of soot around them is looking like could have contacted, they are butterfly cut factory.

have someone double check timing the dowels should line up at 12 every couple rotations and the other timing marks should drop on, won't be every revolution

edit: I'm not sure where your crank mark is in that video.. the oil pump looks like it's a tooth off too?

if that white mark is the crank arrow it's 8or9 off which is bad.
 
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edit: I'm not sure where your crank mark is in that video.. the oil pump looks like it's a tooth off too?

if that white mark is the crank arrow it's 8or9 off which is bad.
As I mentioned above that the timing is completely wrong. In the video he lined up the timing marks on cam gears, if the timing is correct, the dowel pin on the crank sprocket should be at 3 o'clock. But he has it at around 1 o'clock.
 
From the videos, what I can say is,
- Valve timing was wrong. Seems you fixed it.
- You probably have loose tension on the belt, judging by the tensioner pulley bolt position. You have to make sure why it skipped before driving the car again. Otherwise the same thing would happen when you rev up even nothing happens at idle.
- Looks like you have a worn tensioner arm.
- You have no crank plate, so hard to find TDC unless you are used to.

Anyways you should make sure first if valves are bent or not by a leak down test and compression test. The engine fires up doesn't guarantee that valves are not bent.
 
I found TDC with a screwdriver in cylinder 1 like I've seen others suggest in the forums. I won't be running or moving the car until I replace all the timing components, and check compression. With how loud the knocking was before I can't imagine the valves are still sealing properly even if it ran smoothly. I'm just happy it ran even if it was just for a minute, I'll take that as a win for today.
 
I found TDC with a screwdriver in cylinder 1 like I've seen others suggest in the forums.
I don't suggest the screwdriver method when you install the timing belt. This could easier make you put the crank sprocket by a tooth off. Just get a crank plate too when you buy the new timing components. It's very cheap and this also would make the crank sprocket in its position. Now looks like you have the sprocket about a millimeter off towards inside.
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I'll add the crankplate to the list. Also to clarify the photo you added is from the previous time when it was still knocking.


I'll put a picture of what i had it at before starting it up. It also moved slightly counter clockwise from this position once I got the belt around the idlers prior to startup.

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Also to clarify the photo you added is from the previous time when it was still knocking.
Yes that's why you have to check for bent valves anyways... Even the valves and pistons contacting was very little/slightly, the valves are already bent and should be replaced. Let's hope the knocking sound wasn't from valves hitting pistons.
 
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