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Pmads77

Unusual Knock from my Cutlass

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My 1995 Cutlass Supreme is making some unusual noises. I have the 3100 engine with about 145,000 miles that just recently started doing this. The condition worsens when it runs for a brief period of time (30 seconds) then is restarted soon after. If I rev the engine in neutral, this noise happens as well. It is not a cyclical knock. It happens if the AC is off or on so that is out of the question. It sounds like it is coming from the lower part of the engine. Any ideas? Video below:

 

 

Another issue I am facing is an occasional violent shudder in the 5 seconds before coming to a complete stop. It also occurs when I slow down and then accelerate around 10-15 mph. I take my foot off the gas and can accelerate normally after that. It only occurs under warmed up condition. I'm thinking shift solenoid? 4T60E. Any help would be appreciated.

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Here are a couple more videos. The sound quality is not really improved but maybe you might see our hear something. Any tutorial on this forum for diagnosing possible flexplate symptoms? I couldn't find anything in a brief search.

 

 

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Personally it sounds too heavy to be a flexplate, the plate is very thin, if it was cracked it would give off a higher pitched tinny sound.

 

Can you get this same knock to occur if you put the trans in gear and do a torque converter stall with your foot on the brake pedal.

 

the knock is not consistent,

 

something you else might try........pick up a stethoscope to pinpoint where the knock is coming from....

 

http://img12.irobotbox.com/public/upload/product/1263/279/1671279/public958b4e32-d412-4a2e-bf9a-386af44ad033.jpg

 

 

also something you might try is to...eliminate a cylinder (if it is a cylinder) pull the plug wires one at a time then start the engine.....note if the knock does not return each time you deaden a cylinder.

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It's a little hard to tell from the video, but I think it sounds like an issue I had with my Cutlass a few years back. Turned out to be the water pump going out. To confirm, you can try taking the belt off and spinning each of the pulleys fast by hand and see if you can replicate the noise.  

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Update: I took it into a shop a while back and had it checked out. It turns out I had a couple of bent valves that would occasionally stick and bang up against the piston. They ended up sending my heads to a machine shop and overhauling them. It was a bigger job than I would have been comfortable doing myself so I'm glad I took it in. She runs like a dream again and I'm hoping to get at least another 150k out of her!

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If I'm not mistaken, I believe it has a chain. However, they did reset the timing when they had it in. They diagnosed the cause of the original issue as a failing pushrod so the rods were also replaced during the repair.

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On 10/3/2018 at 11:25 PM, Pmads77 said:

If I'm not mistaken, I believe it has a chain. However, they did reset the timing when they had it in. They diagnosed the cause of the original issue as a failing pushrod so the rods were also replaced during the repair.

How long have you had the car and was any work done prior to the knock? I know it's fixed already, I'm just curious though...

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The 3100 is a pushrod engine and uses a timing chain only... The LQ1 uses a belt AND a chain... The chain part is a standard timing chain that runs from the crankshaft to a "Dummy" camshaft which turns the oil pump... It's in the stock camshaft location,,, It's just a shaft with no lobes on it... The belt portion runs from the camshaft to the valve gear, on the top of the heads... If I'm not mistaken GM worked with I'm pretty sure Lola on the head/camshaft/24 valve design...

This post is kinda pointless... It does cover some facts about the GM pushrod vs GM DOHC engines that might not be known to all...

Well,,, that's my story and I'm  sticking to it!!!

Tom B...

If it WAS a DOHC engine,,, Yes, a timing belt would be in order...

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