91 5.0 Knocking sound - Mustang Evolution

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Old 05-19-2012, 06:16 PM   #1
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91 5.0 Knocking sound

Please check this video out and let me know what you think it is. I have already checked the spark plugs and all the header tubes get hot equally. I'm thinking a rocker arm or lifter may be the issue?

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Old 05-19-2012, 06:19 PM   #2
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these sound like reasonable guesses. i would pull the valve cover to verify. you should be able to tell as soon as you take it off.
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Old 05-19-2012, 06:20 PM   #3
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Sounds like a rod bearing maybe has spun.
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Old 05-19-2012, 06:21 PM   #4
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Lifter and rocker arm are easy, rid bearing sounds pretty serious?
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Old 05-19-2012, 06:24 PM   #5
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yeah, if nothings wrong under the valve covers. then look like its time for a boss 302 block and some heads so you can take full advantage of that turbo. like i said though i would pull the valve cover.
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Old 05-19-2012, 06:29 PM   #6
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I was hoping this motor would
last for a yer or two. Kind of sucky.
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Old 05-19-2012, 06:32 PM   #7
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yeah that sux. that noise is definitly a scary sound. i will hope for the best for you man. but if its something on the bottom end it will be time for full rebuild. if its something on the topend i would try to contact the shop who finished your install. because they would have messed with that.
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Old 05-19-2012, 06:35 PM   #8
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Any idea what a rebuild might cost?
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Old 05-19-2012, 06:42 PM   #9
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All depends on what you want ?
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Old 05-19-2012, 06:42 PM   #10
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Re: 91 5.0 Knocking sound

Sounds more like a rocker arm hitting something to me.Listen to the valve covers with a long screwdriver with your ear against the handle.
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Old 05-19-2012, 06:46 PM   #11
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this is gonna vary alot. you have to look at a bunch of thing like : does it need bored, what rebuild kit is used, local shop and maching charges etc etc. with a shop doing it is gonna cost more. this could range from 1300 -2500 very rough guesstimate

but IMO make this upgrade time and just get a boss 302 block or 351. something that will handle the turbo better and leave you room to do H/CI.

then last but not least find a used motor. this is probaly the cheapest option. i know where one is sitting right now and maybe able to get you a deal on it. but it has been sitting for years but from a trusted source.
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Old 05-19-2012, 06:52 PM   #12
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@TH I can't feel the rocker knocking and the noise is sort of centered on the engine. I have had the worst luck
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Old 05-19-2012, 07:11 PM   #13
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Re: 91 5.0 Knocking sound

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@TH I can't feel the rocker knocking and the noise is sort of centered on the engine. I have had the worst luck
Ok.


Usually a rod or main knock will be a deep thunking noise concentrated in the oil pan area.
From the video it sounds like that noise is right at or under the valve cover, but it's really hard to tell. It may be a broken piston skirt or ring land too.
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Old 05-19-2012, 07:13 PM   #14
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I'm gonna look at pushrods an rockers some time this week. If that's not it I'm gonna get another engine probably.
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Old 05-19-2012, 07:36 PM   #15
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Re: 91 5.0 Knocking sound

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I'm gonna look at pushrods an rockers some time this week. If that's not it I'm gonna get another engine probably.
Save up and get you a Boss 302 block (around $1600) then stuff it with forged pistons rods and crankshaft so you won't have to go through this again.
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Old 05-19-2012, 07:48 PM   #16
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That's gonna be a 4k engine.

---------- Post added at 07:48 PM ---------- Previous post was at 07:43 PM ----------

If I bought a good block with forger internals could I run all my stock accessories, intake and heads until I have more money?
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Old 05-19-2012, 10:14 PM   #17
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Re: 91 5.0 Knocking sound

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That's gonna be a 4k engine.

---------- Post added at 07:48 PM ---------- Previous post was at 07:43 PM ----------

If I bought a good block with forged internals could I run all my stock accessories, intake and heads until I have more money?
Yes you could. A stock block with all forged internals would hold up probably a bit better than the factory crank, rods and pistons.
I don't think I'd go overboard on on any "specialty" stock block though.
Your block may be ok, you won't know for sure until you take a look though.


I would add a DSS Main Support System (main studs, girdle & windage tray) and a Valley Girdle Pro to your stock block to help it hold up better.
I chose the DSS Main Support System because the components are made of HD aluminum which helps dampen harmonics and vibrations in the engine. DSS claims their Main Support System will help hold the stock block engine together at up to 650+ HP. The Valley Girdle Pro fastens into the lifter galley and helps tie the top of the block together.


P.S. I got the DSS Main Support System for a stroker 5.0 in case I decided to go that route at a later date.


Something else I am considering doing to my stock 5.0 is to fill the bottom of the block up to the bottom of the side freeze plug holes with "Hard Blok" and tapping out the freeze plug holes in the sides of the block for 1 1/4" cast iron pipe plugs. I believe this will help to further "stabilize" and strengthen the bottom and sides of the block and cut down even more on harmonics and vibrations.
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Old 05-20-2012, 07:50 AM   #18
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Okay, thanks for all the input. I will be taking apart the top end Monday or Tuesday an then we'll have to take it from there.
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Old 05-20-2012, 08:09 AM   #19
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Sounds like a valve broke loose from the roller and that is definitely in the valve cover.. Prob dropped a valve.. That is my guess and every time it travels up the roller is moved and it's smacking the cover.. It doesn't sound catastrophic to me at all.. But we'll see post pics
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Old 05-20-2012, 08:11 AM   #20
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Would I have to remove the head to fix that?
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Old 05-20-2012, 08:13 AM   #21
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I don't think so. You would have to put a new vale retainer in some how but I'm sure it can be done.. Is that your new turbo?
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Old 05-20-2012, 08:15 AM   #22
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Yes, the new Magnum Performance turbo is awesome! I have instant spool and it has a great sound. I went with a 67mm turbo.
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Old 05-20-2012, 08:26 AM   #23
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Hell yeah!! get the intake and valve cover off today if you have time.. We can help you make a game plan from there
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Old 05-20-2012, 08:31 AM   #24
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Today is my 6 wedding anniversary. I woke up told my wife happy anniversary. Her reply was you're not working on your car, then she said happy anniversary. So sorry but it gonna be tomorrow or Tuesday before I can get to it
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Old 05-20-2012, 09:29 AM   #25
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Re: 91 5.0 Knocking sound

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Originally Posted by 90GTNovi2000 View Post
Sounds like a valve broke loose from the roller and that is definitely in the valve cover.. Prob dropped a valve.. That is my guess and every time it travels up the roller is moved and it's smacking the cover.. It doesn't sound catastrophic to me at all.. But we'll see post pics
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Would I have to remove the head to fix that?
A dropped valve is catastrophic and it could very well be the problem.
If it is the issue, then it is likely the valve is bent and the top of the piston is beat up if not punctured.
Yes, you would have to remove the head to replace the valve and possibly tear down the engine to replace the piston.
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Old 05-20-2012, 09:38 AM   #26
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Re: 91 5.0 Knocking sound

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Today is my 6 wedding anniversary. I woke up told my wife happy anniversary. Her reply was you're not working on your car, then she said happy anniversary. So sorry but it gonna be tomorrow or Tuesday before I can get to it
Ah yes, "The Queen" has spoken!
I have heard those very words so many times over the years, that now she no longer even has to utter them. A simple look now suffices to inform me of what my plans will be for the day.








Therefore I get up before she does, practice my "What, I didn't know" look in the mirror a few times and sneak out the door to the shop before she awakes.
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Old 05-20-2012, 10:40 AM   #27
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Can this type of breakage be attributed to old age of the parts. I always hear everyone say the stock engine can hold up to 500hp and I'm in the 300-350 range. So high mileage and old age are probably the culprits?
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Old 05-20-2012, 11:33 AM   #28
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Re: 91 5.0 Knocking sound

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Can this type of breakage be attributed to old age of the parts. I always hear everyone say the stock engine can hold up to 500hp and I'm in the 300-350 range. So high mileage and old age are probably the culprits?
Yes, it could be attributed to metal fatigue, but also over revving, detonation, etc., etc..
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Old 05-20-2012, 12:50 PM   #29
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I was about half throttle, and my car is professionally tuned so it wouldn't be overrevving or detonation IMO.
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Old 05-20-2012, 04:29 PM   #30
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Re: 91 5.0 Knocking sound

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I was about half throttle, and my car is professionally tuned so it wouldn't be overrevving or detonation IMO.
It wouldn't necessarily have to have happened right at that moment, the damage could have been done prior to that and the complete failure just happened at that point.

Professionally tuned or not a bit of bad gas or some other variable could still cause it to happen.
Professional tunes are "then and there" and then you depend on the ECU/chip/tuner to make adjustments for driving, temperature and humidity fluctuations. A hiccup in the system and boom.
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Old 05-20-2012, 05:10 PM   #31
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Okay, that could be.
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Old 05-21-2012, 02:15 PM   #32
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I don't have any loose rockers, any other thoughts?
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Old 05-21-2012, 02:25 PM   #33
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I would turn the motor over a few times by hand and see if you notice anything. Also you can't tell there maybe do a compression test to check the valves. Take the spark plugs out and turn the motor over by hand. If you spun a bearing then it will probably be difficult the turn over. did you ever check your oil pressure when this happened?

But if you didn't notice anything yet there's a good chance its on the bottom end. I'm sure someone else will give you some better testing methods to.
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Old 05-21-2012, 02:27 PM   #34
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I did turn it over a few times and re chek the rockers. My oil pressure is great. I even changed it. The car idols and runs fine.
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Old 05-21-2012, 02:40 PM   #35
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I don't know what else you could check.

If you spun a bearing you wouldn't have good oil pressure. If you would have dropped a valve or collapsed a lifter u would have seen something wrong with the valve train.
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