1994 Mustang loud noise then won’t start

hankth18

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Feb 24, 2021
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Rock Hill, SC
1994 Mustang GT - 306, Trick Flow intake, E303 cam, ported GT40 heads, MSD billet distributor, BBK shortys

Last weekend, I took my car to the muffler shop. When leaving the shop, I was being rowdy to hear my new exhaust. All of a sudden I heard a loud pop/bang and the car immediately lost power and shut off. Checked all under the car looking for leaking fluids, but everything was clear (no oil, coolant, gear lube, etc coming from underneath). Tried spinning the engine over and the engine spun way more freely, as if there was little to no compression in any of the cylinders. Took the cap off the distributor and saw the rotor was still spinning. Initial thought was the timing chain jumped a tooth, but upon tear down the timing chain was fine and the timing marks on the cam/crank sprockets line up perfectly. I haven’t run a compression test yet, I plan on doing that tonight. Any suggestions on what the cause of my problems are?
 
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STEVE PATTON

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Jan 6, 2019
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1994 Mustang GT - 306, Trick Flow intake, E303 cam, ported GT40 heads, MSD billet distributor, BBK shortys

Last weekend, I took my car to the muffler shop. When leaving the shop, I was being rowdy to hear my new exhaust. All of a sudden I heard a loud pop/bang and the car immediately lost power and shut off. Checked all under the car looking for leaking fluids, but everything was clear (no oil, coolant, gear lube, etc coming from underneath). Tried spinning the engine over and the engine spun way more freely, as if there was little to no compression in any of the cylinders. Took the cap off the distributor and saw the rotor was still spinning. Initial thought was the timing chain jumped a tooth, but upon tear down the timing chain was fine and the timing marks on the cam/crank sprockets line up perfectly. I haven’t run a compression test yet, I plan on doing that tonight. Any suggestions on what the cause of my problems are?
That is your next logical move
 

hankth18

Member
Feb 24, 2021
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1
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Rock Hill, SC
I ran a compression test on cylinder #1 and had no compression at all (gauge didn't even budge). So I ended up pulling the valve covers and turns out I have a few bent pushrods and a lot of loose rockers. Turning the engine by hand, all rockers were moving as they should. I guess my next question is if bent pushrods can lead to low/no compression?
 

mostsmooth

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you found you arent getting any compression in cylinder 1, you can check if the piston is moving. that would help point you in the right direction maybe? pull the spark plug and check. or check the compression and piston travel on an easier to access cylinder. or is it crazy to think the pistons arent moving? no compression is either a leak (valve stuck open or some other leak) or nothing moving to make compression (no piston travel). right?

disclaimer: these are suggestions from a person who knows not much. just seems like a logical approach to trying to find where your problem lies.
 

hankth18

Member
Feb 24, 2021
7
1
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24
Rock Hill, SC
Update: Pulled all the rockers, pushrods, and lifters last night. I had 4 bent pushrods, all on intake valves. Cylinder 3 intake pushrod was really bad, and the intake valve is not fully seating.

E82D369B-5E2B-4E63-B0C8-B61FDB83BD53.jpeg E60B7773-347C-410B-80CC-C6416AB8BCC3.jpeg

Looking down the intake runner, it appears that the valve bore is cracked, which I assume is why it’s not closing all the way (see picture, have to look closely).

557489F9-AF2C-413C-A271-C42FB70AADFF.jpeg

The rest of the pushrods just had a slight bow but not perfectly straight as they should be. Roller lifters show signs of wear, but I’m not sure what is normal and what is beyond repair honestly (this is the first engine I’ve torn down on my own). I haven’t yet pulled the cam and heads, but I’m going to do that tonight to check for cam lobe wear and if my pistons are still good. The engine still spins pretty freely by hand, so Im hoping the rotating assembly is still good.
 
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hankth18

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Feb 24, 2021
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Rock Hill, SC
Update: Pulled the passenger side cylinder head, found a stationary piston in cylinder 3. So either broke a rod or a rod bolt. Hopefully the crank/block are salvageable. Time to pull the engine!
 
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hankth18

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Feb 24, 2021
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Rock Hill, SC
Well guys, I got the engine pulled and taken apart over the weekend. The rod journal broke on cylinder 3 and busted the cylinder walls on 3 and 7, so at the very least I need a new block and a few pistons/rods. Every single rod bearing had copper showing, and 3 of the main bearings were the same way so I'm sure that's what caused it to blow. The crank might be able to be saved by a good machinist but it took some damage when it blew. I also measured the stroke just for giggles because I noticed it had hypereutectic pistons and turns out it was actually a 347. So now I'm in somewhat of a pickle as to which is more cost effiecient. Should I:

A) Rebuild what I have with a new block, replace bearings, have my crank turned, and find 2 new pistons/rods that match (hopefully not buy an entire set of 8) OR
B) Find a 351 roller block to build with upgraded pistons?

I wanted to upgrade to some decent aluminum heads anyways, so I plan on doing that whichever way I go. I know that some parts will swap between the two (heads, cams) while others won't (i.e. distributor, lower intake, headers, etc). So I'm curious as to which option will be the most cost efficient considering what I will need to buy for each.