Fresh Engine rebuild... Sound like a rod knock AGAIN

M

MercXr7-5speed

Registered User
For quite a few months now we have been rebuilding the motor on my sons 92 Supercoupe. Almost everything is new.

New crank sensor
New cam sensor
New rods
New bearings
New pistons
All new gaskets
New balancer and bolt
New oil pump
Polished and ported heads
Polished and ported intake
New timing set

And I'm sure there is more I am forgetting. It took a while because I needed to source a good crank and timing cover which I found from a good member here. Now after literally 5 miles, it sound like it's knocking again. I dropped the car at the machine shop and want this guy to hear it. He has a 12 month warranty on the work.

Is there something maybe I'm missing that could sound like a rod knock? Doesn't feel to be misfiring. "Knock" gets louder with rpms. Car is a 92 5 Speed. New clutch components also installed during rebuild.
 
I've had a dip stick hit the crank before and make a metal knocking sound but an engine knock is much more noticeable.

Sorry to hear of your bad luck on this one and good luck.

-Tim
 
MercXr7-5speed said:
For quite a few months now we have been rebuilding the motor on my sons 92 Supercoupe. Almost everything is new.

New crank sensor
New cam sensor
New rods
New bearings
New pistons
All new gaskets
New balancer and bolt
New oil pump
Polished and ported heads
Polished and ported intake
New timing set

And I'm sure there is more I am forgetting. It took a while because I needed to source a good crank and timing cover which I found from a good member here. Now after literally 5 miles, it sound like it's knocking again. I dropped the car at the machine shop and want this guy to hear it. He has a 12 month warranty on the work.

Is there something maybe I'm missing that could sound like a rod knock? Doesn't feel to be misfiring. "Knock" gets louder with rpms. Car is a 92 5 Speed. New clutch components also installed during rebuild.
Click to expand...
Supercharger internal coupler ... put a stethoscope on the blower snout to see if its the sound you are hearing.
 
Take all the belts off, and then listen. Does the sound change with the clutch disengaged? Piston clearance? Check oil pressure with a gauge? The #4 rear main journal is .010" smaller than the other 3.
 
You mentioned it was knocking again, so that's what happened to it initially that it required a rebuild? & it was severe enough the crank couldn't be reused? That's a lot of metal that would have been going through the oil system, was the cooler replaced or flushed & if so, how? If it was still full of debris, it could taken out new bearings at initial start up. Also what was wrong with the front cover? As SC-Al mentioned the S/C crank uses a undersize rear main compared to the N/A 3.8 crank. Did you get a S/C crank & how much machining did it require? 351tt's suggestion about the blower snout is a good point too. Taking belts off will eliminate that from the possibility's. Did the builder pre lube the system & verify pressure's?
 
Thanks all for the suggestions. The engine builder did a pretty decent job and showed me his progress at each step. The crank was shot so we sourced one in excellent shape before the rebuild. Oil cooler was definitely cleaned and the pump was replaced with a remanufactured unit. The engine builder just called and said he really thinks it's an exhaust leak. I need to get it to the shop about 1/4 mile away and have them look at it. They said they might fit me in after 1pm est. Just super nervous about this. We have alot of time and money into making sure this engine would last a long long time. Arp gaskets, arp head studs... We paid attention to every detail... Or at least we hope we did. Have 70mm TB and 5% pulley to install but not until this is completely figured out.

We had a set of modified 3.8 mustang headers for the rebuild but the install shop said they didn't mate to the exhaust. It's an SCP dual exhaust. Mufflers were shot so we had them replaced. I find it hard to believe the headers didn't fit. Also have a dual intercooler with electric fan that will be installed in the spring.
 
MercXr7-5speed said:
For quite a few months now we have been rebuilding the motor on my sons 92 Supercoupe. Almost everything is new.

New crank sensor
New cam sensor
New rods
New bearings
New pistons
All new gaskets
New balancer and bolt
New oil pump
Polished and ported heads
Polished and ported intake
New timing set

And I'm sure there is more I am forgetting. It took a while because I needed to source a good crank and timing cover which I found from a good member here. Now after literally 5 miles, it sound like it's knocking again. I dropped the car at the machine shop and want this guy to hear it. He has a 12 month warranty on the work.

Is there something maybe I'm missing that could sound like a rod knock? Doesn't feel to be misfiring. "Knock" gets louder with rpms. Car is a 92 5 Speed. New clutch components also installed during rebuild.
Click to expand...
Where did you get the new crank sensor-SCP?
 
MercXr7-5speed said:
Almost positive we ordered it from there. Along with the balancer and bolt.

Found this now that it's daytime. I think the pulley is loose. Fingers crossed. Getting new bolts.
View attachment 98930
Click to expand...
Loose bolts for the pulley could make a noise similar to a rod noise I guess-hopefully that's it or the exhaust leak.
Maybe it's just me, but that doesn't look like a new balancer or bolt/washer.
 
When my supercharger coupler was bad it sounded like rocks in a blender. Pull the jackshaft belt off to stop it from turning the blower and you can see if that noise is the coupler. Easy to replace once you get the SC off if it's the coupler. There's 3 pins on the snout and 3 pins on the rotors and a rubber/urethane coupler that they slide into and it wears over time causing noise.

When you say Mustang headers do you mean OEM 3.8 tubular manifolds, or did you buy aftermarket Mustange headers? The 3.8 tubular manifolds have been proven to flow less than outlet ported OEM SC exhaust manifolds.
 
DOUG H said:
Loose bolts for the pulley could make a noise similar to a rod noise I guess-hopefully that's it or the exhaust leak.
Maybe it's just me, but that doesn't look like a new balancer or bolt/washer.
Click to expand...
The balancer is new. I see the rust on the balancer and the bolt but I saw them on the engine while it was on the stand. But your observation isn't wrong. I definitely saw the wobble on the pulley with it running so fingers crossed. The tensioner was wobbling in sync with the noise as well. It's being towed to the mechanic as we speak.
Scott Long said:
When my supercharger coupler was bad it sounded like rocks in a blender. Pull the jackshaft belt off to stop it from turning the blower and you can see if that noise is the coupler. Easy to replace once you get the SC off if it's the coupler. There's 3 pins on the snout and 3 pins on the rotors and a rubber/urethane coupler that they slide into and it wears over time causing noise.

When you say Mustang headers do you mean OEM 3.8 tubular manifolds, or did you buy aftermarket Mustange headers? The 3.8 tubular manifolds have been proven to flow less than outlet ported OEM SC exhaust manifolds.
Click to expand...

It's been awhile since I was really active here but I remember years ago people were using the factory mustang headers in place of the manifolds. It doesn't surprise me that the factory manifolds ported would flow better. Probably better they couldn't install them. The factory ones aren't ported but I might try and find a set to have done.
 
I've had rod knocks, easy to diagnose if you've had one before the sound is very distinctive. I've also had balancers come apart and make all kinds of sounds . The one on my Procharged F150 cracked and it sounded like someone beating on the front cover with a hammer.
 
Welp... Problem solved. It was the crank pulley. The bolts weren't even in all the way. I removed the old ones, discarded them and got new grade 8 bolts to replace them along with lock washers and some blue loctite.. 5s probably would have been fine but they had 8s so.....

It was a good awful sound and it really did sound like a rod knock to me. Crazy. Thank e eryone for your input and suggestions. Much appreciated. Maybe one day someone finds this post and they get lucky with the same goofy issue. Probably not but you never know.
 
MercXr7-5speed said:
Welp... Problem solved. It was the crank pulley. The bolts weren't even in all the way. I removed the old ones, discarded them and got new grade 8 bolts to replace them along with lock washers and some blue loctite.. 5s probably would have been fine but they had 8s so.....

It was a good awful sound and it really did sound like a rod knock to me. Crazy. Thank e eryone for your input and suggestions. Much appreciated. Maybe one day someone finds this post and they get lucky with the same goofy issue. Probably not but you never know.
Click to expand...

For the same reason, crank pulley w/ 2 broken and bent bolts, I now own this gem. Pity that it sat in an enclosed barn for 15 years for being condemed for a rod knock with 149K miles on the motor. After rescuing it and pulling the motor (intake and blower previously removed when work stopped), I foung to the broken bolts. All rods bearings where inspected and replaced with new but the old one's looked fine but for the usual wear on the top side of the bearings on a super charged engine. New engine has all the goodies with Wiseco's 0.030" and runs great.

I am sure your engine builder is relieved to know his work was GOOD! As are you of the good news :)


1704517731363.jpeg
 
Seems to me on my Dayco power bond balancer, that the pulley bolts went in a little deeper, and got a bit tight before being fully seated. I used my thread chasers on both the balancer, and bolts.

XB-70, that's a good looking SC.
 
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