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Raymondo
09-06-2008, 09:37 PM
Hey guys, I have an aggravating problem. Here's the story. My son overheated his '93 SC blowing a headgasket and ruining a head. So tore it down, found no problems but installed rod bearings, new rings, honed the cylinders, new heads and all gaskets. No problems with the Supercharger other than a snout seal leaking which I replaced. Reassembled the engine, it cranked right up and runs strong with the exception of a clacking sound from the driver's side that has a hollow type sound to it. Had a local mechanic look at it and he thought is was a wrist pin, so pulled it back out today, dropped the pan and from my inspection today I cannot find a wrist pin with any play.

So, any help suggestions, ideas, advice, prayers... will be greatly appreciated!

89XR7TD
09-06-2008, 09:45 PM
Just a thought

Tom

QuickMustang
09-06-2008, 09:47 PM
Is it an Auto or stick? Check your torque converter and/or flexplate bolts. That would be my first guess with a hollow sound...Does it get better or worse at higher rpm?

nwnsc
09-06-2008, 09:59 PM
is your son cody? did he blow the HGs? have you checked the lifters?

Raymondo
09-06-2008, 10:50 PM
Hey guys, thanks for the quick responses. The rocker arms were tight and torqued to specs.

It is a 5-speed so those problems probably do not fit.

I did notice that after it warms up the noise is less prominent and you hear it best at higher rpm.

Lifters are one suspect, but not sure. And yes my son is Cody and he did indeed blow a head gasket and a chunk out of one of the heads. :)

KMT
09-06-2008, 11:12 PM
>...clacking sound from the driver's side that has a hollow type sound to it.

Not that you can check now, but do you recall if the noise changed between rev'ing the engine in neutral versus putting a load on it while engaging the clutch?

Raymondo
09-07-2008, 09:12 AM
>...clacking sound from the driver's side that has a hollow type sound to it.

Not that you can check now, but do you recall if the noise changed between rev'ing the engine in neutral versus putting a load on it while engaging the clutch?

Yes it did. At an idle it is barely noticeable, but revving it revealed it. Also, driving it appeared to change in pitch with the flexing of the gas pedal. Strange huh?

Also, it is loudest from within the driver's side wheelwell. But when my buddy and I tore it down yesterday we did not find anything loose. I mean there is some horizontal movement of the connecting rods on the wrist pins as one would suspect, but nothing vertical and all the rod caps and bearing were tight. We loosened them all, checked play and the bearings themselves and everything looks good.

XR7 Dave
09-07-2008, 10:10 AM
Determining exactly what kind of sound you have and where it is mostly coming from will really help pinpoint the exact cause. Some typical noises from an SC motor:


Exhaust leak - this will be a distinct ticking sound that will vary with load. It will be completely quite during foot-off-the-pedal deceleration, but will tick distinctly during acceleration and tick lightly during cruise.
Lifter/rocker arm - this will be a definite "clack" sound meaning that it has 2 sounds in tandem. A loose rocker arm, collapsed lifter, bent pushrod, or sticking or loose valve (bent valve or bad valve guide) will cause this. This type of sound will not vary at all with load but it will vary slightly with rpm. it can be loud at idle and then go away at certain rpms and then come back at other rpms or it can come and go at steady rpms but it will not respond to variations in load but may change with engine temperature.
Rod bearing - This will be a definite ticking sound which will be heard mostly during a free rev and deceleration. Most pronounced in the 2500-3000rpm range, it will be completely quiet under load or acceleration. You would likely have seen clear evidence of this during inspection. The sound you are hearing with rod knock is actually the sound of the piston hitting the head.
Piston slap - Common on forged pistons but not typical for a hyperutectic, many SC motors will in fact have noisy pistons. As the piston goes up and down, when it changes direction it can rock in the bore and actually make noise. Typically the clearances on these motors is such that no noise is heard but the tolerance range for piston skirt clearance has a pretty wide range. (.001-.0035"). If your motor was on the loose side in the first place and you honed the cylinders, it is very possible that your piston clearance is no wide enough that it has started to make some noise. In the case of piston slap, the noise typically goes away once the engine warms up. If you notice the noise going away as you get heat into the motor that is a pretty good sign that you probably have excessive piston clearance and should have bored the block and gone oversize. Piston slap is heard as a cross between a knock and a clack depending on how much clearance there is. Another possibility here is that you put a piston in backwards. The piston pins are offset in the bores in the direction of rotation of the motor. If you put one in backwards it will make all sorts of noise.

Raymondo
09-07-2008, 10:21 AM
Dave, thanks for the great advice. I am leaning toward lifters or piston in backwards. The road bearings are tight, and we did indeed hone the cylinders, but also installed new rings and they are tight...actually had to trim them a bit to make them fit. Can you tell me how to tell if one is indeed in backwards?

Thanks!
Ray

XR7 Dave
09-07-2008, 04:34 PM
Dave, thanks for the great advice. I am leaning toward lifters or piston in backwards. The road bearings are tight, and we did indeed hone the cylinders, but also installed new rings and they are tight...actually had to trim them a bit to make them fit. Can you tell me how to tell if one is indeed in backwards?

Thanks!
Ray

The pistons have a notch in their tops that must face forward. Did you pull the pistons off the rods? I'm thinking probably not. In which case, the rods have a raised "dot" cast into the I-beam that also faced forward when installed at the factory. You should be able to see that from the bottom of the motor.

Rings have no bearing on the piston itself. My totally stock motor has piston slap that you can hear when it's cold. If your motor was loose like that before honing then it could be worse now. What kind/size of rings did you use? Most often the rings I install (Sealed Power or Hastings) have plenty of end gap already. Our custom pistons use "file to fit" rings but the OE stuff is all pre-gapped as far as I've seen.

Raymondo
09-07-2008, 05:05 PM
This engine was a rebuild from about 18 months ago so it has oversized pistons and rings, so I wonder if those pistons would have the mark? Guess I will just have to look. And I did not pull the pistons from the rods. I used Sealed Power 100mm rings and had to file them just a bit.

Thanks a lot!

supercatxr7
09-07-2008, 10:39 PM
I had a similar noise after a rebuild on one occassion. It was actually the plastic cover for the harmonic balancer was loose and causing the knocking noise. Probably not your issue though.

scbird1
09-08-2008, 01:21 AM
Check your oil dip stick. I have seen several that were hitting the crank shaft and causing a wicked noise. I bought one real cheap one time only because the guy thought the engine was toast.

XR7 Dave
09-08-2008, 08:40 AM
This engine was a rebuild from about 18 months ago so it has oversized pistons and rings, so I wonder if those pistons would have the mark? Guess I will just have to look. And I did not pull the pistons from the rods. I used Sealed Power 100mm rings and had to file them just a bit.

Thanks a lot!

Are the pistons +75 or +100? They are etched on top with the numbers. They also have a dot impression on top that tells you which direction goes forward. Also, since it was a rebuild and you blew the headgaskets, you might want to inspect the pistons carefully for a cracked skirt and/or bent connecting rod. This is common with aftermarket cast pistons.