The details; 92 Tbird 302 bored 60 (sonic tested OK), stock crank/rods, hypereutectic pistons, app. compression ration is 9.2 with AFR 165's, stock 89 Mustang HO cam with Scorpion 1.6 roller rockers. Small header leak on drivers side that goes away when the engine warms up.

The rev limiter was at 5K for about 10K miles, but with the new FiTech fuel injection (installed 1,000 miles ago), I raised it to 6k.

The engine build has about 10,000 miles and has seen 5k rpm for short bursts a hundred (??) times but never over a very few seconds while running thru the gears.

Well 4 or 5 hundred miles ago I noticed a very faint, hardly perceptible knock while sitting inside the car. Wasn't able to hear in from outside even with the hood up and leaning into the engine compartment. I decided to not worry about it, if serious it'd get louder and I'd deal with it.

Well now it's louder, easily heard "inside" the car sounds just like a rod, however I still can't hear it from outside. Even put the car up on the lift and couldn't hear anything unusual while underneath with ear right at the pan and bell housing. Knock starts after the engine runs for a couple minutes, then stays constant with rpm.

Pulling plug wires while the wife set inside listening for a change...nothing.

Pushing in the clutch changes nothing.

Yesterday I adjusted the rockers and added another 1/4 turn of preload (1/2 turn total now).....no change.

My next step is to pull a oil sample and send to Blackstone Labs, after collecting the oil sample from the pan, I'll cut the oil filter open and inspect.

So, my first thought is rod however pulling plug wires didn't support that theory, it's a rhythmic deepish sound but still not loud enough to hear outside the car or under the hood, but it's slowly getting louder...

Anyone want to take a guess before I start pulling the engine?

 

Try a mechanic's stethoscope?

 

Wrist pin

 

Do you mean that the sound stays constant regardless of RPM? Or that it matches the rpm's?

 

mrmustang, I'm leaning in that direction....my hope was that if a wrist pin or rod bearing, there'd be a change when the offending cylinder's plug was killed.

.boB, my bad, I should have said the sound tracks or matches the rpm.

I'm temped to drive on, just no wot runs. However I keep imagining the carnage a rouge piston could cause to one of the AFR heads , not to mention everything else in the vicinity if a rod bearing or wrist pin let go.

 

Then I would agree with Mr. Mustang - wrist pin.

IMO, you should tear it down now and fix it when it's easy and you have the time. Don't wait for a catastrophic failure.

 

X2 why wait for the damage to get greater, tear it down now and minimize the amount of internal carnage to your engine.


While you are in there, you can always make some upgrades



Bill S

 

[QUOTE=mrmustang;22062]X2 why wait for the damage to get greater, tear it down now and minimize the amount of internal carnage to your engine.


While you are in there, you can always make some upgrades

Thanks Bill and Bob (seems like "Show should be in their somewhere . I know in my gut you're right. Funny thing is I do have plans to pull the engine/tranny and make some major changes "sometime" just wasn't planning on doing them right now due to other projects.

Planned upgrades are to do a Stein style mod to the extra subframe and run a set of Hedman mix/match ceramic coated headers. My car currently has the typical Monster Miata out sweep exhaust and I want to build a more conventional exhaust system that'll tuck up tighter.

Also plan to change the T5 for one with different gear ratios.

Now I can look at cams , although the stock HO cam is pretty nice for a daily driver type car.

Yep, cam advise is now a top priority.

 

I went TF Stg 2 to match my TF heads. Idle still seems pretty good. Have not had it on the road to see how it runs, but it is a pretty well known/liked cam in the Mustang community.

 

Jason now that you've had some time with the TF cam, any observations you can share. Power/rpm range, idle, low rpm manners and such.

 

Car is still under construction, not yet on road. Had my shoulder rebuilt a few months ago, lots of time lost, plus picked up a few other projects that have taken precedence.

No updates.

 

As mentioned in my related post, Dropping/Installing...engine/subframe from bottom. the engine is now out and on a stand. Yesterday I removed rod caps one at a time, looked at rod bearings and felt for any wrist pin slop. All bearings good and no sloppy wrist pins.

Sortof what I expected but in the process of elimination, had to do the above. One thing I did notice when I pulled the transmission is the throwout bearing showed significantly more contact on one side or the input shaft bearing housing. The throwout bearing feels fine, but I'm wondering if the clutch fork is the source of my mystery noise.

All appeared good at first look of the clutch and throw-out bearing, except for the odd T.O. bearing contact.

One thing I was proud of yesterday is a purchase of tools from the estate of a local Mopar dragracer a couple years ago (Joe Ralph Thompson) particularly a set of slide hammers. I was able to use one to pull the input shaft bearing from the crank. It'd been a bear without that particular tool. One can never have too many tools!

At this point my thinking is I'll mod the extra subframe into a Stein (actually CVX_20 Mike's original design I think?) subframe, order a set of Headman mismatch headers, put it back together with a new throwout bearing and the new (to me) .68 5th gear WTC T5 and see how it goes.