1997 Cobra rebuild

[CourteousCain]

Hey all,

First post here! I bought a '97 Cobra back in '14, when I was 18. I bought it with high miles (140k) and quite a few aftermarket mods done to it. The motor was stock, so it didn't live for long after I bought it. I had it for about 2 months and then it developed a really bad rod knock. I pulled the motor and confirmed the damage - a spun rod bearing on cylinder #7, and then let it sit for 8 years.

I'd been looking into how to rebuild this engine for quite a while, but recently decided to bite the bullet and get it back on the road. I pulled the motor all the way apart and confirmed all the damage:

• 5/8 Rod bearings were toasted
• 4/5 Main bearings were toasted
• The spun rod bearing journal on the crank (cylinder #7) measured .019" under (not evenly though, all the wear is on one side of the crankshaft journal)
• Cams were too wore to confidently reuse
• Rods ends were out of round, and they factory rods are crack capped and really not machine-able
• Followers were scored with a bunch of bearing material
• Lifters were full of bearing-filled oil

With 140k miles, I really wasn't confident in using much of anything from the original motor - my goal with this is longevity. I'm not looking for a crazy high HP build, this is going to be a street car mostly. Besides the block, the heads, and maybe the valves (as of this post, block and heads have yet to go to a machine shop), there is nothing that I'm going to reuse internally.

This is the part list thus far for the rebuild (all parts ordered, some have yet to arrive):
Crankshaft: MMR/Manley 4.6L Forged 8 Bolt crank
Rods: MMR 4340 Forged H Beam Rods with ARP bolts
Pistons: Silverlight/ModMaxRacing 3cc dished hypereutectic pistons (OEM Moly rings) - +.020"
Rod Bearings: Clevite Pro
Cams: Comp Cams 106300
Springs: Manley High Lift 'Nextek' Springs
Lifters: Ford OEM Lifters
Followers: GT500 upgraded followers - M-6529-MSVT
Timing kit: OEM Ford Timing kit - new gears, chains, OEM steel tensioners
Oil Pump: Ford OEM High Volume Oil Pump
Gaskets: Fel-Pro complete 4.6L DOHC kit
MMR Head cooling kit
Misc Sensors and tensioners/pulleys
Water Pump
JBA Shorty Titanium Ceramic Headers
Ford OEM Motor Mounts
Dorman Harmonic Balancer
Screamin Demon Coil Packs
Exedy Mach 350 clutch

When I purchased the car, it already had quite a few upgrades:
4.10 gears
SLP Loudmouth mufflers, X Pipe mid pipe
H&R Lower springs
BBK Upper and lower rear control arms
Eibach front and rear Sway bars + bushings
Tokiko shocks
Full length weld-in sub-frame connectors
Caster/Camber plates
Strut Tower Brace
It should have an electronic speedometer adjuster, but I haven't played around with or even verified if it's installed on the vehicle, but the speedo is off by a large margin
It has short-throw shifter
It also has a Zex Nitrous wet kit - it was hooked up with about the equivalent of 100-110 shot

I ended up wanting to rebuild brakes as well (wanna go fast, gotta stop fast) and ended up with the PowerStop Z26 Drilled/slotted rotors with Ceramic pads.

In addition to purchasing all the parts and having a machine shop verify the tolerances and dimensions of things, I decided to spend a little bit and purchase a bit of piece of mind. I bought a set of mics, as well as a dial bore kit (.7" - 6" ), as well as a straight edge. I also decided, after much research, to bite another bullet and degree the cams. I purchased the Trick Flow timing kit with the 4.6L supplemental kit.
I also plan on doing some mild port-matching and polishing on the intake, as well as the heads. I'm not sure as of now if I'm going to do an IMRC delete or not - my '97 has metal IMRC plates, so it wouldn't be a difficult mod to do.
I measured all of the cylinders for taper, and they didn't measure more than .001" taper in any of the cylinders. They did measure about .003" out of round though. None of the cylinder walls looks terrible, but I'm going to get it bored .020" over. The decks of the block also appeared to be in good condition - no cracks, and from what I could test, they were very straight. The cylinder heads will need to be shaved down some, but that's only due to us marring one a little when we were disassembling the head.

There's only a few things that I'm not 100% sure on, but time will tell, or hopefully someone can answer:
- Piston to valve clearance:
The heads will need at least 2 thousandths taken off if not more, and with the .475 intake and .450 exhaust lift with these cams, am I going to run into piston/valve clearance issues? I'm staying NA, so I went with a small dish piston to keep the CR up.
- Camshaft journal clearances:
My drivers-side front camshaft journal in the head is marred a bit. Nothing crazy, but there's a bit of pitting there. I've heard of there being a bit of room to polish those out and increase clearances there, what is the maximum clearance that I should look for, before having it sent off and a bearing installed? I also purchased the GT500 followers to increase oil pressure in those journals, which I've read helps if you're going to increase those clearances.
- IMRC Delete?
I'm also not sure if deleting the IMRC valves would be a worth-while idea or not. I've got the gear to keep it out of that sub-3000 RPM range, but with the shorty headers and the stage 2 cams, I'm not sure where my power band will be, and if I will be losing on the bottom end or in a noticeable way by getting rid of them. Also, besides just eliminating a potential mechanical failure, is there any benefit to deleting the IMRC valves?
- Camshaft Girdle clearance issues
Am I going to need to notch or cut the camshaft girdles to fit the Comp Cam 106300 cams?


I'm going to attach some photos of some of the findings/failures for now, as well as the car itself, and hopefully in the near future post some more up-lifting pics with shiny new and freshly-machined parts.

Thanks in advance!

 

[98 svt]

Congrats on the car. Look forward to seeing more

 

[CourteousCain]

Hey y'all,

Sorry for the delay in posting, been collecting parts, waiting for the machine shop, and restoring/modifying some things.

Over the past few months, I have:
-Cleaned up the heads prior to dropping them off at the machinist
-Sandblasted/hand sanded and painted the valve covers, upper intake, and coolant crossover tube
-Did an IMRC delete with my stock plates, epoxied and flattened mounting surfaces as best I as could with sand paper and glass. Cleaned up the ridge on the IMRC secondary ports - honestly, just to get practice before polishing the lower intake and head ports, but I think they turned out pretty decent, and it's definitely not going to hurt.
-Awaited (im)patiently for parts to arrive from MMR and Comp Cams, and for parts to get machined


So far, I've received all the parts I should need (in theory), and now am just waiting for parts to come back from the machine shop to get to work. After hearing some less-than-fantastic reviews of the MMR connecting rods, I called and swapped to the Manley forged H-Beam connecting rods with ARP 8740 bolts. They didn't tell me this until I had called and requested to swap over, but the MMR connecting rods for 4.6 stroke were out of stock, with an unknown restock date. They've since pulled them from their website entirely - they have 5.4, but not 4.6. But they upgraded me for free, so I guess I can't complain too much ($489 vs $609).

I've talked with Todd Warren to determine the proper piston to valve, piston to cylinder wall, and timing for what I'm looking for. I haven't had a chance to do anything with the car itself yet either, hopefully I can spare some time soon. I unfortunately live ~5 hours away from where the car is stored and where I'm going to rebuild it.

Hopefully within the next few weeks, I should get the heads, block, and rotating assembly back from the machine shop. From there, it's just going to be finding the time to put aside for it.

I've been spending a good chunk of time researching these motors and have been writing a step-by-step list that I'm going to follow from start to finish. So far I'm at about 120 steps

Stay tuned

 

[CourteousCain]

2nd post to include more pics

 

[CourteousCain]

Hey all!

I got the parts back from the machine shop back in September, and I found some time to make the trek up north to work on it a couple of times so far since.

I made some good progress on the engine. I checked all clearances, ring gap, crank end play, and got the freeze/oil galley plugs in, rotating assembly in, oil pump on, heads on and I’ve notched the girdles for the high lift cams. Next time I go up, I should be able to get the cams in for hopefully the final time, and then get it degreed and then final assembly of the heads.

Once that’s done, we’re going to get a few pieces put on (timing cover, headers, water pump, oil cooler/filter mount, motor mounts, balancer) and then it’ll be put on pause until the weather gets a little warmer to get the car moved over to where I can work on it.

I will need to do a few things to the car to get it ready. I plan on cleaning up the engine bay a bit, I’ve got the new brakes and lock cylinders to get installed, I’ll need to get a locksmith to come and program the new keys, I have to drop and drain the gas tank, and I’ll likely have to get a new carpet. It’s been stored in a barn, and there’s been some unwelcome stinky squatters taking residency in it.

Knock on wood, it’s been a very smooth assembly. The only issue I’ve really run into so far during assembly was an out-of-round cylinder head dowel – but that was the original that the machine shop had put back in. I’d already purchased new ones, so we swapped those out and the new ones worked without issue.

 

[Roots-type]

Nice work

 

[lloyd393]

Did you need to get the cam journals bored?

 

[I_like_turtlez]

It shouldn't have broken at 140K, that really isn't high mileage for these engines, they're specially made and rival top offerings of today, way ahead of their time


Someone obviously didn't change the oil often enough in yours; you hate to see it

Glad to see it's getting back on the road, will follow along =]

 

[CourteousCain]

Nice work

Thanks!

Did you need to get the cam journals bored?

Thankfully not, all they needed was a quick polish on a couple with some scotchbrite. Clearances all measured fine, all around .00175 -.002"

It shouldn't have broken at 140K, that really isn't high mileage for these engines, they're specially made and rival top offerings of today, way ahead of their time


Someone obviously didn't change the oil often enough in yours; you hate to see it

Glad to see it's getting back on the road, will follow along =]

I think the nitrous came into play for the demise of this motor. I have the receipts for almost all of the other work the previous owners did besides the nitrous kit, so I honestly have no clue how long it was getting sprayed. Lack of oil changes could have definitely been a factor too.

Thanks! I'll be working this weekend to get cams final installed and timed. Shouldn't be too long from there before it's ready to go in the car