Rebuild of 408LT1 for J Ahn

GM LT4 heads CNC ported by Advanced Inducdtion

Good looking motor.

Lots of RTV on the back of the valve covers probably to help fix an oil leak

Nabil Guffey noticed quite a few header gasket leaks, (Felpro).

Time for tear-down:  These Crane Gold 1.6 ratio rockers are very high quality.

Right away I noticed something.  I have a hunch the rocker body is hitting the valve spring retainers, (slightly).

The rocker outer tip-edge look like they touch......

You can see marks on almost every valve spring retainer where the rockers touched but it is only a slight mark.  It's a sort of 1/2 moon mark.  I don't remember hearing rocker ticking so this was probably no problem what-so-ever.

Other spring retainers have full circle marks from the rockers. (evidence that valves rotate while in operation).  I think just a little sanding of the rocker edges will give clearance and fix this.

Photos of the heads.  Intake ports look fine.

Combustion chambers look fine.  they also look to have bone stock LT4 valves, (which are very good valves).

Here is the view of the lifter valley and the oil looks great.  There is no debris what-so-ever.

The builder installed debris screens and there is no debris stuck on any of the screens.

The piston tops look normal.  They look to be SRP brand (-16cc).

Another view.

Very interesting oil pan.  (I like it).  Nab Guffey thinks it is a Chevy Truck pan.  It has a longer sump area.

Very good looking bottom end.  No signs of trouble here.

More photos of the bottom end.  Here is the crankshaft part number (35340006000).  Yes that is a true 4.000" stroke 1-piece rear, 4340 steel Eagle crankshaft.  I wondered how a 4.000" stroke could fit under that oil pan.

Inside of oil pan.  There is no metal or debris.  Very good.  The pan is messaged in the back left for stroker clearance but that's the only area.

Looking for a smoking gun.  The motor had a rod knock sound at start up which got quieter after a few seconds.  Kind-a sounded like a spun bearing or just loose bearings.

All rods out.  The bearings looked like they were pounded from detonation.  But they were all intact and they were NOT spun.

The crank rod journals are good.  Very good actually.  The bearings used are Clevite H-series by the way, (I'm pretty sure all were "standard" size but I did not look at all of them for size).

Another view of the crankshaft.

Here is where Baker Engineering stamped a logo and serial number.

The main caps are off and all the main bearings look great.

Here you can see the cam and it looks "STOCK".  I have a hunch that really is a stock GM Impala cam or maybe a Corvette LT4 cam...(not the Hot cam).

Looks like maybe they notched the hub to clear the crank timing sprocket key.  The hub was not so tight on the crank though.  It was way too easy to remove.

This LT4 timing set is always too loose.

Nothing really wrong.  Just that the LT4 set is so sloppy.  You can almost remove the chain by hand.

Good view of the main bearings and cylinder bores.


Don't know why I took a photo of the cam but here it is.  There are no part numbers on the end or the front.  There is just a GM looking part number behind the fuel pump lobe, (GMPT-BC-17***142*GMPT-BC-17***14_2).  It has that stamped and the "14_2" looks like maybe it is "1422".   Well, whatever.  It is about a .460" lift lobe.

Never got a good photo of the pistons before taking to the machine shop.  About 4 of the pistons have skirt shrinking and scuffing. (talked about that while at the machine shop).  The Lunati rods look very nice.

While at the machine shop we found the piston to have 1.150" compression height so that looks up to be part number 144994.  In the SRP catalog that matches the application too.  408ci, 4.030", 4.000" stroke, 5.850" rod, -16cc D-dish.
Talking things over with Bill Koustenis at the machine shop, he and I both think the motor has detonation damage because all the rod bearings were pounded and some of the pistons had shrunk skirts.  If the pistons were stock they would have been cracked.  The 54cc combustion chamber of the LT4 heads make for about an 11.7:1 static compression ratio which is ok but possibly the cam made too much dynamic compression.  Possibly the motor just needs a bigger cam with less dynamic compression.  One good thing about the motor is that it was not run after the rod knock sound began.  That kept an expensive bottom end in good shape and very re-buildable.

Block fresh from a soap and water cleaning.  The machine shop looked it over and found all good.  Just a quick hone on the cylinders.  I pushed out the oil cam bearings and put in new Dura-Bond cam bearings.  The old cam bearings were in good shape though.

I'm putting Clevite "P" series bearings in because they comply, "flex" with the soft stock main caps.  Clearance is .002, .002, .0023, .0025, .0025"

Crank end play is .006"

Custom Ross piston for 408ci (4.000" stroke and 5.85" rod).

The Ross piston has a -14.5cc D-dish and the top ring land is .275" down.

The pistons are Left-Right and so need to be assembled so that the intake/exhaust valve reliefs are in the proper direction.

The piston was specified to run a small nitrous shot, (150hp).

Since this is a 4.000" stroke motor the piston compression height was specified to be 1.150".

Using premium Mahle piston rings.  1.5mm, 1.5mm, 3.0mm  
I specified that the pistons be made to fit this ring set.  The top ring is gapped at .022"

The 2nd ring is filed to .026"   This ring filer is a God-send.

Here is a piston/rod combo with the rings in place.

All of the bores are cleaned about 20 times with rags and auto tranny fluid and Mobil 1 motor oil.  After each rod/piston is installed I rotate the engine and feel and look for trouble.  The oil rings are tricky and can slide off the piston during install and you can feel that when rotating the motor.  I also look for ring-gap marks on the cylinder walls.  There should be no marks.  If a ring has a bur then you'll see marks.

Motor posed for photo after installing all rods/pistons.  The pistons are from .015 to .012" in the hole.  The block was decked only slightly if at all.  It's ok not to deck a block in my opinion if the pistons are not too far in the hole.  I will order up a Victor Reinz head gasket at .026" thickness.  That will give .038 to .041" quench.

Lunati rod bolts torqued to 65ft-lb.  Rod side clearance is .015 to .017"

Installed oil pan for a temporary dust cover and to see if anything interferes.  I wish I had the cam and heads.  Cannot go much further than this until the cam/heads arrive.

Ai CNC ported LT4 head have arrived.  Ai billet core custom cam too.

Let's get busy.  Ai cam goes in pretty easy.

Reused the LT4 timing set but the chain is new.  Cam check with degree wheel.  Even with a loose timing chain the cam came in very close to dead-nuts-on 106 deg lobe centerline.

After installing the Ai cam the #2 and #6 rods bump, (higher lobe lift than previous cam).  Clearancing was performed at the side of the rod shown here.  The rod bolt needed to be clearanced too.

The pistons are .015" in the hole so I selected the .026" Victor Reinz head gasket.

New GM head bolts ready to go.

The motor had 7.200" Comp Cams pushrods.  Now I need 7.000"  I tried all different lengths and it seems like 7.000" will work best.  Right now I have 6.950" pushrods installed.
Valve train installed

One last look at the bottom end

Oil pan on.  That is a new dipstick tube and indicator

Stock hub pressed on.

Now I spin the drill to 2500rpm.  This is a pre-lube and test of the oiling system.  The Crane gold anodized rockers are good quality.

GM LT4 intake manifold gaskets.

LT4 intake manifold

This motor had the full LT4 treatment.

One or two final things-to-do prior to sending to Nabil Guffey who will install the motor into the car.

Install new rear main seal.

Install SCAT flexplate.

Mechanicsville EFI Performance:  Nabil Guffey

Jimmy's 96 SS at Guffey's shop

Almost ready for initial start-up

This is a very stock looking motor.  Stock-ish intake, stock cats, stock exhaust, stock torque converter, stock 3.08 rear gears.....all of that needs to go.
Nabil Guffey installed the 408LT1 and I was there for the initial start-up.  She runs very well.  Good job Nabil.  The motor is actually more quiet than I expected.  The Ross pistons have .006" clearance.  The stock exhaust makes this car quite a street sleeper.

 Ellwein Engines 2008, , email Karl Ellwein