Only reason youíd have to remove the heads is possible interference installing a .300 taller lifter.
May not be an issue for you though.
Thanks, the lifters i will use (Morel 4795) have following specs:
Lifter Type: Hydraulic Roller
Plunger Travel: .015" - .030"
Body Type: Billet
Body Diameter: .842"
Body Height: Stock -> so should be ok.
Wheel Diameter: .750"
Tie Bar: Vertical
RPM Capability: 7000+ RPM
Seat Pressure (Lbs): 100-200
Open Pressure (Lbs): 285-650
Do Not Use Oil Heavier Than 5W40!
IMO you need to remove heads to check piston to valve clearance. I'm not current on the method used today but old school was to put clay on top of piston. No way that I can figure out how to do that without removing the head twice. If there is a new method to check I'm all ears.
Thanks, the method i know is the one where you install a extreme light "checking spring", heads installed. Lonnie P is referring to it down below
for a normal cam swap, heads generally can stay on. Since you are upgrading form flat tappet to roller, you will almost certainly need to change out the valve springs. This can be don on the car (couple tricks to it--air pressue in the cylinder, rope int he cylinder, etc to keep the valves from dropping), but it is probably actually easier for this swap to pull the heads to install the new springs and make sure spring pressures are appropriate for the new cam.
If you also plan to upgrade to 1.6 rockers, the heads may need some grinding (may or may not), in which case, you should 100% pull the heads to avoid any potential debris falling into the bottom end.
just my $.02
Thanks. Stock rocker ratio is actually 1.7, and i am gonna stay with that
Not sure what Iím missing here? 1.7 rocker arms. 781 heads. No grinding should be required. The lifters arenít even close to the head.
yeah correct, 1.7 is stock which i will use, so should be ok.
Are your rocker studs pressed or screwed in ?
You'll need to change springs for the cam. (easier off the car) Checking spring height.
IF you have pressed-in studs, you'll want screw-in studs IMO (really should be off the car)
I also think all MARK IV BBCs have 7/16-14 Screw in studs with adjuster nuts. But i will change to better ARP ones with Polylocks (with internal setscews).
Based on the signature for the original post... this is a 396.
1.7 ratio, screw in studs in all big blocks.....
Now what you have to watch for is piston to valve clearance.
You do this with a dial indicator on the retainer, using a checking spring.
When the piston gets close to TDC, you can push down the rocker till the valve touches the piston & note the amount of travel measured with the dial indicator. If you go too big on the cam, you get to remove the heads & cut valve reliefs in the pistons.
I had this problem on my 396 with a 256/260 .666 lift. I got to tear the entire engine down & cut both the intake & exhaust reliefs.
With stock or TRW type pistons... If you stay relatively mild & under .600 lift, you may be ok.
Other aftermarket pistons have better valve reliefs.
Very good info, thanks.
Of course thats the absolute worst case for me, trying to minimize steps needed for conversion by letting heads on, then resulting in having to cut the pistons... thats something i have to make sure doesnt happen.
Thats why your info is of high value to me.
Is there a way to calculate PTV-clearance? if so, please enlighten me.
Or what else can i do to avoid clearance issues in the first place?
I will go with a full custom cam, but i estimate the timing will be in the 240+ @0.050 and Lift probably 0.600(+).
Chris Straub told me its gonna exceed the semi-custom timing, but doenst know how much till he ran my setup through the simulation.
But i guess it should not exceed the 250s timing-wise, since the cam only hast to provide mixture for a demand of 402 cui. not 454 or even 496.
I have a L78-Block with these pistons: -> do you happen to know/see what kind of valve reliefes they have? is the dome shape .335 an indicator maybe?
Pistons @ 6223 Crankshaft 1053 Steel
L2242NF + .030 = 402 CUI
FORGED .030 OVER**4.124 Bore
TRW / Sealed Power / Federal Mogul**
PISTONS FOR A CHEVY**L-78***396 1st Design Closed Chamber Head
The***skirts**are COATED AND COME WITH PINS.
THEY ARE SET UP FOR PRESSED PINS...
RING LANDS ARE** 5/64"** 5/64"* 3/16" .
Compression figured with .020 deck clearance and .028 gasket.
*102CC HEAD = 11.58 : 1
*109CC HEAD*= 11.00*:1
*117CC HEAD*=*10.00 : 1
*119CC HEAD*=*9.80 : 1
*124 CC HEAD =*9.25 : 1 ....
Specifications Pistons SPEED-PRO L2242F 30 as per Catolog
Chevrolet Eng. Family Big Block
Bore Dia. 4.124
Compression Distance 1.765
Weight (Grams)*657 approx.
Dome Volume 38.3
--> quite some dome volume, but stock i guess !?
Dome Shape .335 dome
--> What does this indicate? just height? and this fully protrudes into the chamber?
Top Ring 5/64
2nd Ring 5/64
Oil Ring 3/16
Pin Style press
Bore Clearance 0.003
Harris, Like mentioned already, if you remove the valve retainer to remove the spring, gravity will cause the valve to drop into the cylinder. Filling the cylinder with air by screwing a air fitting into the spark plug hole (with both valves closed) or feeding rope through the spark plug hole and filling the cylinder up with the rope up against the valve will prevent the valve from falling.
If it was my engine, I would rather replace the springs with the heads off the car. This will minimize any issues that could occur with the head-on methods. If you drop a valve, it is pretty challenging to try to retrieve it. You will have to try to feed a magnet through the valve guide and pull the valve back up. Another benefit is with the heads off, you can inspect the valves and seats when you remove the valve retainer and spring. Then you can also install new, high quality valve seals.
I would also feel better that I have the springs set into the spring pocket nicely and the retainers seated good and the valve seat inspected and cleaned - just an all around better peace of mind that the spring replacement was done properly. I personally feel like doing this with the heads on is a shortcut that I would not take, but that's just me and my .02. A lot of people do it with no issues. With my luck, something would go wrong on the last valve, haha.
Then, with the heads off, you can measure the quench and get new head bolts/studs that have not been stretched and install correct thickness head gasket.
Thanks so much for the info.
haha last valve fail.. classic.
I would let an experienced (US-car) workshop do the conversion for me. They probably are equipped with tools (magnets) for these kind of operations.
But since the full rebuild is only 1300 miles ago, i guess everything should be ok inside the head.
Thats why i think to let them on in the first place..
If i have to take them off, i will go for a compression raising gasket, too.
@everyone: guys you are suys a great help, its really a pleasure being a member of this forum.