Thread: Maybe I'm Not As Bright As I Thought

Tweet

Get yourself a set of checking springs (available at any speed shop, Jegs or Summit), assemble an intake and an exhaust valve in the head with the weak springs and do like Denny said. Sit the head on the block without a gasket and without cinching the head bolts down. Turn the crank by hand to a position about 30-40 degrees BTDC on the exhaust stroke. Push the valves down until they contact the piston. You can measure this with a dial indicator on the valve stem or if you're careful, you can do it with a 6" caliper. Now rotate the crank 5 degrees and push and measure again. Rotate 5 more degrees, push and measure. Do this every 5 degrees until you are about 30-40 degrees on the other side of TDC. If you have 0.080" clearance on the intake and 0.100" on the exhaust all the way through this exercise, you're good to go. The closest you'll be will be before TDC when the piston is chasing the exhaust valve.

Hey, I wanted to update this.

I checked the clearances as described bove, and witht he numbers in hand, went down to Delta Camshaft. They reground the 5.0 H.O. cam to .471" lift, 219 int / 209 exh @.050, 112 deg sep.

The engine's nearly finished -- the last parts arrived yesterday -- and it should be in next weekend.

Also, as I was swapping out the Duraspark with a Pertronix, I found that my vacuum advance was broken; the actuator arm had separated from the pin. Might this have been part of the cause of the front cylinders running so lean? Needless to say, I'm getting a new distributor.

Denny, when I took my 390 apart to get the heads redone, I noticed the same type of coloration on the exhaust valves of the front 2 cylinders as WasII has on his. I also noticed that being the ol geezer I am, I hadn't seen the mismatch in port size between the Edelbrock F-380 manifold and the heads. The manifold ports are the tall ports (2.34" instead of the 1.87" that the head ports are). would this necessarily cause fuel starvation on certain cylinders? Just wondering. Gonna have to put on my old cast iron 4bl intake or buy a new alunimum one. the 3x2's will get sold.

I understand that Denny. What I can't really tell you is why I never noticed the mismatch when I put the motor together.

I guess I was just caught up in the 3X2's momentum and didn't even think to check port sizes. Dumb mistake. Should of sloped the bottom edge of the head ports to match the intake.

When I get them back from the machine shop I'll have to do that or forget using the 3X2's. Just have a lot of money wrapped up in the setup. Thanks for the input.

Yeah, some of us *never* make mistakes when setting up fancy carburetor rigs.

Originally posted by DennyW
Hey, I make mistakes too. I wasn't impling you didn't know. Some times, I just type what I'm thinking, and it sounds, or comes out wrong. The carbs had your mind be-dazzled.

Denny, I know you weren't implying that, it just pi$$es me off that I didn't even think to stop and check it. Oh, well.

Now a question for you and Was II. I've never ported heads before. What is the best tool or bit to use in the Dremel to cut the port down at the entry a ways. Got to go down .500 of an inch. The width is okay. Thanks in advance.

Dude, have you been reading this thread? I'm not the guy to ask about the "best" way to do anything.



That said, I took a carbide rasp bit and put it on a Makita hand drill for the heavy cutting, then used an 80-grit and then a 120-grit stone on a Dremel for the final shaping. I used a wire wheel for the polishing. There's got to be a better way but this did it reasonably fast and pretty well.

I also stuffed paper towels soaked in WD-40 down into the ports before I cut, to catch most of the shavings, which made cleanup way easier.

Thanks, Was II. Yeah the paper towels in the ports is the only way to go there. I do that when I am even cleaning up old gaskets. Appreciate the help.

Originally posted by Oldf100fordman
I understand that Denny. What I can't really tell you is why I never noticed the mismatch when I put the motor together.

I guess I was just caught up in the 3X2's momentum and didn't even think to check port sizes. Dumb mistake. Should of sloped the bottom edge of the head ports to match the intake.

When I get them back from the machine shop I'll have to do that or forget using the 3X2's. Just have a lot of money wrapped up in the setup. Thanks for the input.

I think you're gonna be in just as bad shape if you start cutting on the heads. What you might do is mix up some JB Weld or other metal-impregnated epoxy product and build up the manifold ports to match the head ports. I've done this extensively with Briggs & Stratton Kart racing motors and never had a problem with it breaking up, cracking or otherwise causing any problem under racing conditions. It's something to think about anyway.

I agree with Tech, .5 inch is a lot of grinding, liable to hit water. With that much mismatch, there could have been vacuum leaks, too. I'd save the manifold for my next project, and put one on that matches the heads.