Aluminum Head Question - Team Camaro Tech
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post #1 of 7 (permalink) Old Jul 15th, 03, 10:23 AM Thread Starter
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Jeff
 
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Hello, I just ordered a set of the Edelbrock RPM Aluminum heads for my 350. I was told by the previous owner it had 9.5:1 slightly domed pistons in it. I have not pulled the heads yet to confirm, but the motor currently has a crappy old pair or 1976, 76cc cast iron heads on it. My question is, if these pistons are domed, will there be any clearance issues with the new heads? The new heads are the 70cc combustion chamber heads. If there is no problem with stock cast iron, could there be a problem with the new ones? Any advice would be greatly appreciated. Thanks!
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post #2 of 7 (permalink) Old Jul 15th, 03, 11:43 AM
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Eric
 
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Could be a problem. Just use some clay (I steal my kids PlayDough) on top of the dome piston and set the head on (no gasket)and hold it with a couple bolts. Rotate the engine a couple times then pull the head and measure the thickness of the squished clay. Look carefully at the area around the spark plugs and where the valves opened.

You will want at least .035-.040" between the piston and any part of the head and at least .100" between the valves and piston.

E85 racer and E85 carb builder

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68 Camaro, E85 powered 427" small block. 9.96 @ 133 MPH, 1.319 sixty foot on motor. 5.92 eighth @ 116 with a 1.42 sixty breaking beams with back tire on the bottle
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post #3 of 7 (permalink) Old Jul 15th, 03, 04:37 PM Thread Starter
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Jeff
 
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Thanks Eric68, I was afraid you were going to say rotate the engine. I was hoping to get away with not doing that since I was going to mark my rotor pointing to the firewall and not have to set up NO 1 piston to get things back in order after the head swap. No static way to check the clearance? Could I measure the combustion chamber depth of the old head versus the new ones? or is that not the best way to do it. Is the concern the valve opening and slamming the piston top?
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post #4 of 7 (permalink) Old Jul 16th, 03, 03:17 AM
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Ratpack,

It's even more important to check clearances with dome pistons. Different combustion chamber designs/shapes can fit differently with dome pistons. For example, if the new head's combustion chamber is a different shape than your old heads, they might not be clearanced enough to allow the dome to get up in there and could cause problems. More than likely, you'll be okay, but it's definitely worth the extra time and effort to make sure.

Don't let the rotating the engine part intimidate you. Just make sure you make some markings before rotating it. Make sure you know where the distributor points at TDC on your compression stroke and go from there. It will be easy to get back to this point by watching your valve timing.

You can also just mark your distributor location and be real meticulous about counting the engine revolutions, but you really need a starting reference point, so that's why I threw out TDC on the compression stroke. Don't forget that the crank rotates twice for every rotation of the distributor.

There are plenty here to help you, if you need it.

I recently did a head swap and it wasn't too bad. You'll feel much better knowing you have plenty of clearance before firing it up.

Good luck and don't hesitate to email me if you have any questions.

Marty Lake
1969 Z/28 fathom green X77
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post #5 of 7 (permalink) Old Jul 16th, 03, 03:48 AM Thread Starter
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Jeff
 
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Thank you Marty...I appreciate that. I agree, I have to check the clearance or I'll never feel good about firing it up! Quick question, if I start the disassembly with #1 at TDC, then pull the distributor once I confirm it's pointing to number one in the cap,if I rotate the crank twice to do the clay thing, I should be back at the point where I started from right? and the distributor should drop back in without a problem and align to the oil pump drive rod? I know I'm letting this freak me out...lol.
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post #6 of 7 (permalink) Old Jul 16th, 03, 08:44 AM
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Quote:
Originally posted by Ratpack:
Thank you Marty...I appreciate that. I agree, I have to check the clearance or I'll never feel good about firing it up! Quick question, if I start the disassembly with #1 at TDC, then pull the distributor once I confirm it's pointing to number one in the cap,if I rotate the crank twice to do the clay thing, I should be back at the point where I started from right? and the distributor should drop back in without a problem and align to the oil pump drive rod? I know I'm letting this freak me out...lol.
Yes you're right about rotating the crank twice and being back where you started from as long as you are exactly at the same location on the crankshaft timing marks (which is what I figured you implied).

I took a sharpie and made marks on my distributor and intake manifold, so that I knew exactly where it was positioned prior to removing the distributor.

If you can get the engine to fire up, you might want to take a baseline timing reading so that it gives you something to shoot for when you get her back together, but if you do the sharpie thing like I mentioned above, it should get you in the ball park.

If I remember correctly, I did have to play around with the distributor a bit to get it to drop back in where I had it before. I'm not sure what was causing the problem, maybe some others can chime in (Eric68, PDQ, Chicane???), but I'm thinking that maybe the oil pump wasn't lining up, but I eventually got it back as it was. I think I had to keep pulling it out and reinserting it until the rotor made a revolution and things all lined up. There's probably an easy trick to it, I just don't know exactly what the trick is. This was my first head change and it worked out nice, just took a little longer than expected, but was worth it. Hope this helps.

Marty Lake
1969 Z/28 fathom green X77
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post #7 of 7 (permalink) Old Jul 16th, 03, 01:39 PM
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Bob
 
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If I'm not mistaken you better be ready to rotate that crank after the head swap or I don't think that engine will ever start without the valves adjusted.

Bob
Garnet Red 69/SS396/TH400/355 Posi Sold
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