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  #16 (permalink)  
Old 03-23-2019, 11:23 AM
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Those exhaust ports are raised a fair amount, look at the boss for the head bolt to the bottom of the port compared to a stock head. And the plug is moved too. All good for performance but might make header fit a challenge in some chassis.

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Old 03-23-2019, 06:06 PM
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Yes they are raised a lot, I'm guessing almost an inch. I'm looking at the upper exhaust bolt hole and up to the tab part where you might bolt on an accessory. They look to be about the same distance apart, but the hole for the bolt on accessory hole is above the valve cover sealing surface where on the iron heads that hole is down what appears to be an inch. If that makes any sense at all.
I put an email into them asking how much higher they are.
I'll have to look at my headers again, I think the only problem I'll have is the header hitting the starter (a big stock one) but I have a new mini starter sitting on the shelf. Actually I'd like to get a newer style GM starter that is smaller and shorter. It's too hard to get an adjustment right on the mini ones. The newer stock ones I can just use the 1/8" drill bit measurement between the shaft and the ring gear. And believe me, my starter takes a lot of shimming. Who knows what happened on the assembly line that day when the starter holes were tapped.
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Old 03-31-2019, 10:34 AM
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Quote:
Originally Posted by ericnova72 View Post
That won't change valve-to-piston clearance one bit, so that is really poor advice.
Piston is nearly half way down the cylinder and heading away when the intake valve reaches full lift, no where near the piston at all.

Valve-to-piston collisions happen on the overlap period neat TDC, when the exhaust is just coming to fully closed, the intake is just starting to open, and the piston is just reaching TDC overlap ready to head back down drawing in mixture. All three parts are close to each other in the same small space.

Checking points are between 20 before TDC and 10 after TDC, check every 5 to find the closest point to the intake valve, then check a few degrees either side of that 5 interval to find actual clearance in the assembly.

As far as power, if your 781's are basically stock, no porting, only a 3 angle valve job.... then according to the Head's flow numbers for up to and at your cam lift it could pick up 75-100HP.

For valve to piston clearance mods I the block, you can rent a flycutting tool from Isky, you can carefully free hand it with a Dremel if it is diameter and not depth contact, or of it is just intake depth clearance you can retard the cam as this increases intake clearance and decreases exhaust.
I have also seen where guys have taken an old or spare valve and cut the face using a cut=off disc in a Dremel to resemble a milling cutter and use that like the Isky in-head tool, or solder a small piece of high speed steel or carbide cutting bit to a old valve face and carefully cut with that down in through the installed head using the valve guide as a locator.
Piston Notching Cutter Tool : ISKY Racing Cams, Do It Right

We had a member here, I haven't seen him post in a while, BobCRman, who had used several sets of those heads and never had any problems with them.

I finally put the valve checking springs on today and I came back here for notes. I have the dial indicator on #1 exhaust retainer and was having a hard time zeroing it. I believe with just these weak springs the lifter is collapsing as I watch. I push down on the roller tip to see how much clearance there is and after I let it go it's way off zero and slowly climbing. It had climbed .110" before I came in here to post.
BTW, yes these Comp lifters were like this or worse when new. On startup they always took some oil pressure till they got quiet, sometimes 10 or so minutes on one or two. They're actually better now than when new.



Anyway going past TDC the least I got so far is about .400". That was not trying to zero it, just looking at the indicator to see how much it moves back and forth without time for the lifter to collapse. I'm going to back up and check BTDC. Am I doing this right? And I have a note to myself here that says minimum clearance is .100 exhaust and .080 intake. I'm just getting some idea of what kind of interference I may get with the big valves in the aluminum heads, like are things close now or do I have a lot of room.
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  #19 (permalink)  
Old 03-31-2019, 01:38 PM
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Since you are not checking geometry of the valvetrain at this point, it is easier to get valve-to-piston clearances if you just go ahead and bottom out the valvetrain.
If your checking spring isn't strong enough to keep the lifter piston bottomed out in the lifter, either shim the spring tighter or use the inner spring from a dual valvespring set if you have them.

You're clearance figures are correct, but you can get by with intake clearance down to .060" as there is no chance of float holding the intake open too long to allow it to get hit as the piston is at the bottom of the bore starting to head up when the intake valve closes. Exhaust is the one that can get hit if held open during a float situation.
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Old 03-31-2019, 06:26 PM
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Lucky or Unlucky?

I was trying to check the intake clearance and it was driving me nuts. No matter how I turned the motor I had TONS of clearance. God knows how many times I turned the motor over. I started to think that I had a bad cam but couldn't picture the roller cam getting wiped out that bad. Finally I pushed down on the rod end of the rocker and it's springy. A LOT. About .128" worth of spring action. I adjusted the rocker again getting rid of the spring action minus a little for clearance. Comparing the wear marks on the rods at the guides I see this rod is down lower.


Do do I now know what a collapsed lifter can feel like? (from above anyway) I didn't even hear it last time I ran it.

Am I lucky I found it before other damage happened or unlucky that it happened?

I guess I better not start it the way it is because I don't know if it will pump up to were it should be and the valve hit the piston.

If I want the new heads, I really don't have the money for another set of lifters, I guess if I take it apart and the rest are good I can replace the one pair.
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  #21 (permalink)  
Old 03-31-2019, 06:41 PM
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Nothing wrong with those lifters, they have just had all the oil pumped out of them from your repeated revolutions of the crank, with no oil pressure from the oil pump refilling them.

Bottom them out, make your clearance check, and readjust them back to their normal position, they are fine. Just don't forget that readjustment step

A collapsed lifter is one that either the check valve is damaged or help off it's seat by dirt, or dirt has gotten between the plunger and the plunger bore in the lifter valley and stuck the piston. Will rattle and never quiet up and behave like it was a solid when trying to adjust it....it'll either run and clatter due to clearance in the valvetrain or be too tight and cause a miss due to no clearance at all, with no "hydraulic normal" spot in between.
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Old 03-31-2019, 06:53 PM
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None of the others on that head are like that. And the only reason I turned it so many times is because I didn't realize it leaked down.

But I suppose I can re-adjust the rocker and start it and see if it pumps up?
Yes, important to re-adjust first!
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  #23 (permalink)  
Old 03-31-2019, 07:11 PM
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This pair has had all the preload removed from them when you removed the rockers to put checking springs on....that unloads the check valve.....the others, still all adjusted up will still have the check valve seated holding them full of oil.

Re-adjust and start it up and they will go back to normal.
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Old 04-01-2019, 06:43 AM
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Quote:
Originally Posted by ericnova72 View Post
Since you are not checking geometry of the valvetrain at this point, it is easier to get valve-to-piston clearances if you just go ahead and bottom out the valvetrain.
If your checking spring isn't strong enough to keep the lifter piston bottomed out in the lifter, either shim the spring tighter or use the inner spring from a dual valvespring set if you have them.

You're clearance figures are correct, but you can get by with intake clearance down to .060" as there is no chance of float holding the intake open too long to allow it to get hit as the piston is at the bottom of the bore starting to head up when the intake valve closes. Exhaust is the one that can get hit if held open during a float situation.

What do you mean by "bottom out the valvetrain"?
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Old 04-01-2019, 03:12 PM
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Quote:
Originally Posted by 55 Tony View Post
What do you mean by "bottom out the valvetrain"?
Bottoming out the lifter plunger so that you don't have plunger movement messing up the valve-to-piston clearance check.
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Old 04-06-2019, 04:26 AM
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I finally tried again to check my intake valve to piston clearance and the first time the intake got as small as .074". But I may have had it adjusted a little too tight. Two more times I got .098 and .095 just past TDC. The exhaust has me confused if I did it right because I didn't even need the dial caliper, it never got less than a good 1/4".
I found out that the piston intake valve relief is for up to a .2380" valve, so that sounds like I'm good to go.
What about that exhaust? Does that sound right?
The cam is advanced 2, does it look like if it wasn't I'd be having intake clearance issues?
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Old 04-06-2019, 05:32 AM
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Stupid edit rules! That valve size was supposed to be 2.380".
And about the exhaust, if it has so much clearance now, I am good to go with a larger valve, right?
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Old 04-06-2019, 05:36 AM
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Exhaust typically misses by a mile....SBC's tend to be the same way, you clay up the piston and the exhaust valve doesn't even touch the clay to leave an impression, or leaves just a little 1/8-1/4" long ding in the clay.
That's why unless the BBC piston has a very large dome there isn't even a exhaust valve notch there.

Advancing cam tightens intake piston-to-valve clearance, retarding it opens up intake clearance.....advancing the cam does the opposite for the exhaust valve.

When you advance the cam, you're opening the intake a little sooner, so it is open a little further when that piston is making that arrival up to TDC as the intake valve is opening and the exhaust valve is closing..

I knew what you meant on the valve size, and yes you could go to a bigger exhaust if it was needed....but bigger than the Rect port head common 1.88" size is rarely needed unless this is a heavy nitrous sniffing engine with a lot of exhaust volume to deal with(600HP+ from just the Nitrous kit or kits on top of the engine power.). or an bigger cube over 580" engine.
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Old 04-06-2019, 06:17 AM
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So if I change the cam from the current 2 advanced to straight up I'd have more clearance. I wonder how much? I'm tempted to get the next size up cam but I would also like to see/feel the difference with just the head and intake change and then a bigger cam later.


You had mentioned that Weiend intake. Is that made for a standard square bore or the Dominator? I can't find any dimensions for the dominator stud spacing or the open hole size. I'd like to see just how much work it would be to adapt it. Hmm, they make wood spacers, so why couldn't I make a wooden adapter? Well again I need to know the dimensions to answer that. At least to test it before welding it.
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Old 04-06-2019, 07:20 AM
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Weiand Team G single plane for the BBC was regular Holley 4150/4160 pattern.
I don't remember ever seeing a 4500 pattern example.

You could make a wood adapter, I've got several 1/2" and 1" open spacers made of marine or cabinet grade plywood. Don't use pine, and don't use solid board, it won't stay together and splits.
If you want your homebuilt plywood versions to be more permanent, seal the inside face with a 2-part epoxy to keep fuel from seeping into the wood grain.

The example of that intake I saw was welded, a 1" spacer for a Q-Jet was TIG welded to the Holley flange, and a couple dozen beads were laid along the sides of the original plenum on the back half section of the plenum sides and across the back to make enough material to blend to the Q-Jet nicely and not add 2-3" to the manifold height.
It was a well thought out piece, car it was on really ran well, just breaking into the 8.90's 1/4 mile with a pump gas 496 in a all-steel(except hood), full interior, streetable '68 Nova.
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