The Great Pumpkin - '71 Duster
Following up on my last post. Bit long tonight so settle in and get comfy.
After I finished the cam degree job a few weeks back, I kept thinking that I did it incorrectly. Turns out I was right. It's hard to say what made me go back and re-do it beyond that nagging gut feeling. Theoretically, if you do whatever job you're doing correctly and even go so far as to verify your work, (which I did) there's really no need to go back and check it. I ran into the same scenario from several years ago when I couldn't get the same number consistently. Out of frustration, I kinda just called it good. Bad!
The Comp Cams tool I use to degree cams has a big collar thing that slides over the crank snout and has an internal machined slot that indexes the key. It's held in place with one little set screw. It's got a threaded snout on the outside end to put your ratchet in. To use the degree wheel, you slide it over the threaded portion and it gets sandwiched between the collar and a threaded knurled ring that gets tightened down over the wheel. You then turn the whole works with the ratchet. Frankly, the degree wheel is too small which supposedly makes it less accurate. Next engine I'll get a bigger diameter one.
Regardless, while doing the job a few weeks ago, the stupid collar set screw was slipping. I knew it too but didn't try hard enough to remedy it. Instead, I'd note where the pointer was, start cranking then watch for the wheel to slip. When it did, I'd stop cranking and see how many degrees the wheel moved before the cam did and would factor that into the math. Or, I'd loosen the wheel and move it back to where it started. Obviously that was not a very accurate method and I knew it. Not sure why I was being lazy, I was not in a rush. Sounds cliché but those details are the difference between success and failure.
This time around I paid particular attention to whether the degree wheel was slipping. Before doing anything, I made certain the set screw was 100% locked tight. Big difference when the tool does what it's supposed to do!
In the end, the cam did in fact need to be advanced 4º. When I spoke with Bullet a few weeks ago they said they try to build advance into the grind. That little bit of vagueness made me question whether or not there was actually any advance ground into the cam. There really wasn't.
After a couple more rounds of the inconsistency madness, I had a no-****-Sherlock moment when it dawned on me to take the timing chain off and advance it. The first 2-3 times after advancing it I was still getting the same inconsistent results. WTF?? I could feel my hair falling out. I was almost ready to give up again but after another couple tries something clicked and I was able to repeat the same numbers three times in a row. Amazingly, they were also dead-nuts correct, not even a half degree off. I almost did a dance of joy.
I can say with 100% confidence now that the 108º intake center line is installed at 104º. If I had left it, it would have been 3-4º retarded and I would have been scratching my head trying to figure out why this combo is not making power again.
To be honest, the cam degree discrepancy is giving me the same feeling about how I measured the pushrods. In talking to someone who has way more knowledge and experience than me, he said his small block pushrods usually come in around 7.3-7.35". I'm getting 7.4". If I base my results on his, I'm too long. We're only talking about .050-.060" inch here so I don't think I'm too for off if I am at all. Now that the cam is degreed properly I'll probably go back and re do the pushrods one more time to be sure.
In between all this cam and pushrod measuring lunacy, I decided it was a good idea to check piston to valve clearance. The valve pockets on the pistons are definitely 'generous' so there was little concern of contact to start but if the valve timing is off enough there could be contact. I believe the minimum acceptable clearance is like .80-.100" or so. I've read where people have run much less clearance but I'm not too interested in poking that bear.
I used the goofy clay method. After raiding one of my kids art boxes for modeling clay, I wadded up a couple slabs and coated them with oil to prevent them from sticking to stuff. It's supposed to be about .25" high. I put the head on with a used head gasket and tightened down a few studs about halfway. I ran through two full crank cycles for the actual test. When I popped the head back off, the clay had slid down and sort of jammed itself between the edge of the piston and bore during the second cycle. FFFFAAAAAAKKK! Luckily I was able to blow out the wayward slivers with compressed air. I got it all.
Despite not staying in place, there was enough of an impression made in the clay during the first cycle for reference. I cut it down the middle on the bench and from what I could tell, there seemed to be almost .187" of clearance which is almost double the acceptable amount. I don't think that's right though so I'm going to do it again.
Also ordered a few more things in anticipation of finishing this engine up. Due to sitting in a non-climate controlled garage for several years, my old Pioneer/Powerbond damper rusted. In trying to clean it up, the laser-etched numbers became almost illegible. Rather than mess with it, I broke down and got a cool-guy Fluiddampr. On those, the timing marks are engraved as opposed to laser etched. It's also not supposed to rust and does not need to be honed to fit. Recently they also changed the design which features a recessed front so your pulleys line up. All win. Yes, they're almost double the price of the Pioneer (which is now Powerbond) but a lot of racers swear by them.
Got a bunch of needed gaskets as well including thinner Cometic head gaskets. I have the regular .0039" Fel-Pro 1008 which are fine but since I seem to have excess piston to valve clearance I ordered them in the .027" thickness. The Cometic bore size is also smaller than the Fel Pro by .055" which helps compression. If everything checks out, the c.r. will be 11.4:1.
More to come.
Following up on my last post. Bit long tonight so settle in and get comfy.
After I finished the cam degree job a few weeks back, I kept thinking that I did it incorrectly. Turns out I was right. It's hard to say what made me go back and re-do it beyond that nagging gut feeling. Theoretically, if you do whatever job you're doing correctly and even go so far as to verify your work, (which I did) there's really no need to go back and check it. I ran into the same scenario from several years ago when I couldn't get the same number consistently. Out of frustration, I kinda just called it good. Bad!
The Comp Cams tool I use to degree cams has a big collar thing that slides over the crank snout and has an internal machined slot that indexes the key. It's held in place with one little set screw. It's got a threaded snout on the outside end to put your ratchet in. To use the degree wheel, you slide it over the threaded portion and it gets sandwiched between the collar and a threaded knurled ring that gets tightened down over the wheel. You then turn the whole works with the ratchet. Frankly, the degree wheel is too small which supposedly makes it less accurate. Next engine I'll get a bigger diameter one.
Regardless, while doing the job a few weeks ago, the stupid collar set screw was slipping. I knew it too but didn't try hard enough to remedy it. Instead, I'd note where the pointer was, start cranking then watch for the wheel to slip. When it did, I'd stop cranking and see how many degrees the wheel moved before the cam did and would factor that into the math. Or, I'd loosen the wheel and move it back to where it started. Obviously that was not a very accurate method and I knew it. Not sure why I was being lazy, I was not in a rush. Sounds cliché but those details are the difference between success and failure.
This time around I paid particular attention to whether the degree wheel was slipping. Before doing anything, I made certain the set screw was 100% locked tight. Big difference when the tool does what it's supposed to do!
In the end, the cam did in fact need to be advanced 4º. When I spoke with Bullet a few weeks ago they said they try to build advance into the grind. That little bit of vagueness made me question whether or not there was actually any advance ground into the cam. There really wasn't.
After a couple more rounds of the inconsistency madness, I had a no-****-Sherlock moment when it dawned on me to take the timing chain off and advance it. The first 2-3 times after advancing it I was still getting the same inconsistent results. WTF?? I could feel my hair falling out. I was almost ready to give up again but after another couple tries something clicked and I was able to repeat the same numbers three times in a row. Amazingly, they were also dead-nuts correct, not even a half degree off. I almost did a dance of joy.
I can say with 100% confidence now that the 108º intake center line is installed at 104º. If I had left it, it would have been 3-4º retarded and I would have been scratching my head trying to figure out why this combo is not making power again.
To be honest, the cam degree discrepancy is giving me the same feeling about how I measured the pushrods. In talking to someone who has way more knowledge and experience than me, he said his small block pushrods usually come in around 7.3-7.35". I'm getting 7.4". If I base my results on his, I'm too long. We're only talking about .050-.060" inch here so I don't think I'm too for off if I am at all. Now that the cam is degreed properly I'll probably go back and re do the pushrods one more time to be sure.
In between all this cam and pushrod measuring lunacy, I decided it was a good idea to check piston to valve clearance. The valve pockets on the pistons are definitely 'generous' so there was little concern of contact to start but if the valve timing is off enough there could be contact. I believe the minimum acceptable clearance is like .80-.100" or so. I've read where people have run much less clearance but I'm not too interested in poking that bear.
I used the goofy clay method. After raiding one of my kids art boxes for modeling clay, I wadded up a couple slabs and coated them with oil to prevent them from sticking to stuff. It's supposed to be about .25" high. I put the head on with a used head gasket and tightened down a few studs about halfway. I ran through two full crank cycles for the actual test. When I popped the head back off, the clay had slid down and sort of jammed itself between the edge of the piston and bore during the second cycle. FFFFAAAAAAKKK! Luckily I was able to blow out the wayward slivers with compressed air. I got it all.
Despite not staying in place, there was enough of an impression made in the clay during the first cycle for reference. I cut it down the middle on the bench and from what I could tell, there seemed to be almost .187" of clearance which is almost double the acceptable amount. I don't think that's right though so I'm going to do it again.
Also ordered a few more things in anticipation of finishing this engine up. Due to sitting in a non-climate controlled garage for several years, my old Pioneer/Powerbond damper rusted. In trying to clean it up, the laser-etched numbers became almost illegible. Rather than mess with it, I broke down and got a cool-guy Fluiddampr. On those, the timing marks are engraved as opposed to laser etched. It's also not supposed to rust and does not need to be honed to fit. Recently they also changed the design which features a recessed front so your pulleys line up. All win. Yes, they're almost double the price of the Pioneer (which is now Powerbond) but a lot of racers swear by them.
Got a bunch of needed gaskets as well including thinner Cometic head gaskets. I have the regular .0039" Fel-Pro 1008 which are fine but since I seem to have excess piston to valve clearance I ordered them in the .027" thickness. The Cometic bore size is also smaller than the Fel Pro by .055" which helps compression. If everything checks out, the c.r. will be 11.4:1.
More to come.