Cam Degreeing Question
Thread Starter
Drifting
Joined: Aug 2004
Posts: 1,677
Likes: 1
From: Potomac Falls VA
Cam Degreeing Question
So I checked my centerline to TDC and I took multiple measurements to get a data set instead of a single measurements. The Comp Cams spec is 106deg and my measurements come in at 104-104.25deg. I bought a summit timing set with multiple keyways in the crank. I used the 2deg retard keyway and my measurements come out between 106.25 and 107deg.
I would (ideally) like to avoid drilling out the cam wheel so I am wondering is it better to leave it straight up (104-104.35 degree) or retard to 106.25-107?
As a secondary question, I bought some ARP connecting rod bolts which have extra clearance for a 383 with aggressive cam but I have found that with a little bit of grinding off of the current rod bolts for 3 cylinders, I am now fine and experience no binding / interference. Should I leave well enough alone or replace with the ARP rod bolts? ARP recommend the gauge stretch method but also has a torque method which is what I would use.
Thanks
Shane
I would (ideally) like to avoid drilling out the cam wheel so I am wondering is it better to leave it straight up (104-104.35 degree) or retard to 106.25-107?
As a secondary question, I bought some ARP connecting rod bolts which have extra clearance for a 383 with aggressive cam but I have found that with a little bit of grinding off of the current rod bolts for 3 cylinders, I am now fine and experience no binding / interference. Should I leave well enough alone or replace with the ARP rod bolts? ARP recommend the gauge stretch method but also has a torque method which is what I would use.
Thanks
Shane
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
it's unusual that an off-the-shelf cam doesn't degree pretty much right on. I would double, double check the timing marks, etc.
If you're 100% sure that your measurements are correct, then IMHO I'd degree it so that it matches the cam card spec. Retarding the cam 2 degrees moves the power curve up in the RPM range around 300 RPM, as well as a few other side effects.
As for the rods, grinding on the bolts certainly works and it's been done for a long time. It does weaken the bolt, as it's not designed to be ground that way...so I personally would consider replacing the bolts. This isn't a trivial decision, as you'll have to resize the big end of the rod after the bolts are pressed in...and in both cases you're affecting the balance.
I personally torque for bolt stretch; the tool isn't all that expensive and it's saved my bacon a couple of times with a "stretchy" bolt that would have been a point of failure if I had just torqued it.
All IMHO
If you're 100% sure that your measurements are correct, then IMHO I'd degree it so that it matches the cam card spec. Retarding the cam 2 degrees moves the power curve up in the RPM range around 300 RPM, as well as a few other side effects.
As for the rods, grinding on the bolts certainly works and it's been done for a long time. It does weaken the bolt, as it's not designed to be ground that way...so I personally would consider replacing the bolts. This isn't a trivial decision, as you'll have to resize the big end of the rod after the bolts are pressed in...and in both cases you're affecting the balance.
I personally torque for bolt stretch; the tool isn't all that expensive and it's saved my bacon a couple of times with a "stretchy" bolt that would have been a point of failure if I had just torqued it.
All IMHO
Thread Starter
Drifting
Joined: Aug 2004
Posts: 1,677
Likes: 1
From: Potomac Falls VA
it's unusual that an off-the-shelf cam doesn't degree pretty much right on. I would double, double check the timing marks, etc.
If you're 100% sure that your measurements are correct, then IMHO I'd degree it so that it matches the cam card spec. Retarding the cam 2 degrees moves the power curve up in the RPM range around 300 RPM, as well as a few other side effects.
As for the rods, grinding on the bolts certainly works and it's been done for a long time. It does weaken the bolt, as it's not designed to be ground that way...so I personally would consider replacing the bolts. This isn't a trivial decision, as you'll have to resize the big end of the rod after the bolts are pressed in...and in both cases you're affecting the balance.
I personally torque for bolt stretch; the tool isn't all that expensive and it's saved my bacon a couple of times with a "stretchy" bolt that would have been a point of failure if I had just torqued it.
All IMHO
If you're 100% sure that your measurements are correct, then IMHO I'd degree it so that it matches the cam card spec. Retarding the cam 2 degrees moves the power curve up in the RPM range around 300 RPM, as well as a few other side effects.
As for the rods, grinding on the bolts certainly works and it's been done for a long time. It does weaken the bolt, as it's not designed to be ground that way...so I personally would consider replacing the bolts. This isn't a trivial decision, as you'll have to resize the big end of the rod after the bolts are pressed in...and in both cases you're affecting the balance.
I personally torque for bolt stretch; the tool isn't all that expensive and it's saved my bacon a couple of times with a "stretchy" bolt that would have been a point of failure if I had just torqued it.
All IMHO
Since we took very little off of the bolts, I am starting to think that is the way to go esp since this is a street motor but I am open to doing more as long as it does not break the piggy bank into even more pieces.
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
"Resizing" a rod is a means of restoring the correct inner diameter of the big end of the rod. As a rod wears, the inside diameter of it increases...so after a while there's not enough pressure to hold the bearings in place (what's called "bearing crush") and they break loose...which is called "spinning a bearing."
In resizing, The bolts are pressed out (or the capscrews removed) and a cut is taken on the mating surface of both the cap and the rod. The inner bore is now too small - and not round! New bolts are pressed in (or capscrews replaced) and the rod is torqued in a rod vise. Then the bore is honed to establish the correct inside diameter to hold the bearings, provide the right clearance to the crankshaft rod journal and be as round as we can reasonably make it.
I looked around for a video or something and came up empty...it's kinda hard to describe, but once you see it it's an "ah ha!" moment
You're fine with grinding the bolts - it's been done for a long time with no issues. Just be careful and check all the clearances twice.
In resizing, The bolts are pressed out (or the capscrews removed) and a cut is taken on the mating surface of both the cap and the rod. The inner bore is now too small - and not round! New bolts are pressed in (or capscrews replaced) and the rod is torqued in a rod vise. Then the bore is honed to establish the correct inside diameter to hold the bearings, provide the right clearance to the crankshaft rod journal and be as round as we can reasonably make it.
I looked around for a video or something and came up empty...it's kinda hard to describe, but once you see it it's an "ah ha!" moment
You're fine with grinding the bolts - it's been done for a long time with no issues. Just be careful and check all the clearances twice.
Thread Starter
Drifting
Joined: Aug 2004
Posts: 1,677
Likes: 1
From: Potomac Falls VA
"Resizing" a rod is a means of restoring the correct inner diameter of the big end of the rod. As a rod wears, the inside diameter of it increases...so after a while there's not enough pressure to hold the bearings in place (what's called "bearing crush") and they break loose...which is called "spinning a bearing."
In resizing, The bolts are pressed out (or the capscrews removed) and a cut is taken on the mating surface of both the cap and the rod. The inner bore is now too small - and not round! New bolts are pressed in (or capscrews replaced) and the rod is torqued in a rod vise. Then the bore is honed to establish the correct inside diameter to hold the bearings, provide the right clearance to the crankshaft rod journal and be as round as we can reasonably make it.
I looked around for a video or something and came up empty...it's kinda hard to describe, but once you see it it's an "ah ha!" moment
You're fine with grinding the bolts - it's been done for a long time with no issues. Just be careful and check all the clearances twice.
In resizing, The bolts are pressed out (or the capscrews removed) and a cut is taken on the mating surface of both the cap and the rod. The inner bore is now too small - and not round! New bolts are pressed in (or capscrews replaced) and the rod is torqued in a rod vise. Then the bore is honed to establish the correct inside diameter to hold the bearings, provide the right clearance to the crankshaft rod journal and be as round as we can reasonably make it.
I looked around for a video or something and came up empty...it's kinda hard to describe, but once you see it it's an "ah ha!" moment
You're fine with grinding the bolts - it's been done for a long time with no issues. Just be careful and check all the clearances twice.
1) Is there a good way to check clearances between the cam lobes and connecting rod bolts? I grinded down 3 so there is no more binding but I should probably check all of them. Is it possible to get a feeler gauge in such tight spaces?
2) When I put the rods and pistons back in, do I just re-torque the connecting rod bolts? OR is there a special procedure? Need threadlocker?
Thanks
Shane
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
I apologize in advance for the likely wild back-and-forth about threadlocker you question will cause
But no threadlocker on those bolts - just the lube recommended by the manufacturer. Torque if you have to, bolt stretch is a far better approach and the tool is relatively cheap. Make sure you protect the rod journal by putting some rubber tubing over the rod bolts - and guide the rod carefully while tapping in the piston.
Last edited by billla; Mar 17, 2010 at 09:34 AM.
Thread Starter
Drifting
Joined: Aug 2004
Posts: 1,677
Likes: 1
From: Potomac Falls VA
Yes, you can get a feeler gauge in there. Typically I mock up one throw, one rod at a time, so you can get in there - it's a pain. Then use those two rods as patterns for the rest. Someone will no doubt pop up and say a mock-up isn't required
I apologize in advance for the likely wild back-and-forth about threadlocker you question will cause But no threadlocker on those bolts - just the lube recommended by the manufacturer. Torque if you have to, bolt stretch is a far better approach and the tool is relatively cheap.
Make sure you protect the rod journal by putting some rubber tubing over the rod bolts - and guide the rod carefully while tapping in the piston.
I apologize in advance for the likely wild back-and-forth about threadlocker you question will cause
But no threadlocker on those bolts - just the lube recommended by the manufacturer. Torque if you have to, bolt stretch is a far better approach and the tool is relatively cheap. Make sure you protect the rod journal by putting some rubber tubing over the rod bolts - and guide the rod carefully while tapping in the piston.
In my head, I thought I could remove the connecting rod / piston as a unit, knock out the old connecting rod bolts on the other end and press in the new ones?
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Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
So thinking through this some more, why, when just changing out the connecting rod bolts that hold the rod to the crank do you need resize the connecting rod at the other end with the piston?
In my head, I thought I could remove the connecting rod / piston as a unit, knock out the old connecting rod bolts on the other end and press in the new ones?
In my head, I thought I could remove the connecting rod / piston as a unit, knock out the old connecting rod bolts on the other end and press in the new ones?
All fastners apply different clamping pressures, so they all distort the bore in a particular way. Honing the bore removes those differences, but if we hone with one fastner and then put in a different one, the clamping forces are different and the bore will not be round. This is true with the main bore as well - there's no quicker way to wipe the main journals than to have the block align-honed with stock bolts, then decide at the last minute to switch to ARP studs...without align-honing the bore again. I have to cop to learning that one the hard way back in the early 80's.
Bolts are pressed in, and out - not "knocked" - and always in a fixture to ensure the rod is supported during the operation.
Thread Starter
Drifting
Joined: Aug 2004
Posts: 1,677
Likes: 1
From: Potomac Falls VA
All good questions. You don't need to resize the end with the piston pin ("little end"), just the end that goes around the crank ("big end").
All fastners apply different clamping pressures, so they all distort the bore in a particular way. Honing the bore removes those differences, but if we hone with one fastner and then put in a different one, the clamping forces are different and the bore will not be round. This is true with the main bore as well - there's no quicker way to wipe the main journals than to have the block align-honed with stock bolts, then decide at the last minute to switch to ARP studs...without align-honing the bore again. I have to cop to learning that one the hard way back in the early 80's.
Bolts are pressed in, and out - not "knocked" - and always in a fixture to ensure the rod is supported during the operation.
All fastners apply different clamping pressures, so they all distort the bore in a particular way. Honing the bore removes those differences, but if we hone with one fastner and then put in a different one, the clamping forces are different and the bore will not be round. This is true with the main bore as well - there's no quicker way to wipe the main journals than to have the block align-honed with stock bolts, then decide at the last minute to switch to ARP studs...without align-honing the bore again. I have to cop to learning that one the hard way back in the early 80's.
Bolts are pressed in, and out - not "knocked" - and always in a fixture to ensure the rod is supported during the operation.
Assuming some risk here, I guess, but lets hope it plays out in my favor.
Thread Starter
Drifting
Joined: Aug 2004
Posts: 1,677
Likes: 1
From: Potomac Falls VA
Went through last night and finished clearancing the rest the inner rod bolts. I did not have any binding but I thought I should go through and take a little off of the high points in case higher rpms + heat woud cause some of them to interfere. Seems like a tough judgment call....How much is enough without going too aggressive that the bolts fails. IF guys have been doing these mods for 50-60 years in the garages, it should hopefully work but still worried about the implications of it failing.
Here are a few pics of the engine and the results of the picton0valve clearance.
Here are a few pics of the engine and the results of the picton0valve clearance.