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Tech Editor's DeskProjects, papers, writings, thoughts, musings of our technical editor Joe Padavano. To begin with, he will be making threads and can approve posts to it if he wishes. This can be changed in the future if it does not work out well.
After the discussion here about lifter diameter and a thread on bank angle on FB, I found this from the Apr-Jun 1966 edition of the GM Engineering Journal that covered the development of the Toronado. The only thing that bothers me is that the article says they rotated the lifter centerline THREE degrees away from the cylinder bore centerline, which would put the lifters at 42 deg, not 39. Discuss among yourselves.
Hey, you've got me scribbling on paper trying to work out the math.
I saw something earlier this year with a similar strange doubling of the angle. Can't remember anything else though.
Anyone placing bets on the options?
a) Engineers got it wong
b) Engineers are correct, as long as you're working within their bonkers frame of reference
c) Journal author got it wong
Could it be as simple as that each side of the lifter bank was rotated 3 degrees from cylinder bank centerline? Just an old cow veterinarian, and haven't stayed at a Holiday Inn Express recently
Could it be as simple as that each side of the lifter bank was rotated 3 degrees from cylinder bank centerline? Just an old cow veterinarian, and haven't stayed at a Holiday Inn Express recently
Not to add anything about the 3 degree discrepancy issue....
But I read this a few months ago in an old motorsports magazine from '66 and always wondered why...
Was just doing simplified math - 3+3 = 6 . 45 - 6 = 39. Again just a country cow veterinarian, trained with the axiom if "you hear foot beats think horses not zebras"
Was just doing simplified math - 3+3 = 6 . 45 - 6 = 39. Again just a country cow veterinarian, trained with the axiom if "you hear foot beats think horses not zebras"
3 degrees each bank? 6 total? 45-6=39? I dunno... seems logical._ And doc- you are not "just a veterinarian". I think being a Vet would be tough, since your patients can't help you diagnose the problem.
So it must be straight up is zero degrees? Being 360 degrees a full circle- so 39 degrees is left bank- and 321 degrees is right bank??? Ah I don't know and it doesn't really matter to me- but it is interesting.....
So it must be straight up is zero degrees? Being 360 degrees a full circle- so 39 degrees is left bank- and 321 degrees is right bank??? Ah I don't know and it doesn't really matter to me- but it is interesting.....
Huh? Think this through Greg. If the bores were at different angles relative to vertical, the pushrod length and angle would be different side-to-side.
The block is symmetric. The lifter bores were originally 45 deg from vertical, parallel to the cylinder bores. This article claims that the larger diameter lifter bores required moving the angle three degrees closer to zero ON EACH SIDE to clear the larger machining fixtures on the block machining line. 45-3=42. 42 isn't 39.
So it must be straight up is zero degrees? Being 360 degrees a full circle- so 39 degrees is left bank- and 321 degrees is right bank??? Ah I don't know and it doesn't really matter to me- but it is interesting.....
I think Greg was nearly spot-on, but the math was off. One side (bank) would be 42° while the opposite bank would be 318° relative to a reference bank angle of 45° (both sides would yield a bank angle of 42° representing a total offset of 6° [3°/side]) rotating about a perfectly symmetric circle of 360°.
Sounds logical (to me) the bank angle is 39° (45° - 6° = 39°). Am I incorrect in assuming we're talking about the bank angle of TWO lifters (one on EACH SIDE) and how one relates to the other in a symmetric circle of 360°?
Hey, you've got me scribbling on paper trying to work out the math.
I saw something earlier this year with a similar strange doubling of the angle. Can't remember anything else though.
Anyone placing bets on the options?
a) Engineers got it wong
b) Engineers are correct, as long as you're working within their bonkers frame of reference
c) Journal author got it wong
From my perspective there exists no strange doubling of the angle. The angle remains the same on BOTH sides of a perfectly symmetric circle - 42° EACH SIDE. What you offset on one side of a perfectly symmetric circle you have to offset on the opposite side i.e. 3°/side.
45 - 3 = 42 on ONE SIDE of a plane. The angle is DEFINED on ONE SIDE of a plane. It is NOT defined on two sides of a plane. If an angle (which is defined on ONE SIDE) of a plane is measured @ 45° it must also be defined on the opposite side of the plane @ 45°. 45° x 2 = 90°. We need to recognize there exists a vertex where the x & y lines meet. The lines end at the vertex, which defines the angle contained w/in 180º - not 360°. Each of those lines (x & y) may meet at the vertex but each line equals what? Yeah, you guessed it - 180°. Because a straight line equals 180° it remains that the angle of separation on one side must equal the angle of separation on the opposite side (e.g. x2). What am I missing?
I'm using Euclidean (AKA Plane) geometry to arrive at 39°. Maybe I shouldn't be using plane geometry? A protractor is used to measure/define angles contained w/in semicircles; albeit, a protractor is divided into 180 parts, not 360 parts. It is used to measure the degrees contained in a semicircle. It is used to draw (define) angles on ONE side of a plane e.g. ONE side of a fully symmetric circle. Perhaps, we only disagree on the definitions and/or terms? I'm unclear. But, as I've attempted to establish in the above posts, a declination of 3° on any angle (defined by x & y lines which meet at a common vertex) occurs on only one side of a plane (e.g. 180°). Doesn't declination/offset of 3° on ONE SIDE have to be accommodated by the exact same declination on the opposite side? 3°/side x 2 sides = 6° of separation/offset? If I put this to paper, using Cartesian coordinates won't there exist a separation of 6° (3°/side)? I'm trying to argue my method buy I'm amenable also to understanding where I'm wrong. A 45° angle is measured/defined on ONE SIDE of a circle - it is contained inside of 180°. By convention (and, mathematically) 180° is one half of a circle. The angle is measured/defined inside of 180° - not 360°. If I separate the 45° angle by any amount (3°) the ensuing numerical result must equal a number which is x2 twice the amount on ONE SIDE doesn't it? After all, a semicircle is 180° (one half of 360°). The actual angle (again) is defined w/in the constrains (if you will) of 180° because that is how & where a plane angle is defined using a protractor.
Last edited by Vintage Chief; November 5th, 2023 at 06:40 PM.
the CBA is cam bank angle, not the LBA, which is lifter bank angle. Cam grinders only refer to the CBA , not the LBA.
Cam specs are always referred to in crank degrees, never cam degrees or LBA degrees.
3 degrees difference in LBA is 6 degrees in crankshaft degrees because the crank turns at twice the rate. That’s where the confusion comes in between the 45 deg LBA blocks and the 42 deg LBA later blocks
CBA is the lobe centreline, expressed in crankshaft degrees , to the centreline of the engine. 45-3 for the 42 LBA block, makes the CBA 39 because it’s 6 degrees at the crank
Last edited by CANADIANOLDS; November 13th, 2023 at 05:30 AM.
After the discussion here about lifter diameter and a thread on bank angle on FB, I found this from the Apr-Jun 1966 edition of the GM Engineering Journal that covered the development of the Toronado. The only thing that bothers me is that the article says they rotated the lifter centerline THREE degrees away from the cylinder bore centerline, which would put the lifters at 42 deg, not 39. Discuss among yourselves.
How come they had no problem running even a higher lift cam .475 lift with more duration 328 in later production big blocks, that used the 45 degree lifter angle and .842 dia lifter but were unable to in 66?
How come they had no problem running even a higher lift cam .475 lift with more duration 328 in later production big blocks, that used the 45 degree lifter angle and .842 dia lifter but were unable to in 66?
Later production blocks used the "39 degree" bank angle, not 45. Go back and re-read the paragraph I posted. The change was entirely due to providing clearance for the existing block machining tooling. Larger diameter lifters reduce pressure loads on the cam lobe, reducing the risk of wiping a lobe. With different metallurgy or improved oils, it is obviously possible to use 0.842 lifters with higher lift and duration. Also keep in mind that lift and duration doesn't specify the ramp profile on the lobe, which is really what drives the contact loads.
Later production blocks used the "39 degree" bank angle, not 45. Go back and re-read the paragraph I posted. The change was entirely due to providing clearance for the existing block machining tooling. Larger diameter lifters reduce pressure loads on the cam lobe, reducing the risk of wiping a lobe. With different metallurgy or improved oils, it is obviously possible to use 0.842 lifters with higher lift and duration. Also keep in mind that lift and duration doesn't specify the ramp profile on the lobe, which is really what drives the contact loads.
no, the bigger lifter diameter does not reduce the pressure loads on the lobe. As long as the lobe ramps don’t run off the edge of the lifter face, it doesn’t matter how much bigger the lifter diameter is…load is the same
the same cam in a .921 block does not see less pressure loading on the lobe over an .842” one. in fact, an argument could be made that the lobe in a .921” application see’s more loading because the .921” lifter is approximately 40 grams heavier.
Later production blocks used the "39 degree" bank angle, not 45. Go back and re-read the paragraph I posted. The change was entirely due to providing clearance for the existing block machining tooling. Larger diameter lifters reduce pressure loads on the cam lobe, reducing the risk of wiping a lobe. With different metallurgy or improved oils, it is obviously possible to use 0.842 lifters with higher lift and duration. Also keep in mind that lift and duration doesn't specify the ramp profile on the lobe, which is really what drives the contact loads.
Thanks for the reply Joe.
So they stayed with the 39 degree bank angle and returned to using the 0.842 dia lifter in latter production. Wonder why they did not stay with the .921 dia lifter?
Thanks for the reply Joe.
So they stayed with the 39 degree bank angle and returned to using the 0.842 dia lifter in latter production. Wonder why they did not stay with the .921 dia lifter?
I think they didn’t stay with the .921” because it wasn’t necessary. They started with the .842” , other GM products were using the .842” so to streamline everything, and probably save costs, they went back to the .842”
the engineers at Olds were maybe planning for the future as well with going to the .921” diameter, which will allow for a more aggressive ramp on the cam. we don’t know what they had planned down the road but manufacturers do plan way ahead
no factory Olds cam during the whole second gen V8 run ever needed a .921” lifter diameter
another reason why they may have closed up the lifter bank angle was to allow for much larger cylinder bores. The 403’s oil galleys are also moved inboard to make room for the big bore…that big bore wouldn’t work with the Old style LBA
one thing the original LBA offered was a better pushrod angle to lifter bore centreline. Another thing to remember is the .921” diameter lifter wasn’t a new thing..the first gen rockets all had .921”’s. So they had the tooling already
Last edited by CANADIANOLDS; November 16th, 2023 at 05:34 AM.
Thanks Dale .
The drawing confirms that the later blocks were to have a 42 LBA. There was some speculation on a Facebook thread that the 39 degree CBA camshaft cams were actually ground 42 CBA.
Have you ever measured the cam bank angle of a 39 degree camshaft? The early blocks have a 45 LBA and the camshaft catalog refers to these camshafts as 45 CBA.
So why would the 42 LBA blocks run a 39 CBA?
Thanks Dale .
The drawing confirms that the later blocks were to have a 42 LBA. There was some speculation on a Facebook thread that the 39 degree CBA camshaft cams were actually ground 42 CBA.
Have you ever measured the cam bank angle of a 39 degree camshaft? The early blocks have a 45 LBA and the camshaft catalog refers to these camshafts as 45 CBA.
So why would the 42 LBA blocks run a 39 CBA?
45 LBA’s blocks and 45 CBA cams fit the 90deg V exactly halfway between the 90 on each stroke. When you turn the crank 90deg, the cam turns half that, so that’s 45 , every half stroke(90 crank) the cam is always 45 before or after tdc, mid stroke or bdc.
on a 42 LBA block, when the crank turns 90 deg, the cam is always 39 crank deg from tdc, bdc or mid stroke that’s where the 6 deg’s crank spec comes from.
if you were to put a degree wheel on the cam , it would show a 3 deg diff over the 45 cam set up(on the deg wheel, not crank) at tdc, bdc or mid stroke because it turns at half the rate of crank
Last edited by CANADIANOLDS; November 18th, 2023 at 10:07 AM.
45 LBA’s blocks and 45 CBA cams fit the 90deg V exactly halfway between the 90 on each stroke. When you turn the crank 90deg, the cam turns half that, so that’s 45 , every half stroke(90 crank) the cam is always 45 before or after tdc, mid stroke or bdc.
on a 42 LBA block, when the crank turns 90 deg, the cam is always 39 crank deg from tdc, bdc or mid stroke that’s where the 6 deg’s crank spec comes from.
if you were to put a degree wheel on the cam , it would show a 3 deg diff over the 45 cam set up(on the deg wheel, not crank) at tdc, bdc or mid stroke because it turns at half the rate of crank
October 30th, 2023, 07:31 PM
