Re: Mechanical cam valve adjustment at engine plant
Is there a chance to post the pic here ?
Is there a chance to post the pic here ?
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Re: Mechanical cam valve adjustment at engine plant
I'm sure the engineers knew back then what I figured out about 20 years ago... that on a mechanical lifter cam you can adjust all the inlet valves at 90 deg. ATC from TDC on the firing stroke and all the exhaust valves at 90 degees BTC of the firing stroke, which means two valves at each 90 degree degree crank increment, but neither for that cylinder that is TDC on the compression stroke.
Further they knew, and I measured back in the sixties, that the difference between "hot" (idling at full operating temperature) and cold on a cast iron block-head engine with steel pushrods is NIL! So the engine doesn't have to be hot or running.
I don't why the service manuals say "hot and running". Maybe they thought the cold 90 ATC/90 BTC method was too hard for line mechanics to understand.
Hydraulic lifters can be adjusted at two crank positions as explained in most service manuals because they have very short clearance ramps.
Because mechanical lifter cams have very long constant velocity clearance ramps the lifters may not be on the base circle for the cylinders at TDC. The above procedure guarantees that for ANY cam the lifter on on the base circle.
This procedure is documented in the Hinckley Williams valve adjustment procedure, which is all over the Web. Make sure you get the final Septembler 2008 revision.
DukeComment
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Re: Mechanical cam valve adjustment at engine plant
Duke------
The procedure you mention in your first paragraph is essentially the same as that to be found in the Chevrolet Service Manuals as I referenced above. This procedure is found in the "Engine-Mechanical" section of the manual. The "hot-and-running" procedure is found in the "Tune-Up" section of the manual. I don't know why it's in the manual, at all, either.Last edited by Joe L.; March 5, 2022, 11:03 AM.In Appreciation of John HinckleyComment
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Re: Mechanical cam valve adjustment at engine plant
Here's a link to the 9-23-2008 procedure
thx,
MarkComment
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Re: Mechanical cam valve adjustment at engine plant
Duke, Mark, et al....
The Sep 2008 version is also here in the Database Document Sticky under "Valve Adjustment".... Rich
30-30 SB SOLID LIFTER CAM VALVE ADJUSTMENT.pdf
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Re: Mechanical cam valve adjustment at engine plant
Well,
This may not help, but in my early years when I worked at a dealership there was a 1,000 mile check. Don't know if it was in writing as it was so long ago. by then, the valves were seated and I adjusted them. I agree that with cast parts it's nil. Could be the sales man, but we re-torqued in some cases.
Couldn't use a feeler gage on older cars as the rocked wore to the valve stem and the feeler bridged the gap and the valve was incorrect.
PG valve gapper. Dial indicator was the way.
DomComment
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Re: Mechanical cam valve adjustment at engine plant
Here's a .pdf of the Engine Mechanical/Tune Up Specs and Engine Tune-Up sections of the 1967Chassis Service Manual which is discussed earlier in this thread. As Joe notes, the procedure that Duke and John wrote is essentially the same as that shown in the service manual with some good, additional information added.
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Re: Mechanical cam valve adjustment at engine plant
Duke,
I've got your article on how to adjust valves with 7 90* turns of crank after first adjustment. What is simplest way to mark dampner in 90* intervals? One post said using a stick on timing tape may not be accurate since it might not have same circumference of dampner.
ThanksComment
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Re: Mechanical cam valve adjustment at engine plant
The Chevrolet procedure is not quite the same as the Hinckley-Williams procedure. Chevrolet says you can adjust four mechanical lifters at 180 degrees intervals. Hinckley-Williams says two every 90 degrees.
Back about 15 years ago I got all the lobe lift data for most production cams - in inches to five decimal places every cam degree. I then set up an Excel sheet to compute the dynamic properties - velocity, acceleration, and jerk.
Then I taped a couple of pieces of graph paper together and plotted the 30-30 lobe events over 720 degrees of crankshaft rotation. And from there I measured that the total duration including the constant velocity clearance ramps was a whopping 540 crank degrees, which means the lobes are only on the cam base circle for 180 degrees of every 720 degree (two revolutions) crank event.
Further, at TDC of the compression stroke both lifters are on the clearance ramp about 2-3 thou above the base circle, so if you adjust the valves at TDC they will actually be two to three thou looser than what you think they are.
Additional inspection showed that both inlet and exhaust lifters are well within the base circle at 90 ATC of the power stroke for all inlets and 90 BTC of the compression stroke for all eight cylinders.
The L-72/L-71/LS-6 lobe (same on both sides) is somewhat shorter, like 500-520 degrees and both lifters may be on the base circle at TDC of the compression stroke, but just barely, so I recommend the 30-30 procedure above since there is plenty of margin for error. You only need to be with five or maybe even ten degrees of the TDCs and you're still on the base circle.
The LT-1 cam uses the L-72... lobe on the inlet side (on a smaller base circle) and the 30-30 lobe on the exhaust side. The inlet lifter is on the base circle at TDC, but just barely, and the exhaust lobe is on the clearance ramp, so, again, I recommend the 30-30 procedure.
The Duntov cam is about 450 degrees including the clearance ramps, and you can adjust both valves at TDC of the compression stroke on that cylinder if your 90 degree marks are accurate. Or you can use the 30-30 indexing scheme. It will work for ANY mechanical lifter dam.
Note that page two of the pdf, specifications, lists clearances of the 427/425 at .022/.024" and .024/.028" for the 427/435, yet both cams are identical! What were those guys thinking.
DukeComment
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Re: Mechanical cam valve adjustment at engine plant
There are multiple ways to approach this depending on the engine configuration. As I stated in my previous post, the crankshaft doesn't have to be exactly indexed at each 90 degree interval, just close, and up to ten degrees off is likely more than okay.
Mechanical lifter engines have 8" torsional dampers so the circumference is nominally 8pi, but it's better to measure with a cloth tape, then divide by 4 and use this distance to mark a piece of masking tape, somewhat shorter than the circumference at zero, 90, 180. and 270. Then wrap it around the balancer.
Another method is to set the engine at #1 TDC of the compression stroke. Then eyeball a mark on the outside crank pulley in line with zero on the timing tap. From here use a straight edge to make the 180 mark and a straight edge or square to make the 90 and 270 marks.
You can use chalk, a tire crayon, or a paint mark depending on whether you want to leave then there of erase them if the car is being judged.
DukeComment
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Re: Mechanical cam valve adjustment at engine plant
Duke,
Thank you very much for the detailed explanation of the "bases" - you have to know this to have a complete, clear understanding of how "things" function! I thought that your approach to lay it out on graph paper was great! Funny that you should mention it, but I was scratching my head (when I looked at the Spec sheet also) as to why there was a difference in clearances! Do you have any thoughts at all?
Thank you again......
BobComment
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Re: Mechanical cam valve adjustment at engine plant
No, I have no idea. Here's more to confuse. The Corvette News issue back in '65 that gave the tune-up specs for the new L-78 listed valve clearance as .020/.024".
Here's what I do know. From the drawing data the tops of the clearance ramps are .012" above the base circle, and 1.7 x .012 = .20" rounded to two digits. Big block rocker arms are scaled up versions of small block rockers, and like SB rockers that start at 1.37:1 at low lift and top out at about 1.44:1 with about a 0.3" lobe, big block rockers should have similar behavior, but I've never been able to measure their behavior over the lift cycle or received a valid data set from anyone else.
Until I receive a good data set I recommend .020/.022"
DukeComment
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Re: Mechanical cam valve adjustment at engine plant
Duke,
I have a 1962 340 hp with the Duntov cam. With that cam can I use the "set 4 valves at 180*" technique?Comment
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