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Terry -
Re: 1970 LT-1 Valve Lash, Idle and Idle Mixture Setting
Only one distributor for 1970 LT1 -- TI #1111491? from memory. I have to check my data to be sure. I'll get you the Delco listed vacuum points when I get to my cubby. Only the originally installed intake and distributor will have matching chisel marks, so any changes (timing set, cam, distributor, or intake will throw it off.
Best move is what you suggest: Drive it at 8* advance and move it up until it pings -- that takes into account your real world conditions. You need not be afraid to go as high as 14, if that works with your conditions.TerryComment
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TerryComment
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Re: 1970 LT-1 Valve Lash, Idle and Idle Mixture Setting
One has to remember that after 1968 (1966 in California) all engine spark advance maps were set up for emissions, not performance or fuel economy, and the various crude add-on system like TCS and ported sparke advance just complicated things.
So even if your distributor appears to be OE, one should map out the spark advance with a dial back timing light to see what you have.
To optimize performance, the best place to start is usually the antecedent non-emission controlled engine, which for the LT-1 would be the 365 HP configuration from '64 and '65.
Spark advance specs are in the applicable CSM/Shop Manual. They are also in the AMA specs, which can be downloaded for all years from the GM Heritage Web site.
For full time vacuum advance, all mechanical lifter small blocks should use the B28 VAC. Then get the centrifugal in as quickly as possible. Subtract full centrifugal from 38 to arrive at the optimum initial timing. If it doesn't detonate, you have an optimized spark advance map for performance and fuel economy. If it does detonate you have to either retard the intial or slow down the centrifugal.
DukeComment
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Re: 1970 LT-1 Valve Lash, Idle and Idle Mixture Setting
You old timers remmember how to adjust solid lifters the old fashion way? The old chevy valve cover cut open on top to get to the rockers without dumping oil on the exaust manifold. With the engine running loosen each rocker till it clacked then tighten till the noise stopped plus a quarter turn. we've all done that and it worked great, and I'm not that old.
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Re: 1970 LT-1 Valve Lash, Idle and Idle Mixture Setting
According to several local scrap yards, that's one of the prime reason for the relative 'shortage' of early stamped steel 327 valve covers... Apparently, they're prized for being chopped up to make solid lifter adjust tools.
Being relatively rectangular in shape vs. gently rounded, the cut job to remove the upper plane is simplified...Comment
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Re: 1970 LT-1 Valve Lash, Idle and Idle Mixture Setting
There is no legitimate reason so set valve clearance "hot and running". "Cold and dead" with proper indexing of the crankshaft as outlined in the paper written by John Hinckley and me will achieve much more accurate running clearance and no mess.
I can do the job in less than ten minutes, not including time to R & I the valve covers and other hardware to gain access.
I remember back in the sixties when a racer I knew who did tune-up work tried to talk me into letting him adjust my valves with a P&G tool because it was more accurate than feeler gages. I passed because I thought it was too expensive.
Ten years later when I measured the actual rocker ratio and found that not only was it not 1.5:1, but it varied with lift, I realized that it doesn't make any difference how accurate you set them when the OE recommended settings didn't take into account actual rocker ratio behavior, so even if you set them to within .0001" of the factory recommendation, they would still be a two to seven thou too loose depending on the specific camshaft.
DukeComment
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Re: 1970 LT-1 Valve Lash, Idle and Idle Mixture Setting
How can we find Duke's paper on setting valve lash?Comment
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Re: 1970 LT-1 Valve Lash, Idle and Idle Mixture Setting
technical archiveseat my dustComment
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Re: 1970 LT-1 Valve Lash, Idle and Idle Mixture Setting
Yes, that Web site has the latest revision. There are earlier revisions floating around the Web, and despite my attempts to get them removed or replaced with the latest revision, they are still there.
DukeComment
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Re: 1970 LT-1 Valve Lash, Idle and Idle Mixture Setting
"We all" doesn't include this former midwestern boy. I never adjusted solid lifters in the manner you suggested, and I've done a bunch back in the day. I started out running the engine using clips on the rockers, but still had too much oil on the manifolds and made myself sick. I then went to setting on the TDC/180* method, but ALWAYS at a specific clearance (usually .008" x .016" on factory Duntovs). That always worked well for me, and only recently adopted the Duke/John method. Cut open valve covers never occurred to me; however, we did use something like that on old Chevy sixes, but it was made from scratch.
Stu FoxComment
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Re: 1970 LT-1 Valve Lash, Idle and Idle Mixture Setting
Post #50 describes the procedure for adjusting hydraulic lifters, not solids.
The old "tried and true" method of adjusting solids whether "hot" "warm" or "ambient" is the same, and it works for any and all cams (long clearance ramps, short clearance ramps, "Duntov" "30-30", LT1, etc):
INTAKE ADJUSTMENT: Hand turn the engine in it's normal direction of rotation while watching the exhaust valve on that particular cylinder. When the exhaust valve begins to open, stop and adjust that cylinder's intake valve.
EXHAUST ADJUSTMENT: Rotate the engine until the intake valve is at full lift and then begins to close. When the intake is 1/2 to 3/4 closed, stop and adjust the exhaust valve on that particular cylinder.Comment
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Re: 1970 LT-1 Valve Lash, Idle and Idle Mixture Setting
If you are referring to the TDC #1 and TDC #6 indexing methods, that method ONLY WORKS FOR HYDRAULIC LIFTER CAMSHAFTS.Originally posted by Stuart Fox (28060);528656
I then went to setting on the TDC/180* method, but [U
IT WILL NOT YIELD PROPER CLEARANCES FOR ANY OE MECHANICAL LIFTER CAMSHAFT.
The method recommended in the Hinckley/Williams paper is precise and easy to follow. Beginning at TDC #1 you adjust the two specified valves. Then you rotate the engine 90 degrees seven times and do the two specified valves at each 90 degree increment. There is absolutely no guess work or estimating required. Just follow the cook book and your valves will be at the proper setting clearances.
I usually write down the sequence and valves to adjust at each position and then record the before and after clearances I measure as I go through the process. When the chart is full, the job is done and done right.
The Duntov cam including the clearance ramps is about 450 degrees crankshaft duration and 540 degrees for the 30-30 cam.
I developed the method by plotting out the lobe profiles, including the clearance ramps from the engineering drawing data that lists lobe lift to five decimal places every camshaft degree, and the plots verified that the method ensures that each lifter is on the camshaft base circle.
Indexing at the 90 degree intervals can be +/- at least five degrees and still be on the base circle with plenty of margin, so you don't have to spend a lot of time setting the engine at precisely the 90 crankshaft positions - just get it within a few degrees.
DukeComment
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Re: 1970 LT-1 Valve Lash, Idle and Idle Mixture Setting
Duke, what method did you use to mark the balancer at (90-180-270) respectively.
I assume TDC#1 is the exhaust stroke on cylinder 1.
I want to recheck the correct way the valve lash on my 71 LT1 that Bubba set.
thanks in advanced, love reading your posts.Comment
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Re: 1970 LT-1 Valve Lash, Idle and Idle Mixture Setting
Measure the diameter of your balancer, which is approximately 8". The circumference is then equal to Pi (3.1416) times the diameter.
Cut a piece of half to one-inch wide masking a couple of inches longer than this length, then make a hash mark about one inch from one end and annotate it "0". Now, place hash marks at the quarter, half, three-quarter, and full circumference points, and annotate them 90. 180, 270, and 360 respectively.
Wrap the tape around the balancer indexing the "0" with the notch, and if you did it right, the 360 hash mark should land at the "0" mark, and you can just tear off the final few inches of tape.
You can use this as a temporary indexing scheme or use it as a template to make permanent, or semi-pemanent marks on the balancer.
Setting a cylinder at TDC usually refers to the cylinder being on the end of the compression stroke/beginning of the power stroke transition.
When #1 is at this TDC point, the dist. rotor is pointing to the #1 cap tower, and that's where you start.
DukeComment
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