Discussion on Production Limits vs. Service Limits

[Dennis H.]

I have always been a if it not broke don't fix it kind of guy and that limits are set for a reason.

My 73 L82 has 43,435 original miles and the original owner several years ago was talked into a intake, head and cam swap that I'm going to reverse using the original parts he pulled off the car. Because I'm going that deep into the engine I plan to pull it and just rebuild it while it's out of the car.

During tear down I will measure everything to get a base line of where I stand on the rebuild. That leads me to the cylinder bore part of this production limits vs. service limits discussion.

GM Specs
Production cylinder bore diameter is 3.9995 min and 4.0025 max. No service min or max.
Production cylinder out of round limit is 0.001 max. Service limit is 0.002 max.
Production taper thrust side limit is 0.0005 max. Service limit is 0.005 max.
Production taper relief side limit is 0.001 max. Service limit is 0.005 max.
Production piston clearance limit is 0.0036 min and 0.0042 max. Service limit is 0.0061 max.

Assuming all my measurements fall within the above range any reason not to just run a flex-hone (ball hone) through the cylinders, remeasure and if still good reassemble with new rings and bearings and call it a day?

Not trying to get out of boring .030 over and new pistons just wondering if its really necessary.

Dennis

[Duke W.]

Re: Discussion on Production Limits vs. Service Limits

With so few miles why rebuild the whole engine? Do compression/leak down tests to make sure the engine is currently healthy. When the heads are off you can measure cylinder taper. At only 43K miles I doubt if it's anywhere close to the service limit, and the journals/bearings are likely near new. The original heads with a thick composition gasket will barely get you 8:1 CR. Measure the head and deck surfaces for flatness and if they pass use a Felpro 1094 .015" polymer coated shim gasket.

Measure deck clearance on all cylinders and you can compute the actual CR. OE was advertised as 9:1, but it's likely lower if the decks are high. Anything at or less than 9:1 only needs 87 PON fuel and you should still be able to run pretty aggressive spark advance map.

If it has a nylon cam sprocket timing chain, replace it with the OE replacement truck roller chain, made by Cloyes, about 30 bucks at NAPA for the set.

Duke

[Dennis H.]

Re: Discussion on Production Limits vs. Service Limits

This is going to be a long reply but I want to put all the information out here I have to date on this engine. I can be my worst enemy when it comes to doing more when less is better.

Back story on this 1973 L82 4-speed car;

Owner #1 - 1973 - 2018 drove car a total of 43,180 miles and was garaged all but 4 years (75-78).
Owner #2 - 2019 - 2020 drove car 247 miles in first 10 months of ownership (health reasons)
Owner #3 - 2021 - Now and I have drove car 74 miles

Owner #1 around 2014ish was talked into replacing the cam, heads, intake and carb adding the aftermarket stuff and given what I know about him, this was most likely outsourced. Replacement parts were:

Comp Cams XE 274H-10 camshaft (110 CL)
World S/R I-052 Heads
Edelbrock Torker Intake
Holley 750 Carb

Owner #2 said the car never ran good in the low RPM range and he removed the 750 Holley and replaced it with a 600 (1850). He said the intake needed replaced.

Owner #3 who is I came across the car after it had been setting in his garage for 14 months and other than a normal inspection (body, birdcage, frame etc.) and hearing it run I loaded it on a trailer and came home. When I drove it to DMV and back home (about 4 miles), I knew there was something more than wrong intake going on because car ran like crap and was smoking (white smoke) out the left exhaust pretty bad.

I started my troubleshooting by doing a compression check and had 175-180 psi on all cylinders except #7 that had 30 psi. Upon pulling the valve cover, I found #7 intake push rod bent and rocker jammed into the #7 exhaust spring holding it slightly open.

At this point, I pulled the intake and all the rockers and push rods.
1) Inspected all lifters and there is zero wear, no popped clips etc., they look as new as when they were installed.
2) Gave all the valves a tap with a dead blow hammer and got a good thunk than pushed each valve open and close with the handle of a heavy hammer. All check 4.0
3) Did a leakdown test on all cylinders with each cylinder being at TDC. Lowest reading was 10% and the highest was 17%
4) Ran an endoscope into cylinder #7 and it checks out clean with no visible damage to cylinder walls or piston top.

To be honest I think this #7 intake pushrod issue was unknowingly passed from Owner #1 to #2 and to me. Based on what I know about the history of this car I bet there has not been 1,000 miles put on this car in the last 10-15 years.

At this point I was at a loss as to why the #7 intake push rod was bent so I ordered a new set of GM guided rockers and a set of stock Elgin push rods. I also installed the stock intake and Q-Jet that came off the car and started it up. Other than the loopy idle due to the cam engine runs good and was not smoking out the exhaust as it was doing on my first drive.

From all my research here’s what I think happened. The heads were replaced with World S/R (service replacement) I-052 with no guide plates. These heads when developed in the late 80’s or early 90’s were marketed as GM service replacements because GM was having problems with heads from what I have read on the subject. The mechanic who did this work use the non-guided rockers from the L82 guide plate heads when he should have used guided rockers. I think the non-guided rocker getting out of alignment with the non-guide plate head caused this mechanical interference in the valve train.

I drove the car 70 miles after everything was back together and so far, no issues other than the loopy idle and low RPM manners due to the installed cam.

Car has been setting for a few months now so I started it up today. Couple of pumps of the gas pedal and it fired right off, oil pressure is 35 psi cold and about 33 psi warm. Has very light white smoke out both exhaust pipes at idle.

That is where I stand today on this engine. I can do a cam swap, cam & head swap, engine rebuild or all three at this point. Low hanging fruit would be just a cam swap and throw more miles on it. I really hate the cam that is in this engine. I have already purchased the OEM GM L82 cam and lifters and have those standing by.

Dennis