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Did I wipe a lobe?

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Old 06-14-2018, 05:29 AM   #1  
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Location: Hog Town, Ontario
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Car: 1985 Trans Am
Engine: 350
Transmission: T5

Did I wipe a lobe?

My car was burning oil so I decided to adjust my valves. I used the method where you set it to #1 TDC and set 8 of the valves, then set the other 8 at #6 TDC. I used a 1/2 turn of pre-load.

I started her up and it was running rough as hell. Misfiring and backfiring like crazy. So I shut it down and go back to readjust the valves only to realize I have a solid lifter motor. I assumed it was a hydraulic motor because it's a mid 90's crate engine (truck motor).

Not knowing the specs for my cam, I set my lash to 0.020" using the same method as before (at #1 and #6 TDC). I replaced my spark plugs just to be safe. My wires are only a few months old (and yes they are in the right order). Started it up and it was still running like hot garbage. Running on 6-7 cylinders and backfiring through the carb. It would idle okay, but backfire and miss hard under any load.

So I got through the whole process again using the EOIC method. I got them all set perfectly. I started it up and it sounded normal at idle. No major misfires. Under load it would still backfire through the carb. I set my timing and it still didn't help.

So did I wipe a lobe? This motor has unknown mileage, but based on the blow-by and oil consumption, I'm assuming it's rather high.

What should be my next step?
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Old 06-14-2018, 06:57 AM   #2  
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Re: Did I wipe a lobe?

Adjusting valve lash to fix oil burning? Interesting. While you may or may not have damaged a lobe, to check you are going to have to get a dial indicator and measure lift on each lobe. You can do that at the rocker arm. While you are doing that you can verify base circle and adjust the lash using a slight correction due to the engine being cold (you can find this cold engine correction data online). This will get you to a decent point to start the engine and warm it up so you can set the correct lash at temp. That is, of course, unless you find a bad lobe.

Maybe I’m old school but I don’t subscribe to a lot of the “this is faster and accurate enough” methods of doing things.
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Old 06-14-2018, 09:03 AM   #3  
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Re: Did I wipe a lobe?

Easiest way to locate the base circle with absolutely certain accuracy, is to locate peak lift of the same valve on the cyl that's 4 cyls away in the firing order. E.g. #1 int is on the base circle when #6 int is at peak lift. (heel of lobe vs tip)

Backfiring in the carb could be caused by a wiped exh lobe. Compression test will tell: 1 cyl w very high comp has this failure. It can also be caused by a head gasket: 2 adjacent cyls w low comp, especially 5 & 7.
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