Compression Test Readings Help
Thread Starter
Instructor
Joined: Jan 2013
Posts: 122
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From: Phoenix Arizona
Compression Test Readings Help
Just did a Compression Test on my 69 350. Idles OK But when I put it in gear rpms drop and almost dies. Tracing down vacuum lines and did a dry compression test with the engine warmed up. The car sat for years before I purchased it. It has 77,800 miles on it.
Here are my readings
#1 135 #2 125
#3 125 #4 125
#5 135 #6 123
#7 133 #8 138
Any suggestions will be helpful
Thanks The Captain
Here are my readings
#1 135 #2 125
#3 125 #4 125
#5 135 #6 123
#7 133 #8 138
Any suggestions will be helpful
Thanks The Captain
Race Director
Joined: Apr 2009
Posts: 19,294
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From: Charlotte NC
Make sure your fuel is good. And I also remove and plug the vacuum that goes to the headlights and wiper door. The only vacuum I leave (after it has been checked) is vacuum for power brakes and the distributor. Then when I got the engine running smooth...and road testing it. I re-install the vacuum that was removed and see if the engine starts to "act-up". Then make repairs accordingly....if needed.
DUB
DUB
Thread Starter
Instructor
Joined: Jan 2013
Posts: 122
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From: Phoenix Arizona
Thanks Motor head. I have the idle set at about 750rpms at idle. If I set the idle to high About 950 rmps it shfits hard from park to drive( Auto trans). I was reading in the GM service manuel to set the idle while its in gear. Should I give that a try.
Thanks Again!
Thanks Again!
Thread Starter
Instructor
Joined: Jan 2013
Posts: 122
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From: Phoenix Arizona
Make sure your fuel is good. And I also remove and plug the vacuum that goes to the headlights and wiper door. The only vacuum I leave (after it has been checked) is vacuum for power brakes and the distributor. Then when I got the engine running smooth...and road testing it. I re-install the vacuum that was removed and see if the engine starts to "act-up". Then make repairs accordingly....if needed.
DUB
DUB
Drifting
Joined: Mar 2011
Posts: 1,886
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Compression is good. Chevrolet allows that the lowest cylinder read 75% of the highest. You are at about 91%.
Typically, when a SBC needs a rebuild, it's because the cam is worn. Everything else is pretty robust.
The underhood sticker specs the idle setting speed and procedure. Many of the reproduction houses (Zip, Wilcox, etc.) carry reprodutions of those stickers.
Generally, on an automatic trans equipped car, the idle speed is set with the engine fully warm, in Drive, parking brake set and wheels blocked. Don't rev the engine!
Typically, when a SBC needs a rebuild, it's because the cam is worn. Everything else is pretty robust.
The underhood sticker specs the idle setting speed and procedure. Many of the reproduction houses (Zip, Wilcox, etc.) carry reprodutions of those stickers.
Generally, on an automatic trans equipped car, the idle speed is set with the engine fully warm, in Drive, parking brake set and wheels blocked. Don't rev the engine!
Thread Starter
Instructor
Joined: Jan 2013
Posts: 122
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From: Phoenix Arizona
Thanks for the great info. I dont understand how adjusting the idle makes a differance weather its in park or drive. It would seem if its to high its to high and if its to low its to low. Just my thoughts
Drifting
Joined: Mar 2011
Posts: 1,886
Likes: 9
When you put the car in Drive, the idle speed drops because you are loading the engine against the slipping torque converter. Of course this is the normal way the car idles, at stop signs, stop lights, in traffic, etc.
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Safety Car
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From: Bridgewater nj
Timing is too far retarded. Check your vacuum advance to see if its working. Don't rely on the timing marks as many harmonic balancers shift when they get old. Instead go by sound and feel until you can verify everything is in the right spot.
Race Director
Joined: Apr 2009
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From: Charlotte NC
100%. I use a vacuum gauge when adjusting the timing and go from there.Automatic should be at or around 800 rpm in park and 600 in gear.
DUB
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Instructor
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From: Phoenix Arizona
Thanks!
Thread Starter
Instructor
Joined: Jan 2013
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From: Phoenix Arizona
Hugie 82,Vacuum advance seems to work, I hooked my hand pump to it and gave it about 15 hg and it seems to hold no leaks and it advanced and didnt move. I will relook at the Timing.
Thread Starter
Instructor
Joined: Jan 2013
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From: Phoenix Arizona
Dub, what is the procedure for that. When I check the timimg I will disconnect the vacuum headlights and wiper door for the circuit and go from there.
Race Director
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From: Charlotte NC