Bad valve guides
09-30-2015, 07:20 PM
#1
Racer
Thread Starter
Bad valve guides
This relates to my ’63 327/300:
There is a sporadic miss in #1 cyl, so I replaced the cap, rotor, points, condenser and wires; I also replaced the plug with AC Delco 45R. I adjusted the dwell to 30 and the timing to 8 btdc. This improved the miss, but it’s still there. When I pulled the plugs to give the engine a compression test, I found that the plug to cyl. 1 was oil fouled, but there has never been blue smoke at the exhaust. Cyl. 1 had the least compression at 193 lbs., all others were at 195 to 200 lbs. I hooked up a vacuum gauge and at idle, the pointer fluctuated between 15/16, at 1000 rpms it fluctuated between 16/17 and at 1500 rpm and above (2000) it held steady at 20. I then adjusted the carb as best as I could with the bouncing needle. Do you think that the valve guides might be the cause of the fouled plug and the miss? And how do I test for bad valve guides?
Thanks for the help
Rick
There is a sporadic miss in #1 cyl, so I replaced the cap, rotor, points, condenser and wires; I also replaced the plug with AC Delco 45R. I adjusted the dwell to 30 and the timing to 8 btdc. This improved the miss, but it’s still there. When I pulled the plugs to give the engine a compression test, I found that the plug to cyl. 1 was oil fouled, but there has never been blue smoke at the exhaust. Cyl. 1 had the least compression at 193 lbs., all others were at 195 to 200 lbs. I hooked up a vacuum gauge and at idle, the pointer fluctuated between 15/16, at 1000 rpms it fluctuated between 16/17 and at 1500 rpm and above (2000) it held steady at 20. I then adjusted the carb as best as I could with the bouncing needle. Do you think that the valve guides might be the cause of the fouled plug and the miss? And how do I test for bad valve guides?
Thanks for the help
Rick
09-30-2015, 07:33 PM
#2
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Worn valve guides and seals will let oil into the cylinders during high vacuum situations or from sitting overnight. Coasting down a long hill in 3rd gear, or prolonged idle will result in blue smoke, which will clear up when the engine is held at higher rpm under power. (Low vacuum) Have someone follow you as you get off the gas while in gear from a decent speed. If you have blue smoke out the exhaust, it's guides and or seals. A worn valve guide won't normally cause an engine miss until it fouls a plug. If you have fluctuating vacuum, it's from a burnt valve, a weak valve spring, or flat cam. Time for a leakdown test to determine what your issue actually is.
09-30-2015, 07:45 PM
#4
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Your vacuum gauge and the oil fouled plugged has confirmed you have an issue with number 1 cylinder.
Did you put a new plug into #1 and then run engine with the vacuum gauge on it and check to see if it is still fluctuating.
What I am getting at is you might just have bad valve seals causing the plug fouling and making that cylinder miss fire.
To answer your question on how to check the guides, I have checked for a bad guide by bringing the piston to TDC and removing the valve springs using compressed air in the cylinder.
Then I removed the air so the valves can be moved in the guide to check for wear.
Since it is #1 all you have to do is line up the mark on the crank to the 0 on the timing tab.
As I am typing this I notice GTOguy just replied.
I do not believe it is a burnt valve or a weak spring, which would not oil foul a plug.
They allow 10% difference in compression results.
A cylinder leak down test is when you bring the piston to TDC, put a controlled amount of air into it and then measure how much is escaping. IIRC 10-20% is acceptable.
Joe
Did you put a new plug into #1 and then run engine with the vacuum gauge on it and check to see if it is still fluctuating.
What I am getting at is you might just have bad valve seals causing the plug fouling and making that cylinder miss fire.
To answer your question on how to check the guides, I have checked for a bad guide by bringing the piston to TDC and removing the valve springs using compressed air in the cylinder.
Then I removed the air so the valves can be moved in the guide to check for wear.
Since it is #1 all you have to do is line up the mark on the crank to the 0 on the timing tab.
As I am typing this I notice GTOguy just replied.
I do not believe it is a burnt valve or a weak spring, which would not oil foul a plug.
They allow 10% difference in compression results.
A cylinder leak down test is when you bring the piston to TDC, put a controlled amount of air into it and then measure how much is escaping. IIRC 10-20% is acceptable.
Joe
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09-30-2015, 07:47 PM
#6
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Go on YouTube and look for a video with explanation. It's easier than trying to explain with details on here. 
Dennis
Dennis
09-30-2015, 07:50 PM
#7
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A bad valve guide will not normally cause a vacuum gauge fluctuation unless it's really, really loose to the point of the valve not sealing. You'd hear ticking for sure. Again, research and perform the leakdown test. It will pinpoint your problem with no guesswork and it's easy to do. Keep us posted!
09-30-2015, 07:54 PM
#8
Racer
Thread Starter
I have actually put two new spark plus in #1 thinking that the first might be bad. But it to fouled. The miss that I have appears to be minor; the fouling of the plug is the big mystery for me and I don’t want it to lead to something else.
09-30-2015, 07:56 PM
#9
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It could also be a broken piston or broken piston rings. A leakdown test will verify.
09-30-2015, 07:58 PM
#10
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While you're checking, check the #1 plug wire resistance. Especially if you have repop wires. Your compression is more than outstanding in all cylinders.
09-30-2015, 08:00 PM
#11
Racer
Thread Starter
09-30-2015, 08:01 PM
#12
Racer
Thread Starter
09-30-2015, 08:19 PM
#13
Race Director
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09-30-2015, 09:34 PM
#14
Race Director
Leak down test....
You were given the correct advice in the first reply and several after it....It takes care of the rings....You only have one questionable cylinder and a valve job is probably the answer....as it will have new seals which I feel has already caused the issue and slowly are going away
I don't think bench racing will fix it
I don't think bench racing will fix it
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10-01-2015, 02:14 AM
#16
Melting Slicks
Could just be a bad wire and would have been the first thing I would check. FYI, while your at it giggle/move the ends (especially at the plug boot) during your test. I've tested wires that appeared to have good continuity until I moved them around at the ends then found them to be bad. I've even found this to be the case with brand new wires so I even check those beforehand.Concerning your post (# 12) you'll need a multi meter. Set it to "ohms", connect one lead to one end of the wire then one lead to the other end (doesn't matter which is which) then take reading. Longer wires (such as # 1) will have different readings than shorter ones. If the reading fluctuates (again while moving the wire around) or especially if it reads zero, it's bad.
Gary
Last edited by Gary's '66; 10-01-2015 at 02:58 AM.
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10-01-2015, 05:46 AM
#17
I agree with checking the wire for resistance, I think 3000 ohm/ft max resistance but double check me on that so #1 wire about 10000-11000 ohms. If it checks good consider new valve seals on #1. Does this engine have a high pressure oil pump, how much oil pressure?
Can you describe the history of the engine because that's very good compression, I think the GM service book states 140-160lbs.
Post a picture of the spark plug.
Can you describe the history of the engine because that's very good compression, I think the GM service book states 140-160lbs.
Post a picture of the spark plug.
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10-01-2015, 09:44 AM
#19
Racer
Thread Starter
10-01-2015, 09:57 AM
#20
Racer
Thread Starter
What I did with the wires is switch wires on #1 and #3 and that made no difference #1 still indicated little or no change in engine performance when I pulled the wire from the cap. It had a good spark, cap to wire, can I assume that the wire connection at the boot is good?