1979 engine really bad compression numbers (2 Viewers)

Joined
Jan 22, 2007
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Cruiser is a 1977, with a '79 engine. Rebuilt head installed ~ 9 yrs ago-all new valves/springs/guides, and OEM head gasket. Daily driver. Recently have had to re-adjust dizzy point gap more frequently to keep good vac. Engine started to slowly sound like a cylinder was misfiring. Installed new plugs/points/wires/cap/rotor. While the plugs were out, checked compression(all plugs out and very cold-55 degrees ) #3 cylinder was essentially zero(maybe 10 psi) #2 was ~ 75 psi. All others were > 130 psi. The engine gradually gets better vac after warming up for ~ 5 mins(19 inches--16 at startup)) and the misfire sound seems to go away. Exhaust pipe is fairly clean-no oily residue. Compression has not been checked hot.
Any ideas here from the group? Head gasket maybe?
 
Joined
Jan 22, 2007
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Ok-OK--The valve adjustment will be done as many have suggested--I'll see if I can get some video help from neighbors to document--I'll take as found and as left readings--may take a few days-gotta get a new gasket--
Thanks to all---
 
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Jan 22, 2007
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Valve adj completed-= All in spec except for #4 which was .020 exh-adj to .018(this was not one of the low compression cyls). The 2 cylinders that showed the low compression are still low)-- After adjust compression numbers are the same on #3(20 psi) and #2(60 psi)--Unless there is a cracked valve seat , a piston blowby-is the culprit--even if the valves were crudded up, you would see it in the valve adj as decreased clearance--I think the head is coming off--
 
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Oct 7, 2011
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Austin TX
If you have the valve work done, consider replacing the exhaust valves with Chevy stainless valves. There are some threads on the site about doing it. The Chevy valves are just slightly larger than the OEM valves, so the seats will need to be opened just a bit, and the valve stems are slightly larger, so, if you have slop in the original valve guides, you might avoid having to change the guides if you go to the Chevy valves. The Chevy valve stems will use a slightly different size of Viton stem seals as well. I made the switch last year and I am pretty confident that exhaust valves won't be an issue during my lifetime. I happen to have Sioux valve and seat grinding equipment, so the cost of the job was minimal. I STRONGLY recommend using STONE brand headgaskets. They are identical to the Toyota (same manufacturer) and have the copper rings around all the water holes. Usually available on Amazon for $62. Search for

"Stone JA-11149 Head Gasket"​

 
Joined
Jan 22, 2007
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Alva, Fl.
What were the wet compression #'s?
Ran engine up to op temp(185 deg)--let it cool ~ 15 mins so I didn't burn my fingers-cranked engine over with coil wire removed 10 times on each cyl.

#1 thru #6 were:-
1-138,
2- 62,
3-15,
4- 132,
5- 135,
6- 133--
There are no bubbles in the cooling system when the engine is running--the system temp holds stable at ~ 185 deg in all my driving conditions.
The pressure in # 2 does not bleed over into #3-(ie plug IN #2 and #3 is still low)
Even the cold comp #s are almost the same in #2 and 3 hot
All spark plugs except #3 were tan, with no fouling. #3 had black deposits on it(not wet oil), but the electrodes were not fouled beyond firing
Did not run a leak-down check as, at this point I think it is a waste of time--the head needs to come off to further evaluate-I can always pull the head and fill the cylinders with oil and check in the morning to see if the oil level has dropped--
I might get lucky and find #3 valve guides/seals are leaking(exh)-
I didn't see any broken vlv springs during the adj---and I know without pics-it didn't happen--I'll post a bunch when the head gets off---
 
Joined
Jan 22, 2007
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Alva, Fl.
I could do that, but the results will not change the need to remove the head--(I think that is what you meant by "wet" compression)
Did a couple of cursory checks yesterday--
1. Cardboard check at the exhaust-running---the card board was periodically sucked up against the exhaust as the engine was running--iI think this indicates exh valve leak
2. Pressure gauges installed on the dip stick tube and PCV valve connection while running-no deflection on the gauges-indicates(I think) no(or low) blowby of the pistons/rings
 

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