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#1
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Running hot compression down in 1 cylinder !
Hi, I have a problem with engine running hot. Did compression test all cylinders 145-150 except #6 has 110 psi. Broken ring or bad head gasket? Aren't head gasket issues usually between 2 cylinders? It's a 68- 400 dished icon pistons small bullet cam. Has about 1500 miles and has been running hot from the beginning. Thanks
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67428HO |
#2
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Get your hands on a leakdown tester and that will answer your question.
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1967 GTO, 432 (428+.030), 4-bolt mains, factory Nodular crank, scat rods, icon dished pistons, Lunati HR 243/251@.050, .618/.622 lift, Edelbrock 72cc round port heads, 10.5:1, offy 2-4 intake, Edelbrock 650cfm carbs, Super T10 trans (2.64 first), BOP 10 bolt w/ Eaton posi and 3.36 gears |
#3
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How many miles on this build?
I suggest you get 4 cans of seafoam and aggressively pour into the carb while fully warm. I can not tell you have many times that resolved either low or excessively high cylinder pressure.
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Carburetor building & modification services Servicing the Pontiac community over 20 years |
#4
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possible dropped / bent pushrod, or cam lobe failure too
Recheck compression Air test cylinder with thermostat housing removed, with valves backed off watch for bubbles, listen where air is escaping, roll check pushrods, readjust valves, watch for complete valve operation recheck compression Luke |
#5
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How hot is it running? With #6 on tdc both valves closed, hook compressor to it and listen/feel for air,if air comes out of carb, something with intake valve, exhaust, then its exhaust.
I would think if it had a broken ring it'd smoking and using oil no?
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78 T/A 4SPEED, Original paint, match #’s, mine since ‘99. 77 t/a sold 85 Monte Carlo SS sold 83 Mustang GT sold |
#6
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I'll get a leak down tester. It runs 190-195 when it's 40* outside. Tried water pumps, carb and distributor, that's what led me to the compression test. Thanks!
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67428HO |
#7
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I'll get a leak down tester. It runs 190-195 when it's 40* outside. Tried water pumps, carb and distributor, that's what led me to the compression test.It's a fresh rebuild with all new parts, Has maybe 1500 miles on it. Thanks!
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67428HO |
#8
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Sounds lean.
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#9
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Only useful reply to this thread, IMO. Great advice and it will let you know there the leak in compression is coming from. Professional auto tech here, 40 years experience. FWIW....
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Jeff |
#10
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With one cylinder really not making the power that it should, if any thing the motor should be running cooler then normal!
I think your issue of low comp may be coming from a broken top ring which will not make for signs of oil burning, but will make for a bunch of added friction and heat. I would pull that head on that passenger bank and look for scratch and gouging marks in number 6 walls.
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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! |
#11
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Quote:
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Karl |
#12
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Looks like the head gasket is blown. How can you tell if the block was resurfaced during the build? Are there any factory stampings that would disappear when the block gets resurfaced? Not saying I don't believe the engine builder... But I don't believe the engine builder. Thanks!!
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67428HO |
#13
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Post a few nice well lit pictures...a fresh mill is pretty obvious to a trained eye.
HOw did you determine the problem? |
#14
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I'll get some pics. Took the head off gasket has black mark between #4-#6 but only showed compression down in #6, not sure why?
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67428HO |
#15
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A head gasket leak between cylinders shouldn't make an engine run hot,
now to the cooling system, yes. Post good pics of the combustion chamber too, looking for cracks! An air test was not performed, correct? |
#16
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See pictures
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67428HO |
#17
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FWIW some of the cylinders seem to show signs of detonation.
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"No replacement for displacement!" GTOAA--https://www.gtoaa.org/ |
#18
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How many miles on this engine? Looks like you're burning oil.
Could be the deck isn't flat, or the head could also be the issue. Were the heads milled? I've had head gaskets blow into the water passages, but that doesn't appear to be the case here. Looks like a couple different issues that may, or may not be related. First is the head gasket, which as mentioned could be the block or head not being flat there. It appears you may also have an oil consumption issue which could lead to detonation. This again makes me wonder about the heads. - guide clearances and valve seals specifically. As to the temperature - you said you replaced the water pump. Lots of info about water pumps and how the impeller design and clearance to the backing plate affects cooling here. Did you get a pump with a good, cast impeller? Did you check clearance to the backing plate? What radiator are you using? If an original or used unit, do you know it's internal condition? Temperature can also be affected by timing and fuel. Running lean and/or retarded timing will cause overheating problems. just throwing out all the things I can think of that may be related to your issues.
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---------------------------- '72 Formula 400 Lucerne Blue, Blue Deluxe interior - My first car! '73 Firebird 350/4-speed Black on Black, mix & match. |
#19
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Recored 4 core radiator, all baffles in place, 3 different water pumps clearanced. Car is a 68 -400 Firebird. Never ran as good as I thought it should. 1500 miles engine should be fresh. Thanks!
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67428HO |
#20
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I would confirm that you have the right heads bolts and that they only stick out passed the head gasket no more then 3/4" with the needed washer under the bolt head.
May I ask who built the motor and if the Carb your running on it was new to the motor or had been used before on a hood running motor? Also that head will need a .002" to .003" clean up mill, but I would yank the other head off also to inspect that gasket as it may only be a few heat up and cool down cycles away from blowing out also! Note that whoever you take the head(s) to to get a clean up mill needs to have the ability to produce a near mirror finish on the deck surface if you want to max out gasket life.
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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! Last edited by steve25; 03-31-2020 at 07:34 AM. |
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