65' 327 Compression irregularities
Thread Starter
Heel & Toe
Joined: Oct 2011
Posts: 22
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From: New York
65' 327 Compression irregularities
Hey all, I'm new to Corvettes and restoring in general. I did a dry compression test on a 1965 coupe with a 327 (300 hp) that I inherited from my father after he passed and got some strange readings and was wondering if anyone could explain. Most cylinders averaged around 150-ish, however, I got two outside that range. One cylinder was 140 which isn't as strange as the opposite cylinder which was 188!. I did this test twice and it came back 185 so I know it wasn't a fluke. Any ideas? Thanks!
Race Director
Joined: Jan 2002
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From: Close to DC
C2 of the Year Finalist - Modified 2020
Sorry for the lose of your father. Welcome to the CF, I'm sure he's looking down too see what your doing. I think we need more info. How long has it sat, was it stored by putting oil in the cylinders anything like that? Was it started or turned over, during this time. What is the reading for each cyl.? Variations in reading can be caused by a sticking valve, stuck or broken ring on a piston, carbon build up. Let us know more. 
Dennis
Dennis
Thread Starter
Heel & Toe
Joined: Oct 2011
Posts: 22
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From: New York
Thanks, I actually see him looking down going "You better not break my car or else!" lol He loved this car. It sat for the entire time my father was in the hospital, which was actually almost a year ago. It was run once in December, then it was winterized. I drained the tank, put engine store through the carb, put it on jacks, and taped up the air intake and exhaust. It sat in storage while I finished up my last year at military school, and was taken out of winter storage in May of this year. The spark plugs were changed, the carb got some new gaskets and a slight rebuild, and of course the oil got changed. Since then it has only been ran three times, four if you include today. The compression test numbers are as follows:
Driver side: Passenger side:
188 164
140 155
156 166
166 170
I know it wasn't used a lot before it was put in storage, and I know my father was planning on doing a small rebuild sometime soon, but I wasn't privy as to why. As far I know everything is numbers matching on the car; numbers matching block, heads, 4 speed, and Carter AFB carb. Thanks for the welcome and all the help!
Driver side: Passenger side:
188 164
140 155
156 166
166 170
I know it wasn't used a lot before it was put in storage, and I know my father was planning on doing a small rebuild sometime soon, but I wasn't privy as to why. As far I know everything is numbers matching on the car; numbers matching block, heads, 4 speed, and Carter AFB carb. Thanks for the welcome and all the help!
Team Owner
Joined: Mar 2003
Posts: 26,118
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From: Greenville, Indiana
If it doesn't smoke, doesn't knock and doesn't use a lot of oil then I'd suggest you check the engine pad and make sure you have an original engine. That's the most important feature, isn't it?
Drifting
Joined: Nov 2007
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From: columbus ohio
enjoy it. jim
Burning Brakes
Joined: Mar 2001
Posts: 1,203
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From: dalton ma
I don't think those numbers are radical enough to warrant doing anything right away. Assuming it runs relatively smoothly on all eight cylinders I would wait a while and put some miles on it. Plenty of time for an overhaul off in the future if it really needs one. Bob
Thread Starter
Heel & Toe
Joined: Oct 2011
Posts: 22
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From: New York
Thanks guys, I appreciate it. I was already planning on pulling the motor and getting it cleaned and tested at the machine shop. I'm glad to know I shouldn't be expecting any scary (as well as expensive!) surprises. I just think it's so strange to have one cylinder so high and the rest about the same.
Race Director
Joined: Mar 2009
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From: Canada's capital
2020 Corvette of the Year Finalist (appearance mods)
C1 of Year Finalist (appearance mods) 2019
Nothing to be worried about there, it's probably just a build up of carbon in the chamber, and with a good long drive it will come down. That's a problem for lots of special cars, they never get a long enough drive on a regular basis.
In fact those numbers look great, and I suggest it's a waste of money and time pulling that mill out for checking. Start worrying about important stuff, or when you get a 50lb reading on one only!
In fact those numbers look great, and I suggest it's a waste of money and time pulling that mill out for checking. Start worrying about important stuff, or when you get a 50lb reading on one only!
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Thread Starter
Heel & Toe
Joined: Oct 2011
Posts: 22
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From: New York
Phew, that's great. It's starting to sound like I may just end up pulling and cleaning the motor myself. Even though it's running well it's in desperate need of some TLC on the outside. Thanks for all your help! I see already this site is going to be the go to site for all my vette questions.
Burning Brakes
Joined: Mar 2001
Posts: 1,203
Likes: 147
From: dalton ma
I'm baffled, you have four experienced early Vet owners all saying basically, "leave it alone and drive it" and you have this huge urge to take it apart. Try duct taping a tooth brush on the end of a coat hanger and clean to your hearts content (with the motor in place). Bob
.
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Le Mans Master
Joined: Dec 2007
Posts: 8,000
Likes: 659
From: Puget Sound
While the OP's numbers aren't the worst I've ever seen, they are a source of concern. I have the exact same year and HP motor as the OP and my readings are 185 in 6 cylinders and 180 in the other two. If they were anything like the OP's, I would be tearing it apart to see what is wrong.
Jim
Safety Car
Joined: May 2003
Posts: 4,797
Likes: 239
From: Ocean Township NJ
White lightnin'?
To the OP:
Don't worry about it unless you decide to go down the slippery slope of a complete engine rebuild. Those numbers are within measurement error and God knows there are eight ways to Sunday means to screw up cranking compression readings. Take 'em again tomorrow and they might be very different. Hypothetically, if they were all dead nuts even at 170-180, then you'd pick up maybe 20 horsepower and .25 quart/1000 miles less oil consumption.
Last edited by 65tripleblack; Oct 28, 2011 at 09:00 PM.
Le Mans Master
Joined: Dec 2007
Posts: 8,000
Likes: 659
From: Puget Sound
There is only one way to do it CORRECTLY. Otherwise, the readings mean absolutely NOTHING. You might as well just pull numbers out of your azz.
Safety Car
Joined: May 2003
Posts: 4,797
Likes: 239
From: Ocean Township NJ
The numbers themselves mean very little. It's the relativity of each to the other that has meaning.
Thread Starter
Heel & Toe
Joined: Oct 2011
Posts: 22
Likes: 0
From: New York
I'm baffled, you have four experienced early Vet owners all saying basically, "leave it alone and drive it" and you have this huge urge to take it apart. Try duct taping a tooth brush on the end of a coat hanger and clean to your hearts content (with the motor in place). Bob
.
.
Bob, while criticism is always appreciated, if you had read my last post I was saying I was pulling the motor to clean it and repaint it... NOT take the motor itself apart. Yes, I'll have to do some disassembly to get the motor out, but nothing too radical.
Le Mans Master
Joined: Nov 2008
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From: columbus oh
Team Owner
Joined: Aug 2007
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Army
If the plugs aren't fouling and the blowby and oil consumption aren't excessive and the mileage doesn't go to cr@p I'd probably leave it alone and drive it. May want to reconfirm the compression test...I've seen LOTS of folks do it wrong and come up with pretty crazy numbers...
Team Owner
Joined: Mar 2003
Posts: 26,118
Likes: 1,874
From: Greenville, Indiana
Those compression numbers aren't the best but are by far, more than edequate to indicate that engine has many miles left in it before something needs to be done.
If the OP was a tinkerer that can't leave well enough alone and wants to spend a lot of money, or he is restoring the whole car, now is the opportunity to do so and he will pay for some long term gain which could be money well spent. In the long term.
On the other hand, if the OP is just curious about his readings, has little to no interest in spending money on an engine that doesn't have to have immediate work then the wise thing to do is to forget the engine until it does need work. In the meantime, divert funds/interest to other areas of the car that may be more urgent.
It's not likely the engine compression at this point.
If the OP was a tinkerer that can't leave well enough alone and wants to spend a lot of money, or he is restoring the whole car, now is the opportunity to do so and he will pay for some long term gain which could be money well spent. In the long term.
On the other hand, if the OP is just curious about his readings, has little to no interest in spending money on an engine that doesn't have to have immediate work then the wise thing to do is to forget the engine until it does need work. In the meantime, divert funds/interest to other areas of the car that may be more urgent.
It's not likely the engine compression at this point.
Le Mans Master
Joined: Feb 2008
Posts: 6,528
Likes: 1,938
From: Folsom CA
I agree with many above, your compression numbers are fine. Run it and your numbers will get better. As mentioned above your one cyl with a high reading is probably carboned up. Driving it up a long hill, something that makes the engine work will correct this quickly.
Another old time solution is to get the engine fully warmed up, set your throttle up so it is running at a constant 3,000 RPM, CAREFULLY spray a mist of water directly into the carburator. A mist will clean the piston tops and valve chamber by blowing the carbon right out your exhaust. IF you mess up and pour water into the carb you break pistons and bend connecting rods. Many hose nozzles have a mist feature that can protect you from the big bang and give you clean chambers. The engine will start to stall as you do this and that is OK, just back off and let it pick up again before spraying more in. Should be 3 or 4 minutes work start to finish. Run it and enjoy it. What a great way to keep your Dad alive in the house and smiling down from the clouds above.
Another old time solution is to get the engine fully warmed up, set your throttle up so it is running at a constant 3,000 RPM, CAREFULLY spray a mist of water directly into the carburator. A mist will clean the piston tops and valve chamber by blowing the carbon right out your exhaust. IF you mess up and pour water into the carb you break pistons and bend connecting rods. Many hose nozzles have a mist feature that can protect you from the big bang and give you clean chambers. The engine will start to stall as you do this and that is OK, just back off and let it pick up again before spraying more in. Should be 3 or 4 minutes work start to finish. Run it and enjoy it. What a great way to keep your Dad alive in the house and smiling down from the clouds above.
