 Airlifter
"9th Year" Gold Supporting Member
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Age: 78
Loc: Tazewell county, Virginia
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02-08-24 04:07 PM - Post#2866714
I posted a while back about low compression on #5 cylinder. I'll get back in a bit.
The engine had a miss and I was checking it out today. I pulled the plug wires one at a time to locate the source of the misfire. RPM dropped on all cylinders except #5. I swapped the plug and plug wire out and made no difference. I decided to check the compression again. Compression was around 125 on all cylinders. (Earlier it was down to 90 on #5 when I checked it). I checked dry with engine warm and throttle blocked open.
As mentioned, I changed out the plug and wire and changed the distributor cap. I have Pertronix ignition.
Two questions. What am I missing on checking the misfire? Why did the compression go back up from 90 to 125?
All suggestions and advice appreciated, Pete
1951 styline deluxe sport coupe w/'60 261 engine & 54 powerglide
1965 Corvair Corsa 140 hp 4 speed convertible |
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 Shepherd
Valued Contributor
Posts: 3442
Loc: Lake George, NY
Reg: 11-11-15
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02-08-24 05:03 PM - Post#2866715
In response to Airlifter
The miss is gone now? If so maybe a ring was stuck? No other work was done? Maybe not related, but you can't use solid core wires with Pertronix.
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Airlifter
"9th Year" Gold Supporting Member
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Age: 78
Loc: Tazewell county, Virginia
Reg: 06-07-15
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02-08-24 07:43 PM - Post#2866721
In response to Shepherd
No. The miss is still there and still on #5. When I pull a wire on any other plug the RPM drops significantly but doesn't change at all when I pull #5. All plugs have good color and are dry.
1951 styline deluxe sport coupe w/'60 261 engine & 54 powerglide
1965 Corvair Corsa 140 hp 4 speed convertible |
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Shepherd
Valued Contributor
Posts: 3442
Loc: Lake George, NY
Reg: 11-11-15
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02-08-24 08:34 PM - Post#2866724
In response to Airlifter
Do a leak down test in that cylinder, best way to determine power loss. A leaking valve is not apparent during a compression test. Same as a bad head gasket.
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Airlifter
"9th Year" Gold Supporting Member
Posts: 955
Age: 78
Loc: Tazewell county, Virginia
Reg: 06-07-15
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02-08-24 09:06 PM - Post#2866726
In response to Shepherd
Would that cause the miss?
1951 styline deluxe sport coupe w/'60 261 engine & 54 powerglide
1965 Corvair Corsa 140 hp 4 speed convertible |
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bobt
Contributor
Posts: 412
Loc: colonial heights va
Reg: 06-28-14
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02-09-24 03:35 AM - Post#2866731
In response to Airlifter
Check all of your vacuum hoses for a leak. Do you have vacuum windshield wipers? if you do be sure to check for leaks under the dashboard. The easiest way is just to plug the intake manifold connection to the wipers. Spray carb cleaner around the intake manifold gaskets while the engine is running and see if the rpm changes. bobt
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Airlifter
"9th Year" Gold Supporting Member
Posts: 955
Age: 78
Loc: Tazewell county, Virginia
Reg: 06-07-15
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02-09-24 05:22 AM - Post#2866732
In response to bobt
Thanks again for the responses.
I don't have a leak down tester, yet.
I will check vacuum lines today. I don't have vacuum wipers. I still don't know why the problem always goes back to the same cylinder. A vacuum problem should affect everything I would think.
1951 styline deluxe sport coupe w/'60 261 engine & 54 powerglide
1965 Corvair Corsa 140 hp 4 speed convertible |
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rrausch
"19th Year" Silver Supporting Member
Posts: 15183
Loc: L.A, Cal. & St. Louis...
Reg: 04-07-03
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02-09-24 08:34 AM - Post#2866740
In response to Airlifter
Running on 5 cylinders. Amazingly, in 1968-69 I drove a '53 4-door BelAir with this engine. The previous owner told me he'd been driving it when the engine made one heck of a banging sound, but the sound went away. It used a LOT of oil, but ran for over a year with this hole in the #3 piston.
1953 210 Convertible, 261 with dual Carter YF 966S carbs, P.S., Remote Bendix P.B. Booster.
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Airlifter
"9th Year" Gold Supporting Member
Posts: 955
Age: 78
Loc: Tazewell county, Virginia
Reg: 06-07-15
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02-10-24 09:28 AM - Post#2866769
In response to rrausch
I found the vacuum leak. Unfortunately it is a manifold gasket. I tried tightening manifold bolts but no joy. In process of removing manifold to replace gaskets.
Thanks again.
1951 styline deluxe sport coupe w/'60 261 engine & 54 powerglide
1965 Corvair Corsa 140 hp 4 speed convertible |
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bobb
Super Senior Member
Posts: 6686
Loc: paradise
Reg: 09-05-03
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02-11-24 11:18 AM - Post#2866800
In response to Airlifter
how are you doing compression test? the only good
number is the first needle jump. thats what the engine runs on.
| 70 L camino, grampa engine, g-force 5 spd, road rage suspension. Pray first before all else fails. |
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Airlifter
"9th Year" Gold Supporting Member
Posts: 955
Age: 78
Loc: Tazewell county, Virginia
Reg: 06-07-15
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02-11-24 11:30 AM - Post#2866801
In response to bobb
I let the engine turn 3 times and read the result. It has usually reached the maximum PSI at that point.
1951 styline deluxe sport coupe w/'60 261 engine & 54 powerglide
1965 Corvair Corsa 140 hp 4 speed convertible |
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bobb
Super Senior Member
Posts: 6686
Loc: paradise
Reg: 09-05-03
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02-17-24 10:46 AM - Post#2866974
In response to Airlifter
engines dont turn 3 times before they fire. they fire on every compression stroke. so its the first needle jump that will be your running compression.
| 70 L camino, grampa engine, g-force 5 spd, road rage suspension. Pray first before all else fails. |
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Airlifter
"9th Year" Gold Supporting Member
Posts: 955
Age: 78
Loc: Tazewell county, Virginia
Reg: 06-07-15
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02-17-24 11:31 AM - Post#2866977
In response to bobb
I see your point but the method I use is what I have done for as long as I can remember. All the material that I have found tells me that this is correct. Next time I do a compression test I will try your method.
BTW, the leak at the intake manifold was the culprit.
Thanks, Pete.
1951 styline deluxe sport coupe w/'60 261 engine & 54 powerglide
1965 Corvair Corsa 140 hp 4 speed convertible |
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52_Belair
Senior Member
Posts: 250
Loc: Canby, Oregon
Reg: 03-25-03
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02-17-24 12:10 PM - Post#2866978
In response to bobb
How do you know if the first needle jump is a full compression stroke? Maybe the piston was half way up the cylinder when you hit the starter?
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Shepherd
Valued Contributor
Posts: 3442
Loc: Lake George, NY
Reg: 11-11-15
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02-17-24 06:19 PM - Post#2866987
In response to 52_Belair
Agreed, that's why 3 rotations is the general technique, or a leak down test better yet.
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bobb
Super Senior Member
Posts: 6686
Loc: paradise
Reg: 09-05-03
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02-17-24 09:54 PM - Post#2866992
In response to 52_Belair
you dont know. thats why you test the bad one several times to verify.
| 70 L camino, grampa engine, g-force 5 spd, road rage suspension. Pray first before all else fails. |
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drew1987
"11th Year" Silver Supporting Member
Posts: 3918
Age: 37
Loc: Western NY
Reg: 02-23-14
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02-18-24 08:11 PM - Post#2867021
In response to bobb
So timing and fuel delivery are just fine. That only leaves spark and compression, so if you have spark, perhaps it makes sense to pull the head and see what you've got?
Ironically, it was cylinder 5 that gave up in my splashed-lubed 235 10 years ago. The machine shops were basically all gloom and doom. "with today's oils and gas, you might as well scrap the car and buy a tesla" kind of crap. I SHOULD HAVE taken a new exhaust valve (mine was awfully burned) and a drill and had at it like the poor boy I was hhaha
that said, though, if spark, timing, and fuel are sorted, in an old motor with no computer or MPFI, that only leaves compression. Piston, ring, valve, valvetrain etc
Godspeed
Andrew D. Carapella (Drew)
1950 Chevy Styleline Deluxe
1954 Chevy 3100
Various other "modern classics" |
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bobt
Contributor
Posts: 412
Loc: colonial heights va
Reg: 06-28-14
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02-19-24 03:23 AM - Post#2867027
In response to drew1987
Fix the vacuum leak.
Edited by bobt on 02-19-24 03:25 AM. Reason for edit: No reason given.
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drew1987
"11th Year" Silver Supporting Member
Posts: 3918
Age: 37
Loc: Western NY
Reg: 02-23-14
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02-19-24 06:42 AM - Post#2867030
In response to bobt
Maybe I missed it, but he hasnt identified a vacuum leak right?
Either way - if all is well and one specific cylinder is sharply missing, i'd look to fuel (in a MPFI application so not in this case), spark (make sure the sparkplug is functioning (on modern - also swap coil packs and see if the misfire follows), and compression. We KNOW he has spark. We KNOW he has fuel. We DONT know if he has compression... at this point if you want to eliminate vacuum leaks, block off everything vacuum and then spray around the intake manifold with carb cleaner BUT with only 3 intake ports, I am sure more than just #5 would be acting up. All evidence point to compression. I think its time for a look inside (valves, rings, piston)
Andrew D. Carapella (Drew)
1950 Chevy Styleline Deluxe
1954 Chevy 3100
Various other "modern classics" |
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bobt
Contributor
Posts: 412
Loc: colonial heights va
Reg: 06-28-14
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02-19-24 02:38 PM - Post#2867044
In response to drew1987
Airlifter said that he found a leaking manifold gasket.
Edited by bobt on 02-19-24 02:39 PM. Reason for edit: No reason given.
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drew1987
"11th Year" Silver Supporting Member
Posts: 3918
Age: 37
Loc: Western NY
Reg: 02-23-14
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02-19-24 07:58 PM - Post#2867050
In response to bobt
Oh i did miss that sorry. Yes of course get that sorted before anything deeper but I personally I would be shocked if that wasnt there coincidentally and there is another issue. With only 3 intake ports on the head, i'd think more than one cylinder would react. Either way hope its a cheap fix and manifests itself in an obvious manor =)
Andrew D. Carapella (Drew)
1950 Chevy Styleline Deluxe
1954 Chevy 3100
Various other "modern classics" |
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1958Belairjoe
Newbie
Posts: 20
Loc: FL
Reg: 08-03-23
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02-22-24 02:29 PM - Post#2867137
In response to Airlifter
Good work !!!
hence the phrase "Never Give Up"
I had a very similar problem on 6 cylinder Studebaker , 1960 Lark , the owner gave up on it for 20 years because it would not idle below 1000.
After 4 hours searching I found an 1/8 inch hole drilled into the bottom of the intake manifold.
Plugged vacuum leak and all very good , never give up !!!
Now go enjoy your car !!
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OldRustyWrench52
Newbie
Posts: 22
Loc: So. Florida
Reg: 02-23-20
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02-22-24 02:51 PM - Post#2867138
In response to Airlifter
Did anyone mention the possibility of a flat cam? Had a friend who had a flat cam in a Chevy II and I found the problem when removing the valve cover. The rocker arms barely moved on that cyl and didn't make any noise. Just a thought.
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VWNate
Senior Member
Posts: 393
Loc: Sunny So.Cal.
Reg: 09-25-02
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 02-22-24 03:43 PM - Post#2867141
In response to OldRustyWrench52
Glad you found the intake leak .
When re installing the manifold, start all the bolts snugged up by hand then begin tightening from the center outwards going back and forth .
Remember there are never supposed to be fasteners at the extreme ends ~ only locating pins .
The long 'log' typ manifold crawls at it heats up and cools off at a different temperature than the cylinder head .
Failure to follow the proper order in tightening is the usual cause of leaks and using fasteners at the ends causes breakage .
Do you have the three intake alignment rings ? . they're different for 235/261 engines and when missing they also cause intake leaks, BT & DT .
Don't forget to hold a straightedge against the manifolds ports, sometimes they warp, you can get the assembled intake and exhaust planed dead nuts flat if it's not even .
-Nate
'49 3100 Series Pickup W/'57 235 & Muncie M420 ~ SOLD & Missed .
'69 C10 Stepside shortbed L6 250, TH350, P.S. & P.B. side mount spare also greatly missed . |
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drew1987
"11th Year" Silver Supporting Member
Posts: 3918
Age: 37
Loc: Western NY
Reg: 02-23-14
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02-22-24 03:55 PM - Post#2867143
In response to VWNate
Hey do your back up and running in all 6?
Andrew D. Carapella (Drew)
1950 Chevy Styleline Deluxe
1954 Chevy 3100
Various other "modern classics" |
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Airlifter
"9th Year" Gold Supporting Member
Posts: 955
Age: 78
Loc: Tazewell county, Virginia
Reg: 06-07-15
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02-23-24 08:57 AM - Post#2867158
In response to drew1987
Thanks for all the responses. Let's see if I can respond to the responses. I did tighten the bolts in proper sequence. The alignment rings are in place. The engine is running fine now. I learned something during this process. I did not know that a vacuum leak would affect just one cylinder. Thanks to all.
Pete
1951 styline deluxe sport coupe w/'60 261 engine & 54 powerglide
1965 Corvair Corsa 140 hp 4 speed convertible |
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drew1987
"11th Year" Silver Supporting Member
Posts: 3918
Age: 37
Loc: Western NY
Reg: 02-23-14
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02-23-24 09:42 PM - Post#2867180
In response to Airlifter
Yea I learned the same thing. I knew it would do that in a modern motor as each cylinder has dedicated port but wouldn’t expect that in a Stovebolt. Nice cheap victory
Andrew D. Carapella (Drew)
1950 Chevy Styleline Deluxe
1954 Chevy 3100
Various other "modern classics" |
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