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Compression Test Results with white smoke
#1
Gurus,

I did a compression test on my 1970 302 and the results seem shockingly very high. I tested with a warm engine, all plugs removed and WOT. My plugs are always a nice tan color.

Bottom Line: 6 cylinders were 210 psi and two of them were 215 psi. I rented the compression tester expecting to find 2 or more cylinders notably lower pointing to a head gasket leak or worn valve. I did not find any wide variation in testing, but I think the numbers seem REALLY high compared to what I've read elsewhere.

Any thoughts? My car still pushes white smoke when and only when she is warm. I have a intake manifold gasket and new bolts are in the mail so I'll reseal her later this week. I have a tad bit of an oil leak at the back of the intake manifold.

KR

-Former 70 & 72 Mustang Owner.
-69 Torino GT, Formal Roof, 351W, Edelbrock 600 cfm, Edelbrock 351W Performer RPM intake, headers, AOD trans, dual flowmasters w/H pipe, Pertronix II Billet, 3.5 TRACLOC g/r, 15" Magnum 500s, 100A alt, aluminum radiator, electric fan, Pro-car seats, mini-starter...owned since Dec 13.
-70 Mach 1, 351W, Edelbrock E-Street EFI, VHX instrument cluster, Hooker headers, dual flowmasters, Pertronix II, 15" Magnum 500s, 150A alt, aluminum radiator, dual electric fans, Pro-car seats, mini-starter
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#2
Oil leaking around valve stems. Usually worse cold but if the cylinders are sealed well, thats where it has to come from
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#3
Thank you Jenny, you rock.

Is replacing the valve stem seals a difficult process off the top of your head? I'll do some research on-line, but I'm thinking it's not that difficult for the average Joe.

KR

-Former 70 & 72 Mustang Owner.
-69 Torino GT, Formal Roof, 351W, Edelbrock 600 cfm, Edelbrock 351W Performer RPM intake, headers, AOD trans, dual flowmasters w/H pipe, Pertronix II Billet, 3.5 TRACLOC g/r, 15" Magnum 500s, 100A alt, aluminum radiator, electric fan, Pro-car seats, mini-starter...owned since Dec 13.
-70 Mach 1, 351W, Edelbrock E-Street EFI, VHX instrument cluster, Hooker headers, dual flowmasters, Pertronix II, 15" Magnum 500s, 150A alt, aluminum radiator, dual electric fans, Pro-car seats, mini-starter
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#4
rutkak;123448 Wrote:Gurus,

I did a compression test on my 1970 302 and the results seem shockingly very high. I tested with a warm engine, all plugs removed and WOT. My plugs are always a nice tan color.

Bottom Line: 6 cylinders were 210 psi and two of them were 215 psi. I rented the compression tester expecting to find 2 or more cylinders notably lower pointing to a head gasket leak or worn valve. I did not find any wide variation in testing, but I think the numbers seem REALLY high compared to what I've read elsewhere.

Any thoughts? My car still pushes white smoke when and only when she is warm. I have a intake manifold gasket and new bolts are in the mail so I'll reseal her later this week. I have a tad bit of an oil leak at the back of the intake manifold.

KR

Typo on the readings? That would give you over 14:1 compression. If the numbers are in the 1XX:1 the the ratio is about 7.8:1. These would be really good compression readings and what I would expect for a 302.
-jbojo

-john
(jbojo)
351C 4V cc heads, 10.5 : 1 CR, 290 Herbert cam, Flat top forged pistons, forged connecting rods, Atomic efi,
C6 with Gear Vendor overdrive, 3.89 Tru Trac, Hooker Super Comp with 2 1/2" Pypes Exhaust.        

Some Mod pictures can be seen at:

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#5
Maybe that gauge is off.
Yes, those are tall numbers, especially if you think it may be stock or a mild rebuild.
Are the pistons domed or ???
That can cause detonation, and potentially popped head gasket(s).
Hopefully you'll be able to see a crown through at least one plug hole. A cylinder taking on leaking water will have clean piston crowns, no carbon.

Cam may have not enough overlap (to bleed compression), creating big static compression figures?

I'd guess something is amiss in the compression department for starters... That would worry me a little before white smoke.

Pete - MotoArts Decals and Signs
'71 Sportsroof 351C-4V/4-speed - FINALLY under construction - no, wait, on hold again...
'90 Mustang 7-Up 5.0 ragtop, rolling beater
'66 Sunbeam Tiger Mk.IA, survivor
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#6
Yeah, 210ish is definitely very high for a (presumably) stock 1970 302. I'm going to check my 289 with the same gauge tonight...the gauge must be off. I'd expect that one to read even higher since it's a 1966 C Code.

KR

-Former 70 & 72 Mustang Owner.
-69 Torino GT, Formal Roof, 351W, Edelbrock 600 cfm, Edelbrock 351W Performer RPM intake, headers, AOD trans, dual flowmasters w/H pipe, Pertronix II Billet, 3.5 TRACLOC g/r, 15" Magnum 500s, 100A alt, aluminum radiator, electric fan, Pro-car seats, mini-starter...owned since Dec 13.
-70 Mach 1, 351W, Edelbrock E-Street EFI, VHX instrument cluster, Hooker headers, dual flowmasters, Pertronix II, 15" Magnum 500s, 150A alt, aluminum radiator, dual electric fans, Pro-car seats, mini-starter
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#7
I checked my 73 302 recently and all cylinders were in the 125 to 130 range. I also changed the valve seals with the heads on the engine. Very easy to do.

Rick Bombard
1971 Grabber Green Mach 1 351C 4V
2013 Race Red California Special Convertible
1973 Medium Copper Metallic Convertible 302 4V     SOLD
1953 F-100 project

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#8
Thanks 73Mach1.

The gauge is definitely functional. I tested the compression on my 289 C Code and all cylinders were 145ish. I'll recheck the 302 when I get back from work but I'm pretty confident the engine is stock as stock can be.

On both tests I pulled all the spark plugs, warmed up the engine, disconnected distributor and zip-tied the throttle wide open. The only difference in the two engines is that the 302 has an HEI dizzy but I disconnected it. It's supposed to rain pretty heavily today so we'll see what I can get to. Yeah, 210 is pretty damn high.

I take a look Moto and see what I can see.

-Former 70 & 72 Mustang Owner.
-69 Torino GT, Formal Roof, 351W, Edelbrock 600 cfm, Edelbrock 351W Performer RPM intake, headers, AOD trans, dual flowmasters w/H pipe, Pertronix II Billet, 3.5 TRACLOC g/r, 15" Magnum 500s, 100A alt, aluminum radiator, electric fan, Pro-car seats, mini-starter...owned since Dec 13.
-70 Mach 1, 351W, Edelbrock E-Street EFI, VHX instrument cluster, Hooker headers, dual flowmasters, Pertronix II, 15" Magnum 500s, 150A alt, aluminum radiator, dual electric fans, Pro-car seats, mini-starter
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#9
Gauge readings are high, but the important thing is they are well within 10% of each other.

Valve seals will help, but usually valve guides are due to be done when there is leakage. I'd consider going ahead and pulling the heads and having them overhauled. That would also give you an opportunity for a full visual inspection of chambers and piston tops and bore condition. It is an afternoon's work, but it isn't hard.

[Image: 1_01_07_15_8_53_18.png]

"I love my Hookers!" and "Get some Strange" probably have a different connotation to non automotive enthusiasts!
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#10
I've seen some heads and pistons that had a lot of carbon due to oil burning, but I don't know that carbon could raise the CR that much and that evenly, even if all the valve guides/seals were bad.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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