360 Compression #'s, now what?
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Senior User
Joined: Mar 2007
Posts: 271
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From: arkadelphia, ar
360 Compression #'s, now what?
Ran a compression check on my 73, 360 this morning. Of course the engine is cold as the cam gear is stripped but trying to decide how far to go at this time. The #'s are:
1. 140
2. 140
3. 100, after sqirting a little oil from can 112
4. 98. after squirting a little oil from can 102
5. 138
6. 140
7. 132
8. 132
After doing 5-8, I went back to 3 & 4 and ran them again without any more oil and they were 3-120 and 4-115.
Now that being said, I really don't want to do a complete overhaul at this time, as I want to build a 390 over time and need this truck running in the process. Could it be a head gasket between 3-4? I don't seem to show any of the typical signs of a Hg but don't know.
This engine is very nasty inside. I'm thinking about pulling the heads, checking valves on those 2 cyl, replace head gasket and cam and go. Also isn't 140 a little high for a 360?
Just need some re-assurance I suppose.
1. 140
2. 140
3. 100, after sqirting a little oil from can 112
4. 98. after squirting a little oil from can 102
5. 138
6. 140
7. 132
8. 132
After doing 5-8, I went back to 3 & 4 and ran them again without any more oil and they were 3-120 and 4-115.
Now that being said, I really don't want to do a complete overhaul at this time, as I want to build a 390 over time and need this truck running in the process. Could it be a head gasket between 3-4? I don't seem to show any of the typical signs of a Hg but don't know.
This engine is very nasty inside. I'm thinking about pulling the heads, checking valves on those 2 cyl, replace head gasket and cam and go. Also isn't 140 a little high for a 360?
Just need some re-assurance I suppose.
Elder User
Joined: Dec 2007
Posts: 739
Likes: 1
Just by a fast checking on the numbers I'm leaning towards the start of a head gasket issue. However as Red stated? A leak down test would give you the exact answer, and save some headache. If you have access to an air compressor? Pick up a fitting/adapter for this purpose. Put the cylinder(s) in question at TDC and ensure both valves are closed. (visually check with the valve cover off).
Air charge the cylinder(s) and listen/feel where the air is leaking. If it's a head gasket? You'll feel air escaping from the spark plug hole next door. Intake/exhaust valve issue? Check air flow at tailpipe or coming out of the intake/carb if still installed.
S-
Air charge the cylinder(s) and listen/feel where the air is leaking. If it's a head gasket? You'll feel air escaping from the spark plug hole next door. Intake/exhaust valve issue? Check air flow at tailpipe or coming out of the intake/carb if still installed.
S-
Thread Starter
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Senior User
Joined: Mar 2007
Posts: 271
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From: arkadelphia, ar
Thanks guys.
Already have the rocker arm assem. off both sides, along with intake, (whewh, that's one heavy momma by ya self!), but may try the leak down test. I don't know though, the motor is sooooo internally nasty, I feel like I'll pull the heads and clean 'em up and put valve seals on at least, (from what I see there aren't any, or they are riding the valve) thus getting new head gaskets anyway. I do know the oil passage leading throught the head to the valley where the rockers is completely stopped up with crud.
Already have the rocker arm assem. off both sides, along with intake, (whewh, that's one heavy momma by ya self!), but may try the leak down test. I don't know though, the motor is sooooo internally nasty, I feel like I'll pull the heads and clean 'em up and put valve seals on at least, (from what I see there aren't any, or they are riding the valve) thus getting new head gaskets anyway. I do know the oil passage leading throught the head to the valley where the rockers is completely stopped up with crud.
Thread Starter
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Senior User
Joined: Mar 2007
Posts: 271
Likes: 1
From: arkadelphia, ar
Yeah, I knew my luck would run out eventually. This ole thing sat for so long and was running so good, especially after the timing chain, I couldn't believe it! Was getting 13.8-14 MPG and ran smooth, but freshening up and a few minor mods, Pertronix, new dist., new cam & lifters, and if I can find a 4bbl carb cheap shouldn't hurt. I have a S code manifold that will go back if I find a carb in time. Just haven't found any headers that I can afford right now.
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