Dry/Wet compression #'s

[research monkey]

Just purchased my 72 and had every intention to rebuild the engine but with all the other items on the list of things to do I think I might focus my money elsewhere.  Factory service manual says compression anywhere from 171-185.  I did a dry/wet compression test last week on a cold engine and after reading a bit decided to do another compression test this weekend on a warm engine. 

Results are as follows: 

6/22/19		1	2	3	4	5	6
COLD ENGINE	Dry	165	150	170	165	150	165
	Wet	190	175	190	190	175	190
6/29/19		1	2	3	4	5	6
WARM ENGINE	Dry	150	150	160	165	155	160
	Wet	175	175	180	190	180	190

All plugs were pulled and the same compression gauge was used for all results.  Started with #1 and worked my way back.  Throttle wide open, and cranked about 10 seconds watching the gauge through the windshield.  Wet tests were done with about 5ml / 1 teaspoon of oil in each cylinder. 

Based on the results it looks like the rings just seem a bit worn but all compression numbers are pretty close? 

The car doesnt smoke but feels a bit sluggish.  I'm used to riding motorcycles so my sense of speed might be off.  The car is definitely running rich based on the plugs and I've had a leak in the exhaust (which after running the tests I believe is in the exhaust manifold).   I should mention that the car has been sitting 10 years so it definitely needs everything gone over. 

I'm thinking instead of rebuild, just do a full tune up on the thing and focus on all the other bits (gas tank, brakes, suspension, rust repair).  

 

 

[Patcon]

41 minutes ago, research monkey said:

Just purchased my 72 and had every intention to rebuild the engine but with all the other items on the list of things to do I think I might focus my money elsewhere.  Factory service manual says compression anywhere from 171-185.  I did a dry/wet compression test last week on a cold engine and after reading a bit decided to do another compression test this weekend on a warm engine. 

Results are as follows: 

6/22/19		1	2	3	4	5	6
COLD ENGINE	Dry	165	150	170	165	150	165
	Wet	190	175	190	190	175	190
6/29/19		1	2	3	4	5	6
WARM ENGINE	Dry	150	150	160	165	155	160
	Wet	175	175	180	190	180	190

All plugs were pulled and the same compression gauge was used for all results.  Started with #1 and worked my way back.  Throttle wide open, and cranked about 10 seconds watching the gauge through the windshield.  Wet tests were done with about 5ml / 1 teaspoon of oil in each cylinder. 

Based on the results it looks like the rings just seem a bit worn but all compression numbers are pretty close? 

The car doesnt smoke but feels a bit sluggish.  I'm used to riding motorcycles so my sense of speed might be off.  The car is definitely running rich based on the plugs and I've had a leak in the exhaust (which after running the tests I believe is in the exhaust manifold).   I should mention that the car has been sitting 10 years so it definitely needs everything gone over. 

I'm thinking instead of rebuild, just do a full tune up on the thing and focus on all the other bits (gas tank, brakes, suspension, rust repair).  

 

 

If you are use to riding bikes, then yes, your calibration is way off.

If the car sat for any period of time, then 2 cylinders could have been left at the bottom of the stroke for an extended period of time with the valves open. Some slight bore rusting would make those 2 cylinders measure low. I am too lazy right now to try to figure out if the crankshaft strokes correspond to your actual cylinder numbers. I would run it for a while 6 months to a year and see if the numbers don't even out some. For me, they are only slightly out of range. Being I shoot for all the numbers being within about 15%. 10% being even better, unless the motor is fresh

 

[research monkey]

23 minutes ago, Patcon said:

If the car sat for any period of time, then 2 cylinders could have been left at the bottom of the stroke for an extended period of time with the valves open. Some slight bore rusting would make those 2 cylinders measure low. I am too lazy right now to try to figure out if the crankshaft strokes correspond to your actual cylinder numbers. I would run it for a while 6 months to a year and see if the numbers don't even out some. For me, they are only slightly out of range. Being I shoot for all the numbers being within about 15%. 10% being even better, unless the motor is fresh

 

Never thought about that.  Car sat for 10 years so that could be the case.  Aren't the current numbers all within 15% of each other? Unless i'm calculating wrong. 

[Dave WM]

Just get some run time on it, agree with Patcon, the numbers can improve with use as the rings get use, carbon gets burned up etc...

[Mark Maras]

2 hours ago, research monkey said:

Just purchased my 72 and had every intention to rebuild the engine but with all the other items on the list of things to do I think I might focus my money elsewhere.  Factory service manual says compression anywhere from 171-185.  I did a dry/wet compression test last week on a cold engine and after reading a bit decided to do another compression test this weekend on a warm engine. 

Results are as follows: 

6/22/19		1	2	3	4	5	6
COLD ENGINE	Dry	165	150	170	165	150	165
	Wet	190	175	190	190	175	190
6/29/19		1	2	3	4	5	6
WARM ENGINE	Dry	150	150	160	165	155	160
	Wet	175	175	180	190	180	190

All plugs were pulled and the same compression gauge was used for all results.  Started with #1 and worked my way back.  Throttle wide open, and cranked about 10 seconds watching the gauge through the windshield.  Wet tests were done with about 5ml / 1 teaspoon of oil in each cylinder. 

Based on the results it looks like the rings just seem a bit worn but all compression numbers are pretty close? 

The car doesnt smoke but feels a bit sluggish.  I'm used to riding motorcycles so my sense of speed might be off.  The car is definitely running rich based on the plugs and I've had a leak in the exhaust (which after running the tests I believe is in the exhaust manifold).   I should mention that the car has been sitting 10 years so it definitely needs everything gone over. 

I'm thinking instead of rebuild, just do a full tune up on the thing and focus on all the other bits (gas tank, brakes, suspension, rust repair).  

 

 

 Do a complete tune-up including valve lash. Your compression. #s look good for an engine that has sat. The #s will improve with mileage and a valve adjustment. After adjusting the valves, start it up and verify the cam is getting lots of oil.

[grannyknot]

Those numbers aren't so bad and may improve,  you could put your money elsewhere for the time being and circle back to the engine after a few months of driving and another compression check.  You could run a thicker oil, say 10w/40 and see if that helps, the #1 piston is the one to watch.

[research monkey]

Appreciate the responses guys.  I'll move forward with a full tune up (including rebuilding carbs) now that I have a little confidence in the #'s the the motor as it is. 

5 hours ago, grannyknot said:

Those numbers aren't so bad and may improve,  you could put your money elsewhere for the time being and circle back to the engine after a few months of driving and another compression check.  You could run a thicker oil, say 10w/40 and see if that helps, the #1 piston is the one to watch.

I was thinking of going 15w40 or 20w50 to be honest.  We never get freezing temps near the coast in Southern California. 

[Dave WM]

I run Valvoline 20/50 VR1 in mine (high zinc content for the valve train), central fl temps are mostly 80+ thru about 8 months of the year, lows maybe in the upper 30's for a week.

[research monkey]

3 hours ago, Dave WM said:

I run Valvoline 20/50 VR1 in mine (high zinc content for the valve train), central fl temps are mostly 80+ thru about 8 months of the year, lows maybe in the upper 30's for a week.

I was going to buy the lucas oil 20w50 I think.  3 - 5 qt jugs for $100 is a pretty good - https://www.amazon.com/Lucas-Oil-10684-3PK-20W-50-Petroleum/dp/B009M1LGBU