Cranking Compression Tests

[83_maxima]

I have been curious to conduct cranking compression tests on my Maxis to see what the numbers looked like and to try and get a better idea of why the parts car starts so well consistently - compared to my daily driver Maxi.

Al was gracious enough to loan me his very nice compression tester, so I got after it today. Not the easiest job if you've never done it before, but the second car went faster than the first. I ended up using a combinataion of Al's supplied fittings, so they are all neccesary to do this job.

I started with cylinder 6 (the easiest) and worked my forward to 1.

Cylinder 6:



Cylinder 5, was pretty easy as well. Used the 45 degree adapter:



Cylinder 4 also pretty straight forward. Used the straight adapter here as I did with 6:





Cylinder 3 is the toughest. Took some thinking to make the tester work. First you must loosen up all of the lines, then attatch the GP adapter, the 90' adpater and the gauge, then re-tighten the lines. Crank the starter, then undo the gauge and remove the adpaters. Re-tighten the lines.







Cylinder 2 also requires loosening the lines on injectors 1 & 3





Cylinder 1 is pretty easy again. I used the 45 here too.



.................................................................................................................................

The results:

1981 Daily Driver Maxima [#254] - 154,xxx mi

Cyl 1: 320
Cyl 2: 320
Cyl 3: 280
Cyl 4: 300
Cyl 5: 320
Cyl 6: 300

1981 Parts Maxima [#867] - 209,xxx mi.

Cyl 1: 340
Cyl 2: 440
Cyl 3: 370
Cyl 4: 480
Cyl 5: 400
Cyl 6: 460

Compression numbers better on the parts car, but more than a 20% difference between highest and lowest. Numbers not as good on the DD, but not quite a 20% difference between highest and lowest numbers.

Explains why the parts car starts so much better than the DD.

What do you guys think of these numbers? Some big differences between some of these cylinders.

[asavage]

Does your driver have a solid starter and a good battery? Those are Gawdawful numbers, Ben. 350 is my lower limit for good cold starting; 280 is just terrible.

Cyls No. 1 & 3 on the parts car aren't so hot either. On the LD, under 380 is kind of iffy.

I didn't back off any injector lines when I did the test on my '83 Wagon, and I don't recall there being much drama in getting one or another of the adapters in all of them. Maybe that's just the benefit of poor memory

Check if I've got this right: To summarize the adapters used:

• No. 1 = 45°
• No. 2 = 90° (std)
• No. 3 = 90° (std)
• No. 4 = straight
• No. 5 = 45°
• No. 6 = straight

I thought I had to use the special low-profile 90° adapter on at least one of them.

[83_maxima]

Does your driver have a solid starter and a good battery?

I robbed the 750 CCA Interstate out of the parts car and put it in my driver. The starter looks like it has been replaced. The cranks are definitely slower with my DD than with the parts car.

Those are Gawdawful numbers, Ben. 350 is my lower limit for good cold starting; 280 is just terrible.

Suck! I didn't think they were too good, but hoped they weren't obismal. I've a pretty hard time cold-starting in the winter if it's not plugged in. Was hoping the GP mod would help this some. Maybe I should swap starters.

Would slow cranking produce low numbers? Maybe I need to try it again...

I didn't back off any injector lines when I did the test on my '83 Wagon, and I don't recall there being much drama in getting one or another of the adapters in all of them.

Saw no other way. I could get the adapters on without taking the lines loose, but the lines prevented connection of the gauge.

I thought I had to use the special low-profile 90° adapter on at least one of them.

The rigid coolant line that runs alongside the block prevents use of the low-profile adapter. Not quite long enough to allow the gauge to attach.

[asavage]

The cranks are definitely slower with my DD than with the parts car. . . . Maybe I should swap starters. . . . Would slow cranking produce low numbers?

Yes, a dragging starter will yield lower numbers. There is a cranking RPM spec for the compression test (not that you can easily check the cranking RPM). If you have time, you might try swapping starters, yes.

I noticed that the starter I put in my '83 Wagon cranks quite a bit faster than the Nissan/Hitachi Reman I have in my '82.

Bear in mind that with all other things being equal, lower compression in the DD should mean it cranks faster, not slower. You may have a dragging starter (for whatever reason, but with the track record I have with solenoids . . .).

[83_maxima]

I am curious about the starter. It had a gasser-rated battery, why not a gasser starter? I could see a FLAPS counterperson leading a customer astray.

No more time this weekend most likely, next week or next weekend (out of town). I will get into it soon though. Would like to figure this out before it gets too cold.

[asavage]

I am curious about the starter. It had a gasser-rated battery, why not a gasser starter? I could see a FLAPS counterperson leading a customer astray.

Easily spotted: I had a gasser starter installed on my '83 Wagon, and when I took it out (bad solenoid), I laid it side-by-side with the correct one. Dead giveaway is the position of the motor lead from the solenoid to the motor, because the brushes are on opposite ends.

[Dr. Jones]

Where and approximately how much am I going to forced to part with for a compression tester and adapters?

[asavage]

You can buy a cheap set at Harbor Freight or eBay or equivalent for around US$100.

I just bought a second Snap-On diesel compression testing setup, so I can have a loaner and one in the shop. I have quite a bit over $200 in the Snap-On setup via eBay purchases. In particular, the Snap-On diesel compression gauge is relatively inexpensive but the GP adapter sets go for more than they should by triple!

(And then I went and had another low-profile GP adapter fabricated for testing the SD engines, which was another $80. )

But if you don't need a quality set, the cheap ones will probably do a reasonable job -- I just hate buying cheap tools, I always end up kicking myself later.

[diesel-man]

Dumb question.... have the valves been adjusted on both cars since they have been in your possession?

[LD28 Owner]

I have a U.S. General (A brand name oft found in Harbor Freight stores) Item #93644 Diesel Engine Compression Tester. It has a 1000 psi gauge with quick release hose and 18 fittings. A similar (if not identical) kit is offered on ebay (see item 200177251954) for $36 including shipping by a seller with a decent feedback score.

The adapter instructions list Nissan UD 2.2's with 10 X 1.25 GP's but doesn't list LD or SD Nissans.

I reviewed this thread and looked at the fittings in the kit and it looks like it has everything mentioned in the postings above except the 45 degree adapter (the kit does have a 90 degree adapter). The kit appears to have enough parts to set up three cylinders at once (three 12 X 1.25 GP adapters with 7/16" flare ends and three straight 7/16" flare to quick release fittings) Adding 45 degree capacity would just require obtaining a 45 degree 7/16" flare fitting.

I haven't used this tool yet so I can't vouch for its function but my experience with these inexpensive tools is that they work fine for occasional use and less fine for constant use or critical tasks -- I wouldn't buy a U.S. General socket set or torque wrench but the stuff that is used once a year has served me well and beats the need to run around town to rental yards to find special tools.

Caution: If you go to Harbor Freight's web site and look up item #93644, you come up with a smaller diesel compression tester with far fewer fittings -- I don't have that version and can't speak to its applicability.

[asavage]

1983 Nissan Maxima Wagon (yellow)
13-Aug-06

Compression test
cold engine, all GPs pulled
12mm deep socket (1/4" drive)
pen cap cut off (?)

Cylinder    Adapter        1/4" extension length
1 = 365             45°                       6"
2 = 355             45°                       6"
3 = 335             90° low profile,          6"
                    pointed toward rear
4 = 360             straight                  3"
5 = 350             straight                  3"
6 = 350             straight                  3"