[va3ux]

First post here folks. Looks like a pretty good forum.

I wouldn't mind some feedback on the compression readings I just took on my 2.7. If others here have done it then I'll have something to compare to. The manual only says " 100 psi minimum, no more than 25% variance ". That isn't much to go by but what I've got here satisfies all that.

Here are my numbers as of June 4/06 :

Cylinder Reading Cylinder Reading
2 187 1 185
4 175 3 183
6 185 5 175

2001 Intrepid 2.7 with 239,000 km (148,000 mi). Oil changes at 3000 - 3500 miles; oversized WIX/NAPA Gold 1068 filter. Engine has never been apart.

Thanks in advance....Phil

 

[froggy81500]

Numbers look good. As far as the 25% variance, its the difference between the highest and lowest cylinders. In your case the highest is 187 (#2) and the lowest 175 (#4 & #5). The difference is 8 psi. 8 psi / 187 psi (the highest) is only 4% so you're well within that 25% threshold. Sounds like a healthy engine to me. And almost 150K miles, damn that's great.

The reason for the 25% variance rule, is when you get a really large variance between the cylinders, the engine becomes lopsided in a way. I don't really know another way to explain it. You get some cylinders with more power (those with higher compression) and some cylinders with lower power (lower compression) and likewise the internal components don't rotate at a uniform speed. what you get is a speed up and slow down when it cycles thru the higher and lower compression cylinders. This affects everything. And if its severe enough on a modern engine with a crank position sensor, it could start tripping misfire codes.

 

[lextrep]

From your compression readings it looks like you shouldn't have any worrys about the internal cylinder parts. They are well within the allowable tolerance, and very good for a higher mileage engine.!! One other thing you might take note of if you do it again is the compresion of each cylinder on the first stroke compared to the 4th or 5th stroke, this gives a little more indication of how well the rings are sealing(but with these reading you shouldn't need to do another compression test for a good while unless you experience some kind of running problem)
I assume that you took the readings on a warmed up engine, dry (without adding oil to cylinders)

And WELCOME to this very useful forum, It is always good to read about a 2.7 engine with over 100k that has been well taken care of. :icon_smil

 

[MaxinCanada]

Wish my '99 ran that well Phil. I had my motor rebuilt 2 years ago after spinning a crank bearing. BTW, I'm also VE3TMT.

Max in Kingston

 

[va3ux]

Wish my '99 ran that well Phil. I had my motor rebuilt 2 years ago after spinning a crank bearing. BTW, I'm also VE3TMT.

Max in Kingston

Howdy Max ! I was in Kingston for a few days just a couple of weeks ago. Doin' a bit of work for Queens.

73's .....Phil

 

[va3ux]

From your compression readings it looks like you shouldn't have any worrys about the internal cylinder parts. They are well within the allowable tolerance, and very good for a higher mileage engine.!! One other thing you might take note of if you do it again is the compresion of each cylinder on the first stroke compared to the 4th or 5th stroke, this gives a little more indication of how well the rings are sealing(but with these reading you shouldn't need to do another compression test for a good while unless you experience some kind of running problem)
I assume that you took the readings on a warmed up engine, dry (without adding oil to cylinders)

And WELCOME to this very useful forum, It is always good to read about a 2.7 engine with over 100k that has been well taken care of. :icon_smil

Thanks Lex. Good idea on checking the pressure after just the first stroke. Hadn't thought of that. And yes, the test was done with the engine at full operating temp. No oil or anything added to the cylinders.

I will be repeating the test periodically to see if my Auto-Rx cleaning is helping the ring packs.

Phil