| Author |
Message |
Paul Newman (Newman)
Junior Member
Username: Newman
Post Number: 240
Registered: 12-2001
| | Posted on Sunday, June 16, 2002 - 8:10 am: | |
Another thing to consider when compression testing is the first pump should give you the majority of your final reading rather than work its way up to say 150psi. I only used 6 compression strokes to do my test on a warm engine without using oil. Your compression ring gaps are smaller when warm allowing for a better seal. |
bill v. (Doc)
New member
Username: Doc
Post Number: 36
Registered: 9-2001
| | Posted on Sunday, June 16, 2002 - 7:53 am: | |
Thank you very much for your valued input , gentlemen. It sounds as though you've essentially concurred that these figures aren't all that unusual or bad--which is what the mechanic stated. One other Q--does it necessarily stand to reason that the figures obtained on a warmed-up engine would expectedly be better than on a cold engine, just from normal expansion from heat? The mechanic who did the test felt that , given the normal cold results, that it probably wasn't necessary to go further with a hot test . He also made a staement similar to yours , Ed, that sometimes too much weight is placed upon a test like this ( with a good-running car) due to variability of a number of factors. |
Edward Gault (Irfgt)
Intermediate Member
Username: Irfgt
Post Number: 1480
Registered: 2-2001
| | Posted on Sunday, June 16, 2002 - 7:19 am: | |
The variations between the accuracy of the devices used to take compression and leakage readings is probably higher than the cases of worn out engines. My experience has shown that compression readings are usually needed to confirm a specific complaint versus telling the health of a particular engine. In most cases if an engine runs well and smoothly and has low blowby and does not smoke or knock then the engine is probably in good health. An engine that meets this criteria will almost always have good compression. Compression figures vary tremendously between different engines and equal readings are more important than specific readings. |
Richelson (Richelson)
Member
Username: Richelson
Post Number: 768
Registered: 12-2001
| | Posted on Sunday, June 16, 2002 - 6:26 am: | |
IMO 2% seems a little to good to be true for a 33K engine. 7% sounds more reasonable. 2% is around what I would expect to be an almost new engine. Did you know this mechanic personally or is this the sellers mechanic? The compression figures seem low for a QV but they are around the same range so that is a good point. In other words they don't vary too much from each other. Have you seen the car in person? What is it like? How does it drive etc.? Just MHO. |
William Badurski (Billb)
Junior Member
Username: Billb
Post Number: 59
Registered: 6-2001
| | Posted on Saturday, June 15, 2002 - 11:27 pm: | |
Compression and leak-down tests should be done on a warm engine. The use of oil is sometimes carried out during a second compression test, but not with leak-down. As mentioned in the first reply, the throttle should be held open for both. I personally don't like the use of oil as it masks potential problems. The compression range you saw was good, and also more importantly consistent. The leak-down figures (dry) were also acceptable, especially for a cold engine. 20% is about the maximum one would hope to see.
Bill Badurski
Technical Chairman- FCA |
Paul Newman (Newman)
Junior Member
Username: Newman
Post Number: 238
Registered: 12-2001
| | Posted on Saturday, June 15, 2002 - 10:08 pm: | |
Prior to a rebuild in my 308, I got readings of 170psi with the throttle wide open. It was alot lower with it closed. 170 is very good and I rebuilt mine for other reasons. |
bill v. (Doc)
New member
Username: Doc
Post Number: 35
Registered: 9-2001
| | Posted on Saturday, June 15, 2002 - 9:22 pm: | |
I'm about to purchase an '85 QV, w 33k miles on it, which was recently inspected. The mechanic arrived at compression figures of a range between 135 and 145. The leakdown test was conducted in somewhat of an unconventional manner, I believe, wherein leakdown figures were obtained on a stone cold engine once and then compared with figures obtained on , again, a cold engine with oil squirted into the cylinders. The figures obtained on the "dry" run ranged from a 12% to 20% leakdown. The "wet " test yielded a range of 2% to 7% leakdown( w 2 cylinders showing 0 leak). The mechanic stated that the "wet" test approximates figures which would be obtaned from a hot engine and his impression was that all of these figures were w/i normal range. For those of you who are more mechanically savvy than I am, what do you think of the procedure and the #'s? |