Compression results, maybe not good news? |
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Compression results, maybe not good news? |
EJP914 |
Aug 11 2006, 08:04 PM
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#1
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Member Group: Members Posts: 260 Joined: 14-June 03 From: Monroeville, PA Member No.: 821 |
Just had mechanic give me results of compression test on my "73 1.7.
#1 100 psi #2 120 psi #3 120 psi #4 150 psi He is recommending valve job. I realize the readings are all over the place, but is this guy right? Car was in for valve adjustment, small miss at 2800 RPM, and backfire under decell. Timing and fuel mixture were adjusted. Backfire is still there, but not too bad. Still not smooth accel at 2800 - 300 RPM. During last oil change, I noticed some black soot around the left exhaust pipe on the cylinder head. Can't remember if it was the front or rear cylinder.I suspect small exhaust leak. Would this leak have any bearing on the compression reading for that cylinder? I would appreciate any and all comments on the valve job recommendation and your thought on the compression readings. Thanks for listening! |
G e o r g e |
Aug 11 2006, 08:07 PM
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#2
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Dr Group: Members Posts: 1,905 Joined: 20-September 05 From: Southern Cal Member No.: 4,832 Region Association: None |
i don't have answer for you but you don't need to start a new post after 3 minutes give it some time. (IMG:style_emoticons/default/dry.gif)
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Flat VW |
Aug 11 2006, 08:29 PM
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#3
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Illegal Soapbox Derby Racecar Group: Members Posts: 1,692 Joined: 13-November 04 From: Phoenix, AZ Member No.: 3,105 |
i don't have answer for you but you don't need to start a new post after 3 minutes give it some time. (IMG:style_emoticons/default/dry.gif) Ah, George- stop baggin on the new guy! (IMG:style_emoticons/default/laugh.gif) Three minutes is a long wait for a response around here... ejm914- I do not know either, but an answer, correct or not, will appear here SOON. (IMG:style_emoticons/default/smile.gif) (IMG:style_emoticons/default/welcome.png) John (IMG:style_emoticons/default/wavey.gif) P.S. I hope SirAndy does not run out of either ones or zeros due to the 'double post' . (IMG:style_emoticons/default/rocking nana.gif) |
drive-ability |
Aug 11 2006, 08:37 PM
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#4
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Senior Member Group: Members Posts: 1,169 Joined: 18-March 05 From: Orange County, California Member No.: 3,782 |
I'll give it a shot,
Surely the numbers are disappointing at best. I would really want to be sure the test was administered correctly. I would wonder about the seal in-between the cylinders and the heads. That would surely make a difference in compression readings if there was a leak. It may not change the overall outcome as its likely the heads would have to come off but at least you would be more prepared. I would want to check that as well as preforming a compression test and add some oil to see what the outcome would be. By adding some oil to the cylinder (just a real small amount) if the rings are skewed the readings will jump up to a more normal state, if not then theres another cause / valve or head sealing. My 2 cents Now some real Porsche guy needs to chime in and help me (IMG:style_emoticons/default/screwy.gif) out (IMG:style_emoticons/default/biggrin.gif) |
anthony |
Aug 11 2006, 10:32 PM
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#5
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2270 club Group: Benefactors Posts: 3,107 Joined: 1-February 03 From: SF Bay Area, CA Member No.: 218 |
Does the engine feel weak when you drive it?
I would personally do my own compression check (after the engine is fully warmed up). After you do one cyclinder you can remove the tester, squirt a little oil in the cylinder and then test again. The oil will might help seal the ring. If the compression goes up then you know the problem is rings. If the compression stays the same then the problem is in the valves. How many miles on the engine? It may just be time for a new engine or a big bore kit and some new heads. |
sww914 |
Aug 11 2006, 11:18 PM
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#6
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Advanced Member Group: Members Posts: 2,439 Joined: 4-June 06 Member No.: 6,146 Region Association: None |
Those numbers look like a half-assed compression test to me, at first glance.
If the engine's running mostly OK, I might expect to see 1 cyl a little low, but every compression check I've done was more like 120, 122 118, 125, or 125, 124, 130, 85. Either all pretty close, or one lower. The test they did could be bad, I'd have someone else do another, with the engine warm, and the butterfly open for the test on all 4 cylinders. |
Twystd1 |
Aug 11 2006, 11:55 PM
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#7
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You don't want to know... really..... Group: Members Posts: 2,514 Joined: 12-September 04 From: Newport Beach, California Member No.: 2,743 |
I suggest you perform a leak down test.
This test will REALLY let you know the condition of your rings and valves without tearing the engine apart. It is the next step I would perform after another compression test. (Do that your self..!!) Search Leak down test on this forum... Twystd1 |
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