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| Compression Values for 998 https://www.ausmini.com/forums/viewtopic.php?f=2&t=98600 |
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| Author: | ben23f [ Thu May 23, 2019 9:51 am ] |
| Post subject: | Compression Values for 998 |
Hi All, I did a compression test on my 998 the other day to start diagnosing low power and a bit of smoke when driving. I measured 105psi +/- 2psi in each of the cylinders and was wondering if this is a good value? What is the normal compression value for a 998 engine? I tried searching the forum but could only find mention of compression ratio and not pressure values. Thanks |
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| Author: | gtogreen1969 [ Thu May 23, 2019 11:29 am ] |
| Post subject: | Re: Compression Values for 998 |
That is a little on the low side. I have seen lots of engines between 120psi and 160psi and even higher. Obviously some engines will have very different readings depending on the compression ratio, camshaft overlap, wear in the bore, piston rings and valve seats etc. Also the way you do the test can effect the reading. Was the engine warm, all the spark plugs out, throttle fully open, dry test and wet test. Number of turns on the starter motor. |
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| Author: | ben23f [ Thu May 23, 2019 12:14 pm ] |
| Post subject: | Re: Compression Values for 998 |
Thanks for the info - I thought it was a little low, was expecting 120ish. I did the test with engine warm, all plugs out, and turned until the pressure needle stopped rising. The choke was off and no throttle - unless the linkage does close it slightly? I didn't do anything with the linkages. I'm pretty sure the engine is stock standard from 1976 so not too surprised its worn... Thanks |
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| Author: | gtogreen1969 [ Thu May 23, 2019 12:31 pm ] |
| Post subject: | Re: Compression Values for 998 |
ben23f wrote: Thanks for the info - I thought it was a little low, was expecting 120ish. I did the test with engine warm, all plugs out, and turned until the pressure needle stopped rising. The choke was off and no throttle - unless the linkage does close it slightly? I didn't do anything with the linkages. I'm pretty sure the engine is stock standard from 1976 so not too surprised its worn... Thanks You will get more PSI with the throttle fully open. Having it closed will restrict the air from entering thus giving you less air to compress. If you can do a wet test as well this will help diagnose if the rings are worn. |
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